Program
 
Mon Sep 04 2017
08:00 - 09:30
Registration
09:30 - 09:45
Opening
SF1.1
Chair: Wilson Smith
09:45 - 10:20
SF1.1-I1
Durrant, James
Imperial College London and Swansea University
The kinetics of charge separation, recombination and catalysis on photoelectrodes for water oxidation and reduction
James Durrant
Imperial College London and Swansea University, GB

James Durrant is Professor of Photochemistry in the Department of Chemistry, Imperial College London and Ser Cymru Solar Professor, University of Swansea. His research addresses the photochemistry of new materials for solar energy conversion targeting both solar cells (photovoltaics) and solar to fuel (i.e.: artificial photosynthesis. It is based around employing transient optical and optoelectronic techniques to address materials function, and thereby elucidate design principles which enable technological development. His group is currently addressing the development and functional characterisation of organic solar cells and photoelectrodes for solar fuel generation. More widely, he leads the UK�s Solar Fuels Network and the Welsh government funded S�r Cymru Solar initiative. He has published over 300 research papers and 5 patents, and was recently awarded the 2012 Tilden Prize by the RSC.

Authors
James Durrant a
Affiliations
a, Imperial College London, South Kensington, London,, GB
Abstract

I will address the role of charge carrier dynamics in determining the efficiency of solar driven fuel synthesis, focusing on photoelectrodes for water oxidation and reduction. Experimentally, these studies will be based around transient absorption spectroscopy on timescales from femtoseconds to seconds, which will be correlated with the results of photoelectrochemical analyses of device efficiency. These studies will address the dynamics of charge separation and recombination, as well as the kinetics of water oxidation / reduction at semiconductor / liquid interfaces. Issues which will be addressed will include the underlying photochemistry of oxides, the role of the space charge layers at electrochemical junctions in spatially separating charges, and the role of heterojunctions and catalysts layers in enhancing system efficiency. Particular consideration will be placed on analysis of the mechanism of water oxidation / reduction, and the extent to which oxide surfaces function as heterogeneous catalysts for this reaction. These studies will be based on rate law analysis of water oxidation reduction for different photoelectrodes, and as a function of temperature, pH and kinetic isotope exchange, and correlated with TD-DFT calculations of catalytic mechanism

10:20 - 10:30
Discussion
10:30 - 11:05
SF1.1-I2
Wang, Dunwei
Boston College
Co-Catalysts on Photoelectrodes: Catalyst or Passivation?
Dunwei Wang
Boston College, US
Dunwei Wang graduated from the University of Science and Technology of China in 2000 with a B.S. degree in chemistry. He was then trained at Stanford University (with Hongjie Dai) between 2000 and 2005, where his Ph.D. thesis was awarded the Prize for Young Chemists by the International Union of Pure and Applied Chemistry. After two years’ of postdoctoral study with James R. Heath at Caltech, he joined the faculty of Boston College and is currently an Assistant Professor of Chemistry there. His research concerns the development of new nanoscale materials that can be used for efficient solar energy conversion and storage. He is a recipient of an NSF CAREER award, a Massachusetts Clean Energy Center (MassCEC) Catalyst award, and a Sloan Fellowship.
Authors
James Thorne a, Wei Li a, Erik Liu a, Yanyan Zhao a, Dunwei Wang a
Affiliations
a, Boston College, Department of Chemistry, Boston College, Chestnut Hill, MA, 2467, US
Abstract

Photocatalysis has been recognized as a promising route toward large scale solar energy harvesting and storage but has been developing at a frustratingly low pace.  The lack of suitable materials is a key challenge that limit its development.  To address this issue and realize high-efficiency, low-cost photocatalysis, we need engineered materials with complex functionalities.  Understanding how the overall performance of a photocatalyst is influenced by the various material components, especially at the solid/liquid interface, has therefore become critically important.  Within this context, we present a systematic study aimed at understanding the detailed processes at the photocatalyst/water interface.  In particular, we will discuss whether the application of co-catalysts actually act through the purported mechanism of accelerating charge transfer.  To tease out information important to the understanding, we probed the system under quasi-equilibrium conditions as well as under operation conditions using spectroscopic techniques.  The study was carried out on three distinct material platforms, iron oxide, bismuth vanadate, and Si (with GaN nanowires).  Our results suggest that seemingly similar overall effect by the co-catalysts may be due to fundamentally different reasons.  The understanding has been shown to play critical roles in further optimization of photocatalysts.  We expect to see increasingly more important roles by similar studies on a wide range of photocatalyst systems.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SF1.1-I3
Sivula, Kevin
Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland
Engineering solution-processed semiconductor materials for photoelectrochemical solar fuel production
Kevin Sivula
Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, CH

Kevin Sivula obtained a PhD in chemical engineering from UC Berkeley in 2007. In 2011, after leading a research group in the Laboratory of Photonics and Interfaces at EPFL, he was appointed tenure track assistant professor. He now heads the Laboratory for Molecular Engineering of Optoelectronic Nanomaterials (http://limno.epfl.ch) at EPFL.

Authors
Kevin Sivula a
Affiliations
a, Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, Lausanne, CH
Abstract

The development of robust and inexpensive semiconducting materials that operate at high efficiency are needed to make the direct solar-to-fuel energy conversion by photoelectrochemical cells economically viable. In this presentation our laboratory’s progress in the development new light absorbing materials and co-catalysts will be discussed along with the application toward overall solar water splitting tandem cells for H2 production. Specifically, this talk will highlight recent results with the ternary oxide CuFeO2, 2D transition metal dichalcogenides, and organic (π-conjugated) semiconductors as solution-processed photoelectrodes.

With respect to CuFeO2, in our recent work [1] we demonstrate state-of-the-art sacrificial p-type photocurrent with optimized nanostructuring. Recent results addressing interfacial recombination by the electrochemical characterization of the surface states and attached co-catalysts will be presented along with approaches to overcome the limitations of this material.

In addition, two-dimensional (2-D) transition metal dichalcogenides (TMDs) generally have intriguing electronic properties making them promising candidates for high-efficiency solar energy conversion. However, it is notoriously difficult to fabricate thin films of 2-D TMDs over the large areas required to convert solar energy on a practical scale. We recently developed a simple method to fabricate high-quality thin films of 2-D layered TMDs at low cost and with good efficiency towards solar-to-fuel energy conversion [2]. The challenges with charge transport, separation [3] and water redox catalysis in these systems will also be discussed with respect to the 2D flake size.

Finally, with respect to π-conjugated organic semiconductors, in our recent work [4] we demonstrate a π-conjugated organic semiconductor for the sustained direct solar water oxidation reaction. Aspects of catalysis and charge-carrier separation/transport are discussed.

 

[1] Prevot, M. S.; Li, Y.; Guijarro, N.; Sivula, K. J. Mater. Chem. A 2016, 4, 3018-3026.

[2] Yu, X.; Prevot, M. S.; Guijarro, N.; Sivula, K., Nat. Commun. 2015, 6, 7596.

[3] Yu, X.; Rahmanudin, A.; Jeanbourquin, X. A.; Tsokkou, D.; Guijarro, N.; Banerji, N.; Sivula, K. ACS Energy Lett. 2017, 2, 524.

[4] Bornoz, P.; Prévot, M. S.; Yu, X.; Guijarro, N.; Sivula, K. J. Am. Chem. Soc. 2015, 137, 15338.

12:20 - 12:30
Discussion
12:30 - 13:05
SF1.1-I4
Chorkendorff, Ib
Technical University of Denmark
Water splitting and the making of renewable chemicals.
Ib Chorkendorff
Technical University of Denmark, DK
Authors
Ib Chorkendorff a
Affiliations
a, The Villum Center for the Science of Sustainable Fuels and Chemicals
Abstract

In the future, it is foreseen that we will have transformed our energy supply from fossil fuels to sustainable sources. These will come in the form of solar and wind i.e. in the form of electric energy which is intermittent, thus there will be a need for energy storage in the form of fuels – in particular for those areas that are difficult to electrify, such as aviation and long haul transport. Similarly, will there also be a need for replacing the synthesis of chemicals, which today is based solely on fossil resources. Hydrogen is the simplest solar fuel to produce and while good progress has been made on the hydrogen evolution reaction (HER), ironically it is the oxygen evolution reaction (OER) which is causing the largest energy losses [1]. We shall show how mass selected nanoparticles can be used to elucidate the effectiveness of the various catalysts both for HER [2] and for OER [3, 4]. Hydrogen is an excellent fuel, but very voluminous and it is therefore desirable to have fuels with higher energy densities. Thus, instead of producing hydrogen we could also use the electrochemical cell to hydrogenate CO or CO2. This is also the route to start synthesizing the base chemicals needed for synthesizing chemicals in general. We shall here show how we can investigate the recent ethanol synthesis on oxygen derived Cu found by Kanan et al. [5] and show how acetaldehyde seems to be an important intermediate [6]. New methods for detecting volatile products using a “Sniffer” setup will also be discussed [7] and it will be demonstrated how this principle can be used to study the dynamics of methane and ethylene production on mass-selected Copper nanoparticles [8].

 

References

[1] W She, et al. SCIENCE (2017) 355  DOI: 10.1126/science.aad4998.

[2] E. Kemppainen et al. Energy & Environmental Science, 8 2991 (2015)

[3] E. A. Paoli, et al. Chemical Science, Chemical Science, 6 190 (2015)

[4] B. Besoek et al. in preparation (2017).

[5] A. Verdaguer-Casadevall et al.  J. Am. Chem. Soc. 137  9808 (2015)

[6] E. Bertheussen et al. Angew. Chem. Int. Ed.  55 1450 (2016)

[7] D. T. Bøndergaard, et al. Rev. Sci. Inst.  86 075006 (2015)

[8] D. T. Bøndergaard, et al. Submitted (2017).

13:05 - 13:15
Discussion
SF2.1
Chair: Emilio Palomares
09:45 - 10:20
SF2.1-I1
Burn, Paul
The University of Queensland
Interlayer engineering for high Voc perovskite solar cells
Paul Burn
The University of Queensland, AU
Authors
Paul Burn a
Affiliations
a, The University of Queensland, Bld 68, Level 9, Cooper Rd., Brisbane, 4072, AU
Abstract

Lead-based organohalide perovskites are promising for thin film solar cell technologies as they can be solution processed or deposited by low-temperature evaporation techniques, their opto-electronic properties can be tuned, and they have been shown to be capable of power conversion efficiencies (PCEs) of >20%. A factor that has led to the improvement in perovskite solar cell efficiency has been the use of interfacial engineering to control the open-circuit voltage (Voc). In principle, perovskites can work efficiently in a very simple device architecture – a high quality absorbing layer sandwiched between work function modified anodes and cathodes. In an inverted architecture the holes are collected at the transparent conducting electrode. For inverted solar cells, the hole transport/interlayer material needs to modify the anode such that its work function is close to the ionisation potential of the organohalide perovskite junction to maximise Voc. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can act as an anode work function modifier and is a sufficiently hydrophilic hole transport material to enable the deposition of good quality perovskite films. However, PEDOT:PSS has a relatively low work function, which limits the open-circuit Voc. In this presentation, we will discuss two different methods to modify the work function of the ITO anode to increase the Voc as well as providing a surface energy suitable for depositing a good quality perovskite film. Using these methods Vocs > 1 V and and PCEs of up to 16.5% can achieved for simple solution processed perovskite cells.

10:20 - 10:30
Discussion
10:30 - 11:05
SF2.1-I2
Berry, Joseph
Chemistry and Nanoscience Center, National Renewable Energy Laboratory
Controlling Solution Chemistry towards Upscaling of Perovskite Photovoltaics
Joseph Berry
Chemistry and Nanoscience Center, National Renewable Energy Laboratory, US
Authors
Kai Zhu a, joseph Berry a
Affiliations
a, National Renewable Energy Laboratory Denver
Abstract

Organic-inorganic hybrid halide perovskites have recently emerged as a new class of light absorbers with a rapid progress and impressive efficiencies (>22%) for solar conversion applications. Despite the rapid progress demonstrated by these light absorbers, there is still a lack of understanding of some fundamental material/physical/chemical properties of these materials. There is also a significant processing gap between the lab-scale spin coating and scalable deposition methods toward future roll-to-roll manufacturing. The challenge results from the sensitivity of perovskite crystallization and film formation in different processing conditions. In this presentation, I will present our recent studies toward a better understanding and control of perovskite nucleation, grain growth, and microstructure evolution using solution processing. The precursor chemistry and growth conditions are found to affect significantly the structural and electro-optical properties of perovskite thin films. We also find that the precursor ink chemistry (solvent, coordination chemistry) of perovskite is critical for scalable deposition; but this has largely been underexplored. We present a rational design of perovskite precursor film formation to achieve highly specular films using scalable deposition methods. Using these high quality perovskite films, we have achieved device efficiencies approaching the values obtained on small scale by spin coating. These findings make a significant advance towards commercialization of the perovskite photovoltaic technology. Our recent progress towards stable perovskite solar cells will also be discussed.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SF2.1-I3
Durrant, James
Imperial College London and Swansea University
Charge carrier kinetics and stability challenges in perovskite solar cells
James Durrant
Imperial College London and Swansea University, GB

James Durrant is Professor of Photochemistry in the Department of Chemistry, Imperial College London and Ser Cymru Solar Professor, University of Swansea. His research addresses the photochemistry of new materials for solar energy conversion targeting both solar cells (photovoltaics) and solar to fuel (i.e.: artificial photosynthesis. It is based around employing transient optical and optoelectronic techniques to address materials function, and thereby elucidate design principles which enable technological development. His group is currently addressing the development and functional characterisation of organic solar cells and photoelectrodes for solar fuel generation. More widely, he leads the UK�s Solar Fuels Network and the Welsh government funded S�r Cymru Solar initiative. He has published over 300 research papers and 5 patents, and was recently awarded the 2012 Tilden Prize by the RSC.

Authors
James Durrant a, b
Affiliations
a, Department of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, GB
b, SPECIFIC IKC, College of Engineering, University of Swansea, Swansea, U.K
Abstract

In my talk, I will focus primarily on the charge transfer and recombination processes which are key determinants of the efficiency of methylammonium lead halide perovskite solar cells. Experimentally our studies of charge transfer are based on transient absorption and photoluminescence measurements on timescales from femtoseconds to steady state. I will focus in particular upon the kinetics and efficiency of charge transfer from the photoactive perovskite layer to organic electron and hole collection layers in planar structure films and devices. Topics to be addressed will include the competition between charge transfer and charge trapping / recombination as a function of charge carrier density, material selection and processing and film aging, and the correlations between these processes and device photocurrent generation. The optical studies will be complimented by transient photocurrent and photovoltage studies of charge recombination as a function of photoactive layer and charge collection layer composition, and correlated with measurements of device voltage.

The second part of my talk will address the stability of the same devices, addressing in particular the photoinduced degradation of perovskite devices under oxygen exposure, and how the selection appropriate material choice and film processing can enhance performance.

12:20 - 12:30
Discussion
12:30 - 13:05
SF2.1-I4
Ryan, James
NIMS
Transient optoelectronic studies of inverted perovskite solar cells
James Ryan
NIMS, JP
Authors
James Ryan a
Affiliations
a, National Institute for Materials Science, Japan, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, JP
Abstract

In order for perovskite solar cells (PSCs) to achieve their maximum efficiency it is necessary to clearly understand the key loss processes that govern their performance. In particular, understanding the origin of the open-circuit voltage (VOC) is vital. In PSCs, the VOC can shift considerably depending on the choice of transport layer and device architecture, be it from improved perovskite film quality or a better interface between the perovskite absorber and transport layer.  To probe the recombination dynamics, transient optoelectronic techniques, such as transient photovoltage, transient photocurrent and charge extraction, offer key insights into the non-geminate charge carrier dynamics in solar cells and can explain the difference in VOC between different devices. These techniques have been employed with great success in organic and dye-sensitized solar cells. However, in PSCs the application of these techniques is non-trivial. In this talk I will present some of our recent studies on PSCs using transient optoelectronic techniques and highlight some the challenges we have faced in interpreting the data.

13:05 - 13:15
Discussion
13:15 - 15:00
Lunch
13:15 - 14:45
Lunch
SF1.2
Chair: Shane Ardo
14:50 - 15:00
SF1.2-S1
Ji, Kwangsun
Energy & Environment Materials & Devices Team / Materials & Devices Advanced Research Institute /LG Electronics /Seoul, Korea
LG Materials & Devices Advanced Research
Kwangsun Ji
Energy & Environment Materials & Devices Team / Materials & Devices Advanced Research Institute /LG Electronics /Seoul, Korea
Authors
Kwangsun Ji a
Affiliations
a, LG TCM, LG Electronics, Paveletskaya sq.2/3, Moscow, RU
Abstract

sponsor's talk
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15:00 - 15:35
SF1.2-I1
Esposito, Daniel
Columbia University, US
Oxide-Encapsulated Electrocatalysts for Solar Fuels Production
Daniel Esposito
Columbia University, US
Authors
Daniel Esposito a
Affiliations
a, Columbia University, US
Abstract

Electrocatalysts are essential components of many electrochemical technologies that are expected to be the “work horses” of a clean energy future. In our lab, we are developing novel electrocatalyst and photoelectrode architectures based on transition metal electrocatalysts that have been encapsulated by ultra-thin metal oxide overlayers. These oxide layers are synthesized with a room temperature process and deposited as uniform layers onto metallic thin films and nanoparticles.  Importantly, these oxide overlayers are found to serve as “nano-membranes” that can be permeable to certain electroactive species and thereby enable efficient and selective electrocatalysis at the metal oxide / metal interface. By systematically varying the thickness of the oxide overlayer, we explore its transport properties and influence on the stability of the underlying transition metals during long term operation as hydrogen evolution catalysts. Oxide-encapsulated electrocatalysts have also been deposited onto the surface of photoelectrodes, revealing the additional advantage of greatly decreasing charge transfer resistance between the semiconductor and the nanoparticle electrocatalyst. Overall, these studies highlight the potential of well-defined oxide-encapsulated electrocatalysts to serve as a tunable, efficient, and stable platform for a variety of electrochemical reactions.    

15:35 - 15:45
Discussion
SF2.2
Chair: Joseph Berry
15:00 - 15:30
SF2.2-O1
Mora-Seró, Iván
Institute of Advanced Materials (INAM), Universitat Jaume I
Tailoring Properties in Perovskite Solar Cells
Iván Mora-Seró
Institute of Advanced Materials (INAM), Universitat Jaume I, ES

Iván Mora-Seró (1974, M. Sc. Physics 1997, Ph. D. Physics 2004) is researcher at Universitat Jaume I de Castelló (Spain). His research during the Ph.D. at Universitat de València (Spain) was centered in the crystal growth of semiconductors II-VI with narrow gap. On February 2002 he joined the University Jaume I. From this date until nowadays his research work has been developed in: electronic transport in nanostructured devices, photovoltaics, photocatalysis, making both experimental and theoretical work. Currently he is associate professor at University Jaume I and he is Principal Researcher (Research Division F4) of the Institute of Advanced Materials (INAM). Recent research activity was focused on new concepts for photovoltaic conversion and light emission based on nanoscaled devices and semiconductor materials following two mean lines: quantum dot solar cells with especial attention to sensitized devices and lead halide perovskite solar cells and LEDs, been this last line probably the current hottest topic in the development of new solar cells.

Authors
Ivan Mora-Sero a
Affiliations
a, Institute of Advanced Materials (INAM), Universitat Jaume I, Avinguda de Vicent Sos Baynat, Castelló de la Plana, ES
Abstract

Halide Perovskite can be prepared from solution methods at low temperature, and consequently they can be fabricated without large and expensive facilities, can be easily combined with other materials and efficiencies higher than 22% have been certified. In addition, halide perovskite constitutes a broad family of materials that allow tailoring the properties for advanced solar cells configurations of for other kinds of electronic devices However despites the unprecedentedly fast increase of the reported efficiencies, especially in the last four years, the working mechanisms of this kind of devices are not completely understood. Transport, recombination, injection at the contacts or J-V curve hysteresis are strongly dependent on the cell configuration, as the use of scaffold, the perovskite and on surface engineering and also on the growth conditions. In this talk, I analyze the effect in the solar cell performance of different engineering and also on the preparation of Br based perovskites.

15:30 - 16:00
SF2.2-O2
Luther, Joey
National Renewable Energy Laboratory
Influence of Electrode Interfaces on the Stability of Perovskite Solar Cells: Unencapsulated Perovskite Solar Cells for >1000 Hours of Ambient Operational Stability
Joey Luther
National Renewable Energy Laboratory, US

Joseph M. Luther obtained B.S. degrees in Electrical and Computer Engineering from North Carolina State University in 2001. At NCSU he began his research career under the direction of Salah Bedair, who was the first to fabricate a tandem junction solar cell. Luther worked on growth and characterization high-efficiency III-V materials including GaN and GaAsN. His interest in photovoltaics sent him to the National Renewable Energy Laboratory (NREL) to pursue graduate work. He obtained a Masters of Science in Electrical Engineering from the University of Colorado while researching effects of defects in bulk semiconductors in NREL�s Measurements and Characterization Division. In 2005, He joined Art Nozik�s group at NREL and studied semiconductor nanocrystals for multiple exciton generation for which he was awarded a Ph.D. in Physics from Colorado School of Mines. As a postdoctoral fellow, he studied fundamental synthesis and novel properties of nanomaterials under the direction Paul Alivisatos at the University of California and Lawrence Berkeley National Laboratory. In 2009, he rejoined NREL as a senior research scientist. His research interests lie in the growth, electronic coupling and optical properties of colloidal nanocrystals and quantum dots.

Authors
Joseph Luther a
Affiliations
a, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado, 80401, US
Abstract

Jeffrey A. Christians,1 Philip Schulz,1 Erin M. Sanehira,1,2 Jonathan S. Tinkham,3 Tracy H. Schloemer,3 Steven P. Harvey,1 Bertrand J. Tremolet de Villers,1 Alan Sellinger,1,3 Kai Zhu, 1 Joseph J. Berry,1 and Joseph M. Luther1

1NREL, Golden, CO

2University of Washington, Seattle, WA 

3Department of Chemistry, Colorado School of Mines, Golden, CO 

The efficiency of halide perovskite solar cells has reached parity with commercially available thin film photovoltaic absorbers. Because of this, their future commercial prospects appear to hinge upon their long-term operational stability. Recent work has provided insight into the moisture instability, thermal instability, phase instability, and phase segregation of the halide perovskite absorbers themselves. This work has translated into much improved device-level operational stability, yet the combined effects of light (including UV-light), oxygen, and moisture remain problematic.

In this work, we investigate the performance of n-i-p perovskite solar cells which are held, unencapsulated, under continual simulated solar illumination in ambient conditions. We demonstrate that degradation is driven by the heterointerfaces in the device stack and systematically engineer the interfaces in the device to improve operational stability. Replacing the Li+-containing spiro-OMeTAD with a Li+-free hole transport material (HTM), EH44, we achieve comparable power conversion efficiency and a factor of 4 better operational stability. Using Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) of devices at various stages of degradation, we observe an irreversible redistribution of components in the perovskite layer when TiO2 is used as the electron transport layer (ETL) which correlates to the initial burn-in which the devices exhibit under illumination. We find that this redistribution and the burn-in which the devices experience is driven by the TiO2/perovskite interface and can be significantly reduced by the use of a nanoparticle SnO2 ETL in place of TiO2. By utilizing MoOx/Al electrodes in place of Au, which can migrate into the devi ce stack, we develop a SnO2/perovskite/EH44/MoOx/Al device stack with very promising stability. This systematic approach to stability results in a device which retains 94% of its peak power conversion efficiency despite 1000 hrs of continual, unencapsulated operation in ambient conditions. This represents a >3 order of magnitude improvement over standard TiO2/perovskite/spiro-OMeTAD/Au devices with the same perovskite absorber layer. This dramatic improvement in stability, despite the combined stresses of UV-light, oxygen, and moisture, demonstrates the importance of carefully designed interfaces for realizing true long-term perovskite solar cell stability.

16:00 - 16:30
SF2.2-O3
Bisquert, Juan
Institute of Advanced Materials (INAM), Universitat Jaume I
Optoelectronic impedances of thin film solar cells
Juan Bisquert
Institute of Advanced Materials (INAM), Universitat Jaume I, ES

Juan Bisquert (pHD Universitat de València, 1991) is a Professor of applied physics at Universitat Jaume I de Castelló, Spain. He is the director of the Institute of Advanced Materials at UJI. He authored 360 peer reviewed papers, and a series of books including Nanostructured Energy Devices (1. Equilibrium Concepts and Kinetics, 2. Foundations of Carrier Transport) and 3. Physics of Solar Cells: Perovskites, Organics, and Photovoltaics Fundamentals (CRC Press).  His h-index 82, and is currently a Senior Editor of the Journal of Physical Chemistry Letters. He conducts experimental and theoretical research on materials and devices for production and storage of clean energies. His main topics of interest are materials and processes in perovskite solar cells and solar fuel production. He has developed the application of measurement techniques and physical modeling of nanostructured energy devices, that relate the device operation with the elementary steps that take place at the nanoscale dimension: charge transfer, carrier transport, chemical reaction, etc., especially in the field of impedance spectroscopy, as well as general device models. He has been distinguished in the 2014-2017 list of ISI Highly Cited Researchers.

 

Authors
Juan Bisquert a
Affiliations
a, Institute of Advanced Materials (INAM), Universitat Jaume I, Avinguda de Vicent Sos Baynat, Castelló de la Plana, ES
Abstract

The experimental investigation of transfer functions in small perturbation frequency modulated techniques provides important information on the electronic and kinetic processes of thin film solar cells. In this talk we present recent advances of impedance spectroscopy of perovskite solar cells, including the analysis of different capacitive processes, charge transfer associated to interface properties, and the connection of IS to hysteresis. In order to probe additional light indued properties it is important to apply the methods of modulated light intensity, be measuring either modulated voltage or current output. A general connection of the correspondent transfer functions is investigated, as well as the meaning of the low frequency value. We examiner the connection of these techniques in different settings, such as electrochemcial systems and luminescent materials as quantum dots. 

    
Reference: Luca Bertoluzzi, Juan Bisquert
Investigating the Consistency of Models for Water Splitting Systems by Light and Voltage Modulated Techniques
The Journal of Physical Chemistry Letters, 8, 172-180 (2017)

16:30 - 17:00
Abstract not programmed
SF1.2.1
Chair: Shane Ardo
15:45 - 16:00
SF1.2.1-O1
Gimenez Julia, Sixto
Institute of Advanced Materials (INAM), Universitat Jaume I
Tuning the functionalities of Bismuth Vanadate. From water splitting photoanodes to photocapacitive devices
Sixto Gimenez Julia
Institute of Advanced Materials (INAM), Universitat Jaume I, ES

Sixto Giménez (M. Sc. Physics 1996, Ph. D. Physics 2002) is Associate Professor at Universitat Jaume I de Castelló (Spain). His professional career has been focused on the study of micro and nanostructured materials for different applications spanning from structural components to optoelectronic devices. During his PhD thesis at the University of Navarra, he studied the relationship between processing of metallic and ceramic powders, their sintering behavior and mechanical properties. He took a Post-Doc position at the Katholiek Universiteit Leuven where he focused on the development of non-destructive and in-situ characterization techniques of the sintering behavior of metallic porous materials.  In January 2008, he joined the Group of Photovoltaic and Optoelectronic Devices of University Jaume I where he is involved in the development of new concepts for photovoltaic and photoelectrochemical devices based on nanoscaled materials, particularly studying the optoelectronic and electrochemical responses of the devices by electrical impedance spectroscopy. He has co-authored more than 80 scientific papers in international journals and has received more than 5000 citations. His current h-index is 31. 

Authors
Sixto Gimenez a, Drialys Cardenas-Morcoso a
Affiliations
a, Institute of Advanced Materials (INAM), Universitat Jaume I, Avinguda de Vicent Sos Baynat, Castelló de la Plana, ES
Abstract

Bismuth Vanadate has emerged as one of the most interesting n-type metal oxides for different applications. As a photoanode for water oxidation, this material holds the record solar to hydrogen (STH) conversion efficiency (8.1 %) among the family of metal oxides, when combined with a double-junction GaAs/InGaAsP photovoltaic device.[1] Additionally, impressive enhancement of the photoelectrochemical behavior has been reported upon prolonged illumination at open circuit conditions.[2, 3] In the present contribution, we show that the functionalities of BiVO4 can be tuned upon modification of the semiconductor-liquid interface by the deposition of different nanometric layers/particles. Enhanced photoelectrochemical water oxidation is demonstrated upon deposition of Fe2O3, AgPO3, and CoFe Prussian blue nanoparticles.[4] The mechanistic insights leading to improved functional performance will be discussed. Alternatively, when combined with lead oxide, Bismuth Vanadate provides a synergistic photocapacitive platform with high specific capacitance, high open circuit potential and stable charge/discharge cycling, opening promising research avenues in the development of novel solar energy storage strategies.[5]

References

[1] Y. Pihosh, I. Turkevych, K. Mawatari, J. Uemura, Y. Kazoe, S. Kosar, K. Makita, T. Sugaya, T. Matsui, D. Fujita, M. Tosa, M. Kondo and T. Kitamori, Scientific Reports, 2015, 5, 11141.

[2] B.J. Trzesniewski and W.A. Smith, Journal of Materials Chemistry A, 2016, 4, 2919-2926.

[3] B.J. Trzesniewski, I.A. Digdaya, I. Herraiz-Cardona, S. Ravishankar, T. Nagaki, D.A. Vermaas, A. Longo, S. Gimenez and W.A. Smith, Energy and Environmental Science, (2017), in press.

[4] M.N. Shaddad, M.A. Ghanem, A.M. Al-Mayouf, S. Gimenez, J. Bisquert and I. Herraiz-Cardona, Chemsuschem, 2016, 9, 2779-2783.

[5] S. Safshekan, I. Herraiz-Cardona, D. Cardenas-Morcoso, R. Ojani, M. Haro, S. Gimenez, ACS Energy Letters, 2017, 2 (2), 469–475.

16:00 - 16:15
SF1.2.1-O2
Stefik, Morgan
University of South Carolina
Bismuth Vanadate : SF-ALD and Remarkable Post-Synthetic Treatments
Morgan Stefik
University of South Carolina
Authors
Morgan Stefik a
Affiliations
a, University of South Carolina, Department of Chemistry and Biochemistry
Abstract

The fabrication of porous nanocomposites is crucial to enable efficient PEC devices based upon low-mobility absorbers such as oxides. The controlled fabrication of promising multinary absorbers such as BiVO4 as layers within porous and conducting scaffolds has remained challenging. Thus far most reports of composite BiVO4 devices have suffered from non-uniform depositions. ALD is an ideal method, however prior demonstrations were limited to non-stoichiometric BiVxOy or required an etch step. We have developed a Surface Functionalized ALD route with tunable Bi:V stoichiometry that enables the first production of phase-pure scheelite by SF-ALD. Most notably, the PEC performance of SF-ALD BiVO4 exhibited a remarkable sensitivity to post-synthetic treatments where IPCE changes as large as 400% resulted from a simple PEC activation step. The results are considered in the context of other emerging post-synthetic modifications of multinary absorbers. These insights may play a continued role in optimization and stability as new multinary compounds are elaborated towards solar fuels.

                                                                                   

1) Stefik, M. Atomic Layer Deposition of Bismuth Vanadates for Solar Energy Materials. ChemSusChem 2016, 9, 1727-1735.

2) Lamm, B.; Sarkar, A. Stefik, M. Surface Functionalized Atomic Layer Deposition of Bismuth Vanadate for Single-Phase Scheelite. Journal of Materials Chemistry A 2017, 5, 6060 – 6069.

16:15 - 16:30
SF1.2.1-O3
Tilley, David
University of Zurich
Highly Active Sb2Se3-based Photocathodes for Solar Hydrogen Production
David Tilley
University of Zurich, CH
Authors
Rajiv Ramanujam Prabhakar a, Wilman Septina a, Sebastian Siol b, René Wick a, Thomas Moehl a, David Tilley a
Affiliations
a, University of Zurich, Department of Chemistry, Winterthurerstrasse, 190, Zürich, CH
b, EMPA - Swiss Federal Laboratories for Materials Science and Technology, Überland Strasse, 129, Dübendorf, CH
Abstract

Although photocathodes that are based on Si, GaInP2, GaP and copper indium gallium sulphide/selenide (CIGS) exhibit high solar-to-hydrogen conversion efficiencies, they either contain rare elements or require high cost processing techniques. In order to compete with crystalline silicon-based photovoltaic-coupled electrolysis for widespread solar hydrogen generation, new materials are required that are simultaneously high efficiency, Earth-abundant, and stable in an aqueous electrolyte.

In this work, we report highly active photocathodes based on Sb2Se3 that feature low cost and abundant HER catalysts. Photocurrents exceeding 12 mA cm-2 have been obtained at 0 V vs RHE and photocurrents exceeding 20 mA cm-2 at more negative bias (in 1 M H2SO4, under simulated one sun AM 1.5 G irradiation). These photocathodes show high incident photon to current conversion efficiencies over the entire visible spectrum, and until the band gap of Sb2Se3 (1.2 eV). Although the photocathodes showed a ~20% decrease in the photocurrent during chronoamperometry at 0 V vs RHE for 2 hours, the photocurrent was restored upon re-application of the HER catalyst.

16:30 - 16:45
SF1.2.1-O4
Suter, Silvan
Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland
Quantitative Structural and Transport Analysis of Morphologically-Complex Photoelectrodes
Silvan Suter
Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, CH
Authors
Silvan Suter a, Yannick Gaudy a, Sophia Haussener a
Affiliations
Abstract

The morphology of semiconductor photoelectrodes significantly affects the performance of photoelectrochemical devices. Complex anisotropic morphologies are important for overcoming performance limiting bulk transport properties of semiconductor materials, but are often also an unintended outcome of the fabrication process. A better understanding of morphology-induced transport limitations of photoelectrodes is needed.

We used a coupled experimental-numerical approach to quantitatively characterize morphologically-complex photoelectrodes (nano- to micrometer thick semiconductor-films composed of mesoscopic structural units with nano-scale structural details). We utilized a 3D-microscopy method, FIB-SEM tomography with a high resolution of 4x4x4 nm3, to obtain a grey value array representing the photoelectrode morphology. The digital structure was segmented based on trainable machine-learning algorithms to subsequently quantify performance-related morphological parameters.

We applied this method to two distinct photoelectrodes, different in structure, composition, and scale: i) a particle-based lanthanum titanium oxynitride electrode with a film thickness of a few micrometers, and ii) a ‘cauliflower-like’ structured hematite electrode with a film thickness of a few hundred nanometers. The digitalized morphology of each of the two films was used to quantify specific surface, mean feature dimensions, and film homogeneity. Further, the structural characteristics in the meso and nano-scale, including the shape and orientation of these structural details, were quantified.

The digitalized photoelectrode morphologies were then used in direct pore-level simulations to understand transport around and in the semiconductor. Charge carrier generation rates in the semiconductor phase were calculated by an electromagnetic wave propagation simulation based on spatially resolved material density profiles. The generation rates were mapped onto the semiconductor-electrolyte interface and limitations in the diffusive ion transport in the electrolyte were investigated with a finite volume solver.

The FIB-SEM tomography, with its high, nanometer-scale resolution, reveals precise structural information of semiconductor films at the submicrometer scale. The methodology proofs to be applicable to various photoelectrodes and provides a unique insight into their morphologies. The analysis of the 3D-data obtained allows for the qualitative and quantitative assessment of performance-related morphological parameters, and can characterize and identify limiting transport phenomena in the structure in order to guide the morphology and fabrication of optimized photoelectrodes.

16:45 - 17:00
SF1.2.1-O5
Francàs Forcada, Laia
Imperial College London
Shining light on the role of catalysts layers on BiVO4 for water oxidation.
Laia Francàs Forcada
Imperial College London, GB
Authors
Laia Francas Forcada a, Sacha Corby a, Shababa Selim a, Camilo Mesa a, Yimeng Ma a, b, Dongho Lee c, Kyoung-Shin Choi c, James Durrant a
Affiliations
a, Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706, USA.
Abstract

Hydrogen and other solar fuels have been appointed as the energy vectors of the future. With natural photosynthesis as inspiration, we can develop a device capable of splitting water using sunlight, obtaining oxygen and hydrogen. [1], [2]

Although rapid progress is being made in the field, the efficiency of artificial systems still remains modest. Several metal oxide semiconductors have been shown to be good candidates to carry out the reactions of water oxidation (Fe2O3, BiVO4, TiO2) and proton reduction (Cu2O structures). The addition of different catalyst layers has been proven to improve the performance of the bare material. However, the role of these new layers is still in debate, hence further understanding is key for the rational design of better photoelectrode architectures.  

In this talk, I will focus on the study of different catalyst layers on semiconductors. For this study I will use spectroscopic techniques such as, Transient Absorption Spectroscopy (TAS), PhotoInduced Absorbance spectroscopy (PIAS) [3] and spectroelectrochemistry. All the kinetic information extracted from these experiments will be analysed and compared to depict which are the key points that we need to take into account when depositing a catalyst overlayer.

 

 

 

 

 

References:

[1] S. Berardi, S. Drouet, L. Francàs, C. Gimbert-Suriñach, M. Guttentag, C. Richmond, T. Stoll, A. Llobet, Chem. Soc. Rev.43 (2014), 7501.

[2] Y. Tachibana, L. Vayssieres, James R. Durrant Nature photonics 5 (2012), 511.

[3] F. Le Formal, E. Pastor, S. D. Tilley, C. A. Mesa, S. R. Pendlebury, M. Grätzel and J. R. Durrant, J. Am. Chem. Soc. 137 (2015), 6629.

17:00 - 17:15
SF1.2.1-O6
Rohloff, Martin
Technical University of Berlin
Fluorinated BiVO4 – Enhancement of Photoelectrochemical Performance for Water Oxidation by Fluorine Incorporation
Martin Rohloff
Technical University of Berlin, DE
Authors
Martin Rohloff a, Björn Anke b, Martin Lerch b, Anna Fischer a
Affiliations
a, Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg
Abstract

The n-type semiconductor bismuth vanadate (BiVO4) has recently gained a lot of attention as photoanode material for visible-light induced water oxidation. Its absorption in the visible domain (band gap energy of 2.4 eV), its suitable band edge positions compared to the OER half reaction, its stability against photo-corrosion as well as its low cost, make BiVO4 one of the most interesting ternary oxide materials for light-induced oxygen evolution from water. One major drawback for BiVO4 is its poor bulk electronic conductivity; problem, which however can be overcome by doping as well as by improved structural design.

In contrast to well-known cation doping, we present a new approach of anion substitution in BiVO4 photoanodes. A new solid-vapor reaction method for the treatment of BiVO4 powder with HF(g) at ambient pressure and in inert gas atmosphere was developed to reproducibly substitute oxygen by fluorine. Obtained powder samples were characterized extensively by means of chemical and structural analysis as well as by electron microscopy. Using electrophoretic deposition and taking advantage of the low-temperature sintering of BiVO4, the as-synthesized powders were processed to photoanodes, allowing the (photo-)electrochemical characterization of F:BiVO4 regarding water oxidation compared to its pristine counterpart. Higher photocurrents were obtained for the fluorine-modified BiVO4 anode. Photocurrent transient analysis revealed that surface hole recombination is drastically reduced for the F:BiVO4 sample. Additionally, Mott-Schottky-type electrochemical impedance spectroscopy revealed the F:BiVO4 material to profit from a bigger amount of free charge carriers as well as from a cathodically shifted flat band potential.

Our results demonstrate the widely unapplied field of anion doping to be a viable tool to optimize photoanode properties with respect to photoelectrochemical water oxidation.

This work was funded by the DFG SPP1613 program.

SF1.2.2
Chair: Curtis Berlinguette
15:45 - 16:00
SF1.2.2-O1
Garcia Santaclara, Jara
Department of Chemical Engineering, Delft University of Technology, The Netherlands
Design Guidelines of MOFs for Photocatalytic H2 Production
Jara Garcia Santaclara
Department of Chemical Engineering, Delft University of Technology, The Netherlands, NL
Authors
Jara Garcia Santaclara a, Alma Olivos-Suarez a, Sonia Castellanos a, Freek Kapteijn a, Monique van der Veen a, Jorge Gascon a
Affiliations
a, Department of Chemical Engineering, Delft University of Technology, The Netherlands, Van der Maasweg, 9, Delft, NL
Abstract

Metal-organic frameworks (MOFs) have been recently used as custom designed materials for artificial photosynthesis, i.e. CO2 reduction and H2 evolution (HER). However, their performance is still limited, and fundamental understanding of the photocatalytic process by MOFs offers a great contribution to move forward this field.

Given the large photostability of Ti-and Zr based MOFs, these M4+-based (d0) solids are the most attractive for perspective application in photocatalysis. In this work we use two frameworks, namely NH2-MIL-125(Ti) and NH2-UiO-66(Zr), as examples to better understand photocatalytic processes in MOFs by using (spectro)electrochemistry and ultrafast spectroscopy and highlight the importance of the location of excited states (metal to organic linker) on photocatalytic performance.

Although the robust NH2-UiO-66(Zr) framework possesses excellent light absorption properties, its photoactivity is limited as a consequence of the poor overlap of the d-orbital of Zr and the π* orbital of the ligand. Both frontier orbitals (HOCO and LUCO) are localized at the organic linker, resulting in short exciton lifetimes and decreased photocatalytic performance. As a shortcut to this disadvantage, we demonstrate that the post-synthetic metal modification (PSM) of Ti4+ into the UiO-66(Zr) framework enhances its photocatalytic performance in visible light HER and proves the great impact of the metal precursor in PSM for photocatalysis.

In contrast, the good photocatalytic performance of NH2-MIL-125(Ti) is a consequence of an optimal overlap of ligand (HOMO) and metal (LUMO) orbitals that favours LMCT. Recent studies have shown that certain cobalt-base inorganic compounds can catalyse hydrogen evolution in electrocatalysis. Thus, the requirement of an extra component (photosensitizer) is mandatory for photocatalysis. Taking advantage of the porosity at MOFs, we combined the Ti-based NH2-MIL-125(Ti) and encapsulated a Co catalyst to give a boost to the photocatalyst design. Our recent studies show that the local structure and the whole MOF scaffold are involved in the reaction, demonstrating the importance of the molecular and spatial arrangement of the Co-species inside the NH2-MIL-125(Ti) pore space.

16:00 - 16:15
SF1.2.2-O2
Hod, Idan
Ben-Gurion University of the Negev
Metal-Organic Frameworks as an Enzyme-Inspired Heterogeneous Platform for Electrocatalytic CO2 Reduction
Idan Hod
Ben-Gurion University of the Negev
Authors
Idan Hod a
Affiliations
a, Ben-Gurion University of the Negev, Dept. of solar energy and envronmental physics, Inst. for desert research, Ben-Gurion Univ., Sede Boker campus, Midereshet Ben-Gurion, Midereshet Ben-Gurion, IL
Abstract

In a world that is running out of natural resources, there is a growing need to design and develop sustainable and green energy resources. In that respect, electrochemically driven reduction of CO2 to form liquid alternative fuels holds the potential to provide a route for future carbon neutral energy economy. Nevertheless, the slow kinetics of this catalytic reaction demands the development of efficient catalysts in order to drive it at lower overpotentials. Indeed, a variety of molecular catalysts based on metal complexes are capable of electrochemically reducing CO2. Yet, despite the significant progress in this field, practical realization of molecular catalysts will have to involve a simple and robust way to assemble high concentration of these catalysts in an ordered, reactant-accessible fashion onto a conductive electrode. 

Our group utilizes Metal-Organic Frameworks (MOFs) as a platform for heterogenizing CO2 reduction molecular catalysts. Their unique properties (porosity and flexible chemical functionality), enables us to use MOFs for integrating all the different functional elements needed for efficient catalysts: 1) immobilization of molecular catalysts, 2) electron transport elements, 3) mass transport channels, and 4) modulation of catalyst secondary environment. Thus, in essence, MOFs could possess all of the functional ingredients of a catalytic enzyme.  

In this talk, I will present our recent proof-of-principle study on electrocatalytic CO2 reduction activity of MOFs incorporating molecular catalysts such as Fe-tetraphenylporphyrin and Mn(bpy)(CO)3Br.

References:

1. Hod, I.; Sampson, M. D.; Deria, P.; Kubiak, C. P.; Farha, O. K.; Hupp, J. T. “Fe-Porphyrin Based MOF Films as High-Surface-Concentration, Heterogeneous Catalysts for Electrochemical Reduction of CO2”, ACS Catalysis, 2015, 5, 6302-6309.

2. Hod, I.; Deria, P.; Bury, M.; Mondloch, J. E.; Kung, T. C; So, M.; Sampson, M. D.; Peters, A.; Kubiak, C. P.; Farha, O. K.; Hupp, J. T. “A Porous, Proton Relaying, Metal-Organic Framework Material that Accelerates Electrochemical Hydrogen Evolution”, Nature Communications, 2015, 6, 8304.

16:15 - 16:30
SF1.2.2-O3
Hegner, Franziska
Institute of Chemical Research of Catalonia (ICIQ)
Enhanced Photoanode Activity with Co-Fe Prussian blue as genuine Water Oxidation Catalyst
Franziska Hegner
Institute of Chemical Research of Catalonia (ICIQ), ES
Authors
Franziska Hegner a, Nuria Lopez a, Galán Jose-Ramon a, Gimenez Sixto b
Affiliations
Abstract

The development of an efficient, cheap and robust water-splitting catalyst remains the bottleneck step to realizing artificial photosynthesis. Materials based on Prussian blue (iron(III)hexacyanoferrate(II)), which fulfill all those criteria, have shown high catalytic activities with exceeding long-term stabilities.

Notwithstanding, the detailed catalytic mechanisms remain unclear. In combining experimental methods with theoretical calculations we want to elucidate the underlying photo-physical mechanisms and its determining factors, such as electronic structure and charge-transfer properties.

For this, catalytic systems were prepared by modifying well-known photo catalytic materials, such as α-Fe2O3 and BiVO4, with cobalt iron analogues of Prussian blue (CoFe-PB, Cox[Fe(CN)6]y). The use of CoFe-PB as a co-catalyst largely increases the photocurrent and significantly lowers the onset potential of light-induced water oxidation. Moreover, it is highly stable over a wide range of pH. We studied the electrochemical behaviour, catalytic efficiency and impedance under light and electrical field conditions. Also transient absorption spectroscopy (TAS) is used to gain more information about the behaviour of the system.

We employed various theoretical simulations based on Density Functional Theory, DFT, and evaluated their applicability. It was found that common DFT methods are insufficient to accurately describe the complex electronic and magnetic structure of Prussian blues and functionals of a higher degree of complexity are needed. With this, we developed a computational approach to investigate these systems. Moreover, we found out new insights about the electronic and magnetic structure, which might be crucial to its photo catalytic applications.

16:30 - 16:45
SF1.2.2-O4
Zhao, Yihui
FOM Institute DIFFER
Tungsten trioxide Thin Films Fabricated by Radio Frequency Sputtering and by Atomic Layer Deposition for Water Splitting
Yihui Zhao
FOM Institute DIFFER, NL
Authors
Yihui Zhao a, Shashank Balasubramanyam b, Ageeth Bol b, Anja Bieberle-Hütter a
Affiliations
a, DIFFER – Dutch Institute for Fundamental Energy Research, the Netherlands, www.differ.nl
b, Department of Applied Physics, Eindhoven University of Technology (TU/e), the Netherlands
Abstract

Abstract

Tungsten trioxide (WO3) is a promising material for photo-electrochemical (PEC) water splitting because of its good photoelectron mobility (~12 cm2V-1s-1 at RT), suitable band-gap (2.6-2.8 eV) and good chemical stability [1-3]. The microstructure, chemical states and internal defects play a sensitive in the PEC properties of WO3 [1,3]. In this study, WO3 thin films were grown on FTO-glass substrates by reactive radio frequency (RF) sputtering and by plasma enhanced atomic layer deposition (ALD), respectively. As-deposited films were annealed in a tubular furnace in different atmosphere with different ratios of nitrogen (N2) and oxygen (O2) as well as air. The structural properties were evaluated by XRD, XPS and SEM and photo-electrochemical properties were studied with cyclic voltammetry and electrochemical impedance spectroscopy in 0.5 M H2SO4 electrolyte. The results show that significantly higher photocurrent was obtained for ALD WO3 thin films during PEC water splitting than RF sputtered WO3 films. Moreover, the ALD WO3 films annealed in N2 revealed the best performance of PEC water splitting, while there is no significant difference in the structural and photo-electrochemical properties for RF sputtered WO3 films annealed in different atmosphere. In our presentation, we will relate the structural and chemical properties of the different WO3 thin films with the PEC properties and from this will conclude about how to process and design high performing electrodes for water splitting.

Reference

[1] Mi, Zhanaidarova, Brunschwig, Gray, Lewis, Energy Environ. Sci., 2012, 5, 5694–5700.

[2] Zhu, Chong, Chan, ChemSusChem, 2014, 7, 2974 – 2997.

[3] Wang, Ling, Wang, Yang, Wang, Zhang, Li, Energy Environ. Sci., 2012, 5, 6180–6187.

16:45 - 17:15
SF1.2.2-I1
Haussener, Sophia
Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland
Modelling approaches to guide best conceptual device classes and research pathways for photo-driven processing of chemical commodities
Sophia Haussener
Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, CH

Sophia Haussener is an Assistant Professor heading the Laboratory of Renewable Energy Science and Engineering at the Ecole Polytechnique F�d�rale de Lausanne (EPFL). Her current research is focused on providing design guidelines for thermal, thermochemical, and photoelectrochemical energy conversion reactors through multi-physics modelling and experimentation. Her research interests include: thermal sciences, fluid dynamics, charge transfer, electro-magnetism, and thermo/electro/photochemistry in complex multi-phase media on multiple scales. She received her MSc (2007) and PhD (2010) in Mechanical Engineering from ETH Zurich. She was a postdoctoral researcher at the Joint Center of Artificial Photosynthesis (JCAP) and the Lawrence Berkeley National Laboratory (LBNL) between 2011 and 2012. She has published over 40 articles in peer-reviewed journals and conference proceedings, and 2 books. She has been awarded the ETH medal (2011), the Dimitris N. Chorafas Foundation award (2011), and the ABB Forschungspreis (2012). She serves as an Associate Editor for the Journal of Renewable and Sustainable Energy and as a deputy head of the Swiss Competence Center of Energy Research on storage.

Authors
Sophia Haussener a
Affiliations
a, Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, Lausanne, CH
Abstract

The functionality of photo-driven electrochemical devices relies on complicated and coupled multi-physics processes, happening on multiple temporal and spatial scales. Device modelling can efficiently and actively support the choice of the most interesting – in terms of efficiency, cost, robustness, scalability, and practicability – conceptual design pathways, material choices, and operating approaches.

Models of photo-driven electrochemical devices and components can incorporate a wide range of physical phenomena and complexity. I will discuss the merit of and lessons learned from device models incorporating different degree of complexity and dimensionality. This will include i) steady and transient 0-dimensional model for the discussion of material choices, degradation and device integration, ii) steady 1-dimensional models to understand the semiconductor-electrolyte interface’s role on the performance of photocatalytic and photoelectrochemical device designs, iii) stead 2-dimensional models for the discussion of the effect of temperature and het management on the performance, and iv) 3-dimensional model for the detailed understanding of transport limitations in morphologically-complex photoelectrodes.

17:15 - 18:45
Poster Exhibition
 
Tue Sep 05 2017
SF1.3
Chair: Kevin Sivula
09:00 - 09:35
SF1.3-I1
Ardo, Shane
University of California Irvine
Engineering Bipolar Ion-Exchange Membranes to Enable New Functions Relevant to Photoelectrochemical Applications
Shane Ardo
University of California Irvine, US
Authors
William White a, Christopher Sanborn a, David Fabian a, Ronald Reiter a, Shane Ardo a, b
Affiliations
a, Department of Chemistry, University of California, Irvine, CA 92617 USA
b, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92617 USA
Abstract

Although integral to the operation of photoelectrochemical devices, few research groups develop membranes specifically engineered for photoelectrochemical applications. There is a great need for this, because the membrane electrolyte is generally the limiting factor in device sustainability and practicality due to limitations from ion crossover, alkaline instability, cost of perfluorinated membranes, and embrittlement in the presence of CO2.

In my presentation I will report on my research group’s recent results on the (photo)electrochemical behavior of novel bipolar ion-exchange membranes. Bipolar membranes are a class of polymeric ion-selective materials that consist of a cation-conductive polymer that is in intimate contact with an anion-conductive polymer. They are unique among the ion-selective membranes in that they can separate and maintain pH differences across the membrane even during the passage of ionic current. This ability arises from the presence of an electric potential space-charge region that is formed during initial ion equilibration through generation, recombination, drift, and diffusion transport processes.

Using bipolar ion-exchange membranes, my research group identified a condition where the energy required to electrolyze water was seemingly less than 1.23 V. We showed that this was due to unsustainable transport of ions other than protons and hydroxides and lack of compete formation of the space-charge region. This subtlety is one of several that are absolutely critical to correctly interpreting the current–voltage behavior of bipolar membranes. With an understanding of how to interpret electrochemical data obtained using bipolar membranes, I will report on my research group’s recent demonstration of ionic power generation through solar light harvesting in novel dye-sensitized bipolar ion-exchange membranes. Visible light was used to drive endergonic excited-state proton transfer from a cation-conductive membrane covalently modified with photoacid molecules. Photoacids convert the energy in light into a change in the chemical potential of a proton via weakening of a protic functional group on the photoacid, i.e. a decrease in its pKa. A cation-conductive membrane served as the proton-selective contact while an anion-conductive membrane served as the hydroxide-selective contact such that visible-light absorption resulted in photovoltaic action, i.e. a photocurrent and a photovoltage.

In the past half-decade, semiconductors that form the backbone of all photoelectrochemical devices have benefitted from nanostructuring, dye-sensitization, and other non-traditional innovations, yet no commercial photoelectrochemical technologies exist. Passive ion-exchange membranes that are critical to these devices have had few new developments; we believe that innovations in membrane science can help enable commercialization.

09:35 - 09:45
Discussion
09:45 - 10:20
SF1.3-I2
Oh, Jihun
Korea Advanced Institute of Science and Technology (KAIST)
Silicon Photosynthetic Cells for Efficient and Selective Solar Chemical Production
Jihun Oh
Korea Advanced Institute of Science and Technology (KAIST)
Authors
Jihun Oh a
Affiliations
a, Korea Advanced Institute of Science and Technology (KAIST)
Abstract

Solar chemical production attracts intense interest for converting solar energy into storable and distributable chemicals. While numerous semiconductors have been investigated, Si is among most promising semiconductors due to its bandgap of 1.12 eV. Here, I’ll present our recent works on Si photoelectrodes for efficient and selective photoelectrochemical (PEC) solar chemical production. Firstly, I’ll introduce a new PEC photoelectrode architecture which can maximize both light absorption and electrocatalysis on a photoelectrode. This architecture utilizes a high surface area, nanostructured cocatalysts locally defined on a photoelectrode. This local nanostructured cocatalysts provide large reaction sites and also allow light absorption in the photoelectrode. Along with PEC device modeling, we fabricate a model PEC device using Si photoanode with local Ni inverse opal (IO) nanostructures. By systematically changing surface coverage and surface area of Ni IOs on Si photoanodes, PEC devices physics of our photoelectrodes were investigated. In the second part of talk, I’ll talk about Si photocathodes with nanoporous Au cocatalysts for solar CO2 reduction reaction. The nanoporous Au cocatalysts is formed by simple electrochemical oxidation and reduction of Au thin films. Our Si photocathode with the nanoporous Au cocatalysts shows excellent CO2 reduction selectivity more than 90%. In the presentation, PEC performance of our Si electrode will be presented in detail.

10:20 - 10:30
Discussion
10:30 - 11:05
SF1.3-I3
Hammarström, Leif
Uppsala University, Sweden
Molecular Approaches to Solar Fuels
Leif Hammarström
Uppsala University, Sweden, SE
Authors
Leif Hammarström a
Affiliations
a, Department of Chemistry, Ångström Laboratory, Uppsala University, Lägerhyddsvägen, 1, Uppsala, SE
Abstract

Molecular catalysts for solar fuels processes can be tuned to a large extent via chemical design. This means a greater challenge but also a greater potential, if the design principles are understood and implemented. Important examples of molecular catalysts are enzymes, which often achieve high rates and turnover numbers by a carefully designed higher coordination sphere around their active sites. This induces stability, product specificity and typically low catalytic overpotential. It also manages the release and/or uptake of protons that controls the rate of the redox processes by proton-coupled electron transfer (PCET).  However, for solar fuels applications in man-made systems, enzymes are often costly to prepare, they have large footprints and are often unstable outside the living organism. It is therefore both of fundamental and practical interest to investigate to what extent synthetic, small molecule catalysts can be tuned and improved, based on the inspiration from enzymes.

Rational design of catalysts and comparative studies rely on detailed information about the mechanism of catalysis that in most cases is not readily available. Unbiased information on the catalyst performance is needed, beyond simple benchmarking that is subject to the conditions chosen. Detailed mechanistic studies electrochemical and spectroscopic methods can provide a good understanding of the catalyst function under different conditions.

In my lecture I will describe these issues and give examples from the literature and our own work in the Swedish Consortium for Artificial Photosynthesis. This includes the design of the catalysts’ 2nd coordination sphere, and their immobilization in molecular matrices and on surfaces. We have made extensive studies of how to control and understand PCET reactions, which we believe can guide the design of greatly improved molecular solar fuels catalysts. I will also give examples of our use of transient UV/VIS and mid-IR spectroscopy to resolve highly reactive intermediates of molecular catalysts and enzymes, and elucidate their structures, both in solution and immobilized on photoactive electrodes.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SF1.3-I4
Min, Byoung Koun
Korea Institute of Science and Technology (KIST)
Bifunctional photoelectrode by bilateral fabrication of photovoltaics and electrocatalyst
Byoung Koun Min
Korea Institute of Science and Technology (KIST), KR
Authors
Byoung Koun MIn a
Affiliations
a, Clean Energy Research Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seongbuk-gu, Seoul, 136, KR
Abstract

A photoelectrode for solar-chemical production system was constructed by Cu(InxGa1-x)(SySe1-y)2 (CIGS) thin film based solar cell technology. Particularly, low cost solution process was applied to synthesize CIGS thin films which were also tried to be fabricated on low cost and earth abundant material substrate, stainless steel (SS). Since the SS can act as an electrocatalyst for oxygen evolution reaction (OER) the CIGS on SS would have bifunctionality of photo-charge generation and overpotential reduction for water oxidation. In order to prepare highly efficient bifunctional CIGS photoelectrode the electrocatalytic properties of SS were investigated with respect to the individual process for the CIGS film synthesis (e.g. oxidation, sulfurization, and selenization). We found that the harsh oxidation of SS resulted in the formation of OER active-surface structure of NiOOH. In addition, both sulfurization and selenization of SS were found to assist the formation of Ni-Fe mixed oxide phase on SS during OER. These results imply the possibility of bilateral synthesis of the efficient photoelectrode composed of CIGS thin film solar cell and OER catalyst in a single substrate. The details of the synthetic method and characterization of each component and the solar-fuel chemical system will be discussed in the presentation.

12:20 - 12:30
Discussion
12:30 - 12:45
SF1.3-O1
Cui, Wei
University of Zurich
Deconvolution of Photovoltaic and Electrocatalytic Performance in Water Splitting Photocathodes by Dual Working Electrode Photoelectrochemistry
Wei Cui
University of Zurich, CH
Authors
Wei Cui a, David Tilley a
Affiliations
a, Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, CH-8057
Abstract

Water splitting photoelectrodes, based on buried p–n junctions, usually offer an improved photovoltage and therefore a higher solar-to-hydrogen efficiency in tandem cells. These photocathodes can be modelled as a photovoltaic junction in series with an electrocatalyst and in many cases a protective layer is necessary as well. Due to the complexity of the devices, a method enabling the deconvolution of the photovoltaic and electrocatalytic performance would provide key insight into how to improve the overall performance. In this work, we further developed the dual-working-electrode (DWE) technique to probe the surface potential of protected photocathodes during operation. As a result, properties of the buried p–n junction can be accessed, independent of the surface kinetics. Additionally, we can gain the information related to the charge transfer through the electrode/electrolyte interface independent of the photovoltaic properties. What's more, the DWE technique provides a clearer understanding of the photocathode degradation during stability tests. A pn+-Si/TiO2 photocathode is used as a model platform for developing the DWE technique, and then the versatility of the method is demonstrated through application to an emerging material system Cu2O/Ga2O3/TiO2.

12:45 - 13:00
SF1.3-O2
Mitoraj, Dariusz
University of Ulm
Ultrasmall Cocatalyst Nanoparticles for Efficient Photoelectrocatalysis: Optical Properties and Electrolyte Effects
Dariusz Mitoraj
University of Ulm, DE
Authors
Dariusz Mitoraj a, Radim Beranek a
Affiliations
Abstract

The coupling of light absorbers to cocatalysts is of fundamental importance for efficient solar-driven photoelectrocatalytic water splitting.1,2 Recently we achieved effective loading of visible light-active porous hybrid TiO2-PH (PH – polyheptazine, “graphitic carbon nitride”) photoanodes for water photooxidation with ultrasmall (~1-2 nm), highly disordered CoO(OH)x nanoparticles using a two-step impregnation method.3 Under visible light (λ > 420 nm) irradiation, the resulting photoanodes significantly outperformed photoanodes loaded with conventional cobalt-based cocatalyst (Co-Pi) comprising larger nanoparticles (~5 nm) both in terms of Faradaic efficiency of oxygen evolution (by the factor of 2) and performance stability under long-term irradiation.

The contribution will focus on elucidating the advantages of using ultrasmall CoO(OH)x nanoparticles as cocatalysts. Specifically, due to their high transparency in visible range, higher loading of porous photoanodes with cobalt catalytic sites could be achieved, while the photocurrent losses due to parasitic light absorption by the cocatalyst are minimized. Importantly, EXAFS data recorded before and after photoelectrocatalysis indicated that the significant enhancement in stability of ultrasmall CoO(OH)x nanoparticles in borate as compared to phosphate electrolytes can be explained by the difference in structural ordering dictated by interaction of the electrolyte anions with cobalt ions.

The impact of structural and optical properties of cocatalysts as well as the strong influence of the electrolyte composition on the activity and stability of photoelectrocatalytic systems comprising transition metal oxide electrocatalysts will be discussed in detail.

References

[1] M. Bledowski, L. Wang, S. Neubert, D. Mitoraj, R. Beranek, J. Phys. Chem., 2014, 118, 18951-18961.

[2] O. Khavryuchenko, L. Wang, D. Mitoraj, G. H. Peslherbe, R. Beranek, J. Coord. Chem., 2015, 68, 3317-3327.

[3] L. Wang, D. Mitoraj, O. V. Khavryuchenko, S. Turner, T. Jacob, R. Hockling, R. Beranek, ACS Catal. 2017, submitted.

13:00 - 13:15
SF1.3-O3
Ma, Ming
Department of Chemical Engineering, Delft University of Technology, The Netherlands
Electrochemical Reduction of CO2 on Compositionally Variant Au-Pt Bimetallic Thin Films
Ming Ma
Department of Chemical Engineering, Delft University of Technology, The Netherlands, NL

Ming Ma (马明) received his Master degree in Materials Science and Engineering (M Sc) in 2011 at China University of Petroleum. Now He is a PhD candidate in the laboratory of Wilson A. Smith, at Department of Chemical Engineering, Delft University of Technology. His research mainly focuses on heterogeneous nanocatalysts for the electrochemical reduction of CO2, including the fabrication, characterization, catalytic performance and reaction mechanism of nanostructured metallic catalysts.
His publications can be found: https://www.researchgate.net/profile/Ming_Ma17

Authors
Ming Ma a, Heine Hansen b, Marco Valenti a, Wilson Smith a
Affiliations
a, Department of Chemical Engineering, Delft University of Technology, The Netherlands, Van der Maasweg, 9, Delft, NL
b, Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, DK-4000, Roskilde, DK
Abstract

The electroreduction of CO2 on Au-Pt bimetallic films with tunable compositions was examined, which provides a platform for exploring the correlation of the catalytic activity with the composition of bimetallic electrocatalysts. The Au-Pt alloy films were prepared by a magnetron sputtering co-deposition technique with controllable composition, showing that the syngas ratio (CO:H2) could be tailored by systematically controlling the binary composition. The tunable catalytic selectivity is ascribed to the change of binding strength of COOH and CO intermediates, affected by the surface electronic structure (d-band center energy) which is linked to the surface composition of the bimetallic films. Notably, a d-band center was gradually shifted away from Fermi level with increasing Au content, which correspondingly weakens the binding strength of the COOH and CO intermediates, resulting in the distinct catalytic activity in the reduction of CO2 with tunable compositions. In addition, the formation of formic acid in the bimetallic systems at reduced overpotentials and higher yield indicates that synergistic effects can facilitate reaction pathways for products that are not accessible with the individual components.

SF2.3
Chair: Annamaria Petrozza
09:00 - 09:35
SF2.3-I1
Stingelin, Natalie
Georgia Tech
Solution-Processed Photovoltaics: Opportunities provided by Use of Material Science Tools
Natalie Stingelin
Georgia Tech, US

Natalie Stingelin (Stutzmann) FRSC is a Full Professor of Organic Functional Materials at the Georgia Institute of Technology, with prior positions at Imperial College London; the Cavendish Laboratory, University of Cambridge; the Philips Research Laboratories, Eindhoven; and ETH Zürich. She was an External Senior Fellow at the Freiburg Institute for Advanced Studies and is Associate Editor of the RSC journal ‘Journal of Materials Chemistry C’. She was awarded the Institute of Materials, Minerals & Mining's Rosenhain Medal and Prize (2014) and the Chinese Academy of Sciences (CAS) President's International Fellowship Initiative (PIFI) Award for Visiting Scientists (2015); she was the Chair of the 2016 Gordon Conference on 'Electronic Processes in Organic Materials' as well as the Zing conference on ‘Organic Semiconductors’. She has published >160 papers and 6 issued patents. Her research interests encompass organic electronics & photonics, bioelectronics, physical chemistry of organic functional materials, and smart inorganic/organic hybrid systems.

Authors
Natalie Stingelin a
Affiliations
a, Georgia Tech, 901 Atlantic Drive, Atlanta, 30332, US
Abstract

In the past decade, significant progress has been made in the fabrication of organic photovoltaic devices (OPVs), predominantly due to important improvements of existing materials and the creation of a wealth of novel compounds. Many challenges, however, still exist. Real understanding of what structural and electronic features determine, for instance, the short-circuit current (Jsc), open-circuit voltage (Voc) and fill factor are still lacking; and the role of charge transfer states and which charge transfer states are critical for efficient charge generation are still debated. Here we attempt to obtain further insight of relevant structure/processing/performance interrelations using classical polymer processing ‘tools’. We present a survey on the principles of structure development of this material family and how it can be manipulated, with focus on how to control the phase morphology and important interfaces (molecular and between different phase regions). Goal is to tailor and tune the final ‘morphology’ towards establishing correlations with relevant device characteristics. Examples are given based on polymer:fullerene solar cells as well as solution-processed perovskite structures.

09:35 - 09:45
Discussion
09:45 - 10:20
SF2.3-I2
DELGADO, JUAN LUIS
IKERBASQUE, Basque Foundation for Science
Perovskite:fullerene blend films for halide perovskite solar cells
JUAN LUIS DELGADO
IKERBASQUE, Basque Foundation for Science, ES
Authors
juan luis Delgado b, c, Ivet Kosta a, Silvia Collavini b, Sebastian völker b, Hans Grande a, Ramón Tena-Zaera a, Jorge Pascual a, b
Affiliations
a, IK4-CIDETEC, Parque Tecnológico de San Sebastián, Paseo Miramón 196, Donostia-San Sebastián 20009, Spain.
b, POLYMAT, University of the Basque Country UPV/EHU, Avenida de Tolosa 72, 20018 Donostia-San Sebastián, Spain.
c, Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
Abstract

The perovskite:fullerene blend films have recently shown outstanding results, including hysteresis minimization and enhanced stability, in halide perovskite solar cells [1]. In particular, we demonstrated CH3NH3PbI3:[70]fullerene films may be used as advanced light harvesters in efficient electron transport layer (ETL)-free solar cells [2], which are based on a simplified architecture that may be very appealing for the future industrial production of the perovskite-based PV technology. In this talk, apart from a short review on the application of perovskite:fullerene blend films in solar cells, the use of a variety of novel chemically modified fullerenes showing different electron accepting capabilities will be presented. The existing correlation between the LUMO energy level of the fullerene component and the open circuit voltage of the solar cells will also be discussed. In particular, blend films with isoxazolino[60] fullerenes will be highlighted by showing state-of-the-art power conversion efficiency (i.e. 14.3% [3]) for ETL-free architectures. Differences between [60] and [70]fullerenes in perovskite-based blend films will be also discussed. Interestingly, in contrast to their use as ETL in which the poorer electron mobility and visible light transmittance of [70]fullerene limit the performance of the solar cells [4], [70]fullerene seems to be better candidate for the blend films. Additionally, the use of a co-solvent for the processing of the perovskite:fullerene blend films may have a significant impact on the solar cell performance. The effect of the co-solvent on the microstructural and optoelectronic properties of the blend films will be discussed. Some practical guidelines for the choice of an appropriate co-solvent will be given. As an example, aromatic templates (e.g. o-xylene) will be proposed to be particularly beneficial compared to analogous aliphatic ones (e.g. methylcyclohexane). All in all, an overview and perspective analysis of perovskite:fullerene blends for halide perovskite solar cells will be provided.

References

Y. Shao, Z. Xiao, C. Bi, Y. Yuan, J. Huang, Nat. Commun. 2014, 5, 5784. J. Xu et al. Nat. Commun. 2015, 6, 7081.

J. Pascual et al. “Electron Transport Layer-Free Solar Cells Based on Perovskite–Fullerene Blend Films with Enhanced Performance and Stability” ChemSusChem 2016, 9, 2679–2685

R. Sandoval-Torrientes et al. “ Modified Fullerenes for Efficient Electron Transport Layer-

Free Perovskite/Fullerene Blend-Based Solar Cells” ChemSusChem 2017, 10, 2023–2029

S. Collavini et al. “Efficient Regular Perovskite Solar Cells Based on Pristine [70]Fullerene as Electron-Selective Contact” ChemSusChem 2016, 9, 1263–1270

10:20 - 10:30
Discussion
10:30 - 11:05
SF2.3-I3
Ferguson, Andrew
National Renewable Energy Laboratory
RAMP-ing the discovery of high-performance organic photovoltaic materials
Andrew Ferguson
National Renewable Energy Laboratory, US
Authors
Andrew Ferguson a, Bryon Larson a, Bertrand Tremolet de Villers a, Ross Larsen a
Affiliations
a, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado, 80401, US
Abstract

Organic semiconductors (OSCs) have found numerous applications in thin film electronic devices, including displays, sensors, lighting, and solar cells. OSCs offer the advantage that they can be modified by synthetic chemists to fulfill specific needs, and that they are not limited to being made from single elements or compositional alloys. For example, organic photovoltaics (OPVs) have reached nearly 13% power conversion efficiency (PCE) in small area devices using traditional polymer-fullerene blends, yet non-polymer and non-fullerene composites are now also showing PCEs above 10%. The flexibility offered by synthetic manipulation also presents a challenge: progress towards the discovery of next-generation, high-performance materials can be stifled by the bottleneck of device optimization through process engineering. High-throughput screening techniques that provide high fidelity performance metrics can circumvent this problem and will become important tools to accelerate material development. Here, we introduce such a tool, based on unique microwave conductivity capabilities, and illustrate a cost- and time-effective approach to evaluate the potential of promising new materials. We demonstrate the power of this approach, by correlating figures of merit from our screening tool to the OPV device performance for a library of current state-of-the-art OSCs, based on both polymer and small molecule chemical structure motifs. In the context of polymeric materials, we show that our screening process is independent of the processing conditions used to form thin films (something that cannot be said of device-based screening approaches) and we highlight the sensitivity of the screening process to physicochemical properties (e.g., molecular weight), suggesting that our tool can even be employed for batch-to-batch quality control. Finally, we will show that, in addition to the microwave conductivity figures of merit, other rapidly-accessed material properties must also be considered prior to devoting time and labor to device processing and architecture optimization. We assert that our approach has the potential to save significant effort by focusing attention on optimizing the performance of the most promising candidate materials.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SF2.3-I4
Rumbles, Garry
University of Colorado Boulder
Generating Long-lived Charges in Doped Conjugated Polymers: Controlling Carrier Delocalization
Garry Rumbles
University of Colorado Boulder

Education and Training University of Southampton, U.K., Chemistry with Electronics B.Sc. (honors), 1980 University of London, U.K., Molecular Photochemistry, Ph.D., 1984 Research and Professional Experience Laboratory Fellow. NREL, 2008�present Professor Adjoint. Department of Chemistry and Biochemistry, University of Colorado, Boulder, 2009�present Fellow. Renewable and Sustainable Energy Institute, 2009�present Group Manager. Chemical and Biosciences Center, NREL, 2004�2009 Scientist. NREL, 2001�2008 Visiting Professor. Department of Chemistry, Imperial College, London, U.K., 2001-present Sabbatical Scientist. NREL, 1999�2001 Lecturer, Senior Lecturer, Reader. Department of Chemistry, Imperial College, London, U.K., 1989�2001

Authors
Garry Rumbles a
Affiliations
a, National Renewable Energy Laboratory Denver
Abstract

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12:20 - 12:30
Discussion
12:30 - 13:05
SF2.3-I5
Walzer, Karsten
Heliatek GmbH
Organic Solar Films: From the Lab to the Field
Karsten Walzer
Heliatek GmbH, DE
Authors
Karsten Walzer a
Affiliations
a, Heliatek GmbH, Treidlerstraße 3, Dresden, 01139, DE
Abstract

We report on the latest progress on oligomer based vacuum deposited tandem and multi-junction solar cells. Efficiencies above 13% together with excellent durability are now routinely achieved for lab scale multi-junction cells. The world’s first fully integrated roll-to-roll-production tool for organic tandem junction solar cells on PET substrate film has been successfully ramped-up and delivers high quality solar films with efficiencies above 7% on the active area.

We will also discuss both the intrinsic and the extrinsic lifetimes of glass and flexible modules and identify key factors necessary to insure high lifetimes. Additionally, we will show a number of demonstration objects successfully installed by Heliatek and its partners as well as their observed lifetime and yield under real outdoor conditions and their dependence on different factors such as temperature and illumination.

As a next step, reduction of device complexity suggests the use of integrated front sheets. To do so, we will combine ultrabarrier films with transparent electrode function. The EU project ALABO develops the required technologies, especially regarding laser structuring of OPV on barrier foils. We will report latest progress in this field.

13:05 - 13:15
Discussion
13:15 - 15:00
Lunch
SF1.4.1
Chair: Daniel Esposito
15:00 - 15:15
SF1.4.1-O1
Parkinson, Bruce
University of Wyoming
Solar Fuels: Future Prospects?
Bruce Parkinson
University of Wyoming
Bruce Parkinson received his BS in chemistry at Iowa State University in 1972 and his PhD from Caltech in 1977 and was a post-doctoral scientist at Bell Laboratories in 1978. He then spent time at the Ames Laboratory and the Solar Energy Research Institute (now known as the National Renewable Energy Laboratory). He moved to the Central Research and Development Department of the DuPont Company in 1985 and in 1991 he became Professor of Chemistry at Colorado State University until his recent departure to join the Department of Chemistry and the School of Energy Resources at the University of Wyoming. His current research covers a wide range of areas including materials chemistry, surface chemistry and photoelectrochemical energy conversion. He has more than 220 peer-reviewed publications and holds 5 US patents.
Authors
bruce Parkinson a
Affiliations
a, University of Wyoming, Department of Chemistry, Laramie, 82071
Abstract

The cost of photovoltaic systems decrease has decreased rapidly where now the cost of the solar panels is now exceeded by balance of systems cost. The cost of electrolyzers will be decreasing as they are scaled and have the advantage of producing hydrogen where you want it and when you want it and at pressure. These facts mean that the window for direct solar photoelectrolysis is rapidly closing. The only hope is that a new stable, efficient, inexpensive, defect-tolerant and scalable new materials are identified that can quickly improve the efficiency of photoelectrolysis much like the hybrid perovskites are have done for photovoltaic devices. This talk will review the progress in combinatorial approaches to discover new materials for photoelectrolysis with some examples including one from the Solar Hydrogen activity Research Kit (SHArK) Project, a distributed science project that provides undergraduates and high school students with the resources to produce and screen metal oxide semiconductors for photoelectrolysis activity. In addition the reasons for producing hydrogen from water rather than direct carbon dioxide reduction to produce fuels will be reviewed. A new system for storing solar energy directly as redox equivalents, a solar chargeable redox flow battery, will also be introduced and its advantages and disadvantages compared to solar hydrogen generation will be discussed.

15:15 - 15:30
SF1.4.1-O2
Hermans, Yannick
Tu Darmstadt/UBordeaux
PES band alignment study of BiVO4 with common oxidation cocatalysts
Yannick Hermans
Tu Darmstadt/UBordeaux
Authors
Yannick Hermans a, b, Wolframm Jaegermann b, Andreas Klein b, Thierry Toupance a
Affiliations
a, UBordeaux
b, TU Darmstadt, Surface Science, Jovanka-Bontschits-Str. 2, Darmstadt, 64287, DE
Abstract

Photocatalysis with visible light is of broad interest as it allows to use sunlight for the production of hydrogen and to destroy harmful chemicals in a photochemical process.

In recent years BiVO4 has proven to be an excellent candidate for water oxidation, especially in a photoelectrochemical cell (PEC) setup. The most important advantage with respect to TiO2 is that BiVO4 has a narrow bandgap (2.4 eV) sensitive for visible light. Additionally, BiVO4 is made from low cost nontoxic materials and has a good stability during solar energy conversion. However, BiVO4 has a few inherent limits, where slow oxygen evolution kinetics and inefficient charge carrier separation are the most important.

These problems may be solved by creating BiVO4 based heterostructures as p-n junctions enhance charge carrier separation and cocatalysts improve the oxygen evolution kinetics. However, it is in general difficult to deconvolute the different effects any additional material may have on the photocatalyst performance.

In our ongoing research we try to specifically investigate how space charge layers at the BiVO4 interface affect the performance when a hetero structure is created. For this purpose we use PES (XPS, UPS) to analyze the junction of an in-situ formed heterointerface between a clean BiVO4 thin film substrate and an overlayer stepwise deposited by magnetron sputtering. From the core level binding energy shifts of BiVO4 and overlayer, band bending at the interface can be evaluated. These band bending values were then combined with UPS spectra and XPS valence band spectra to assess the band alignment at the heterointerface. So far, we have investigated how the oxidation cocatalysts RuO2, NiO and Co3O4 align with BiVO4.

15:30 - 15:45
SF1.4.1-O3
Andreu, Teresa
Catalonia Institute for Energy Research (IREC)
A photoelectrochemical flow cell design for the efficient CO2 conversion to fuels
Teresa Andreu
Catalonia Institute for Energy Research (IREC), ES
Authors
Teresa Andreu a, Erdem Irtem a, Nina Carretero a, Felix Urbain a, Carles Ros a, Maria Dolores Hernández-Alonso b, Germán Penelas-Pérez b, Joan Ramon Morante a, c
Affiliations
a, Catalonia Institute for Energy Research (IREC), Jardins de les Dones de Negre 1, Sant Adria del Besos, ES
b, Repsol Technology Center, Carretera de Extremadura A-5, km 18, 28935 Móstoles, Madrid, ES
c, Universitat de Barcelona, Unitat de Biofísica, Facultat de Medicina, C/ Casanova 143, Barcelona, 08036, ES
Abstract

The efficient photoreduction of CO2 using solar energy is one of the current challenges in catalysis. Similarly to solar hydrogen, a photoelectrochemical approach can lead to a more efficient fuel production than conventional photocatalysis by a controlled charge-carrier separation and the possibility to avoid the reoxidation of the reduced CO2 products by the use of a two-compartment cell. In this work, it will be presented how the PEC approach can be competitive towards the coupling of photovoltaic devices and carbon dioxide electrolysers to became a real alternative for solar energy storage as fuels, by means of focusing on the optimization of the individual key parameters such as the electronic transference of the photoelectrode, their overpotentials to oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide activation (CO2RR) and cell configuration (current distribution, electrolytes and membranes). Our PEC configuration has been a distinctive design enabling direct solar-to-fuel conversion employing a catalyst loaded GDE coupled to a photoanode within a continuous flow system. Two strategies were proposed to enhance the overall product efficiency to formate or syngas which are (i) adjustment of cathode dimensions and (ii) concentration of solar light on the photoanode. With the TiO2 photoanode, at an applied bias potential of 1.2 V, faradaic efficiencies of 40–65% for HCOO production were obtained on the Sn cathode, reaching energy efficiencies up to 70%. When using high efficient photoanodes, such as silicon, the photovoltage can be tuned between 0.6 V and 2.4 V by connecting up to four junction cells in series and thus, allowing bias free photoelectrolyis with optimized faradaic efficiency. The presented results prove that optimized system efficiency could be obtained with a stable photoanode providing a large photovoltage for OER and a GDE cathode with improved CO2 mass transfer which paves the way towards efficient synthesis of industrial solar fuels.

15:45 - 16:00
SF1.4.1-O4
Westerik, Pieter
University of Twente
Silicon membrane architecture for unassisted solar water splitting with separate product gasses
Pieter Westerik
University of Twente, NL

Pieter Westerik was born in Ngqeleni, South Africa on August 26th 1988. He received his BSc in Advanced Technology at the University of Twente with a study on nonlinear effects in electrostatically driven MEMS cantilevers in 2011. In 2014 he received a MSc in Electrical Engineering at the same university with a thesis in which he designed, fabricated and tested bio-inspired tympanal ears. As of March 2014 he started as a PhD student at the MCS group at the University of Twente. He is researching a micropillar based solar energy to hydrogen conversion device, with an emphasis on the technological challenges of the envisioned device.

Authors
Pieter Westerik a, Wouter Vijselaar a, Erwin Berenschot a, Juriaan Huskens a, Han Gardeniers a
Affiliations
a, MESA+ Institute for Nanotechnology, University of Twente
Abstract

Solar water splitting devices, which can directly produce hydrogen with only sunlight and water as inputs, are recognized as a promising way to overcome the intermittent nature of renewable energy resources. Besides efficient conversion of incident photons to sufficient photovoltage and photocurrent to split water, such devices face many challenges e.g. catalysis, ion transport, gas separation, etc. . Here, we present a device architecture which keeps the produced oxygen and hydrogen separate and provides low ion transport overpotential at the same time. The basis for this device architecture is a silicon membrane structure with micropores. In 1 M NaOH, a transport overpotential of 10 mV at 10 mA/cm2 was achieved while still 97 % of the surface area consists of silicon, which can be used for light absorption. Even if 99.7 % is used for light absorption, this overpotential is still only 100 mV. This was achieved by fabricating a very thin (< 40 μm) silicon substrate and introducing small pores (3 μm diameter) in it. The pitch of these holes was varied between 14 and 229 μm to create different porosities. Stability is achieved by completely protecting the silicon from the electrolyte using metallic conductors on the outer surfaces, and silicon nitride inside the pores. Earth abundant catalysts are applied on the front- and backside to further reduce the total overpotential for water splitting. Preliminary results also show the possibility of adding a second semiconductor material to create a tandem device, which shows that this device has promise for performing unassisted water splitting.

16:00 - 16:15
SF1.4.1-O5
Prabhakar, Rajiv Ramanujam
University of Zurich
Efficient Earth Abundant Copper Sulphide Photocathodes for Solar Water Splitting
Rajiv Ramanujam Prabhakar
University of Zurich, CH
Authors
Rajiv Ramanujam Prabhakar a, Wilman Septina a, David Tilley a
Affiliations
a, Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, CH-8057
Abstract

Although the best photocathodes for solar water splitting such as Si, GaInP2, GaP and copper indium gallium sulphide/selenide (CIGS) exhibit high solar to hydrogen conversion efficiencies, they either constitute rare metals or require high cost processing techniques. In order to develop large scale deployment of photoelectrochemical cells, there is a need to develop highly efficient PEC using low cost manufacturing techniques and earth abundant materials.

In this work, copper sulphide (Cu2-xS) were prepared using a simple sulphurization of copper metal. X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDX) indicate that the films were Cu2-xS. These films were found to be a degenerate semiconductor from Mott-Schottky analysis (of the order of 1022 cm-3). Photoelectrochemical cells (PEC) were fabricated using these films by using CdS as a n-type electron extraction layer and followed by a protective TiO2 layer and then a Pt catalyst. Photocurrents of ~ 1.5 mA/cm2 were obtained from this PEC device at 0 V vs RHE in a pH 7 phosphate buffer with 1 hour of stability. Various strategies to improve the photocurrent and stability of these PECs will be discussed.

16:15 - 16:30
SF1.4.1-O6
Hofmann, Jan Philipp
Eindhoven University of Technology, NL
Stabilization of trapped charge carriers in TiO2 by adsorbed water: a combined time-resolved FTIR spectroscopy and DFT+U study
Jan Philipp Hofmann
Eindhoven University of Technology, NL
Authors
Anton Litke a, Yaqiong Su a, Emiel J.M. Hensen a, Jan Philipp Hofmann a
Affiliations
a, Eindhoven University of Technology, NL
Abstract

Scalable technology for efficient solar-to-chemical energy conversion is one of the most sought after processes for storage of intermittently available renewable energy. Photocatalytic water splitting can potentially address this issue. However, efficiency of most photocatalytic systems remains very low due to the mismatch between short lifetimes of photogenerated charge carriers (fs–ns) and slow kinetics of the redox reactions (s–min). In some instances trapping of photogenerated electrons and/or holes can substantially increase their lifetimes enabling the desired redox reactions. Therefore, an in-depth understanding of charge carrier trapping and the influence of surface groups and adsorbates on this process is key for rational material optimization.

In this work we used rapid scan time-resolved diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) to study dynamics of long-living photogenerated electrons (PGE) in TiO2 P25 at subsecond to minutes timescale. We found that the signal of PGE was substantially stronger and their decay rates were slower in the presence of associated adsorbed water on the nanoparticle surface as compared to TiO2 samples dehydrated at elevated temperatures. Temperature-dependent measurements revealed that the PGE decay rates in hydrated TiO2 follow Arrhenius-type behavior in the 293–423 K temperature range with Ea = (0.06 – 0.17 eV) but became temperature independent at T > 473 K and T < 273 K. TiO2 dehydrated at high temperature exhibited hysteresis of PGE decay rates which were temperature-independent even when the material was cooled below 473 K. Materials behavior was restored upon rehydration. Temperature-dependent measurements performed with the TiO2 samples subjected to different pretreatments revealed a prominent dependence of the apparent activation energy with materials hydration. Based on the experimental results and a theoretical DFT+U analysis we conclude that hydrogen-bonding between associated adsorbed water and the oxide surface stabilizes surface-trapped holes and slows down charge carrier recombination rates.

published as: A. Litke et al., J. Phys. Chem. C 121, 7514, 2017.

 

 

16:30 - 16:45
SF1.4.1-O7
Sugiyama, Masakazu
The University of Tokyo
Polarization engineered photocathode using InGaN/AlN heterostructure for zero-bias solar water splitting
Masakazu Sugiyama
The University of Tokyo, JP
Authors
Akihiro Nakamura a, Hiroaki Maruyama a, Yoshiaki Nakano a, Katsushi Fujii b, Masakazu Sugiyama a
Affiliations
a, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JP
Abstract

III-nitride semiconductors are promising candidates for the photoelectrodes in solar water splitting because of their stability in electrolyte and the wide bandgap to straddle the redox potentials for the evolutions of hydrogen and oxygen. However, the wide bandgap is not suitable for the absorption of visible photons and a tandem structure consisting of narrower-gap InGaN is necessary for high energy efficiency. Conventional InGaN layers grown on group-III polar surfaces has a large drawback of polarization-induced electric field which hinders carrier extraction to the surface of the semiconductor structure. We have proposed a novel tandem structure in which a thin AlN sandwiched by InGaN (or GaN) serves as a tunnel junction and the polarization-induced field assists the transport of carriers to the designated surfaces. This novel structure employs group-III polar crystal layers and it can be grown with conventional metalorganic vapor-phase epitaxy process. Furthermore, the structure functions as a photocathode which is more tolerant against surface corrosion compared with a photoanode. So far, the performance of a photocarhode by nitride semiconductors has been very poor due to the inferior crystal quality of p-type nitride layers. Our polarization-engineered tandem structure with a thin AlN interlayer allows a low-doped n-type layer on the electrode surface to function as a photocathode. As a result, the novel photocathode performs in much more stable manner than a photoanode using the same low-doped n-type layer.
The development of the new structure started from the optimization of layer thicknesses, especially for the AlN interlayer. Thinner layer is better for the tunneling of carriers but the polarization-induced field to align the conduction and valence band edges at both sides of the AlN needs thicker AlN layer. The next bottleneck existed in the crystal quality of the AlN layer. A thin AlN layer grown in a coherent manner to the (In)GaN layers at the both sides, with the maximum tensile strain in the AlN, was necessary to maximize the polarization-induced electric field. However, the AlN/(In)GaN interface is very susceptive to atomic interdiffusion. Crystal growth method was improved substantially in order to minimize such diffusion. Last but not least, the growth of high-quality InGaN is mandatory, which has been realized by using GaN native substrates.
Such structural optimization and the improved growth technology allows us to fabricate a n-InGaN/AlN/n-GaN tandem photocathode, and the onset potential of photocurrent exceeded the redox potential for oxygen evolution.  

16:45 - 17:00
SF1.4.1-O8
Daiyan, Rahman
Particles and Catalysis Research Group, School of Chemical Engineering,
Tin catalysts for Conversion of Carbon Dioxide into Formate
Rahman Daiyan
Particles and Catalysis Research Group, School of Chemical Engineering,, AU

I am a Doctoral Candidate in the field of Chemical Engineering at The University of New South Wales. My research direction is to explore artificial photosynthesis through the development of solar induced catalytic conversion of carbon dioxide to hydrocarbons.

Growing up in the gas and power facilities of Bangladesh, I always took an active interest in sustainable energy. I did my Bachelor of Engineering in Mechanical Engineering from The Hong Kong University of Science and Technology. My undergraduate education involved holistic research in the solar and fuel cells.

My core competency lies in project management and leadership winning two international competitions. I take strong interest in strategy, planning, simulation and an analytic approach to problem solving.

Authors
Rahman Daiyan a
Affiliations
a, Particles and Catalysis Research Group, School of Chemical Engineering,, The University of New South Wales, Kensington, 2052, AU
Abstract

Rising levels of CO2 accumulation in the atmosphere has attracted considerable interest in technologies capable of CO2 capture, storage and conversion. [1,2] One promising route for CO2 reduction is through the electrochemical reduction of CO2 (CO2RR) using heterogeneous catalysts to produce value added chemicals such as CO, formate, ethanol and methanol. [3–5] CO2RR is carried out in ambient conditions through the application of an external electrical bias and the method mimics the photosynthesis process occurring in plants. The electricity required for CO2RR can be drawn from solar PV cells, which will provide additional benefits of storing the diffusive and intermittent renewable energy resource in the form of chemical fuels. In recent times, the conversion of CO2 to liquid products is becoming more desirable, as the products can be easily stored and transported for subsequent usage within the current infrastructure. In this regard, we have developed simple, scalable and cost-effective surface modified Sn foils that achieve a high selectivity for conversion of CO2 to formate (HCOO-), attaining a FEHCOO- (Faradaic Efficiency for HCOO-) of 77.40% at an applied potential of -1.09 V with a current density of 4.80 mA cm-2[6] To further improve the attainable current densities for HCOO- production, we also designed highly crystalline nanostructured SnO2 electrocatalysts that were shown to demonstrate improved mass transport properties that resulted in one of the highest catalytic activities at low overpotential region and achieved a maximum FEHCOO- of 75% and large current densities of 10.80 mA cm-2 at -1.15 V.

[1]       J. P. Jones, G. K. S. Prakash, G. A. Olah, Isr. J. Chem. 2014, 54, 1451–1466.

[2]       A. M. Appel, J. E. Bercaw, A. B. Bocarsly, H. Dobbek, D. L. Dubois, M. Dupuis, J.            G. Ferry, E. Fujita, R. Hille, P. J. A. Kenis, et al., 2012.

[3]       M. Gattrell, N. Gupta, A. Co, Energy Convers. Manag. 2007, 48, 1255–1265.

[4]       R. Daiyan, X. Lu, Y. H. Ng, R. Amal, ChemistrySelect 2017, 2, 879–884.

[5]       X. Lu, T. H. Tan, Y. H. Ng, R. Amal, Chem. - A Eur. J. 2016, 2052, 1–7.

[6]       R. Daiyan, X. Lu, Y. H. Ng, R. Amal, Catal. Sci. Technol., 2017, DOI:         10.1039/c7cy00246g.

 

SF1.4.2
Chair: Yogesh Surendranath
15:00 - 15:15
SF1.4.2-O1
Bae, Dowon
Technical University of Denmark
Strategies for photoelectrode protection: A case study of an extremely stable TiO2 protected c-Si device
Dowon Bae
Technical University of Denmark, DK
Authors
Dowon Bae a, Brian Seger a, Thomas Pedersen b, Ole Hansen b, Peter Vesborg a, Ib Chorknedorff a
Affiliations
a, Department of Physics, Technical University of Denmark, Fysikvej, 312, Dept. of Physics, Kgs. Lyngby, 2800, DK
b, Department of Micro- and Nanotechnology, Technical University of Denmark, ¨ªrsteds Plads, 345B, Dept. of Micro- and Nanotechnology, Kgs. Lyngby, 2800, DK
Abstract

Photoelectrochemical (PEC) water splitting is a promising approach to provide clean and storable fuel (i.e. hydrogen) directly from sunlight and water. However, major challenges still have to be overcome before commercialization can be achieved. One of the largest barriers to overcome is to obtain a stable PEC reaction in either strongly basic or acidic electrolytes without degradation of the semiconductor photoelectrodes.1 In this work, we discuss fundamental aspects of protection strategies for achieving stable solid/liquid interfaces. Besides, we also cover protection layer approaches and their stabilities for a wide variety of experimental photoelectrodes for water splitting.

Then as a case study, transparent TiO2 protected c-Si based photoelectrodes for both hydrogen and oxygen evolution (HER and OER, respectively) are discussed in-depth. The detailed working principles based on the band alignment are outlined to understand how the carriers can be injected and transferred to solid/liquid interfaces in PEC systems. Particularly, we demonstrate an extremely stable HER at pH 0 for more than 80 days under the red-light (λ ≥ 635 nm) using a TiO2 protected MOS (metal-oxide-semiconductor) based c-Si photocathode.2 So far, this is the longest stability reported in photocatalytic water reduction. Importantly, the long-term stability experiment contains day/night cyclic test that can evaluate the intrinsic stability of the protection layer.

Detailed analysis using SEM (scanning electronic microscopy), XPS (X-ray photoelectron spectroscopy) and ICP-MS (inductively coupled plasma mass spectrometry) revealed that the degradation in photocurrent mainly results from carbon contamination, which decreases reactivity and blocks the light absorption. Finally, we discuss key aspects which should be addressed in continued work on realizing a reliable and practical PEC solar water splitting device.

1. D. Bae, B. Seger, P. C. K. Vesborg, O. Hansen and I. Chorkendorff, Chem. Soc. Rev., 2017.

2. D. Bae, T. Pedersen, B. Seger, B. Iandolo, O. Hansen, P. C. K. Vesborg and I. Chorkendorff, Catal. Today, 2016.

15:15 - 15:30
SF1.4.2-O2
Moehl, Thomas
UZH
Investigation of ALD TiO2 Protection Layers for Water Splitting Photoelectrodes
Thomas Moehl
UZH
Authors
Thomas Moehl a, Jihye Suh a, Laurent Sévery a, René Wick a, David Tilley a
Affiliations
a, Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, CH-8057
Abstract

Protective overlayers for light absorbers in photoelectrochemical (PEC) water splitting devices have gained considerable attention in recent years. They stabilize light absorbers which would normally be prone to chemical side reaction leading to degradation of the absorber. Atomic Layer Deposition (ALD) enables conformal and reproducible ultrathin protective layer growth even on highly structured substrates. One of the most widely investigated protective layers is amorphous TiO2, deposited by ALD at relatively low temperature (120-150 °C). We have thoroughly investigated these ALD TiO2 layers, deposited from tetrakis-(dimethylamido)titanium(IV) at 120 and 150°C, for their chemical composition as well as optical and electrochemical properties. Our main findings reveal a change of the flat band potential with thickness, reaching a stable value of about -50 to -100 mV vs RHE for films >30 nm with doping densities of ~ 1020 cm3. Furthermore, compared to Al2O3, such TiO2 layers always show higher leakage currents. Practical thicknesses to achieve pinhole-free films are discussed, and the damaging impact of O-rings on such electrochemical devices is evaluated.

15:30 - 15:45
SF1.4.2-O3
Koike, Kayo
RIKEN - Japan
Role and model of NiO on n-type GaN Photoanode for Water Splitting
Kayo Koike
RIKEN - Japan, JP
Authors
Kayo Koike a, Kazuhiro Yamamoto b, Satoshi Ohara b, Masakazu Sugiyama c, Satoshi Wada a, Katsushi fujii d
Affiliations
a, Photonics Control Technology Team, Advanced Photonics Technology Development Group, RIKEN, Wako,Japan
b, Joining and Welding Research Institute Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047, JAPAN
c, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JP
Abstract

Solar energy converted hydrogen is becoming much more attractive as an energy storage material recently. We are focusing on the hydrogen generation by using photoelectrochemical (PEC) water splitting as a solar energy conversion. GaN was believed to be a suitable material for evaluate this method because GaN has good chemical stability and high crystal quality. However, it is difficult to maintain stable photocurrent using the n-type GaN photoanode due to anodic corrosion in PEC reactions although GaN has good chemical stability. In order to overcome this corrosion problem, NiO-loading was proposed, however, the mechanisms of this NiO-loading on n-type GaN to improve the corrosion was obscured. Thus, we discuss the mechanisms and propose the model in this report.
The experiments were performed with using n-type GaN (C.C. 2.0×1017 cm-3) as a working electrode grown by MOVPE. The NiO was deposited as NiO island shape by Ni(OH)2 dispersed solution. The counter electrode was Pt and the light was Xe-lamp. The photocurrent density as functions of time was measured for 180 min.
Firstly, we investigated the dependence of electrolyte. The NiO worked only in basic solutions, and NiO dissolved in acidic solutions. Secondly, we indicated the differences of the properties of PEC between the NiO islands and NiO layer on n-type GaN. The NiO layer showed rarely reaction due to the high resistivity. In contrast, the NiO islands showed excellent catalytic properties. Thirdly, the effect of NiO loaded ratio for the photocurrent density was evaluated. When the NiO loaded ratio was smaller, the effect of suppression of anodic corrosion became weaker. Finally, the color of the loaded NiO was observed. The color of NiO changed from transparent to black after the PEC reaction. It is proposed that the NiO on GaN changes from Ni2+ to Ni3+ during the PEC reaction. This phenomenon is probably photochromism due to the hole transport from n-type GaN to NiO. Considering all these results, we propose the band diagram between GaN and NiO. The important point of this diagram is that the valence band of semiconductor photoanode should be lower than that of loaded catalytic material. In addition, OH- concentration has an important role for PEC reaction probably because of the carrier transfer between the catalytic material and water. When the band diagram and the electrolyte condition are similar to this, the other catalytic material also expects to show similar effect.

15:45 - 16:00
SF1.4.2-O4
Kashiwaya, Shun
Technische Universität Darmstadt, Institut für Materialwissenschaft
Work function of the anatase (001) and (101) facet in different surface states
Shun Kashiwaya
Technische Universität Darmstadt, Institut für Materialwissenschaft
Authors
Shun Kashiwaya a, Andreas Klein a, Wolfram Jaegermann a
Affiliations
a, TU Darmstadt, Surface Science, Jovanka-Bontschits-Str. 2, Darmstadt, 64287, DE
Abstract

TiO2 has been intensively studied in a range of application such as solar energy conversion and photocatalysis [1]. Among different polymorphs, anatase TiO2 is generally considered as a superior photocatalyst due to its longer carrier lifetime and higher electron mobility [2]. Since the crystallographic orientation and the surface termination of metal oxides determine the electronic properties, there has been an increasing interest in the fundamental physical properties of single crystalline anatase. Ohno et al. [3] discovered the selective deposition of Pt and PbO2 on the specific orientations of rutile and anatase via photo-deposition, indicating that the faces help in the separation of photoinduced electrons and holes. The result suggests that anatase (101) provides the effective reduction site whereas anatase (001) work as the oxidation site. Despite of the importance of crystal facets, the information on the electronic properties of single crystal anatase is sparse. Especially work function plays a crucial role in electrochemical reactions as its value governs the energy junction at the interface of metal/anatase, semiconductor/anatase, and electrolyte/anatase. In this work, we performed in-situ Ultraviolet photoelectron spectroscopy to determine the work function of the anatase (001) and (101) facet in different surface states. A range of variation for obtained work function was about 2 eV between 4.5 and 6.5 eV. Our results suggest that a surface preparation has to be taken into account considerably as the value of work function drastically varies on the surface states, and could provide a practical information in terms of the energy band alignment of anatase interfaces.

 

[1] DIEBOLD, Ulrike. Surface science reports, 2003, 48.5: 53-229.

[2] SELCUK, Sencer; SELLONI, Annabella. Nature Materials, 2016, 15.10: 1107-1112.

[3] OHNO, Teruhisa; SARUKAWA, Koji; MATSUMURA, Michio. New journal of chemistry, 2002, 26.9: 1167-1170.

16:00 - 16:15
SF1.4.2-O5
Maruyama, Hiroaki
The University of Tokyo
Pt co-catalyst by photo-electrodeposition on tandem nitride semiconductor photocathode for zero-bias solar water splitting
Hiroaki Maruyama
The University of Tokyo, JP
Authors
Hiroaki Maruyama a, Akihiro Nakamura a, Yoshiaki Nakano a, Katsushi Fujii b, Masakazu Sugiyama a
Affiliations
a, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JP
Abstract

Nitride semiconductor is an interesting photocathode material for water splitting, but the preceding research suffered from low efficiency due to the wide bandgap and poor crystalline quality of p-type nitride crystals. We have proposed a tandem nitride electrode structure, n--GaN (low-doped n-GaN) /AlN/n-GaN contact/substrate. This structure can function as a photocathode without using p-type layers, and it can be extended to multi-junction structure consisted of InGaN layers for better utilization of visible photons. By optimizing the structure and the crystal growth method, it was demonstrated that the onset potential of photocurrent can slightly exceed the redox potential for oxygen evolution (EoO2/H2O). However, the onset potential was more negative than expected and the cathodic current at EoO2/H2O was too low. Two major issues were identified: (1) excessive overpotential at the photocathode, and (2) leak current through the photo-active top n--GaN to the n-GaN bottom contact. The latter is the anodic (reverse) current from the bottom contact through the pinholes in top n--GaN, which are not easy to be removed completely.

In order to solve the issue, we here aim at the selective introduction of co-catalyst on the surface of n--GaN active layer. Pt was chosen as a well-known co-catalyst for H2 evolution with low overpotential. We propose the wise use of Pt electrodeposition: selective introduction of Pt on the n--GaN surface using photo-induced cathodic current. In this method, no Pt was deposited on the exposed part of n-GaN contact at the bottom of the pinholes. It is expected that only the cathodic current generated in the top n--GaN active layer is enhanced by Pt co-catalyst. This is indeed a self-alignment process.

As compared with the electrodeposition in dark, photo-electrodeposition allowed us to obtain fine and dense Pt particles (10~100 nm in diameter and ~1010 cm-2 in density) as confirmed by AFM observation. As a result, the onset potential for cathodic current shifted to positive direction and the cathodic current increased. The improvement brought about the Pt selective introduction is especially drastic on the tandem photocathode with large number of pinholes on the top layer. When this technology was applied to the tandem photocathode with the most successful crystal growth with much reduced number of pinholes, the onset potential well exceeded EoO2/H2O. Cathodic current at EoO2/H2O amounted to 81 μA/cm2, which is a promising value for zero-bias water splitting.

16:15 - 16:30
SF1.4.2-O6
Zeidler, Andreas
Technical University of Munich
Photo-catalytic carbon dioxide reduction with InGaN photo-electrodes
Andreas Zeidler
Technical University of Munich, DE
Authors
Andreas Zeidler a, Viktoria Kunzelmann a, Martin Stutzmann a
Affiliations
Abstract

Photo-catalytic carbon dioxide (CO2) reduction is one of the most promising prospects for energy storage. The possibility to reduce the content of CO2 in the atmosphere by photo-catalytic CO2 conversion into solar fuels intensifies the interest to investigate this topic even more. Yet, many different issues have to be coped with before CO2 reduction can take a major role in future energy technology. One is the challenge to influence the CO2 reduction process in order to increase the amount of desired products. The use of indium gallium nitride (InGaN) as a working electrode may solve this issue. By adjusting the alloy composition of InGaN, it is possible to tune the band level energies, which might enhance the production of specific products, such as ethanol. In addition to this, InGaN is relatively stable under working conditions and is able to provide high-energy electrons, necessary for CO2 reduction.

The focus of the current work is the fabrication and characterization of such InGaN photo-electrodes. Using plasma-assisted Molecular Beam Epitaxy, we are able to precisely control the n- and p-type doping and alloy composition of the grown InGaN. To investigate the crystal quality of these samples we use High Resolution X-ray Diffraction and low temperature Photoluminescence, which provides information about the defects and in addition delivers the band gap energy. Kelvin Force Probe Microscopy offers interesting information about the surface potential landscape of the samples under illumination and Hall measurements reveal their charge carrier density. By using Cyclic Voltammetry and Impedance Spectroscopy, we are able to get insight into the charge transfer processes between the InGaN electrodes and suitable electrolytes.

16:30 - 17:05
SF1.4.2-I1
Deutsch, Todd
National Renewable Energy Laboratory
Over 16% Solar-to-Hydrogen Photo-Electrochemical Water Splitting on III-V Multijunction Semiconductors
Todd Deutsch
National Renewable Energy Laboratory, US

Dr. Deutsch has been studying photoelectrochemical (PEC) water splitting since interning in Dr. John A. Turner’s lab at NREL in 1999 and 2000. He performed his graduate studies on III-V semiconductor water-splitting systems under the joint guidance of Dr. Turner and Prof. Carl A. Koval in the Chemistry Department at the University of Colorado Boulder.

Todd officially joined NREL as a postdoctoral scholar in Dr. Turner’s group in August 2006 and became a staff scientist two years later. He works on identifying and characterizing appropriate materials for generating hydrogen fuel from water using sunlight as the only energy input. Recently, his work has focused on inverted metamorphic multijunction III-V semiconductors and corrosion remediation strategies for high-efficiency water-splitting photoelectrodes. Todd has been honored as an Outstanding Mentor by the U.S. Department of Energy, Office of Science nine times in recognition of his work as an advisor to more than 30 students in the Science Undergraduate Laboratory Internship (SULI) program at NREL.

Authors
Todd Deutsch a
Affiliations
a, National Renewable Energy Laboratories
Abstract

In order to economically generate renewable hydrogen fuel from solar energy using semiconductor-based devices, the U.S. Department of Energy Fuel Cells Technology Office has established technical targets of over 20% solar-to-hydrogen (STH) efficiency with several thousand hours of stability under operating conditions [1]. We have modeled attainable efficiencies of tandem absorbers that, for the first time, considered the absorption of sunlight by water [2]. We used this modeling to identify top and bottom semiconductor bandgap combinations that should be targeted to achieve maximal STH efficiency.

We had to employ several key solid-state technological advances to achieve STH efficiencies exceeding 16% [3]. The first improvement was to increase the device current via a non-lattice-matched 1.2 eV InGaAs grown using the inverted metamorphic multijunction technique developed by NREL’s III-V photovoltaics group. The second modification was to add a thin n-GaInP2 layer to p-GaInP2 to generate a "buried junction", which increased the photocurrent onset or Voc of the device by several hundred mV and enabled 14% STH efficiency. Finally, we increased the top junction photon conversion efficiency by adding an AlInP "window layer", which is commonly used in solid-state PV devices to reduce surface recombination. Through the use of a collimating tube, we measured our devices outdoors under direct solar illumination and verified over 16% STH conversion efficiency. I will also briefly introduce pitfalls of common experimental procedures that can influence the accuracy of measured STH efficiencies, which can be exaggerated for mulitjunction absorbers.

The largest loss in our current system is reflection at the semiconductor/electrolyte interface, so I will address the photon management strategies we use to achieve greater parity between measured efficiency and the theoretical limit. Capturing a significant portion of the ~25% of photons lost to reflection at this interface should allow the realization of devices that exceed 20% STH efficiency.

[1] http://energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf

[2] H. Döscher et al., Energy Environ. Sci. 7, 2951 (2016).

[3] J. Young et al., Nature Energy, 2, 17028 (2017).

17:05 - 17:15
Discussion
SF2.4
Chair: Beatriz Martin Garcia
15:00 - 15:35
SF2.4-I1
Petrozza, Annamaria
Istituto Italiano di Tecnologia
Understanding Defect Physics in Metal-halide Perovskites for Optimizing Optoelectronic Devices
Annamaria Petrozza
Istituto Italiano di Tecnologia, IT

Annamaria Petrozza received her PhD in Physics from the University of Cambridge (UK) in 2008 with a thesis on the study of optoelectronic processes at organic and hybrid semiconductors interfaces under the supervision of Dr. J.S. Kim and Prof Sir R.H. Friend. From July 2008 to December 2009 she worked as research scientist at the Sharp Laboratories of Europe, Ltd on the development of new market competitive solar cell technologies (Dye Sensitized Solar cells/Colloidal Quantum Dots Sensitized Solar cells). Since January 2010 she has a Team Leader position at the Center for Nano Science and Technology -IIT@POLIMI. She is in charge of the development of photovoltaic devices and their characterization by time-resolved and cw Photoinduced Absorption Spectroscopy, Time-resolved Photoluminescence and electrical measurements. Her research work mainly aims to shed light on interfacial optoelectronic mechanisms, which are fundamental for the optimization of operational processes, with the goal of improving device efficiency and stability.

Authors
Annamaria Petrozza a
Affiliations
a, Istituto Italiano di Tecnologia (IIT), Genova, Italy, Via Morego, 30, Genova, IT
Abstract

Semiconducting metal-halide perovskites present various types of chemical interactions which give them a characteristic fluctuating structure sensitive to the operating conditions of the device, to which they adjust. This makes the control of structure-properties relationship, especially at interfaces where the device realizes its function, the crucial step in order to control devices operation. In particular, given their simple processability at relatively low temperature, one can expect an intrinsic level of structural/chemical disorder of the semiconductor which results in the formation of defects.

Here I will review our understanding in the identification of key parameters which must be taken into consideration in order to evaluate the suscettibility of the perovkite crystals (2D and 3D) to the formation of defects, allowing one to proceed through a predictive synthetic procedure. I will discuss the role of defect physics in determing the open circuit voltage of metal halide perovskite solar cells and present technological strategies for the optimization of devices which include: 1) the engineering of the charge extracting layer (CEL), which accounts not only for the energy level alignment between the CELs and the perovskite, but also for the quality of the microstructure of the perovskite bulk film that is driven by the substrate surface;  and 2)  the use of inks based on colloidal suspensions of nanoparticles which lead to a high level of control over the material quality and device reliability,  and offer more versatile processing routes by decoupling crystal growth from film formation.

15:35 - 15:45
Discussion
15:45 - 16:20
SF2.4-I2
Jung, Hyun Suk
Sungkyunkwan University
Exploitation of Nanomaterials and Process for Facilitating Commercialization of Perovskite Solar Cells
Hyun Suk Jung
Sungkyunkwan University, KR
Hyun Suk Jung is an associate professor in school of advanced materials science & engineering at Sungkyunkwan university (SKKU). He received his BS, MS, and PhD degrees in materials science & engineering from Seoul National University (SNU), in 1997, 1999, and 2004, respectively. He joined Los Alamos National Laboratory (LANL) as a director’s postdoctoral fellow in 2005. He had worked for Kookmin University (KMU) since 2006 and joined SKKU in 2011. He published over 130 peer-reviewed papers regarding synthesis of inorganic nanomaterials and dye-sensitized solar cells. He presently researches perovskite solar cells and flexible solar cells.
Authors
Hyun Suk Jung a
Affiliations
a, School of Advanced Materials Science & Engineering, Sungkyunkwan University, Cheoncheon-dong, Jangan-gu, Suwon-si, Gyeongggi-do, Suwon, 440746, KR
Abstract

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 22% and further improvements are expected up to 25%. These novel organometal halide perovskite absorbers which possess exceptionally strong and broad light absorption enable to approach the performances of the best thin film technologies. To commercialize these great solar cells, there are many bottlenecks such as long term stability, large scale fabrication process, and environmental issues.

In this presentation, we introduce our recent efforts to facilitate commercialization of perovskite solar cells.1-5 For examples, we introduce a recycling technology of perovskite solar cells, which will facilitate the commercialization as well as solve the environmental issues of perovskite solar cells.4 Moreover, Br-concentration gradient perovskite materials were realized by using HBr treatment of perovskite materials.5 The enhancement in hole extraction was verified from measurement of photoluminescence spectroscopy. Also, we are going to discuss about stability issue of perovskite materials regarding charge generation and extraction.

(1) B. J. Kim, D.H. Kim, Y.-Y. Lee, H.-W. Shin, G. S. Han, J. S. Hong, K. Mahmood, T. Ahn, Y.-C. Joo, K. S. Hong, N.-G. Park, S. Lee and H. S, Jung, Energy Environ. Sci., 2015, 8, 916.

(2) M.-C. Kim, B. J. Kim, J. Yoon, J.-W. Lee, D. Suh, N.-G. Park, M. Choi and H. S. Jung, Nanoscale , 2015, 7, 20725.

(3) S. Jang, J. Yoon, K. Ha, M.-C. Kim, D. H. Kim, S. M. Kim, S. M. Kang, S. J. Park, H. S. Jung, and M. Choi, Nano Energy, 2016, 22, 499.

(4) B. J. Kim, D. H. Kim, S. L. Kwon, S. Y. Park, Z. Li, K. Zhu and H. S. Jung, Nature Communications, 2016, 7, 11735.

(5) M.-C Kim, B. Jo Kim, D.-Y. Son, N.-G. Park, H. S. Jung, and M. Choi, Nano Lett., 2016, 16, 5756.

16:20 - 16:30
Discussion
16:30 - 16:45
SF2.4-O1
Thumu, Udayabhaskararao
Weizmann Institute of Science
Dynamic ligand control of crystalline phase and habit in cesium lead halide nanoparticles
Udayabhaskararao Thumu
Weizmann Institute of Science, IL
Authors
Udayabhaskararao Thumu a, Miri Kazes a, Lothar Houben b, Ayelet Teitelboim a, Dan Oron a
Affiliations
a, Department of Physics of Complex Systems, Weizmann Institute of Science, Herzl Street, 234, Rehovot, IL
b, Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, IL
Abstract

Active control over the shape, composition and crystalline habit of nanocrystals is a long sought-after goal. Various methods have been shown to enable post-synthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can be induced at room temperature solely by modification of the ligand composition in solution.1,2 This scheme does not only enable fabrication of high purity monodisperse Cs4PbX6 nanoparticles with controlled sizes. Rather, dependent on the Cs4PbX6 nanoparticles final size afforded by reaction time, the back reaction yields CsPbX3 nanoplatelets with controlled thickness. These results provide insight on the very significant role of the exact ligand composition on surface stabilization (and, concomitantly, destabilization) in lead halide perovskites, and present a new post-synthetic pathway to control their morphology and composition.
References:
1. Thumu Udayabhaskararao, Miri Kazes, Lothar Houben, Hong lin, Dan Oron Chem. Mater., 2017, 29 (3), pp 1302–1308
2. Thumu Udayabhaskararao, Miri Kazes, Lothar Houben, Ayelet Teitelboim, Dan Oron
arXiv:1702.05382

20:00 - 22:00
Social Dinner
 
Wed Sep 06 2017
SF1.5
Chair: Dunwei Wang
09:00 - 09:35
SF1.5-I1
Berlinguette, Curtis
University of British Columbia
Converting CO2 into something useful
Curtis Berlinguette
University of British Columbia, CA
Dr. Curtis P. Berlinguette is an Associate Professor of Chemistry and Chemical & Biological Engineering at the University of British Columbia. After graduating with a B.Sc. in 2000 from the University of Alberta, Dr. Berlinguette headed to Texas A&M University to pursue a Ph.D. in Inorganic Chemistry (Advisor: Prof. K. R. Dunbar) before doing two years of postdoctoral studies at Harvard University (Advisor: Prof. R. H. Holm). He started his independent career at the University of Calgary in 2006 before moving his program to the University of British Columbia in 2013. He currently leads a research program fully dedicated to solar energy conversion, which includes the design of novel nanoscale materials for advanced solar cells, and developing economically viable ways of storing solar electricity as high density fuels. Dr. Berlinguette holds several patents, has authored over 50 scientific articles, and holds a Tier II Canada Research Chair and an Alfred P. Sloan Research Fellowship.
Authors
Curtis Berlinguette a
Affiliations
a, The University of British Columbia, 2036 Main Mall, Vancouver, BC, CA
Abstract

The primary mission of our program is to use inexpensive renewable energy to convert feedstocks into higher value products. One key theme is the development of (photo)electrocatalytic reactions that convert sunlight directly or indirectly into products with economic value. The use of carbon dioxide as a feedstock for conversion reactions represents a highly compelling scenario because the carbon containing products can be deployed in global fuel and chemical markets with robust infrastructures. Innovative approaches are still needed, however, in order to realize a commercially viable carbon dioxide conversion system. This presentation will outline our proof-of-principle methodologies for mediating interfacial carbon dioxide reduction reactions that produce value-added chemicals, and identifying conditions where breakdown of the active catalytic materials is avoided. These efforts include (but are not limited to) driving up the rates of carbon dioxide reduction to industrially meaningful current densities, and coupling carbon dioxide reduction with other reactions to increase the productivity of an overall system.

09:35 - 09:45
Discussion
09:45 - 10:20
SF1.5-I2
Koper, Marc
Leiden University
Mechanisms of electrocatalytic CO2 reduction
Marc Koper
Leiden University, NL

Marc T.M. Koper is Professor of Surface Chemistry and Catalysis at Leiden University, The Netherlands. He received his PhD degree (1994) from Utrecht University (The Netherlands) in the field of electrochemistry. He was an EU Marie Curie postdoctoral fellow at the University of Ulm (Germany) and a Fellow of Royal Netherlands Academy of Arts and Sciences (KNAW) at Eindhoven University of Technology, before moving to Leiden University in 2005. His main research interests are in fundamental aspects of electrocatalysis, proton-coupled electron transfer, theoretical electrochemistry, and electrochemical surface science.

Authors
Marc Koper a
Affiliations
a, Leiden University, Leiden Institute of Chemistry, Leiden, 2300, NL
Abstract

This talk will outline a simple but general analysis for multiple proton-electron transfer reactions, based on the microscopic theory of proton-coupled electron transfer reactions, recent developments in the thermodynamic theory of multi-step electron transfer reactions, and the experimental realization that many multiple proton-coupled electron transfer reactions feature decoupled proton-electron steps in their mechanism. It is shown that decoupling of proton and electron transfer leads to a strong pH dependence of the overall catalytic reaction, implying an optimal pH for high catalytic turnover, and an associated optimal catalyst at the optimal pH. When more than one catalytic intermediate is involved, scaling relationships between intermediates may dictate the optimal catalyst and limit the extent of reversibility that may be achievable for a multiple proton-electron-transfer reaction. These scaling relationships follow from a valence-bond-type binding of intermediates to the catalyst surface. The theory is discussed in relation to the electrocatalytic reduction of CO2, focusing on the importance of charged intermediates, their pH dependence and structure sensitivity.

 

10:20 - 10:30
Discussion
10:30 - 11:05
SF1.5-I3
Surendranath, Yogesh
MIT
Mechanistic Insights Into Selective CO2-to-Fuels Catalysis
Yogesh Surendranath
MIT, US
Authors
Yogesh Surendranath a, Anna Wuttig a, Youngmin Yoon a, Sahr Khan a
Affiliations
a, Massachusetts Institute Of Technology, 77 Massachusetts Avenue, Room 2-216, Cambridge, 2139
Abstract

The widespread utilization of renewable energy will require energy dense and cost-effective methods for storage. This challenge could be met by using renewable electricity to drive the reduction of carbon dioxide to energy dense carbonaceous fuels. However, many fuels are accessible over a narrow range in electrochemical potential, requiring a detailed mechanistic understanding of the key factors that control kinetic branching in these reactions. Using in situ surface-enhanced infrared reflection absorption spectrcopy, we have measured the adsorption isotherms of carbon monoxide on Cu and Au surfaces , revealing how the dynamics of this common intermediate gate the formation of higher order fuel products. Using complementary electrochemical kinetic studies, we have uncovered the disparate proton coupling requirements for hydrogen evolution relative to carbon dioxide reduction and we have applied this understanding to systematically tune product distribution in CO2-to-fuels catalysis by varying the mesostructure of the catalyst. Our latest mechanistic findings in this area will be discussed.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SF1.5-I4
nakamura, ryuhei
RIKEN Center for Sustainable Resource Science
Element Strategy of Oxygen Evolution Electrocatalysis Based on in-situ Identification of Intermediate Species
ryuhei nakamura
RIKEN Center for Sustainable Resource Science
Authors
ryuhei nakamura a
Affiliations
a, RIKEN Center for Sustainable Resource Science
Abstract

Oxygen evolution electrocatalysis has received extensive attention due to its significance in biology, chemistry, and technology. However, it is still unclear how the abundant 3d-elements can be used to drive the four-electron oxidation of water as efficiently as in Nature. In this presentation, we will propose a design strategy concerning the optimization of the charge accumulation process based on our ongoing spectroelectrochemical study on Mn, Fe, and Ir oxygen evolution catalysts. Spectroscopic identification of the reaction intermediates showed that the activity of MnO2 and Fe2O3 was dictated by the generation of Mn3+ and Fe4+, whereas in the case of IrOx, the activity did not correlate with the valence change of Ir. The efficiency of charge accumulation through valence change is closely linked with the spin configuration of the metal center, because charge disproportionation, which was found to inhibit charge accumulation in the high-spin 3d metals, requires an electron in the eg orbital. In addition to directly increasing the overpotential through the generation of an unstable intermediate, charge disproportionation inhibits charge accumulation by dissipating the total oxidative energy of the system. The model proposed in this study may help explain why low-spin 4d/5d rare metals are often more active than the abundant high-spin 3d materials for multi-electron transfer reactions in general, and provides new insight into how active 3d-metal catalysts can be synthesized by optimizing the energetics of both bond formation and charge accumulation.

12:20 - 12:30
Discussion
12:30 - 13:05
SF1.5-I5
Frei, Heinz
Lawrence Berkeley National Laboratory
Nanoscale Oxide Based Core-Shell Assembly for Photocatalytic Reduction of CO2 by H2O
Heinz Frei
Lawrence Berkeley National Laboratory, US
Heinz Frei is a Senior Scientist at Lawrence Berkeley National Laboratory in Berkeley, California. He studied chemistry at the Swiss Federal Institute of Technology (ETH) Zurich and received his doctorate degree at ETH in the Laboratory of Physical Chemistry. After a postdoctoral stay at the Chemistry Department of the University of California at Berkeley, he started a research group in solar photochemistry at LBNL with focus on chemistry with near infrared light, work for which he received the Werner Prize. Over the past two decades, Frei has established new methods for utilizing visible and near infrared light for the environmentally friendly synthesis of useful chemicals, and for the chemical storage of solar photons. Currently, his research effort focuses on the scientific challenges of the direct conversion of carbon dioxide and water to a liquid fuel by artificial photosynthesis. A frequent plenary lecturer at international conferences and member of Department of Energy workshop panels, he has co-organized several symposia of sunlight to fuel conversion in the past few years and has been elected Vice Chair of the Gordon Research Conference on Solar Fuels (2012). He led the Interface Project of the Joint Center for Artificial Photosynthesis (JCAP) and is currently Acting Director of the JCAP North Site.
Authors
Heinz Frei a
Affiliations
a, Molecular Biophysics and Integrated Bioimaging Division Lawrence Berkeley National Laboratory Berkeley, CA 94720
Abstract

Our goal is to complete the photosynthetic cycle of CO2 reduction by H2O under membrane separation of the half reactions on the nanoscale in order to minimize side reactions and charge transport efficiency losses, and enable the design of scalable systems. Co oxide nanotubes surrounded by ultrathin silica shells with embedded molecular wires (para-oligo(phenylene vinylene)) for tight control of electron transport are being developed as water oxidation catalyst-membrane assemblies driven by all-inorganic heterobinuclear light absorbers (e.g. ZrOCo). On the reductive side, a photodeposition method using the ZrOCo charge transfer chromophore allowed the spatially directed assembly of a cuprous oxide nanocluster for CO2 reduction.

Femtosecond transient absorption spectroscopy of photo-induced hole transfer to Co oxide catalyst water oxidation catalyst across the silica-embedded wires allowed the direct observation of charge arrival on the wire molecule, which takes place in less than a ps. Charge separation was indicated by the emerging wire radical cation. Subsequent forward transfer of the positive charge to the Co oxide particle occurred in 250 ps, exceeding known hole transfer rates from anchored molecular light absorbers to metal oxide catalyst particles for water oxidation by several orders of magnitude. Arrival of holes on Co3O4 was indicated by bleach at 485 nm. The finding indicates that molecular light absorbers coupled to metal oxide catalysts by silica-embedded oligo(phenylene vinylene) offers an approach for integrated artificial photosystems featuring efficient hole transfer while enabling product separation on the nanoscale.

The nanometer-thin dense phase silica layers with embedded organic wires covalently anchored on the surface of Co oxide water oxidation catalyst were shown by visible light sensitized electrochemical measurements to tightly control transport of charges across the proton conducting, O2 impermeable membrane by the orbital energetics of the wire molecules. Visible light sensitization using Ru(bpy)3 resulted in short circuit current (27 e-s-1wire-1), consistent with favorable alignment of the [Ru(bpy)3]3+ potential with respect to the HOMO energy of the wire. By contrast, visible light-generated reduced Sn porphyrin did not induce current because the potential is situated in the HOMO-LUMO gap of the wire. The finding demonstrates rectifying property of the light absorber-wire assembly.

Mechanisms of water H2O and CO2 reduction on metal or metal oxide nanoparticle catalysts are elucidated by time-resolved ATR FT-IR spectroscopy under photocatalytic conditions by identifying transient surface intermediates. Recent new insights from the spectroscopic studies will be discussed.

13:05 - 13:15
Discussion
SF2.5
Chair: Garry Rumbles
09:00 - 09:35
SF2.5-I1
de Mello, John
Imperial College London
Flow-based synthesis of electronic materials
John de Mello
Imperial College London, GB
Authors
John de Mello a, b
Affiliations
a, Norwegian University of Science and Technology (NTNU), Insitutt for materialteknologi, Trondheim, 7491, NO
Abstract

Solution-based plastic electronics (PE) manufactured by fast roll-to-roll coating is a promising technology for fabricating large-area electronic devices such as photovoltaic modules, lighting panels and displays at a fraction of the cost of conventional electronics. However, for the technology to succeed, the cost and performance of PE materials and devices must be greatly improved relative to current levels. Here I will describe a scalable approach to preparing high quality PE materials based on droplet microfluidics, which offers greatly improved control over materials properties compared to conventional batch synthesis. The method can be applied to a broad range of electronic materials, including quantum dots, metal nanocrystals and semiconducting polymers, and offers a viable solution to the challenge of producing high quality PE materials in quantities sufficient for industrial application. Key advantages of the microfluidic approach will be discussed, together with a number of challenges that must be addressed in order to reach commercial viability.

09:35 - 09:45
Discussion
09:45 - 10:20
SF2.5-I2
Chabinyc, Michael
University of California, Santa Barbara
Transport and Microstructure in Materials for Solution Processable Solar Cells
Michael Chabinyc
University of California, Santa Barbara
Authors
Michael Chabinyc a
Affiliations
a, Materials, University of California Santa Barbara, University of California, Santa Barbara, 93106, US
Abstract

Solution-processed materials have significant promise for future generation solar cells. We will discuss our efforts to understand charge transport and carrier lifetimes as a function of structure in two classes of materials for thin film solar cells.

Organic photovoltaics have a bulk heterojunction (BHJ) structure where an electron donor and acceptor meet in a bicontinuous network with nanoscale dimensions. The development of non-fullerene acceptors has led to prospects for improvement of their power conversion efficiency through reduced losses in the open circuit voltage. We will discuss recent work to understand the origin of these effects in non-fullerene acceptors through microstructural studies and device characterization.

Hybrid organic metal halides, such as CH3NH3PbI3, have garnered significant attention because they are earth-abundant, solution processable materials with high power conversion efficiency. The origin of the observed long carrier lifetimes in these materials that improve their electronic properties are still under significant debate. We will present our recent work on the properties of layered materials systems formed by replacement of halide ions by the pseudohalide thiocyanate (SCN-) and by the introduction of a mixed organic cations to form Ruddlesden-Popper structures. Using time-resolved microwave conductivity (TRMC), the carrier mobility of CH3NH3Pb(SCN)2I was found to be relatively high and comparable to that of polycrystalline CH3NH3PbIalong with similar carrier lifetimes. In contrast, the layered R-P materials layered with organic cations do not show such apparent long lifetimes. We will present structural studies of polycrystalline thin films that help to address this difference in behavior.

10:20 - 10:30
Discussion
10:30 - 11:05
SF2.5-I3
Caironi, Mario
Istituto Italiano di Tecnologia (IIT), Genova, Italy
Ion migration effects and photoconductivity in hybrid perovskite optoelectronic devices
Mario Caironi
Istituto Italiano di Tecnologia (IIT), Genova, Italy, IT
Authors
Mario Caironi a
Affiliations
a, Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, I-20133 Milan, Italy
Abstract

Solution-processable hybrid perovskite photovoltaics combine potential for low-cost fabrication with high power-conversion efficiency. The observation of slow transient and hysteretic effects observed in perovskite-absorber devices, which has severely affected current density–voltage (J-V) measurements and efficiency determination in early reports, has spurred further efforts in exploring the working mechanisms of such opto-electronic devices. Ion migration towards the electrode regions has been recently and independently reported by several group as a source of hysteresis and self-sustained field within various 3D perovskite semiconductors. A variety of dynamics have been reported, which differ in magnitude and time scale, depending both on the specific device architecture and, in particular, on the adopted charge extraction layer, highlighting a considerable effect of contact interfaces on transients in perovskite based devices.

I will first report on the role played by charge extracting layers on the slow transient behavior of CH3NH3PbI3 perovskite based solar cells. Such transients are found to notably modify the open circuit voltage also in the very first J-V scans of so called “hysteresis-free” devices integrating a Phenyl-C61-butyric acid methyl ester (PCBM) charge extraction layer. I will highlight how, under device operation, iodide ions migrate to the electron extracting layer: this effect requires a pre-conditioning of the device, i.e. a repetition of J-V scans, is needed to achieve completely stable J-V characteristics under illumination. The interaction of PCBM with migrating ions and the effect of PCBM on the photoconductivity of perovskite semiconductors will also be illustrated.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:15
SF2.5-O1
Ardo, Shane
University of California Irvine
Using Electrocatalysis to Overcome Efficiency Bottlenecks in Iodine-Based Dye-Sensitized Solar Cells
Shane Ardo
University of California Irvine, US
Authors
Shane Ardo a, Joseph M. Cardon a, Kevin Tkacz a, Jacqueline Angsono a, Gregory Krueper a, Hsiang-Yun Chen a
Affiliations
a, University of California Irvine, 2412 Engineering Hall, Irvine, 92617, US
Abstract

Thin films of mesoscopic metal-oxide semiconductors containing surface-bound dyes could serve as low-cost and robust alternatives to silicon for photovoltaic applications. However, their energy-conversion efficiencies are only half as large as those of silicon. To increase efficiency, my research group is incorporating electrocatalysts to drive multiple-electron-transfer halide redox chemistry at the dye-sensitized photoanode. This design scheme allows for dyes that are weaker oxidants when oxidized, therefore extending dye absorption into the near-infrared spectral region and increasing projected solar-cell efficiencies to beyond 20%.

Effective implementation of this innovative design requires three major developments: (1) near-infrared-absorbing dyes, (2) efficient electrocatalysis of two-electron-transfer iodide oxidation, and (3) generation of the active state of electrocatalysts via single-electron-transfer events with dyes. Toward (1), we have designed and synthesized new Os(II)–polypyridyl dyes that absorb light out to ~1 µm. Toward (2), we have identified two molecular motifs that drive the two-electron-transfer oxidation of iodide at low overpotential. Toward (3), using nanosecond transient absorption spectroscopy we have showed that a dye-sensitized mesoporous thin film of anatase TiO2 nanocrystallites and functionalized with molecular charge acceptors can accumulate multiple oxidizing equivalents by single-electron-transfer events with oxidized dyes and through requisite self-exchange electron-transfer between surface-anchored dye molecules. This is the first report that has unequivocally shown such behavior under conditions of low-fluence (solar) excitation. Monte Carlo simulations support the observed behavior and the results are consistent with a mechanism where ~100 self-exchange electron-transfer events occur between dye molecules prior to oxidation of the molecular charge acceptors. Slow charge recombination between electrons in TiO2 and the oxidized molecules anchored to the surface of TiO2 enabled this demonstration. My research group also recently observed that the rate of self-exchange electron-transfer between surface-anchored dye molecules is highly dependent on the nature of the supporting electrolyte cations. The most rapid self-exchange processes were observed when mixed electrolytes of Li+ and n-tetrabutylammonium+ were utilized, suggesting that a synergism exists between cations. I will also report on my research group’s recent efforts to couple the three processes described above and demonstrate a new world-record iodine-based dye-sensitized solar cell.

The proof-of-concept demonstrations described herein validate the new proposed mechanistic processes and suggest that there may in fact be clear pathways to enable dye-sensitized devices with > 20% efficiency.

12:15 - 12:30
SF2.5-O2
Lanzetta, Luis
Imperial College London
Visible Emitting 2D Hybrid Tin Halide Perovskites for Use in Light-Emitting Devices
Luis Lanzetta
Imperial College London, GB
Authors
Luis Lanzetta a, Jose Manuel Marin-Beloqui a, Irene Sanchez-Molina a, Dong Ding a, Saif A. Haque a
Affiliations
a, Imperial College London, South Kensington, London,, GB
Abstract

Organic lead halide perovskites have emerged as an outstanding class of materials for optoelectronic applications, with numerous examples in the fields of photovoltaics and light-emitting diodes. Nevertheless, the toxicity of lead is an issue of major concern that needs to be addressed for the commercialisation of this novel technology. The use of tin as a replacement for lead has been studied with promising results, although tin-based perovskites are significantly more sensitive to ambient conditions and exhibit unwanted metallic conductivity due to a self-doping issue.

Reduced-dimensionality perovskites have been recently introduced as a way of increasing material and device stability in lead-based materials. However, this approach has not been explored for device applications in hybrid tin halide perovskites. Interestingly, the metal-like behaviour of 3D systems (e.g. CH3NH3SnI3) can be suppressed by replacing methylammonium by larger organic cations (phenylethlyammonium, butylammonium) to induce the formation of 2D structures that present semiconducting properties1. This talk will cover the latest advances of our group in the field of low-dimensional hybrid tin halide perovskites. Specifically, the tunable optical properties of our materials, their photoluminescence characteristics and their capability to act as TiO2 sensitizers will be discussed. Finally, the incorporation of 2D tin-based perovskites into proof-of-principle light-emitting devices will be shown.

 

1            D. B. Mitzi, C. a. Feild, W. T. a. Harrison and  a. M. Guloy, Nature, 1994, 369, 467–469.

12:30 - 12:45
SF2.5-O3
Liu, Quan
ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology
Two-resonance tapping cavity for broadband light confinement in thin film photovoltaic cells
Quan Liu
ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, ES
Authors
Quan Liu a, Johann Toudert a, Silvia Colodrero a, Jordi Martorell a, Jordi Martorell b
Affiliations
a, ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Avinguda Carl Friedrich Gauss, 3, Castelldefels, ES
b, Departament de Física i Enginyeria Nuclear, UPC, Terrassa, ES
Abstract

Two-resonance tapping cavity for broadband light confinement in thin film photovoltaic cells

 

 

After decades of thin film photovoltaic technology development, many different physical phenomena have been considered and partial success in improving the cell efficiency has been reached when a certain degree of light trapping has been demonstrated. However, light-trapping or confinement has never been shown to be critical to achieve record performing thin film cells.

In this work, we implement a two-resonance tapping cavity (TRTC) to reach an optimal broadband confinement for electromagnetic waves.[1] We demonstrate that the combination of an insulator cavity layer with a metal cavity layer leads to the formation of an optical cavity that can be made to resonate at two non-harmonic frequencies. The increase in energy storage capacity relies in the inharmonicity of the electromagnetic field propagation within the TRTC. We demonstrate that the energy confinement capacity seen is to a large extent independent of the material composition or thickness of the active layer. We experimentally measured and certified record efficiencies (>11%) for a PTB7-Th polymer cell and predicted that when the TRTC is applied to a perovskite cell the EQE would closely match the IQE for a broad frequency range predicting ultimate efficiencies for single junction cells based on perovskites.

 [1] Q. Liu, P. Romero-Gomez, P. Mantilla-Perez, S. Colodrero, J. Toudert, J. Martorell, Adv. Energy Mater. 2017, 1700356.

 

12:45 - 13:00
SF2.5-O4
Martin Garcia, Beatriz
Istituto Italiano di Tecnologia (IIT), Genova, Italy
PbS QD solar cells with improved stability under ambient conditions through integration of reduced graphene oxide
Beatriz Martin Garcia
Istituto Italiano di Tecnologia (IIT), Genova, Italy, IT

-

Authors
Beatriz Martín-García a, Yu Bi b, Mirko Prato a, Davide Spirito a, Roman Krahne a, Gerasimos Konstantatos b, Iwan Moreels a
Affiliations
a, Istituto Italiano di Tecnologia (IIT), Genova, Italy, Via Morego, 30, Genova, IT
b, ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Avinguda Carl Friedrich Gauss, 3, Castelldefels, ES
Abstract

Preserving the performance of photovoltaic devices exposed to atmospheric factors such as humidity, oxygen, high temperature or UV irradiation is key for practical application. For PbS quantum dot (QD) solar cells, the presence of oxygen promotes the formation of PbO or PbSOx, often resulting in device failure.[1,2] To address this issue, we developed a coating strategy consisting of spin-coating a PbS-silane functionalized reduced graphene oxide (PbS-rGO) hybrid material[3] as protective layer. Measurements of the power conversion efficiency (PCE) over time demonstrate that solar cells with a PbS-rGO film integrated into the absorber layer show an enhanced stability, especially under humid conditions.

The solar cells absorber layer consists of PbS:EMII (200nm)[4] / PbS:EDT (10 nm) / PbS-rGO:EDT (44 nm) films. An average (best) PCE of 5.7% (7.6%) was achieved, comparable to corresponding PbS reference cells where we obtained 8.2% (9.0%). Continuous illumination of the devices and exposure to a saturated water vapor environment demonstrated the unique advantage of the PbS-rGO layer. Device stability in the first case was slightly improved, with a relative decrease of PCE of 37% after 168h of continuous illumination, compared to 46% for the PbS reference cells. More importantly, when exposing the PbS-rGO solar cells to a saturated water vapor atmosphere for 5 days, they retained 96% of the initial PCE, while the PCE of the PbS reference cells was reduced to about 50% of its initial value. As result, even the absolute PCE of the PbS-rGO solar cells surpassed the reference cells after 24h. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed that device failure in the PbS reference cells under humid conditions is due to formation of PbSOx crystals and cracks in the PbS film. Such degradation was not observed in the PbS-rGO devices.

Our results contribute toward the practical implementation of QD solar cells and, given the versatility of the silane-functionalized rGO, the approach can also be extended to other solution-processed devices which suffer from atmospheric stability, as organic or perovskite solar cells.

 

Acknowledgements

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No-696656 (GrapheneCore1).

References

[1]       J. Tang et al., ACS Nano 2010, 4, 869.

[2]       G. Zhai et al., Appl. Phys. Lett. 2011, 99, 63512.

[3]       B. Martin-Garcia et al., J. Mater. Chem. C 2015, 3, 7088.

[4]       Y. Cao, et al., Nat. Energy 2016, 1, 16035.

13:00 - 13:15
Abstract not programmed
13:15 - 13:25
Closing
16:30 - 18:05
Registration 7-8 Sept
 
Thu Sep 07 2017
07:30 - 08:45
Registration
08:45 - 09:00
Opening
SE1.1
Chair: Jonathan Owen
09:00 - 09:35
SE1.1-I1
Talapin, Dmitri
University of Chicago
Synthetic methodology for semiconductor nanomaterials: challenges and opportunities
Dmitri Talapin
University of Chicago, US
Dmitri Talapin is a Professor of Chemistry at University of Chicago. His research interests revolve around inorganic nanomaterials, spanning from synthetic methodology to device fabrication, with the desire of turning colloidal nanostructures into competitive materials for electronics and optoelectronics. He received his doctorate degree from University of Hamburg, Germany in 2002 under supervision of Horst Weller. In 2003 he joined IBM Research Division at T. J. Watson Research Center as a postdoctoral fellow to work with Chris Murray on synthesis and self-assembly of semiconductor nanostructures. In 2005 he moved to Lawrence Berkeley National Laboratory as a staff scientist at the Molecular Foundry and finally joined faculty at the University of Chicago in 2007. His recent recognitions include MRS Outstanding Young Investigator Award (2011); Camille Dreyfus Teacher Scholar Award (2010); David and Lucile Packard Fellowship in Science and Engineering (2009); NSF CAREER Award (2009) and Alfred P. Sloan Research Fellowship (2009).
Authors
Dmitri Talapin a, b
Affiliations
a, University of Chicago, 929 East 57th st, Chicago, 60637, US
b, Argonne National Laboratory, Center for Nanoscale Materials, 9700 South Cass Avenue Bldg 440, Lemont, Illinois 60439, US
Abstract

Colloidal chemistry has revolutionized the synthesis of inorganic nanomaterials. The field has evolved tremendously, both in the fundamental understanding of nucleation, growth and surface chemistry of nanocrystals and in the ability to provide a toolset for the preparation of functional materials with precisely engineered size, shape, and structure. However, the current methodology has several limitations that need to be carefully explored and addressed.

The lack of atomic precision in the synthesis of functional nanomaterials restricts the ability to harness all the power of this broad and diverse class of materials. Real nanomaterials always vary in size to a certain extent. This variation introduces inhomogeneous broadening of the absorption and emission spectra and reduces charge carrier mobilities in nanocrystal films. The polydispersity originates from a weak size dependence of the free energy related to the addition or removal of individual atoms to/from a nanoscale object. In this case, size distribution can only be controlled by kinetic factors and it would be difficult to further improve the homogeneity of kinetically controlled reaction products. We discuss a paradigm-shifting approach for the colloidal synthesis of nanomaterials with minimal, ideally no, size distribution. The goal is to establish means to thermodynamically control nanomaterials synthesis using a sequence of two complementary self-limiting surface reactions. This concept is inspired by the success of gas-phase atomic layer deposition (ALD) widely used in microelectronics and other fields. Our studies show that the ALD concept can be implemented in solution and, when applied to colloidal nanomaterials, enables layer-by-layer growth of crystalline lattices with true atomic precision.

The other general limitation of traditional colloidal chemistry is related to the thermal stability of organic solvents at high temperatures required for some hard-to-crystallize materials. Very few organic substances remain liquid above 400°C, and solvent or ligands decomposition becomes a serious problem at even higher temperatures. The use of inorganic salts as solvents eliminates this issue and brings new opportunities. As an example, colloidal synthesis of GaAs nanocrystals was unsuccessful for over 20 years. We found that GaAs NCs synthesized in organic solvents generally have a high concentration of vacancies and antisite defects. Annealing of the colloid in a molten salt at 500°C eliminated these structural defects without NC sintering. We envision multiple exciting opportunities for colloidal chemistry in molten salts.

09:35 - 09:45
Discussion
09:45 - 10:20
SE1.1-I2
Ithurria, Sandrine
Ecole Superieure de Physique et de Chimie Industrielles
2D nanoplatelets of II-VI semiconductors: from material synthesis to optoelectronic devices
Sandrine Ithurria
Ecole Superieure de Physique et de Chimie Industrielles

i

Authors
Sandrine Ithurria a
Affiliations
a, ESPCI, Laboratory of Physics and Study of Materials
Abstract

My talk will review the progress of our group about the growth of 2D nanoplatelets (NPLs) of metal chalcogenides. The story will start with the synthesis of cadmium chalcogenides (CdSe, CdS and CdTe) NPLs and discuss both their growth process and specific optical features.1 In particular the NPLs present the narrowest optical features obtained, so far, for colloidal nanoparticles.

I will then move to the growth of heterostructures. As fragile objects, the growth of core/shell nanoparticules has required the development of specific low temperature method such as the colloidal Atomic Layer Deposition method.2 I will also discuss the integration of the CdSe/CdS NPLs into devices and how their 2D aspects affect their optoelectronic properties in particular through their large excitonic binding energy.3,4

2D shape also allows the growth of specific heterostructures with core/crown geometry which leads to a new degree of freedom for the design of the excitonic transition.5,6

Finally I will discuss the growth of mercury chalcogenides NPLs using a cation exchange approach. Compared to spherical quantum dots emitting in the same range of wavelength, the HgTe NPLs present a similar PL efficiency (10%) but with a far narrower emission (60meV for an emission at 880nm).7 To finish I will mention how the transport and phototransport properties of the material are strongly affected by a change of the capping ligands.

Reference

(1)         Ithurria, S.; Tessier, M. D.; Mahler, B.; Lobo, R. P. S. M.; Dubertret, B.; Efros, A. L., Nature Materials, 2011, 10, 936–941.

(2)         Ithurria, S.; Talapin, D. V., J. Am. Chem. Soc. 2012, 134, 18585–18590.

(3)         Lhuillier, E.; Dayen, J. F.; Thomas, D. O.; Robin, A.; Doudin, B.; Dubertret, B., Nano Lett. 2015, 15, 1736–1742.

(4)         Lhuillier, E.; Robin, A.; Ithurria, S.; Aubin, H.; Dubertret, B., Nano Lett. 2014, 14, 2715–2719.

(5)         Tessier, M. D.; Spinicelli, P.; Dupont, D.; Patriarche, G.; Ithurria, S.; Dubertret, B., Nano Lett. 2014, 14, 207–213.

(6)         Pedetti, S.; Ithurria, S.; Heuclin, H.; Patriarche, G.; Dubertret, B., J. Am. Chem. Soc. 2014, 136, 16430–16438.

(7)         Izquierdo, E.; Robin, A.; Keuleyan, S.; Lequeux, N.; Lhuillier, E.; Ithurria, S. , J. Am. Chem. Soc. 2016, 138, 10496–10501.

10:20 - 10:30
Discussion
10:30 - 11:05
SE1.1-I3
Kovalenko, Maksym
ETH Zurich
Colloidal APbX3 nanocrystals [A=Cs+, CH3NH3+, CH(NH2)2+, X=Cl, Br, I] with bright photoluminescence spanning from ultraviolet to near-infrared spectral regions
Maksym Kovalenko
ETH Zurich, CH

Maksym Kovalenko has been a tenure-track Assistant Professor of Inorganic Chemistry at ETH Zurich since July 2011 and Associate professor from January 2017. His group is also partially hosted by EMPA (Swiss Federal Laboratories for Materials Science and Technology) to support his highly interdisciplinary research program. He completed graduate studies at Johannes Kepler University Linz (Austria, 2004-2007, with Prof. Wolfgang Heiss), followed by postdoctoral training at the University of Chicago (USA, 2008-2011, with Prof. Dmitri Talapin). His present scientific focus is on the development of new synthesis methods for inorganic nanomaterials, their surface chemistry engineering, and assembly into macroscopically large solids. His ultimate, practical goal is to provide novel inorganic materials for optoelectronics, rechargeable Li-ion batteries, post-Li-battery materials, and catalysis. He is the recipient of an ERC Consolidator Grant 2018, ERC Starting Grant 2012, Ruzicka Preis 2013 and Werner Prize 2016. He is also a Highly Cited Researcher 2018 (by Clarivate Analytics).

Authors
Maksym Kovalenko a, b
Affiliations
a, Department of Chemistry and Applied Biosciences, Institute of Inorganic Chemistry, ETH Zürich, Vladimir Prelog Weg 1, 8093 Zürich, CH
b, Laboratory for Thin Films and Photovoltaics, Empa − Swiss Federal Laboratories for Materials Science and Technology, Switzerland, Überland Strasse, 129, Dübendorf, CH
Abstract

Chemically synthesized inorganic nanocrystals (NCs) are considered to be promising building blocks for a broad spectrum of applications including electronic, thermoelectric, and photovoltaic devices. We have synthesized monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors [1]. Their bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 NCs is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90% and also low thresholds for stimulated emission [2]. Post-synthestic chemical transformations of colloidal NCs, such as ion-exchange reactions, provide an avenue to compositional fine tuning or to otherwise inaccessible materials and morphologies [3]. Similar synthesis methodologies are well suited also for hybrid perovskite nanocrystals based on methylammonium (MA) and formamidinium cations (FA): MAPbX3 [4], FAPbBr3 [5], Cs1-xFAxPbI3 and FAPbI3 [6]. In particular, Cs- and FA-based NCs (Figure below) are highly promising for luminescence downconversion (bright and narrow emission at 530 and 640 nm), for infrared light-emitting diodes and as precursors/inks for perovskite solar cells. In this talk, we will discuss the synthesis methodologies and optical properties of these novel APbX3 NCs. 

L. Protesescu et al. Nano Letters 2015, 15, 3692–3696

G. Nedelcu et al. Nano Letters 2015, 15, 5635–5640

S. Yakunin et al. Nature Communications 2015, 9, 8056.

O. Vybornyi et al. Nanoscale 2016, 8, 6278-6283

L. Protesescu et al. J. Am. Chem. Soc. 2016, 138, 14202–14205

L. Protesescu et al. ACS Nano 2017, 11, 3119–3134

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SE1.1-I4
Murray, Christopher B.
Philadelphia University
Design and assembly of coupled multicomponent nanocrystal superlattices and quasicrystalline assemblies and superparticles
Christopher B. Murray
Philadelphia University, US
Authors
Christopher B. Murray a, b, Yaoting Wu a, Blaise Fleury a, Stan Najmr a, Davit Jishkariani a, Katherine C Elbert a, Cherie R. Kagan a, b, c, Da Wang d, Alfons van Blaaderen d
Affiliations
a, University of Pennsylvania, 200 South 33rd Street, Philadelphia, 19104, US
Abstract

Studies of the preparation and properties of colloidal crystals comprised of nanocrystals (NCs) of controlled composition, size, shape, and surface functionalization provides insight into the fundamental organization of matter on multiple lengths scales. In this talk, we will share progress in the preparation of extended 3D periodic superlattice films and discuss the design rules that direct the formation of quasicrystalline systems.  These NC assemblies offer novel platforms exploration of the cross coupling of physical properties as the quantum confined electronic states of semiconductor NCs interact with the plasmonic resonances of co-assembled noble metals and with nanomagnets, leading to hybrid properties on the mesoscale. To date, the programming of NC assemblies (extended lattices and discrete superparticles) has largely leveraged control of NC size and shape in combination with relatively simple surface functionalization by surfactants for close NC coupling and has leveraged DNA and polymers for larger NC spacings.  The design of ligands and surface passivation can direct the organization and optimize the interaction between NCs and impart patchy/direction functionalization is of particular interest. We will share our efforts design surface ligands using a wider range of supermolecular chemistry and develop dendrimer-based stabilizers. These dendrimer / NC hybrids allow precise geometric and chemical control of the superlattice assembly symmetry and lattice spacing that govern NC interactions.

12:20 - 12:30
Discussion
12:30 - 12:45
SE1.1-O1
Berends, Anne
Universiteit Utrecht
Surface chemistry determines fate of shell overgrowth or alloying reactions in CuInS2 nanocrystals
Anne Berends
Universiteit Utrecht, NL
Authors
Anne Berends a, Ward van der Stam a, Jan Philipp Hofmann b, Eva Bladt c, Johannes Meeldijk d, Sara Bals c, Celso de Mello Donega a
Affiliations
a, Molecular Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology
b, Electron Microscopy for Materials Research (EMAT),, University of Antwerp,Groenenborgerlaan 171, 2020 Antwerp
Abstract

Over the last decades, the scientific community has accumulated extensive knowledge over colloidal nanocrystals (NCs) of II-VI semiconductors. It is by now well-established that defects in these materials are mostly located at the surface and invariably lead to exciton trapping, which is typically followed by non-radiative decay or inefficient radiative recombination resulting in strongly red-shifted photoluminescence (PL) with low quantum yields (QYs). Consequently, overgrowth of shells of wider band-gap semiconductors effectively blocks exciton trapping, thereby allowing near-unity PLQYs to be achieved.

In contrast, I-III-VI2 semiconductors (e.g., CuInS2) have a very rich defect chemistry and, as a result, NCs of these materials have not only surface defects but also a variety of native defects, such as vacancies and anti-site defects. Interestingly, radiative recombination in I-III-VI2 NCs involves hole localization in intrinsic defects, which can lead to PLQYs as high as 85%, provided the surface is passivated by suitable shells [1]. However, ZnS shelling of I-III-VI2 NCs has been reported to invariably lead to blue-shifts in both the absorption and PL spectra, ranging from tens to hundreds of meV [2]. These spectral blue-shifts have been attributed to a number of reasons: etching of the core prior to shell overgrowth, shell ingrowth by cation exchange, or alloy formation due to interdiffusion [2].

These observations imply that the outcome of shelling reactions on I-III-VI2 colloidal NCs results from a complex interplay between several processes taking place in solution, at the surface of and within the core NC. However, a fundamental understanding of the parameters determining the balance between these different reaction pathways is still lacking. In this work, we address this need by investigating the role of the surface chemistry of CuInS2 NCs. To this end, we use XPS, EDS, and ICP to study the chemical composition of CuInS2 NCs which are subsequently used as cores in ZnS shelling reactions. The effect of different washing procedures and batch-to-batch variability is also investigated. Our results show that the surface composition of the core NCs is a critical variable that, in combination with the reactivity of the precursors and the reaction temperature, can be used to tune the extent of the post-shelling spectral shifts, yielding for the first time CuInS2/ZnS core/shell NCs displaying red-shifted absorption and PL spectra.  

[1] Berends et al., J. Phys. Chem. Lett. 2016, 7, 3503.

[2] van der Stam et al., ChemPhysChem, 2016, 17, 559.

12:45 - 13:00
SE1.1-O2
Jagielski, Jakub
ETH Zurich
Colloidal Quantum Confined Perovskites for Ultrapure Green Optoelectronics: Synthesis and Applications
Jakub Jagielski
ETH Zurich, CH
Authors
Jakub Jagielski a, Sudhir Kumar a, Chih-Jen Shih a
Affiliations
a, Institute for Chemical & Bioengineering, Department of Chemistry & Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg, 1, Zürich, CH
Abstract

Hybrid lead halide perovskites, described by a formula ABX3, recently emerged as a new class of semiconducting materials for various optoelectronic devices. Especially, colloidal perovskites exhibit numerous favorable properties, such as high photoluminescence quantum yield (PLQY), tunable bandgap, defect tolerance, high charge carrier mobility, large exciton binding energy (EB), outstanding color purity (FWHM < 25 nm) and low cost of production, for high efficiency solution-processed light-emitting diodes (LEDs). Analogously to conventional, inorganic quantum dots (QDs), quantum confinement effects could be observed upon forming colloidal perovskite nanoplatelets (NPLs) with thicknesses below ~10 unit cells (n < 10). Taking MAPbBr3 for example, here we demonstrate a facile synthetic route to obtain monodisperse colloidal solutions of layered perovskites with precise control from n = 1 to n = 7-10 layers. These layer controlled perovskite NPLs not only offers a color-tunable emission, but also enhance the EB. The resultant high EB is crucial to enable efficient radiative recombination of excitons. Most interestingly, our layer controlled NPLs also showed record high solid-state PLQYs (50-90%) for blue and green emission. With the aid of computational methods, we indicate the changes in the crystal lattice depending on the NPL surrounding, which are responsible for such high performance of NPLs in the spin-coated thin films. These quantum confined perovskite NPLs exhibited excellent results in both active layer LEDs and down-converted (DC)-LEDs. The active layer LED shows a maximum luminous efficacy of 7.7 lm/W, which is highest among all colloidal pure-green LEDs. On the other hand, our DC-LED also outperforms the conventional InGaN based green LEDs. This opens an avenue towards low-cost and high-throughput production of solution-processed LEDs.

13:00 - 13:15
SE1.1-O3
Jang, Youngjin
Schulich Faculty of Chemistry, Technion, Israel
Colloidal synthesis of SnTe nanocrystals and SnTe-based core/shell nanocrystals by cation exchange combined with Kirkendall effect
Youngjin Jang
Schulich Faculty of Chemistry, Technion, Israel, IL
Authors
Youngjin Jang a, Arthur Shapiro a, Aldona Sashchiuk a, Efrat Lifshitz a
Affiliations
a, Schulich Faculty of Chemistry, Russell Berrie Nanotechnology Institute, Solid State Institute, Technion-Israel Institute of Technology
Abstract

 The controlled synthesis of narrow bandgap nanocrystals (NCs) is highly important scientific and technological issue. The lead chalcogenides have showed a good performance in various applications, however, practical applications using these materials have been hindered due to the high toxicity of lead. Recently, tin chalcogenides have been considered as the promising alternative for narrow bandgap materials because of its low toxicity and earth-abundance. Among tin chalcogenides, SnTe is a direct bandgap semiconductor (0.18 eV at 300 K), thus it is most promising material with infrared optical activity. Here, we present the facile solution-phase synthesis of SnTe NCs and their corresponding core/shell NCs. We synthesized monodisperse and highly crystalline SnTe NCs by employing a cheap and less toxic precursor and a reducing agent to enhance low reactivity of precursors. Moreover, we developed a synthetic procedure for the synthesis of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. 

SE2.1
Chair: Daniel Vanmaekelbergh
09:00 - 09:35
Abstract not programmed
09:35 - 09:45
Discussion
09:45 - 10:20
SE2.1-I1
Morais Smith, Cristiane
Utrecht University
Graphene: the good, the bad, the nano & the pseudo
Cristiane Morais Smith
Utrecht University, NL
Authors
Christiane deMorais a
Affiliations
Abstract

Graphene is probably the most fascinating material ever discovered, but it has a drawback: it does not exhibit the quantum spin Hall effect. By creating honeycomb lattices of compounds other than carbon, novel materials with unexpected properties may emerge. A key question is: if we build a honeycomb lattice out of semiconducting nanocrystals, is it going to behave like graphene or like the semiconducting building blocks?

I will show that these systems, which were recently experimentally synthesized [1], combine the best of the two materials. They exhibit a gap at zero energy, as well as Dirac cones at finite energies. In addition, a honeycomb lattice made of CdSe nanocrystals displays topological properties in the valence band [2], whereas for HgTe very large topological gaps are predicted to occur in the conduction p-bands [3]. These artificial materials open the possibility to engineer high-orbital physics with Dirac electrons and to realize quantum (spin) Hall phases at room-T [3].

Then, I will discuss the effect of dynamical electromagnetic interactions in massive and massless 2D systems like transition-metal dichalcogenides and graphene. By using the pseudo-QED approach, quantized edge states emerge and give rise, respectively, to a quantum Hall Effect (massive) [4] and a quantum Valley Hall effect (massless) [5], as a consequence of the parity anomaly.

[1] M. P. Boneschanscher et al., Science 344, 1377 (2014).

[2] E. Kalesaki et al., Phys. Rev. X 4, 011010 (2014).

[3] W. Beugeling et al., Nature Communications 6, 6316 (2015).

[4] L.O. Nascimento et al., arXiv:1702.01573

[5] E. C. Marino et al., Phys. Rev. X 5, 011040 (2015).

10:20 - 10:30
Discussion
10:30 - 11:05
Abstract not programmed
11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SE2.1-I2
Talapin, Dmitri
University of Chicago
Colloidal nanocrystals for thin-film optoelectronics
Dmitri Talapin
University of Chicago, US
Dmitri Talapin is a Professor of Chemistry at University of Chicago. His research interests revolve around inorganic nanomaterials, spanning from synthetic methodology to device fabrication, with the desire of turning colloidal nanostructures into competitive materials for electronics and optoelectronics. He received his doctorate degree from University of Hamburg, Germany in 2002 under supervision of Horst Weller. In 2003 he joined IBM Research Division at T. J. Watson Research Center as a postdoctoral fellow to work with Chris Murray on synthesis and self-assembly of semiconductor nanostructures. In 2005 he moved to Lawrence Berkeley National Laboratory as a staff scientist at the Molecular Foundry and finally joined faculty at the University of Chicago in 2007. His recent recognitions include MRS Outstanding Young Investigator Award (2011); Camille Dreyfus Teacher Scholar Award (2010); David and Lucile Packard Fellowship in Science and Engineering (2009); NSF CAREER Award (2009) and Alfred P. Sloan Research Fellowship (2009).
Authors
Dmitri Talapin a, b
Affiliations
a, University of Chicago, 929 East 57th st, Chicago, 60637, US
b, Argonne National Laboratory, Center for Nanoscale Materials, 9700 South Cass Avenue Bldg 440, Lemont, Illinois 60439, US
Abstract

Development of nanostructured materials has introduced revolutionary approaches for materials processing and electronic structure engineering. These materials can offer the advantages of crystalline inorganic solids combined with inexpensive solution-based device fabrication. Along these lines, semiconductor quantum dots are explored as the functional elements for printable electronics, light emitting devices, photodetectors and solar cells. All these applications require efficient coupling between individual nanostructured components. I will discuss emerging advances in the surface chemistry of semiconducting nanostructures that are poised to enable advances in additive manufacturing of semiconducting and multifunctional materials. Specifically, I will discuss inorganic linkers that permit electronic coupling between the nanocrystals and new semiconducting "solders" that transform to form high quality inorganic semiconductors. I will also introduce a general chemical approach for photoresist-free, direct optical lithography of functional inorganic nanomaterials (DOLFIN). Examples of patterned materials include metals, semiconductors, oxides, and magnetic and rare earth compositions. No organic impurities are present in the patterned layers, which helps achieve good electronic and optical properties. The conductivity, carrier mobility, dielectric, and luminescence properties of optically patterned layers are on par with the properties of state-of-the-art solution-processed materials. The ability to directly pattern all-inorganic layers using a light exposure dose comparable to that of organic photoresists opens up new opportunities for thin-film device manufacturing.

12:20 - 12:30
Discussion
12:30 - 13:05
SE2.1-I3
Morpurgo, Alberto
University of Genève, CH
Transport through ionic liquid gated 2D materials
Alberto Morpurgo
University of Genève, CH
Authors
Alberto Morpurgo a
Affiliations
a, University of Genève, CH
Abstract

Ionic liquid gating has proven to be a powerful techniques to accumulate very large density of charge carriers at surfaces of many different materials, reaching levels well in excess of 1014 cm-2. In this talk I will give an overview of our work on ionic liquid gating of semiconducting transition metal dichalcogenides, focusing on different aspects characteristic of both semiconductor physics and superconductivity. In the first part of the talk I will show the possibility to achieve high-quality ambipolar transport, to use ambipolar ionic liquid gated transistors to measure the semiconducting band-gap, and to realize light-emitting transistors. Most of the experiment concenrs individual materials, but we also recently achived ionic liquid gating of van der Waals heterstructures, which offer the potential to probe new phenomena. In the second part of the talk I will present our work on gate induced superconductivity, and show a number of interesting resulty, including the fact that gate-induced superconductivity in MoS2 persists down to the level of individual monolayers. 

13:05 - 13:15
Discussion
SE3.1
Chair: Tierui Zhang
09:00 - 09:35
SE3.1-I4
Zhu, Hongwei
OIL Lab, Tsinghua University
Graphene-on-surfaces: structural design and multifunctional applications
Hongwei Zhu
OIL Lab, Tsinghua University

Dr. Zhu is a Professor of School of Materials Science and Engineering, Tsinghua University. He received his B.S. degree in Mechanical Engineering (1998) and Ph.D. degree in Materials Processing Engineering (2003) at Tsinghua University. After Post Doc. studies in Japan and USA, he began his independent career as a faculty member at Tsinghua University (2008~present). His research involves multi-scale synthesis and assembly, characterizations and applications of materials. He has authored 2 books and 6 invited book chapters, received 16 CN patents, 1 US patent and published 200+ papers with a H-index of 51.

Authors
Hongwei Zhu a
Affiliations
a, School of materials science and engineering, Tsinghua University, Room 2421, Yifu Science and Technology Building, Tsinghua University, Beijing, 100084, CN
Abstract

Graphene has the potential for creating thin film devices, owing to its two-dimensionality and structural flatness. Assembling graphene-based building blocks into hybrid structures or composites with diverse targeted structures has attracted considerable interests for generating new properties and expanding its potential applications. The integration of graphene into a device always involves its interaction with supporting substrates, making this interaction critical to its real-life applications. This presentation will focus on three "graphene-on-surfaces" hybrid structures: I) Graphene-on-semiconductor: Graphene-on-Si can function as a quality Schottky junction with high photoelectric conversion. Graphene serves multiple functions as transparent electrode, active junction layer, hole collector and anti-reflection layer in graphene-on-semiconductor heterojunction photo-devices, such as solar cells and photodetectors, and could be extended to other optoelectronics; II) Graphene-on-polymer: Tiling structures are designed in graphene, composing overlapped graphene plates and realize high sensitivity strain sensing, which can measure either tiny or large strains with record high gauge factors. By combining artificial intelligence with digital signal processing, the graphene based sensing system represents a new smart tool to classify and analyze signals in fields of vital signs monitoring, robotics, fatigue detection, and in vitro diagnostics; III) Graphene-on-ceramic: Graphene oxide (GO)-based membranes are developed for highly efficient ion separation and water desalination. Due to the narrow dimension of nano-capillaries and the co-existence of sp2 aromatic channels with various oxygen functionalities, GO membranes can afford excellent selectivity towards various ions based on molecular sieving effect and diverse chemical interactions, showing promises in filtration and separation for water treatment applications.

09:35 - 09:45
Discussion
09:45 - 10:00
SE3.1-O2
Zhao, Guoke
School of materials science and engineering, Tsinghua University
Integration of Perovskite Quantum Dots into Graphene-Si Heterojunction Solar cells
Guoke Zhao
School of materials science and engineering, Tsinghua University, CN
Authors
Guoke Zhao a, Hongwei Zhu a
Affiliations
a, Tsinghua University, Yifu Building Room 2422, Tsinghua University,Haidian District, Beijing, 100084, CN
Abstract

Lead-based halide perovskite quantum dots (LPQDs) have attracted great attention in recent years as light harvesting materials for photoelectric applications because of their unique properties, such as direct band gap, large absorption coefficient, high carrier mobility, and tunable band structure. However, the large surface-to-volume ratio makes them tend to aggregate and introduces surface defects, leading to fast electron-hole recombination. The flexible two-dimensional (2D) feature of graphene and its superior electrical properties make it a promising candidate for acting as the loading platform of LPQDs to prevent undesired aggregation, thus work as effective carriers extractor and transporter. Combining the advantages of graphene and well-developed Si technologies is a good choice to expand its applications. The first graphene-Si heterojunction solar cell was demonstrated in 2010, in which graphene functioned as a transparent window layer and a carrier transporting layer while Si played a role in photogeneration. In the past years, its power conversion efficiency has been improved from 1.7% to 15.6% with delicate electrical and optical designs, including doping of graphene, interface passivation and anti-reflection coating.

Properly integrating nanostructures might promote light adsorption and the efficiency is expected to be further improved. Graphene sensitized with colloidal PbS, ZnO and LPQDs light harvesters was developed for efficient photodetection. Integrating LPQDs into the graphene-Si heterostructure may introduce some new characteristics or lead to improvements in device performance. Their size, composition, morphology and surface ligands are tailorable to optimize the charge transfer between quantum dots and the interactions with graphene. Liquid phase synthesis also offers great flexibility in device structure design with relatively facile techniques. 

10:00 - 10:35
SE3.1-I1
Parkinson, Bruce
University of Wyoming
Van der Waals Epitaxial Growth, Patterning and Properties of 2D Transition Metal Dichalcogenides
Bruce Parkinson
University of Wyoming
Bruce Parkinson received his BS in chemistry at Iowa State University in 1972 and his PhD from Caltech in 1977 and was a post-doctoral scientist at Bell Laboratories in 1978. He then spent time at the Ames Laboratory and the Solar Energy Research Institute (now known as the National Renewable Energy Laboratory). He moved to the Central Research and Development Department of the DuPont Company in 1985 and in 1991 he became Professor of Chemistry at Colorado State University until his recent departure to join the Department of Chemistry and the School of Energy Resources at the University of Wyoming. His current research covers a wide range of areas including materials chemistry, surface chemistry and photoelectrochemical energy conversion. He has more than 220 peer-reviewed publications and holds 5 US patents.
Authors
Bruce Parkinson a
Affiliations
a, University of Wyoming, Department of Chemistry, Laramie, 82071
Abstract

Following the demonstration that single layers of graphite have interesting properties, the layered structure transition metal dichalcogenides have also become the subject of intensive research. The term “van der Waals epitaxy” was coined in early publications where thin layers of 2D materials were deposited on other 2D materials. We have used molecular beam epitaxy to grow a variety of 2D materials, such as MoSe2 and WSe2 on other 2D materials such as MoS2 and SnS2. Scanning tunneling microscopy (STM) was used to image the Moiré patterns generated by the lattice mismatch between the layers. Recent work has reinterpreted the nature of these STM images and this will be discussed. Both atomic force microscopy (AFM) and STM can pattern the materials by etching them away a layer at a time only in the areas scanned. The rate of etching with the AFM was proportional to the applied force when operating in contact mode. A single layer nanostructured diode and transistor structures were demonstrated by selectively patterning through multiple layers.

10:35 - 10:45
Discussion
10:45 - 11:15
SE3.1-O1
Mastria, Rosanna
Istituto di Nanotecnologia CNR-Nanotec
Synthesis and characterization of two-dimensional colloidal WS2 nanosheets as promising building blocks for highly conductive WS2 thin-films
Rosanna Mastria
Istituto di Nanotecnologia CNR-Nanotec, IT
Authors
Rosanna Mastria a, Salvatore Gambino a, b, Riccardo Scarfiello a, Adriano Cola c, Concetta Nobile a, Cinzia Giannini d, P. Davide Cozzoli a, b, Aurora Rizzo a
Affiliations
a, IMM-CNR, Institute for Microelectronics and Microsystems – Unit of Lecce, Via Monteroni, Lecce, IT
b, IC CNR, Institute of Crystallography, via Amendola 122/O, I-70126 Bari, Italy
Abstract

Owing to their appealing photophysical and mechanical properties, two-dimensional nanostructures of semiconducting transition-metal dichalcogenides (2D-TMCs), such as MoS2, WS2, MoSe2, and WSe2 in the mono- to few-layer regime, are considered very promising nanomaterials for several applications, ranging from optoelectronics, energy storage/conversion to catalysis. However, the synthesis of free-standing, easy-to-manipulate 2D-TMCs with controllable thickness and lateral dimensions is challenging, because their poor chemical and mechanical stability promotes a tendency to collapse into useless bulk-like aggregates or micrometer-size structures. To address these difficulties, colloidal methods are currently being regarded as powerful alternative routes to the scalable synthesis of solution-processable 2D-TMCs.  

Here we report a solution-phase synthesis of colloidally stable 2D-WS2 crystalline nanosheets via a sulfidation process. In our approach, preformed colloidal nonstoichiometric tungsten oxide (WO3-x) nanocrystals, used as starting sacrificial templates, are induced to react with a suitable sulfur precursor in a hot surfactant medium to yield 2D-WS2 nanosheets. The advantage of this method relies in the fine control over the chemical and structural conversion of WO3-x nanocrystal precursors, which is achievable by tuning the sulfidation conditions during the entire reaction course. We have monitored the progress of the transformation, identifying the reaction pathways through which the WO3-x nanocrystals are gradually converted to a mixed-phase WO3-x/WS2 nanostructure intermediates and finally into 2D-WS2 nanosheets. Each reaction step has been characterized by a combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning TEM, and optical absorption analyses.  

Colloidal WS2 nanosheets are subsequently deposited by layer-by-layer self-assembly technique to obtain smooth and homogeneous multiflake WS2 thin-films, as confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. We studied the conduction properties of WS2 thin films by 4-probes and temperature-dependent I-V measurements. We report conductivity values as high as 2.6*10-1 S cm-1 for an as cast film. The increase of the conductivity as the temperature increases confirms the semiconducting behaviour of the WS2 films.  

In conclusion, we demonstrate that sulfidation solution approach is a powerful way for the synthesis of colloidally stable 2D-WS2 nanostructures, which can be used as building blocks for the fabrication of highly efficient solution-processed optoelectronic devices.

11:15 - 11:45
Coffee Break
11:45 - 12:20
SE3.1-I2
Albero Sancho, Josep
ITQ (UPV-CSIC)
Oriented 2.0.0 Cu2O nanoplatelets supported on few-layers graphene as efficient visible light photocatalyst for overall water splitting
Josep Albero Sancho
ITQ (UPV-CSIC)
Authors
Diego Mateo a, Ivan Esteve-Adell a, Josep Albero a, Ana Primo a, Hermenegildo Garcia a
Affiliations
a, ITQ (UPV-CSIC)
Abstract

Cu2O nanoplatelets with preferential 2.0.0 facet orientation supported on few layers graphene (fl-G) were prepared as thin films in a single step by pyrolysis at 900 0C under inert atmosphere of the Cu2+-chitosan precursor.  Cu2O /fl-G films exhibit a photocatalytic activity for overall water splitting of 19.5 mmol/gCu+G·h. This value is about 4 orders of magnitude higher than the photocatalytic activity measured for unoriented Cu2O nanoparticles on few-layers graphene or than commercial Cu2O nanoparticles and about three orders of magnitude higher than the activity reported in the literature for Cu2O nanoparticles. In addition, Cu2O nanoparticles on few-layers graphene retain about 50 % of its photocatalytic activity after 6 days of continuous irradiation, exhibiting long-term H2 production. It is proposed that this activity and stability arises from the combination of preferential 2.0.0 facet orientation, strong Cu2O–graphene grafting and the role of graphene as cocatalyst.

12:20 - 12:30
Discussion
12:30 - 13:05
SE3.1-I3
Ponomarenko, Leonid
Lancaster University, UK
High-temperature quantum oscillations in graphene superlattices
Leonid Ponomarenko
Lancaster University, UK
Authors
Leonid Ponomarenko a, Roshan Krishna Kumar a, b, Xi Chen b, Gregory Auton b, Artem Mishchenko b, Denis Bandurin b, Sergey Morozov c, Yang Cao b, Katya Khestanova b, Moshe Ben Shalom b, Vladimir Falko d, Andre Geim b
Affiliations
a, Lancaster University, UK
b, Manchester University, UK, GB
c, Institute of Microelectronics Technology, Chernogolovka, Russia
d, National Graphene Institute, Manchester, UK
Abstract

Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and magneto-oscillatory behavior in their properties, such as Shubnikov-de Haas oscilations and quantum Hall effect. Cryogenic temperatures are usually required to observe phenomena. We show that superlattices formed in graphene on hexagonal boron nitride substrate support a different type of quantum oscillations that do not rely on Landau quantization. The period of oscilations is directly related to the lattice parameter of the superlattice. The oscillations are extremely robust and persist well above room temperature in magnetic fields of only a few T. We attribute this phenomenon to repetitive changes in the electronic structure of superlattices such that charge carriers experience effectively no magnetic field at simple fractions of the flux quantum per superlattice unit cell. Our work points at unexplored physics in Hofstadter butterfly systems at high temperatures.

  

13:05 - 13:15
Discussion
13:15 - 15:00
Lunch
SE1.2
Chair: Maksym Kovalenko
15:00 - 15:35
SE1.2-I1
Owen, Jonathan
Columbia University
The coordination chemistry of colloidal quantum dots.
Jonathan Owen
Columbia University, US

Jonathan Owen received a B.S. in Chemistry from the University of Wisconsin-Madison, and a Ph.D. in Chemistry from CalTech. As a graduate student in the lab of Professor John Bercaw he studied the kinetics and mechanism of methane C-H activation. In 2005 he joined the lab of Professor Paul Alivisatos as a Petroleum Research Fund Alternative Energy Fellow to study the crystallization and derivatization of colloidal semiconductor nanocrystals. In 2009 he joined the faculty at Columbia University as an Assistant Professor of Chemistry where his group continues to study the synthesis and surface chemistry of colloidal semiconductor nanocrystals. For this work, he has received early career awards from the Department of Energy, the National Science Foundation, 3M, and DuPont.

Authors
Jonathan Owen a
Affiliations
a, Department of Chemistry, Columbia University, 3000 Broadway, New York, NY 10027, US
Abstract

I will describe the coordination chemistry of CdSe nanocrystals with an emphasis on our measurements of ligand binding affinity. Using NMR spectroscopy we have probed the steric and electronic factors that determine the binding affinities of neutral ligands and measured the affinities of those ligands relative to tri-n-butylphosphine. In addition, I will discuss the binding of anionic ligands that balance charge with outer sphere cations to stoichiometric nanocrystals and the importance of this motif to the synthesis and isolation of stoichiometric nanocrystals. In particular, we have found that carboxylate, phosphonate, and carbamate anions have high affinities for stoichiometric nanocrystals.  Moreover, our studies have shown that the stabilization of colloidal dispersions by neutral ligands is poor, suggesting that nanocrystals are rarely stabilized by this coordination motif alone.  Using a displacement strategy described in a recent publication (JACS, 2017, (139), 3227 - 3226) we have been able to prepare CdSe nanocrystals with a pure amine ligand shell.  Using these nanocrystals, we have prepared nanocrystal thin films with high field effect electron transport mobilities (> 10 cm^2/V/sec).

15:35 - 15:45
Discussion
15:45 - 16:20
SE1.2-I2
Infante, Ivan
Vrije University Amsterdam (VU) - NL
Trap States in Colloidal II-VI and IV-VI Semiconductor Nanocrystals
Ivan Infante
Vrije University Amsterdam (VU) - NL, NL
Authors
Ivan Infante a
Affiliations
a, Vrije University Amsterdam (VU) - NL, De Boelelaan 1081, Amsterdam, NL
Abstract

Controlling the surface of colloidal nanocrystals is paramount to maintain colloidal stability and to tune structural and electronic properties, but also for reducing the presence of trap states that deteriorate their optoelectronic performance. Here, we use density functional theory (DFT) to analyze the electronic structure of II-VI and IV-VI nanocrystals by adding trap states “on-prupose”. We find that effectively stoichiometric II-VI nanocrystals present surface traps only when two coordinated chalcogen atoms are formed on the surface, usually after Z-type displacement. Under-coordinated surface metal atoms, on the other hand, produce states within the conduction band and contribute to wavefunction delocalization rather than electron trapping. In IV-VI this type of traps does not occur. Effectively non-stoichiometric nanocrystals, on the other hand, has several flavors of traps that can be classified depending on how they are created (anion or cation vacancy, ligand removal, etc.). We employ a simplified molecular orbital picture to illustrates the pathways in which such mid-gap states form.

16:20 - 16:30
Discussion
16:30 - 16:45
SE1.2-O1
Pan, Jun
Division of Physical Sciences and Engineering, Solar and Photovoltaic Engineering Research Center (SPERC), King Abdullah University of Science and Technology KAUST
Surface passivation of perovskite quantum dots for high photo-stability and efficient light emitting diodes
Jun Pan
Division of Physical Sciences and Engineering, Solar and Photovoltaic Engineering Research Center (SPERC), King Abdullah University of Science and Technology KAUST, SA
Authors
Jun Pan a, Osman Bakr a
Affiliations
a, Division of Physical Sciences and Engineering, Solar and Photovoltaic Engineering Research Center (SPERC), King Abdullah University of Science and Technology KAUST, Thuwal, SA
Abstract

Due to their the narrow band emission, high photoluminescence quantum yields (PLQYs), color tunability, and solution processability, all inorganic perovskite quantum dots (APQDs) have attracted much attention for use in thin film displays and solid-state lighting applications. Despite their impressive metrics, however, poor stability—particularly with respect to temperature, moisture, and light exposure—remains a ubiquitous impediment for virtually all perovskite materials and devices. The lack of stability has prevented the practical and commercial utilization of perovskite optoelectronics. Typically, APQDs are capped by long alkyl ligands such as oleic acid and oleylamine to achieve high PLQY and high dispersibility in nonpolar solvents such as toluene and octane. APQD light-emitting diode (LED) – so far stabilized and processed with the relatively insulating ligands – display poor efficiency. The poor carrier transport in these films, as a result of the inability to utilize shorter conducting ligands to stabilize APQDs, has been the major bottleneck preventing their realization in efficient devices. Here we overcome this limitation by designing a two-step ligand exchange strategy to replace the long carbon chain ligands on APQD with halide ion-pair ligands (e.g., di-dodecyl dimethyl ammonium bromide, DDAB). We show that attempts to directly exchange APQD with halide ion-pair ligands results in the severe degradation of their luminescence. Only by devising an intermediate step to desorb protonated oleylamine, can APQDs be exchange with a quaternary ammonium halide ion pair. APQDs capped with halide ion pair enabled us to fabricate LEDs with high external quantum efficiency (EQE). We achieved the highest efficiencies for green and blue APQD LEDs, exhibiting EQEs of 3.9% and 1.9% respectively. With the new ligand passivation technique, perovskite QDs present high photoluminescence quantum yield (PLQY) with remarakably high operational stability in ambient conditions (60±5% lab humidity) and high pump fluences, thus overcoming one of the major challenges impeding the development of perovskite-based applications.

16:45 - 17:00
SE1.2-O2
Ten Brinck, Stephanie
Vrije University Amsterdam (VU) - NL
Surface Termination, Morphology and Bright Photoluminescence of Cesium Lead Halide Perovskite Nanocrystals
Stephanie Ten Brinck
Vrije University Amsterdam (VU) - NL, NL
Authors
Stephanie ten Brinck a, Ivan Infante a
Affiliations
a, Vrije University Amsterdam (VU) - NL, De Boelelaan 1081, Amsterdam, NL
Abstract

Colloidal perovskite nanocrystals (PNCs) of all-inorganic materials (CsPbX3, X = Cl-, Br- and I-) have emerged as a promising new class of nanomaterials due to their exceptional optoelectronic properties. Even as-synthesized and unpurified, these materials can reach a photoluminescence quantum yield (PLQY) of up to 90%, exhibit tunable and narrow emission bandwidths in the visible spectrum and have a high tolerance against defects. The origins of these outstanding properties are however still largely unknown, especially when compared to analogous semiconductor nanocrystals such as lead chalcogenides, for which it is still difficult to reach a PLQY beyond 20%.

To get a better understanding of the properties of CsPbX3 PNCs, we construct cesium lead halide models while taking into account experimental conditions. We perform density functional theory calculations on these models and we analyze the effect of size, shape and halide composition on the electronic structure. Our models are nominally free of trap states and exhibit both a clear quantum confinement and halide effect. We show that the electronic structure is only affected slightly upon removal of ligands from the surface, indicating that these PNCs are unexpectedly robust towards degradation of the nanocrystal.

Lastly, we use computational tools to investigate excitation of PNCs by photons with a greater energy than the band gap. We first perform ab initio molecular dynamics calculations on our PNC models and follow them up with excitation dynamics calculations. Using these calculations, we analyze properties such as the cooling rate of excited electrons and their holes, the coupling between states that are relevant for excited-state processes and the dephasing time of an excited system. We perform these calculations on PNC models of different sizes and materials composition and discuss the trends between these different models.

SE2.2
Chair: Christopher B. Murray
15:00 - 15:35
SE2.2-I1
Moreels, Iwan
Department of Chemistry, Ghent University
Band Structure Engineering in Core/Shell and Core/Crown CdSe-Based Nanoplatelets
Iwan Moreels
Department of Chemistry, Ghent University, BE

I obtained my PhD degree in applied physics at Ghent University in 2009, studying near-infrared lead salt quantum dots. This was followed by a postdoc on quantum dot emission dynamics at Ghent University in collaboration with the IBM Zurich research lab. In 2012 I joined the Istituto Italiano di Tecnologia, where I led the Nanocrystal Photonics Lab in the Nanochemistry Department. In 2017 I returned to Ghent University as associate professor, focusing mostly on 2D and strained nanocrystals. The research in our group ranges from the synthesis of novel fluorescent nanocrystals to optical spectroscopy and photonic applications.

Authors
Iwan Moreels a
Affiliations
a, Istituto Italiano di Tecnologia (IIT), Genova, Italy, Via Morego, 30, Genova, IT
Abstract

Colloidal CdSe nanoplatelets are 2D semiconductor nanocrystals with opto-electronic properties that are similar to quantum wells. Being synthesized via bottom-up approaches, CdSe nanoplatelets typically have a thickness less than 2 nm, leading to strong confinement of the electron and hole wave functions in the vertical direction, while larger lateral dimensions give rise to a weak-to-intermediate confinement regime. They are often suspended in organic solvents or embedded in polymer films, enhancing Coulomb interactions through a low-dielectric environment. In addition, a variety of heterostructures can be synthesized with core/shell and core/crown geometries. In this talk, I will focus on the synthesis of two types of 2D heteronanoplatelets, both based on CdSe nanoplatelet cores.

First, we synthesized CdSe/ZnS core/shell nanoplatelets using a novel single-source precursor route. Here the ZnS shell is grown predominately on CdSe top and bottom planes. Despite a type-I band alignment, optical spectroscopy revealed that the band edge red shifts significantly upon shell growth. Starting from 515 nm-emitting CdSe nanoplatelets, we obtained a continuous shift of the emission peak toward 611 nm for the final CdSe/ZnS core/shell nanocrystals. K·p calculations revealed contributions to the red shift from both exciton delocalization, as well as a reduced electron-hole attraction due to a modified surface polarization induced by the ZnS shell.

Second, type-II CdSe/CdTe core/crown nanocrystals were synthesized with a CdS interfacial barrier between core and crown. Here the CdS and CdTe region were grown on the side facets of the CdSe core. The cascaded CdSe/CdS/CdTe band offsets allow for electron relaxation into the CdSe region, while the low conduction band energy of CdS yields a tunneling barrier between core and crown for the hole. Compared to CdSe/CdTe nanoplatelets without a barrier, we observed an enhanced CdSe emission and even two-photon upconversion, both enabled through the restricted hole relaxation induced by the CdS barrier.

The results highlight that the opto-electronic properties and carrier dynamics in 2D materials can be carefully steered via both quantum confinement and Coulomb interactions, by targeted material synthesis that takes advantages of both strong and weak confinement regimes. It allows for optimal design of 2D nanoplatelet heterostructures toward different photonic applications, such as light-emitting or energy harvesting devices.

Acknowledgments. This project has received funding from the Ministero degli Affari Esteri e della Cooperazione Internazionale (IONX-NC4SOL) and the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 696656 (GrapheneCore1).

15:35 - 15:45
Discussion
15:45 - 16:20
SE2.2-I2
Slot, Marlou
Universiteit Utrecht
Experimental realization and characterization of an electronic Lieb lattice
Marlou Slot
Universiteit Utrecht, NL
Authors
Marlou Slot a, Thomas Gardenier a, Peter Jacobse a, Guido van Miert b, Sander Kempkes b, Stephan Zevenhuizen a, Cristiane Morais Smith b, Daniel Vanmaekelbergh a, Ingmar Swart a
Affiliations
Abstract

Geometry, whether on the atomic or nanoscale, is a key factor for the electronic band structure of materials. Some specific geometries give rise to novel and potentially useful electronic bands. For example, a honeycomb lattice leads to Dirac-type bands where the charge carriers behave as massless particles. Theoretical predictions are triggering the exploration of novel two-dimensional (2D) geometries, such as graphynes and the kagomé and Lieb lattices.
The Lieb lattice is the 2D analogue of the 3D lattice exhibited by perovskites: it is a square-depleted lattice, which is characterized by a band structure featuring Dirac cones intersected by a flat band. Whereas photonic and cold-atom Lieb lattices have been demonstrated1, an electronic equivalent in 2D is difficult to realize in an existing material. In principle, lithography could be used to impose a Lieb pattern on a 2D electron gas. Alternatively, a strategy similar to the one employed for generating artificial graphene could be used2.
Here, we present an electronic Lieb lattice formed by the surface state electrons of Cu(111) confined by an array of carbon monoxide molecules positioned with a scanning tunnelling microscope3. Using scanning tunnelling microscopy, spectroscopy and wavefunction mapping, we confirm the predicted characteristic electronic structure of the Lieb lattice. The experimental findings are corroborated by muffin-tin and tight-binding calculations. At higher energies, second-order electronic patterns are observed, which are equivalent to a super-Lieb lattice.
The Cu(111)/CO system is an ideal model system, as it allows one to tune parameters that cannot be easily varied in a real solid-state material. The inherent versatility and the direct access to structural and electronic characterization allow a reality check for advanced theory and a first step in the design of truly novel electronic materials.

[1] D. Guzmán-Silva et al., New J. Phys. 16, 063061 (2014); S. Taie et al., Science Adv. 1, 1500854 (2015)
[2] K.K. Gomes et al., Nature 483, 306–310 (2012)
[3] M.R. Slot et al., Nat. Phys. (2017), doi:10.1038/nphys4105

16:20 - 16:30
Discussion
16:30 - 16:45
SE2.2-O1
Post, Christiaan
Universiteit Utrecht
Fabrication of honeycomb semiconductors using electron beam lithography
Christiaan Post
Universiteit Utrecht, NL
Authors
Christiaan Post a
Affiliations
Abstract

Graphene is a two-dimensional flat material which exhibits fascinating physical properties due to its honeycomb lattice structure. Calculations [1] and experiments [2] have shown that charge carriers have a linear energy dispersion (Dirac cones) near the corners of the Brillouin zone, indicating that they behave like massless particles. These fundamental properties result in interesting optical and electrical characteristics in this material.

My research will focus on the fabrication and characterization of artificial graphene by nano pattering inside a high mobility two-dimensional electron gas confined in an InGaAs/InAlAs quantum well. Electron beam lithography is used to create a mask with a honeycomb structure, which will be used to etch inside the surface of the sample. Main goal of my project aims at revealing Dirac cones in the band structure of the electrons by performing low-temperature transport measurements, optical measurements and local-probe spectroscopy in a scanning tunneling microscopy setup.

I would like to present the first results of this research, which consist of the fabrication of honeycomb semiconductors using electron beam lithography. 

This research is performed in collaboration with the institute d’electronique, de microelectronique et de nanotechnologie (IEMN) at Lille, France.

16:45 - 17:00
Abstract not programmed
SE3.2
Chair: Bruce Parkinson
15:00 - 15:30
SE3.2-O1
Scarfiello, Riccardo
Consiglio Nazionale delle Ricerche (CNR)
Direct synthesis and characterization of colloidal WS2nanoplatelets
Riccardo Scarfiello
Consiglio Nazionale delle Ricerche (CNR), IT
Authors
Riccardo Scarfiello a
Affiliations
a, Consiglio Nazionale delle Ricerche (CNR), via elce di sotto 8, Perugia, 0, IT
Abstract

The tailored fabrication and advanced characterization of two-dimensional nanostructures of transition-metal dichalcogenides (2D-TMCs), such as MoS2, WS2, MoSe2, and WSe2 made of a single to few stacked atomic layers, represent hot research topics of extreme significance to the broad (nano)materials science community as these nanomaterials stand out as the inorganic analogues of graphene. 2D-TMCs exhibit unique thickness-dependent properties that make them considerably attractive for several applications, such as photovoltaic devices, lithium-ion batteries, hydrogen-evolving photocatalysts, transistors, and memory devices. However, the production of individually addressable, easily-processable 2D-TMCs with controllable and uniform thickness and lateral dimensions is very challenging. The currently available repertory of 2D-TMCs mostly comprises sheet-like nanostructures with irregular micrometer-scale extended edges derived by liquid-phase exfoliation of corresponding bulk materials or by vapour-phase deposition on solid substrates, which inherently suffer from low chemical and mechanical stability against folding, wrinkling and uncontrolled aggregation when post-synthesis manipulated for device integration. Recently, wet-chemical synthetic approaches have emerged a powerful alternative routes to achieve morphologically and structurally controlled 2D-TMDs in the form of robust freestanding nanostructures with finely adjusted geometric parameters, stabilized by organic ligands bound to their surface and, hence, sufficiently stable in the liquid phase to be safely manipulated and transferred to applications.

In this contribution, we describe an effective liquid-phase synthetic protocol for the synthesis of colloidal 2D-WS2 and 2D-WSe2 nanocrystals with tunable platelet- or sheet-like habits via a direct surfactant-assisted pyrolytic route. By adjusting synthetic parameters, the lateral edge sizes and morphology of the nanocrystals can be varied within the sub-50 nm regime. We have monitored the reaction progress by the combination of different techniques of structural-morphological investigation (XRD, SEM, TEM) and spectroscopic measurements. We demonstrate that the developed an easy-handling soft organic-template approach leads to soluble and stable 2D-WS2 and 2D-WSe2 nanostructures with high structural and optical quality.

15:30 - 15:45
SE3.2-O4
Li, Jing
Tsinghua University, CN
Nanofibrous Membrane of Graphene Oxide/Polyacrylonitrile Composite with a Low Filtration Resistance for the Effective Capture of PM2.5
Jing Li
Tsinghua University, CN
Authors
Jing Li a, Hongwei Zhu a
Affiliations
a, Tsinghua University, Yifu Building Room 2422, Tsinghua University,Haidian District, Beijing, 100084, CN
Abstract

Particulate matter (PM) pollution has become one of the most severe environmental issues because of its hazardous effects on human health. Therefore, the development of a cost-effective and energy-efficient air filter is highly desirable. Recently, nanofibrous membranes have been extensively studied for PM filtration owing to their high specific surface area and slip effect of air flow on their surface. In the present work, graphene oxide (GO)@ polyacrylonitrile (PAN) composite nanofibrous membranes named GOPAN possessing olive-like beads on a string structure and high porosity were controllably fabricated via electrospinning method. The prepared GOPAN membranes were demonstrated as air filters for the first time. The olive-like structure engendered by GO expansion of the inter-fiber voids substantially reduced the pressure drop of air filter. Meanwhile, nanofibers deposited on non-woven fabric scaffold improved the collision probability of the large airborne particles, thus ensuring a graded filtration performance without compromising filtration efficiency. Upon GO decoration, the PM2.5 removal efficiency was improved substantially compared with the original PAN. In particular, GOPAN membrane prepared with optimized addition of GO exhibited the highest efficiency (99.97%) with a low pressure drop (8 Pa) to aerosol particles under an airflow velocity of 5.31 cm/s. The significant enhancement of the air filter properties is attributed to the GO decoration and the designed olive-like bead macrostructures. The developed GOPAN composite membranes in this work have the potential for the development and manufacture a new generation of filter media with enhanced filtration capacity and low pressure drop for air filtration and other commercial applications.

15:45 - 16:00
SE3.2-O5
Mateo Mateo, Diego
ITQ (UPV-CSIC)
111 oriented Au nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting
Diego Mateo Mateo
ITQ (UPV-CSIC)
Authors
Diego Mateo a, Ivan Esteve-Adell a, Josep Albero a, Ana Primo a, Hermenegildo Garcia a
Affiliations
a, ITQ (UPV-CSIC)
Abstract

111 facet oriented Au nanoplatelets on multilayer G films on quartz (Au /ml-G, Au  meaning 111 oriented Au, ml-G meaning multilayer graphene) have been prepared in a single step by pyrolysis at 900 oC of chitosan films containing HAuCl4.  After pyrolysis the resulting Au /ml-G films were characterized by chemical analysis (Au content 1 mg×cm-2), Raman spectroscopy (G and D bands, IG/ID ratio of 1.13), AFM (dimensions of Au nanoplatelets 10-20 nm high, 5-25 nm wide), XRD (single diffraction peak at 38 o) and electron microscopy. Orientation of 111 facet was determined by comparison of the FESEM images with that of Kikuchi images of back scattered electron diffraction in electron microscopy. The resulting (Au /ml-G) was found to be a highly active photocatalyst for overall water splitting into H2 and O2 in the absence of sacrificial electron donors, achieving H2 production rate of 1.2 molH2 gcomposite-1 h-1. Photo response measurements show that the material exhibits catalytic activity upon irradiation to the Au  plasmon band in the visible region (φ = 560 nm). This remarkable photocatalytic activity arises from the strong Au-G interaction.

16:00 - 16:15
SE3.2-O2
Min, Wang
OIL Lab, Tsinghua University
Safe synthesis and application of two-dimensional MXene Ti3C2Tx
Wang Min
OIL Lab, Tsinghua University

EDUCATION:

2012.09—2016.06 B.S. in Materials Science and Engineering, Jilin University;

2016.09—present, Ph.D. Candidate in materials processing, Tsinghua University;

Authors
Min Wang a, Hongwei Zhu a
Affiliations
a, Tsinghua University, Yifu Building Room 2422, Tsinghua University,Haidian District, Beijing, 100084, CN
Abstract

In 2011, the first two-dimensional (2D) Ti3C2Tx nanosheet was exfoliated from Ti3AlC2 bulk crystal in hydrofluoric acid, which brought a new family of 2D materials called MXene to the stage of scientific research. The starting materials, MAX phases, are ternary carbides, nitrides or carbonitrides with a Mn+1AXn (n=1, 2, 3) formula, where M represents an early transition metal, A is predominantly element of group IIIA or IVA and X is C or N element. The term “MXene” is derived from selective etching of A-group from MAX phase and the resultant graphene-like nanosheet. The surfaces of MXenes are always terminated with -F, -OH or =O groups, hence, the MXene is referred to as Mn+1XnTx, where T represents the surface group and x is the corresponding number. This new material family is already attracting significant interest because of its excellent properties, especially for Ti3C2Tx, which could be applied to various fields, such as transparent conductive electrodes, environmental remediation, electromagnetic interference absorption and shielding, energy storage and electrocatalysis. Up to now, two main mature but dangerous etching routes of Ti3AlC2: hydrofluoric acid etching and hydrochloric acid/lithium fluoride etching, and other trials using fluorides and bifluorides, nevertheless are still with high hazards. Herein, we aim to develop a safely efficient etching protocol: hydrothermal synthesis of MXene using calcium sulfide or sodium formate as etchant, which is also a fluoride-free method, followed by sonication-assisted liquid exfoliation. Finally the Ti3C2Tx film is obtained by pulsed laser deposition-assisted technique, and its applications in environmental remediation and energy storage will be explored.

16:15 - 16:30
SE3.2-O3
Ren, Huan
University of Limerick, Ireland
Synthesis and characterization of Cu2ZnSnSe4 tetrapod nanocrystals
Huan Ren
University of Limerick, Ireland, IE
Authors
Huan Ren a
Affiliations
a, University of Limerick, Ireland, Materials & Surface Science Institute, University of Limerick,, Limerick, 0, IE
Abstract

Cu2ZnSnSe4 (CZTSe) nanocrystals (NCs) combine many promising properties, such as high optical absorption coefficient and improved thermoelectric properties[1]. The multinary composition of CZTSe NCs offers a high flexibility for targeted-application tuning without the usage of toxic elements or elements of extreme rarity.[2] Moreover, polytypic Cu2ZnSnS4, Cu2ZnSn(SSe)4 NCs have shown promising optical properties in previous research.[3-5]  Amongst polytypic NCs, tetrapod-shaped NCs are particularly interesting. The 3 dimensional structure gives the tetrapods more tunable parameters, such as arm length and width.[6, 7]

Herein, the synthesis of Cu2ZnSnSe4 (CZTSe) tetrapod NCs using hot injection approach is reported. The quaternary copper selenide based NCs consist of a cubic core and four tetrahedrally attached short wurtzite arms. CZTSe tetrapod NCs are the first polytypic structure and the first 3D structure reported in CZTSe NCs. Zn composition in NCs is varied from 2.2% to 7.6% (atomic%, SEM-EDS) which is a considerable improvement from the low Zn compositions reported in other researches on CZTSe NCs.[8] Furthermore, it is observed that as the zinc composition increases, the core to arms volume ratio increases accordingly. Other characterization techniques such as Raman spectroscopy, X-ray diffraction, photoluminescence are employed to understand the structure better.

 

 

References:

 

1.             Coughlan, C., et al., Chem. Rev., 2017. 117(9): p. 5865-6109.

2.             Aldakov, D., et al., J. Mater. Chem. C, 2013. 1(24): p. 3756-3776.

3.             Coughlan, C., et al., CrystEngComm, 2015. 17(36): p. 6914-6922.

4.             Singh, S., et al., Chem. Mater., 2015. 27(13): p. 4742-4748.

5.             Singh, A., et al., J. Am. Chem. Soc., 2012. 134(6): p. 2910-2913.

6.             Manna, L., et al., Nat. Mater., 2003. 2(6): p. 382-5.

7.             Wang, J., et al., J. Am. Chem. Soc., 2013. 135(21): p. 7835-8.

8.             Shavel, A., et al., J. Am. Chem. Soc., 2010. 132(13): p. 4514-4515.

17:00 - 18:30
Poster exhibition
20:00 - 22:00
Social Dinner
 
Fri Sep 08 2017
SE1.3
Chair: Vanessa Wood
09:00 - 09:35
SE1.3-I1
Scheele, Marcus
University of Tuebingen
Living on the Edge: Excitons at the Quantum Dot/Organic Semiconductor Interface
Marcus Scheele
University of Tuebingen, DE
Authors
Marcus Scheele a
Affiliations
a, University of Tübingen, Auf der Morgenstelle, Tübingen, DE
Abstract

Excitons are ubiquitous in optoelectronic applications of inorganic quantum dots (QD) and organic semiconductor molecules (OSC) alike, but their nature is significantly distinct in these two classes of materials. Efficient dielectric screening in QDs leads to the formation of Wannier-Mott excitons with large radii and small dissociation energies. In contrast, small Frenkel excitons with large binding energies are formed in OSCs upon optical excitation. The distinct character of these two types of excitons invokes fundamental dissimilarities in the mechanism and probability of formation of excitons with different spin states. While the occurrence of singlets, triplets, charge-transfer states and excited state dimers (“excimers”) is well understood individually for each material class, an entirely new question is how readily these excitons are formed at the QD/OSC interface.

In this presentation, I will show that the concept of coupled organic-inorganic nanostructures (COIN) provides an ideal tool to study and exploit such interfacial excitons. [1] A typical material consists of periodically alternating QDs and monolayers of coordinating OSCs at the QD surface, which act as electronic coupling agents to promote charge carrier transport across the lattice of QDs. [2-4] I will demonstrate how PbS QDs are utilized as sensitizers to convert near infrared photons into singlets, triplets or excimers in the OSC monolayers as well as how their probability of formation and lifetime depends on the type of OSC.  

The application potential for photon upconversion and spin-selective transport in thin films will be discussed.

 

References

 

[1] Scheele, M., Bruetting, W. & Schreiber, F. Phys. Chem. Chem. Phys. 17 (2015), 97–111. 

[2] André, A., Scheele, M. et al. Chem. Mater. 27 (2015), 8105–8115.

[3] Scheele, M. Alivisatos, A.P. et al. ACS Nano 8 (2014), 2532–2540.

[4] André, A., Scheele, M. et al. Chem. Comm. 53 (2017), 1700-1703.

09:35 - 09:45
Discussion
09:45 - 10:20
SE1.3-I2
Kagan, Cherie
University of Pennsylvania
Role of Surface Chemistry on Charge Carrier Transport in Quantum Dot Solids
Cherie Kagan
University of Pennsylvania, US
Cherie R. Kagan is the Stephen J. Angello Professor of Electrical and Systems Engineering, Professor of Materials Science and Engineering, and Professor of Chemistry at the University of Pennsylvania. Kagan graduated from the University of Pennsylvania in 1991 with a BSE in Materials Science and Engineering and a BA Mathematics. She earned her PhD in Materials Science and Engineering from the Massachusetts Institute of Technology in 1996 working with Moungi G. Bawendi. In 1996, she went to Bell Labs as a postdoctoral fellow and in 1998, she joined IBM’s T. J. Watson Research Center, where she most recently managed the “Molecular Assemblies and Devices Group.” In 2007, she joined the faculty of the University of Pennsylvania. Kagan is an Associate Editor of ACS Nano and serves on the editorial boards of Nano Letters and NanoToday. The Kagan group’s research interests are in the chemical and physical properties of nanostructured and organic materials and in integrating these materials in electronic, optoelectronic, optical, thermoelectric and bioelectronic devices. The group combines the flexibility of chemistry and bottom-up assembly with top-down fabrication techniques to design novel materials and devices. The group explores the structure and function of these materials and devices using spatially- and temporally-resolved optical spectroscopies, AC and DC electrical techniques, electrochemistry, scanning probe and electron microscopies and analytical measurements. Kagan is co-director of The Penn Center for Energy Innovation and serves on the World Economic Forum, Global Agenda Council on Nanotechnology; on the Department of Energy, Basic Energy Sciences Materials Council; and on the advisory board of the US Summer Schools in Condensed Matter and Materials Physics. She served on the Materials Research Society’s Board of Directors from 2007-2009 and the editorial board of the ACS Applied Materials and Interfaces from 2008-2011
Authors
Cherie Kagan a
Affiliations
a, University of Pennsylvania, 200 South 33rd Street, Philadelphia, 19104, US
Abstract

Colloidal semiconductor quantum dots (QDs) are promising materials for electronic and optoelectronic devices due to their size tunable electronic and optical properties and the solution-based processes that enable the integration of these materials into devices. However, the long, insulating ligands commonly employed in the synthesis of colloidal QDs inhibit strong interparticle coupling and charge transport once QDs are assembled into the solid state as QD arrays. A general approach to increase carrier mobility is to reduce the interparticle spacing by ligand exchange. During solution-based deposition and ligand exchange of QD thin films, the QD surfaces are often “attacked” by solvents or ligands, creating surface defect sites. These surface defects generate in-gap states that may scatter mobile carriers and reduce the lifetime of photogenerated carriers by trapping. In this talk, I will describe methods to synthetically control and spectroscopically probe the density and occupancy of defect states at the QD surface and at QD-device interfaces and their importance to creating high mobility and long lifetime QD materials for electronic and optoelectronic devices.

10:20 - 10:30
Discussion
10:30 - 11:05
SE1.3-I3
Luther, Joey
National Renewable Energy Laboratory
Perovskite Quantum Dot Solar Cells—Stable Cubic CsPbI3 Films for High-Efficiency Photovoltaics
Joey Luther
National Renewable Energy Laboratory, US

Joseph M. Luther obtained B.S. degrees in Electrical and Computer Engineering from North Carolina State University in 2001. At NCSU he began his research career under the direction of Salah Bedair, who was the first to fabricate a tandem junction solar cell. Luther worked on growth and characterization high-efficiency III-V materials including GaN and GaAsN. His interest in photovoltaics sent him to the National Renewable Energy Laboratory (NREL) to pursue graduate work. He obtained a Masters of Science in Electrical Engineering from the University of Colorado while researching effects of defects in bulk semiconductors in NREL�s Measurements and Characterization Division. In 2005, He joined Art Nozik�s group at NREL and studied semiconductor nanocrystals for multiple exciton generation for which he was awarded a Ph.D. in Physics from Colorado School of Mines. As a postdoctoral fellow, he studied fundamental synthesis and novel properties of nanomaterials under the direction Paul Alivisatos at the University of California and Lawrence Berkeley National Laboratory. In 2009, he rejoined NREL as a senior research scientist. His research interests lie in the growth, electronic coupling and optical properties of colloidal nanocrystals and quantum dots.

Authors
Joey Luther a
Affiliations
a, NREL, 16253 Denver West Parkway, Golden, 80401, US
Abstract

We demonstrate QD photovoltaic cells with an open-circuit voltage of 1.23 volts and power conversion efficiency of 13.4%. Despite very little research on this specific material system to date, the performance surpasses that of any other QD solar cell.  This new material system has incredible potential for many applications in optoelectronics, including multijunction photovoltaics, solid state lighting and display technology.  Here, I will present the basics behind the perovskite revolution over the past several years and a forward look into where this technology could make the greatest impact.

CsPbI3 is an all-inorganic analog to the hybrid organic cation halide perovskites, but the cubic phase of bulk CsPbI3 (a-CsPbI3)—the variant with desirable band gap—is only stable at high temperatures under conventional constructs. We describe the formation of α-CsPbI3 QD films through a colloidal quantum dot route that are phase-stable for months in ambient air. The films exhibit long-range electronic transport and are used to fabricate colloidal perovskite quantum dot solar cells. The modified size/phase stability will be discussed.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SE1.3-I4
Wise, Frank
Cornell University
Properties of Lead-Salt Nanosheets
Frank Wise
Cornell University, US
Authors
Frank Wise a
Affiliations
a, Cornell University, Bard Hall, 214 Ithaca, NY 14850, USA, Ithaca, US
Abstract

Two-dimensional (2D) single-crystalline semiconductor nanosheets have drawn growing interest within nanoscience research, because may offer superior charge transport compared to assemblies of nanocrystals or nanowires, while still exhibiting size-dependent physical phenomena. Lead chalcogenides (IV-VI) are attractive materials for optoelectronic applications in the near-infrared region. However, only a few examples of lead chalcogenide nansheets have been reported. We will present new methods for the synthesis and surface modification of colloidal PbS nanosheets. New syntheses produce PbS NSs with tunable thickness and shape. Inorganic surface passivation is an effective method to reduce surface trap states in colloidal nanostructures. We show that PbS/CdS core/shell nanosheets can be synthesized. Structural and chemical characterization confirms the presence of the CdS shell, and the optical properties will be reported.

1 1 1  1 1  1 1 1 1 1 1 1 1  1 1  1 1 1 1 1 1 1 1  1 1  1 1 1

12:20 - 12:30
Discussion
12:30 - 12:45
SE1.3-O1
Bohmer, Marcel
Lumileds
On chip quantum dots for efficient white LEDs
Marcel Bohmer
Lumileds
Authors
marcel bohmer a, jacques heuts a, stefan grabowski b, sumit gangwal c, danielle chamberlin c, daniel estrada c, ken shimizu c
Affiliations
a, Lumileds, Device Architecture, Netherlands
b, Lumileds Phosphor Center Aachen, Germany
c, Lumileds, San Jose
Abstract

Quantum dots for illumination are preferably applied directly on chip such that they can be applied in the same configuration as regular phosphors used for down conversion on blue LEDs to create white light of a desired color temperature. We here report the use of red quantum dots as a narrow band red down conversion material. Because the emission of photons outside the eye-sensitivity curve is minimized, this leads to improvements in the efficiency compared to state of the art materials of 5% for cool white and 15% for warm white LEDs. in the application LEDs have to operate at high blue flux, high temperature and humidity for long times. The developed technology meets the requirements set for these conditions, which will be outlined in this presentation. When incorporated into lamps, the gains may be larger because the LEDs can be driven at lower temperature and drive current, which makes them more efficient.

12:45 - 13:00
SE1.3-O2
van der Stam, Ward
Delft University of technology
Electrochemically Tuning the Doping Density, Crystal Structure and Radiative Recombination of Cu2-xS Nanocrystals
Ward van der Stam
Delft University of technology, NL
Authors
Ward van der Stam a, Solrun Gudjonsdottir a, Wiel Evers a, Arjan Houtepen a
Affiliations
a, Chemical Engineering, Optoelectronic Materials, TU Delft, Julianalaan 136, 2628 BL Delft, The Netherlands, NL
Abstract

Copper sulfide (Cu2-xS) nanocrystals have been shown to possess highly tunable localized surface plasmon resonances (LSPRs) in the near-infrared (NIR) spectral region, depending on the amount of Cu+ vacancies.[1,2,3] Here, we present that we can reversibly tune the hole carrier density, and hence, the LSPR in the NIR spectral region, of covellite CuS nanocrystals by spectroelectrochemical methods. We have prepared thin films of degenerately p-doped CuS nanocrystals and by controlling the potential in an electrochemical cell we inject electrons into the NCs, which annihilates the excess holes in the top of the valence band (and hence the LSPR) and shifts the band edge towards the NIR. Furthermore, the injected electrons reduce the covalent disulfide bonds in the covellite CuS unit cell, which results in the reduction of the anionic sublattice from an overall -1 oxidation state to an oxidation state of -2.[3] The electrochemical charge injection is fully reversible and we can cycle several times between a thin film of covellite CuS NCs (Eg = 2.0 eV, strong LSPR) and low-chalcocite Cu2S NCs (Eg = 1.2 eV, no LSPR) by reducing and oxidizing the sulfide sublattice, as evidenced by X-ray Diffractometry and Raman spectroscopy measurements. Interestingly, we find that the fully stoichiometric low-chalcocite Cu2S nanocrystals prepared with our electrochemical approach display efficient air stable radiative recombination near the band edge, centered around 1050 nm. These stoichiometric low-chalcocite Cu2S nanocrystals are obtained by electrochemical reduction of the anionic sublattice and irreversible intercalation of Cu+ ions into the lattice. Our results show that we have dynamic control over the hole doping density and the crystal structure of Cu2-xS nanocrystals, eventually resulting in air stable NIR photoluminescence, which might impact on the successful implementation of copper sulfide nanocrystals into photovoltaic devices or applications such as NIR optical switches and smart windows.

References

[1] J. Luther et al., Nat. Mater., 2011, 10, 36

[2] W. van der Stam, A. C. Berends. C. de Mello Donega, ChemPhysChem, 2016, 17, 559.

[3] Y. Xie et al., J. Am. Chem. Soc., 2013, 135, 17630.

13:00 - 13:15
SE1.3-O3
Samadi Khoshkhoo, Mahdi
Eberhard Karls Universität Tübingen
Tunable Charge Transport by Multiple Inelastic Cotunneling in ITO Nanocrystal Superlattices
Mahdi Samadi Khoshkhoo
Eberhard Karls Universität Tübingen, DE

Since 5/2014 PhD student in the group of Dr. Marcus Scheele, Institute of Physical and Theoretical Chemistry, Eberhard Karls University Tübingen, Tübingen, Germany.

2012 – 2014 Research assistant in the group of Prof. F. Afshar Taromi, Polymer Engineering and Color Technology Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.

7/2011-10/2011 Research visit at Leibniz Institute for Solid State and Materials Research (IFW Dresden) with Prof. B. Büchner, Prof. M. Knupfer, and Dr. A. Koitzsch, Dresden, Germany.

2010 – 2012 Master course of Polymer Engineering - Polymerization Process in the group of Prof. F. Afshar Taromi, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.

2006 – 2010 Bachelor course of Polymer Science and Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.

Authors
Mahdi Samadi Khoshkhoo a, Santanu Maiti b, Frank Schreiber b, c, Thomas Chassé a, c, Marcus Scheele a, c
Affiliations
a, University of Tübingen, Auf der Morgenstelle, Tübingen, DE
Abstract

Macroscopic superlattices of tin-doped indium oxide (ITO) nanocrystals (NCs) are prepared by self-assembly at the air/liquid interface followed by simultaneous ligand exchange with the organic semiconductors M-4,4’,4’’,4’’’-tetraaminophthalocyanine (M4APc, M = Cu, Co, Fe, Ni, Zn). By using X-ray photoelectron spectroscopy (XPS), grazing-incidence small-angle X-ray scattering (GISAXS), ultraviolet-visible-near infrared (UV–vis–NIR) spectroscopy, we demonstrate that the semiconductor molecules largely replace the native surfactant from the ITO NC surface and act as cross-linkers between neighboring particles. Using NCs produced from a single synthesis batch that are separated by similar interparticle distance (i.e. similar barrier length) but different ligand molecules (i.e. different barrier height), allows us to carefully study the influence of the organic capping layer on the transport properties. Transport measurements, focusing on the effect of the metal center of the ligand, reveal a ligand-dependent increase in electrical conductance by 6-9 orders of magnitude, suggesting that M4APc provides efficient electronic coupling for neighboring ITO NCs. The resulting I–V characteristics as well as the temperature dependence (7 - 300 K) of the zero-voltage conductance indicates that at low temperatures, transport across the arrays occurs via a sequence of inelastic cotunneling events, each involving ~3-4 ITO NCs. Our results indicate that the dielectric constant of semiconductor ligands, which is strongly affected by the metal center of molecule, significantly modulates charge transport, the Coulomb charging energy, and the localization length in particular.

SE2.3
Chair: Dmitri Talapin
09:00 - 09:35
SE2.3-I1
Murray, Christopher B.
Philadelphia University
Building modular 2D systems though nanocrystal assembly and surface exchange.
Christopher B. Murray
Philadelphia University, US
Authors
Christopher B. Murray a, b, Yaoting Wu a, Siming Li c, Blaise Fleury a, Stan Najmr a, Natalie Gogtsi b, Cherie R. Kagan a, b, d, Jason B. Baxter c
Affiliations
a, Department of Chemical & Biological Engineering, Drexel University
Abstract

Colloidal nanocrystals (NCs) with controlled composition, size, and shape and surface functionalization provide ideal building blocks for the assembly of new 2D materials and devices. Monodisperse colloidal NCs serve as "artificial atoms" with tunable electronic, and optical properties that can be assembled on the “Mesoscale” to yield properties that combine the best attributes of the isolated quantum systems and the extended electronic transport of traditional semiconductor thin films. In this talk, we will briefly outline progress in synthesis, purification, and integration of size and shape controlled single phase NCs as well as core-shell and heterostructure NCs into 2D arrays through liquid air interfacial assembly and scalable dipcoating processes. Chemical tailoring of NC shape and ligand structure can program the assembly of NC 2D sheets and thin films. The coupling between the NC building blocks can be modified further by exchange of the surface stabilizing ligands to direct the orientation and linking of neighboring NCs. The modular assembly of these NCs allows the desirable features of their underlying quantum character to be retained, or even enhanced by the interactions between the NCs and the hybridization drives the emergence of new delocalized properties.The electronic and optical properties of these coupled systems will be probed through a combination of direct electrical and non-contact optical techniques. Progress in devices and circuits based on these will be shared.

************

09:35 - 09:45
Discussion
09:45 - 10:20
SE2.3-I2
Wise, Frank
Role of Disorder in Atomically-Coherent Quantum-Dot Solids
Frank Wise
Authors
Frank Wise a
Affiliations
a, Cornell University, Bard Hall, 214 Ithaca, NY 14850, USA, Ithaca, US
Abstract

Role of Disorder in Atomically-Coherent Quantu-Dot Solids

Recently, the fabrication of quasi-two-dimensional superlattices of oriented and epitaxially-connected nanocrystals was reported. The structures exhibit both short- and long-range order. Calculations of the electronic states of such “atomically-coherent” assemblies reveal bandwidths that imply promising transport properties. We will report on the synthesis of atomically-coherent superlattices of PbSe nanocrystals, along with structural characterization by x-ray diffraction and high-resolution electron microscopy.  Studies of charge transport show that disorder plays a major role in the properties of existing nanocrystal solids. Prospects for achieving true band transport in these structures will be discussed.

 

 

 

i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

10:20 - 10:30
Discussion
10:30 - 11:05
SE2.3-I3
Louie, Steven G.
University of California at Berkeley
Quantum Phenomena in Atomically Thin Two-Dimensional Materials
Steven G. Louie
University of California at Berkeley
Authors
Steven G. Louie a
Affiliations
a, University of California at Berkeley and Lawrence Berkeley National Laboratory
Abstract

Interaction and symmetry effects, as well as environmental screening effects, dominate many properties of reduced-dimensional systems and nanostructures. These effects often lead to manifestation of concepts and phenomena that may not be so prominent or have not been seen in bulk materials. In this talk, we present some new physical phenomena found in recent theoretical and computational studies of atomically thin two-dimensional materials. A number of highly interesting and unexpected phenomena have been discovered – e.g., strongly bound excitons with unusual energy level structures and optical selection rules; exchange-induced light-like (massless) exciton dispersion; tunable optical and plasmonic properties; electron supercollimation by 1D disorder in graphene and related 2D Dirac materials; and novel topological phases in graphene nanoribbons. We describe their physical origin and compare theoretical predictions with experimental results.

This work was supported in part by the National Science Foundation, the U.S. Department of Energy and the Office of Naval Research.

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SE2.3-I4
Siebbeles, Laurens
TU Delft
Effects of Nanogeometry on Carrier Multiplication in 2D Lead Chalcogenide Materials
Laurens Siebbeles
TU Delft, NL

Laurens Siebbeles (1963) is leader of the Opto-Electronic Materials Section and deputy head of the Dept. of Chemical Engineering at the Delft University of Technology in The Netherlands. His research involves studies of the motion of electrons in novel nanostructured materials that have potential applications in e.g. solar cells, light-emitting diodes and nanoelectronics. Materials of interest include organic nanostructured materials, semiconductor quantum dots, nanorods and two-dimensional materials. Studies on charge and exciton dynamics are carried out using ultrafast time-resolved laser techniques and high-energy electron pulses in combination with quantum theoretical modeling.

Authors
Laurens Siebbeles a
Affiliations
a, Chemical Engineering, Optoelectronic Materials, TU Delft, Julianalaan 136, 2628 BL Delft, The Netherlands, NL
Abstract

Absorption of sufficiently energetic photons in a bulk semiconductor leads to hot electrons and holes that usually cool to the band edge by thermal relaxation. In semiconductor nanomaterials this cooling can be intercepted by excitation of additional electrons across the band gap. In this way, one photon generates multiple electron-hole pairs via a process known as Carrier Multiplication (CM), which is of interest for the development of highly efficient solar cells and photodetectors.

We studied charge carrier photogeneration, CM, charge mobility and decay in: a) films of PbSe quantum dots coupled by organic ligands, and b) 2D percolative networks of PbSe quantum dots connected by atomic bonds. The studies were performed using ultrafast pump-probe spectroscopy with optical or terahertz conductivity detection.

The nanogeometry of the material was found to have enormous effects on the charge mobility and the yield of free charges resulting from CM. In 2D percolative PbSe networks CM occurs in a step-like fashion with threshold near the minimum energy of twice the band gap. In these 2D materials the CM efficiency and charge mobility are much higher than for films of QDs that are coupled by organic ligands. The effects of nanogeometry on the efficiency of CM and impact on power conversion in photovoltaic devices will be discussed.

12:20 - 12:30
Discussion
12:30 - 13:05
Abstract not programmed
13:05 - 13:15
Discussion
SE3.3
Chair: Hongwei Zhu
09:00 - 09:35
SE3.3-I1
Zhang, Tierui
Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS)
2D nanostructured photocatalysts for efficient solar fuels
Tierui Zhang
Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS)
Authors
Tierui Zhang a
Affiliations
a, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences
Abstract

 

Photocatalysis has been considered as a promising green technology to solve the energy and environmental problems through the photocatalytic water splitting into hydrogen production and photoreduction of CO2 into high value-added hydrocarbons. The current change is to develop highly efficient photocatalys. Nanostructured materials for photocatalysis have attracted considerable attention due to their unique physical and chemical properties compared with their corresponding bulk materials. Among various architectures, two-dimensional (2D) nanosheets with thickness generally below 100 nm are of great promise for highly efficient photocatalysis. Herein, some very recent research progress in my group has been summarized on the rational design and controlled synthesis of 2D nanostructured photocatalysts for highly efficient visible light-driven H2 evolution and photocatalytic conversion of CO2 or CO into high value-added hydrocarbons by enhancing the light absorbance and separation of electron-hole pairs of photocatalysts. I) By developing high conductive Cd nanosheet support for CdS, the quantum efficiency of photocatalytic H2 production of CdS/Cd achieved 33% at 420 nm; II) By creating more oxygen defects in ultrathin ZnAl-LDH nanosheets, the photocatalytic reduction of CO2 with water over ZnAl-LDH exhibited stable activity of ≈7.6 μmol g-1 h-1; III) By constructing heterogeneous interface structure, NiO/Ni nanocatalysts exhibited an unexpectedly high selectivity of 60% for C2-C7 hydrocarbons in the CO hydrogenation reaction under visible-light irradiation.

  

  

09:35 - 09:45
Discussion
09:45 - 10:20
SE3.3-I2
Papakonstantinou, Pagona
Ulster University, UK
2D crystals for Electrocatalysis
Pagona Papakonstantinou
Ulster University, UK
Authors
Pagona Papakonstantinou a
Affiliations
a, Engineering Research Institute (ERI), School of Engineering, Ulster University, Newtownabbey, BT37 0QB, UK
Abstract

One of the emerging applications of 2 Dimensional materials is in electrocatalysis. This area is key to the development of energy conversion and storage devices such as batteries, fuel cells, electrolysers and photo-electrochemical cells. The focus of our work is to develop inexpensive, stable and catalytically active materials for the oxygen and hydrogen reactions, that can compete the performance of precious based catalysts.

In this talk, I will describe new results on addressing key challenges involved in optimizing catalytic performance in transition metal dichalcogenides (TMD) and heteroatom doped graphene. In particular, I will describe the effect of solvents in ink preparation and  electrochemical activation for the hydrogen evolution reaction (HER) characteristics such as Tafel slope and current densities of TMDs. I will summarize our important developments in 2D materials including the size selection of exfoliated layers using sequential centrifugation[1-5].  New results on the hidden role of metal impurities on nitrogen doped graphene for influencing the oxygen reduction reaction performance will also be presented.

 Benson, J. et al. “Electrocatalytic Hydrogen Evolution reaction on edges of a few layer Molybdenum disulfide nanodots”, ACS Applied Materials and Interfaces, 7 (2015) 14113.

 Benson et al. “Tuning the catalytic activity of graphene nanosheets for oxygen reduction reaction via size and thickness reduction”, ACS Applied Materials & Interfaces, 6 (2014) 19726.

Wang, T. et al. “Size‐Dependent Enhancement of Electrocatalytic Oxygen‐Reduction and Hydrogen‐Evolution Performance of MoS2 Particles”,Chemistry-A European Journal 19 (2013), 11939.

Wang, T. et al. “Enhanced Electrocatalytic Activity for Hydrogen Evolution Reaction from Self-Assembled Monodispersed Molybdenum Sulfides nanoparticles on an Au electrode”, Energy Environ. Sci., 6 (2013) 625.

 

10:20 - 10:30
Discussion
10:30 - 11:05
SE3.3-I3
Shalom, Menny
Department of Chemistry, Ben-Gurion University of the Negev
Carbon Nitride Materials for Artificial Photosynthesis
Menny Shalom
Department of Chemistry, Ben-Gurion University of the Negev, IL
Authors
Menny Shalom a
Affiliations
a, Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, IL
Abstract

One of the promising technologies for future alternative energy sources is the direct conversion of sunlight into chemical and electrical energy by using artificial photosynthesis. Artificial photosynthesis has attracted great interest over the last decades, especially for its potential to produce clean and cheap renewable energy without dependence on fossil fuels and without carbon dioxide emission. Artificial photosynthesis applications span from many fields such as: solar fuel production, water splitting, photo-degradation of pollutants, and catalysis of other chemical reactions, e.g. for the production of fine chemicals. An important challenge in artificial photosynthesis is the development of stable and inexpensive catalysts that can harvest the visible light in solar spectrum. Although the great progress in this field over the last years, the energy conversion efficiency of artificial photosynthesis remained low. Therefore, new approaches and new materials as photocatalysts and photoelectrocatalysts should be introduced for the improvements of artificial photosynthesis conversion efficiencies. While most of the research in this field is focused on metal based semiconductors (metal oxides, sulfides and nitrides) as photo (electro)catalysts, in the last years metal-free graphitic carbon nitride (g-CN) materials have attracted widespread attention due to their (electro)catalytic and photocatalytic activity alongside their low price and simple synthesis. In this talk I will show our recent progress in carbon nitride synthesis by using supramolecular chemistry to synthesize well-defined structures of g-CN such as hollow boxes, spheres, tubes and spherical macroscopic assemblies with the possibility to control their photophysical and photocatalytic properties. I will demonstrate in particular their operation as promising materials for artificial photosynthesis and other photoelectronic applications. I will introduce new approaches to grow g-CN layers with altered properties on conductive substrates for photoelectrochemical application. The growth mechanism of g-CN on flat and porous substrates as well as their chemical, photophysical, electronic and charge transfer properties will be discussed

11:05 - 11:15
Discussion
11:15 - 11:45
Coffee Break
11:45 - 12:20
SE3.3-I4
Vázquez, Ester
Universidad de Castilla-La Mancha
Graphene for Bioapplications: Preparation, Cytotoxicity and In-tegration in 3D-scaffolds
Ester Vázquez
Universidad de Castilla-La Mancha
Authors
Ester Vázquez a, b
Affiliations
a, Instituto Regional de Investigación Científica Aplicada (IRICA), Universidad de Castilla-La Mancha, Ciudad Real, (Spain)
b, Departamento de Química Orgánica, Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Ciudad Real, (Spain)
Abstract

Graphene has emerged as a new material, with outstanding mechanical and electronic properties that will permit a broad range of applications, from microelectronics to composite or even medicine. Although there has been a huge effort directed in the area of nanomedicine, biomedical applications of graphene derivatives have, so far, mainly focused on graphene oxide and reduce graphene oxide. The main reason for this fact is the difficulty to obtain pristine graphene flakes, directly in water or in culture media, due to the intrinsic hydrophobicity of this material.

Our group have recently described an interesting approach for the preparation of stable dispersions of graphene in water, without detergents or any other additives, driven by an easy and eco-friendly ball milling approach.1 These aqueous suspensions can be rapidly frozen and, subsequently, lyophilized giving rise to a very soft and low-density black powder.2 Powders of graphene can be safely stored or shipped and they can be readily dispersed in culture media within the presence or absence of serum and antibiotics.

During this talk, we will discuss (i) optimized ways to generate graphene dispersions in culture media; (ii) studies of interaction of so-prepared solutions with cells. (ii) the use of graphene in polymeric 3D structures for drug delivery purposes3 and for 3D cell culture media.

References:

1. M. Yi and Z. Shen, (2015) J. Mater. Chem. A, 3, 11700–11715.

2. V. León, J. M. González-Domínguez, J. L. G. Fierro, M. Prato and E. Vázquez, (2016) Nanoscale, 8, 14548–14555.

3. S. Merino, C. Martín, K. Kostarelos, M. Prato and E. Vázquez (2015). ACS Nano, 9, 4686-4697.

12:20 - 12:30
Discussion
12:30 - 12:45
SE3.3-O1
Ruirui, Hu
Tsinghua University
A Graphene Oxide Controlled Wrinkled and Sandwich-Structured Nanofiltration Composite Membrane with Ultrafast Water Transport
Hu Ruirui
Tsinghua University, CN
Authors
Ruirui Hu a, Hongwei Zhu a
Affiliations
a, School of materials science and engineering, Tsinghua University, Room 2421, Yifu Science and Technology Building, Tsinghua University, Beijing, 100084, CN
Abstract

Membranes with high permeability and selectivity are desired for energy-efficient liquid separation. In this work, a highly wrinkled surface and ultrafast water transport channels centered in a polyamide membrane were prepared by in-situ embedding graphene oxide (GO) nanosheets into the separation layer of a nanofiltration (NF) membrane via an interfacial polymerization. The wrinkled morphology was achieved by adjusting the GO lateral size and additive content of GO. The distribution of GO nanosheets in the composite membrane was revealed at a low magnification with TEM, and GO nanosheets were well confined right in the middle of the sub-20 nm ultrathin polyamide membrane. The incorporation of GO also improved the hydrophilicity of the composite membrane. The rough and hydrophilic surface enabled the attraction of large amounts of water molecules to the membrane, and the sub-20nm membrane thickness and two-dimension capillary network formed by the stacked GO nanosheets accelerated the transport of water molecules through the membrane. Consequently, this wrinkled and sandwich structured ultrathin NF composite membrane overcame the trade-off between flux and retention of commercial membranes, and gave an unprecedented water flux up to 258 LMH/MPa and a high salt rejection to MgSO4 over 90% simultaneously, which were five-fold higher than those of commercial NF membranes. Moreover, to achieve a certain separation performance, the composite membrane requires a much lower operation pressure. Our work provides a novel strategy to break the bottleneck of traditional polymeric NF membranes with a strikingly decreased energy consumption, and bring the notable advantages of GO, the most promising candidate for water purification, closer to practical applications.

12:45 - 13:00
SE3.3-O2
Huang, Meirong
Department of Material Science and Engineering, Tsinghua University
Gradient-doped bulky crystalline BiVO4 for water splitting
Meirong Huang
Department of Material Science and Engineering, Tsinghua University

2012 to 2016, China University of Petroleum, Material Science and Engeering, Bachelor

2016-now, Tsinghua University, Catalytic material, Ph.D candidate 

Authors
Meirong Huang a, Hongwei Zhu a
Affiliations
a, Tsinghua University, Yifu Building Room 2422, Tsinghua University,Haidian District, Beijing, 100084, CN
Abstract

Photoelectrochemical (PEC) water splitting provides an attractive way to convert sunlight into chemical fuels from water. However, the development of efficient and stable photoanodes for oxygen evolution reactions (OERs) is still challenging because of the high activation energy and poor carriers separation. BiVO4 known for its deep valance band and excellent stability in near-neutral aqueous solutions is one of the most attractive photoanode candidates. Various strategies, including doping, and depositing CoPi, NiFeOx-Bi and Ni/Fe layered-double-hydroxide (LDH) for OER kinetics improvement and constructing p-n junctions for carriers recombination suppression, have been developed. As BiVO4 has a longer carrier lifetime (~40 ns) compared to other oxide photoanodes, preparation of bulky crystals and gradient doping in BiVO4 are efficient strategies to improve the carrier mobility and decrease the carriers recombination for further enhancing its photocatalytic performance. Bulky crystalline BiVO4 of less crystal defects (e.g., grain boundary) can decrease the carrier traps and recombination sites. Gradient-doped bulky crystalline BiVO4 will construct a built-in electric field with a distributing band bending to improve the mobility and separation of photogenerated carriers. In this work, first, electrodeposition of monoclinic BiOI on FTO substrate under an appropriate voltage is carried out, and solutions with different pHs are employed to introduce a distributing doping content. After the deposition of BiOI, the samples are annealed to obtain BiVO4. Next, a thin interfacial layer of SnO2 (~10 nm) between FTO and BiVO4 is introduced to prevent recombination at the FTO/BiVO4 interface. Finally, NiFeOx-Bi catalyst or Ni/Fe LDH is deposited on the surface of BiVO4 to optimize the overall catalytic performance.

13:00 - 13:15
SE3.3-O3
Almeida, Guilherme
Istituto Italiano di Tecnologia
Colloidal Monolayer β-In2Se3 Nanosheets with High Photoresponsivity
Guilherme Almeida
Istituto Italiano di Tecnologia, IT
Authors
Guilherme Almeida a, d, Sedat Dogan a, Giovanni Bertoni e, Cinzia Giannini f, Roberto Gaspari b, Stefano Perissinotto c, Roman Krahne a, Liberato Manna a
Affiliations
a, Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT), Genova, Italy, Via Morego, 30, Genova, IT
b, CompuNet, Istituto Italiano di Tecnologia, Genova, Italy, Via Morego, 30, Genova, IT
c, Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, I-20133 Milan, Italy
d, DCCI, Università degli Studi di Genova, Via Dodecaneso, 31, 16146, Genova, Italy
e, IMEM-CNR, Parco Area delle Scienze 37/A, I-43124 Parma, Italy
f, Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, via Amendola 122/O, 70126 Bari, Italy
Abstract

Two-dimensional (2D) semiconducting materials of layered metal chalcogenides have been extensively explored during the last decade to complement graphene for ultra-thin and flexible electronic applications.1,2 In this work3, we report a low-temperature wet-chemical synthesis of β-In2Se3 nanosheets with monolayer thickness and tunable lateral sizes from ~300 nm to ~900 nm, using short aminonitriles (dicyandiamide or cyanamide) as shape controlling agents. The phase and the monolayer nature of the nanosheets were ascertained by analysing the intensity ratio between two diffraction peaks from two-dimensional slabs of the various phases, determined by diffraction simulations. These findings were further backed-up by comparing and fitting the experimental X-ray diffraction pattern with Debye Formula simulated patterns and with side-view high-resolution transmission electron microscopy imaging and simulation. The β-In2Se3 nanosheets were found to be indirect band-gap semiconductors (Eg=1.55 eV) and single nanosheet photodetectors demonstrated photo-responsivities up to 104 A/W in the visible range (with light powers in the fW range) and response times of 2-3 ms. These values are orders of magnitude better than most photoconductors based on 2D transition metal dichalcogenides and compete with the best devices based on other 2D III-VI materials.4

References

1.           Wang, Q. H. et al. Nat. Nanotechnol. 7 (2012) 699–712

2.           Yuan, H. et al. Acc. Chem. Res. 48 (2015) 81–90

3.           Almeida et al.J. Am. Chem. Soc. 139 (8) (2017) 3005–3011

4.           Buscema, M. et al. Chem Soc Rev 44 (2015) 3691–3718

13:15 - 13:25
Closing
13:15 - 15:00
Lunch
SE1.4
Chair: Frank Wise
15:00 - 15:35
SE1.4-I1
Kambhampati, Patanjali
McGill University
On the nature of the surface of semiconductor nanocrystals
Patanjali Kambhampati
McGill University, CA

Patanjali Kambhampati. BA Carleton College USA (1992), PHD University of Texas (USA) 1998, PDF University of Texas (USA) 1999 - 2001. Professor of Chemistry McGill University (2003 - present). Research focus of semiconductor nanostructures and femtosecond laser spectroscopy.

Authors
Patanjali Kambhampati a
Affiliations
a, McGill University, 3480 University Street, Montreal, 0, CA
Abstract

The size dependence of semiconductor nanocrystals has been well explored for decades. This well-known size dependence enables NC to be used in lighting applications based upon the narrow emission from the core excitons. These excitonics of the core are well studied and well exploited in applications. In stark contrast the surface of the NC is at the forefront of a modern understanding NC. While there are some initial works on the surface science of NC, there is as yet no work on whether the surface maintains size dependent phenomena. Moreover can any size dependent surface phenomena be exploited in optical applications?

 

Here we reveal the size dependence of the surface emission from CdSe semiconductor nanocrystals for the first time. Via careful synthetic control of the sizes and surface passivations of ultrasmall CdSe NC, we show that there is a clear size dependence to specific aspects of the surface emission. The fraction of light emitted from the surface increases with surface area. We rationalize this observation in light of a strong size dependence to the surface Gibbs energy. This size dependence to the surface Gibbs energy provides a rational route to creating white light from a single nanocrystal.

15:35 - 15:45
Discussion
15:45 - 16:20
SE1.4-I2
Wood, Vanessa
ETH Zurich
Nanocrystal Surface Engineering
Vanessa Wood
ETH Zurich, CH

Vanessa Wood is a professor in the Department of Information Technology and Electrical Engineering at ETH Zurich, where she heads the Laboratory for Nanoelectronics. Before joining ETH in 2011, she was a postdoctoral associate in the laboratory of Professor Yet-Ming Chiang and Professor Craig Carter in the Department of Materials Science and Engineering at MIT, performing research on novel lithium-ion battery systems. She received her MSc and PhD from the Department of Electrical Engineering and Computer Science at MIT. Her graduate work was done in the group of Professor Vladimir Bulović and focused on the development of optoelectronic devices containing colloidally synthesized quantum dots.

Authors
Vanessa Wood a
Affiliations
a, Laboratory for Nanoelectronics, Department of Information Technology and Electrical Engineering, ETH Zurich, Gloriastrasse, 35, Zürich, CH
Abstract

In this talk, I will discuss recent work from our group on characterizing, simulating, and engineering nanocrystal surfaces. First, I will present ab initio molecular dynamics (AIMD) on experimentally-relevant sized lead sulfide (PbS) NCs constructed with thiol or Cl, Br, and I anion surfaces. These simulations allow us to investigate the vibrational and dynamic electronic structure. We show that electron-phonon interactions can experimentally explain observed thermal broadening and carrier cooling rates in Pb-chalcogenide NCs. We demonstrate that electron-phonon interactions are suppressed in halide terminated NCs due reduction of both the thermal displacement of surface atoms and the spatial overlap of the charge carriers with these large vibrations. This work showing how surface engineering – guided by simulations – can be used to systematically control carrier dynamics emphasizes how important exact knowledge of NC shape and atomic structure it.  A simple particle in a sphere is no longer sufficient. With the increasing complexity of multi-shell and graded core-shell structures, determining the exact shape and structure of NCs is challenging.  Here, I will discuss how a combination of x-ray scattering and electron microscopy techniques can be used to obtain the detailed structures needed for simulation.

16:20 - 16:30
Discussion
16:30 - 16:45
SE1.4-O1
Rabouw, Freddy
Universiteit Utrecht
Trapping and charging in individual quantum dots studied using fluorescence correlation analysis
Freddy Rabouw
Universiteit Utrecht, NL
Authors
Freddy Rabouw a, Felipe Antolinez a, David Norris a
Affiliations
a, ETH Zurich, Rämistrasse, 101, Zürich, CH
Abstract

Even after 20 years of research, the phenomenon of blinking of individual quantum dots is poorly understood. Studies usually rely on time-binning the experimental data. The results have been used to propose and validate models for the mechanisms of blinking, involving charging of the quantum dot and/or variable non-radiative recombination rates of excitons. Such models involve excited-state processes with characteristic timescales spanning from nanoseconds (exciton recombination) to seconds (blinking). However, time-binning experimental data sets a limit on the maximum achievable time resolution of the order of a few milliseconds, depending on the count rate from a single quantum dot. This complicates model validation and therefore the understanding of blinking.

Here, we use fluorescence correlation (i.e. photon statistics) to study the full time range from nanoseconds to seconds relevant to the emission dynamics of individual CdSe/CdS quantum dots. In particular, we examine *fast* blinking events on sub-millisecond timescales usually hidden by time binning. Even if the intensity trace seems to show binary ON–OFF blinking, the underlying dynamics may be more complex. A typical single quantum dot randomly switches between periods of efficient optical cycling (ON) and periods of Auger recombination (OFF), but also experiences periods of increased charge-carrier trapping. We discuss how to distinguish quenching due to Auger recombination from quenching due to trapping, and study the dynamics of these processes as a function of CdS shell thickness.

16:45 - 17:00
SE1.4-O2
Giansante, Carlo
Istituto di Nanotecnologia, CNR-Nanotec
On How Surface Chemistry Affects the Ground State Optoelectronic Properties of Colloidal Quantum Dots
Carlo Giansante
Istituto di Nanotecnologia, CNR-Nanotec, IT
Authors
Carlo Giansante a, b
Affiliations
a, Istituto di Nanotecnologia CNR-Nanotec, via Monteroni, Lecce, IT
b, Universita` del Salento, Via per Arnesano, Lecce, IT
Abstract

Surface chemistry modification of as-synthesized colloidal inorganic semiconductor nanocrystals (QDs), commonly referred to as ligand exchange, is mandatory towards effective QD-based optoelectronic and photocatalytic applications. The widespread recourse to ligand exchange procedures is leading to uncover, somehow serendipitously, the marked impact exerted by chemical species at nanoscopic surfaces on the ground state optoelectronic properties of QDs: indeed, QD surface modification has been shown to induce, among others, band edge energy shifting,[1] optical band gap reduction,[2] and broadband optical absorption enhancement[3] to an extent beyond any expectation based on commonly accepted models. However, the proposed explanations to these experimental findings often contradict each other, albeit observed for analogous QD systems, thus providing elusive answers to the questions raised by the observed phenomena.

Here I discuss such contradictions and suggest a comprehensive description of the colloidal QD electronic structure that relies on the notion of inherent ligand/core orbital mixing, thus suggesting the inadequacy of conceiving ligands at the QD surface as molecular dipoles or dielectric shell.

 

[1]   a) M. Soreni-Harari et al., Nano Lett. 2008, 8, 678; b) P. R. Brown et al., ACS Nano 2014, 8, 5863.

[2]   a) R. Koole et al., J. Phys. Chem. 2007, 111, 11208; b) A. Wolcott et al., J. Phys. Chem. Lett. 2011, 2, 795; c) M. T. Frederick et al., Nano Lett. 2011, 11, 5455; d) M. T. Frederick et al., Nano Lett. 2013, 13, 287.

[3]   a) C. Giansante et al., J. Am. Chem. Soc. 2015, 137, 1875; b) D. Debellis et al., Nano Lett. 2017, 17, 1248.

 

SE2.4
Chair: Cherie Kagan
15:00 - 15:15
SE2.4-O1
Kazes, Miri
Weizmann Institute of Science
Strain Induced Type-II Band Alignment Control in CdSe Nanoplatelets / ZnS Sensitized Solar Cells
Miri Kazes
Weizmann Institute of Science, IL
Authors
Miri Kazes a, Songping Luo b, Dan Oron a, Hong Lin b
Affiliations
a, School of materials science and engineering, Tsinghua University, Room 2421, Yifu Science and Technology Building, Tsinghua University, Beijing, 100084, CN
Abstract

The use of colloidal semiconductor nanoparticles (NPs) as sensitizers in solar cells have long been desired owing to their low cost and ease of processing. Colloidal CdSe nanoplatelets (NPLs) are a new class of NPs that have a well-defined thickness of only a few atomic monolayers and lateral dimensions of tens of nanometers. This geometry gives rise to a 2D electronic confinement with a continuous density of states allowing for an inherently high carrier density upon optical excitation and a reduced non-radiative Auger recombination rates. In addition, the high aspect ratio of NPLs leads to a significantly increased intrinsic linear absorption compared to quantum dots or rods making NPLs more efficient light absorbers as compared to their counterparts.

Here, colloidal CdSe nanoplatelets (NPLs) deposited on TiO2 and overcoated by ZnS were explored as light absorbers in semiconductor sensitized solar cells (SSSCs). Significant red-shifts of both absorption and steady-state photoluminescence (PL) along with rapid PL quenching suggest a type-II band alignment at the interface of the CdSe NPL and the ZnS barrier layer grown on the NPLs layer, as confirmed by energy band measurements. The considerable red shift leads to enhanced spectral absorption coverage and the sharp band edge absorption suggests a defect free interface. Cell characterization show an increased open-circuit voltage of 664 mV using a polysulfide electrolyte, which can be attributed to a photo-induced dipole (PID) effect created by the spatial charge separation across the nanoplatelet sensitizers. The observed short-circuit current density of 11.14 mA cm-2 approaches the maximal theoretical current density for this choice of absorber, yielding an internal quantum efficiency (IQE) of close to 100%, a clear signature of excellent charge transport and collection yields. An improved cell design that will offer a controlled orientation of NPLs arrays is expected to realize the full advantage of this material.

15:15 - 15:30
SE2.4-O2
Thumu, Udayabhaskararao
Weizmann Institute of Science
New approaches to control the self-assembly of gold nanoparticles and their surface-enhanced Raman scattering properties
Udayabhaskararao Thumu
Weizmann Institute of Science, IL
Authors
Udayabhaskararao Thumu a, Lothar Houben c, d, e, Ayelet Teitelboim a, Rafal Klajn a, Thomas Altantzis b, Marc Coronado-Puchau f, Judit Langer f, Ronit Popovitz-Biro c, Luis M. Liz-Marzán f, g, Lela Vuković h, Petr Král i, j, Sara Bals b, Rafal Klajn a
Affiliations
a, Department of Physics of Complex Systems, Weizmann Institute of Science, Herzl Street, 234, Rehovot, IL
b, Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, IL
c, Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, IL
d, Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, 52425 Jülich, Germany
e, Peter Grünberg Institut, Forschungszentrum Jülich, 52425 Jülich, Germany
f, CIC biomaGUNE, Paseo de Miramón 182, 20014 Donostia-San Sebastián, Spain
g, Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
h, Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, USA
i, Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
j, Department of Biopharmaceutical Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
Abstract

 New approaches to control the self-assembly of gold nanoparticles and their surface-enhanced Raman scattering

Thumu Udayabhaskararao,1 Thomas Altantzis,2 Lothar Houben,3,4,5 Marc Coronado-Puchau,6 Judith Langer,6 Ronit Popovitz-Biro,3 Luis M. Liz-Marzán,6,7 Lela Vuković,8 Petr Král,9,10,11 Sara Bals,2 Rafal Klajn1*

Ordered arrays or superlattices consisting of nanocrystals (NCs) of different diameter represent an important class of materials. There have been advanced methods to assemble nanoparticles of two different materials into binary nanoparticle superlattices (BNSLs).1 Recently, Rafal et al. has reported highly organized monocomponent helical structures formed from magnetic cubes.2 But this process is limited only to magnetic inorganic materials. On the other hand, there were no unique approaches to make highly organized non-close packed self-assembled structures in the size regime below 20 nm. For example, self-assembly of alkanethiol-protected gold nanoparticles can only give rise to close-packed structures such as hexagonal or FCC arrangements. It is challenging to produce superlattices of inorganic nanoparticles into loosely packed arrangements. Despite these advances in template-assisted arrangement of inorganic nanoparticles,3 little progress has been made over controlling the desired structure of the superlattices. Here, we developed a new approach based on post-modification of BNSLs to create unprecedented monocomponent nanoparticle crystals. We demonstrate the formation various non-close packed monocomponent structures. We have examined several different NP arrays as substrates for surface-enhanced Raman scattering (SERS) and found the best arrays for superior signal enhancement properties.

 

References:

A. Dong, J. Chen, P. M. Vora, J. M. Kikkawa C. B. Murray Nature 2010, 466, 474.

G. Singh, H. Chan, A. Baskin, E. Gelman, N. Repnin, P. Král, R. Klajn Science 2014, 345, 1149.

S. Y. Park, A. K. R. Lytton-Jean, B. Lee, S. Weigand, G. C. Schatz, C. A. Mirkin, Nature 2008, 451, 553.

15:30 - 15:45
SE2.4-O3
Lauth, Jannika
Delft Technical University
Tuning the Photoluminescence and Carrier Multiplication Properties in Ultrathin 2D PbS Nanoplatelets
Jannika Lauth
Delft Technical University, NL
Authors
Jannika Lauth a, Francisco Manteiga Vázquez a, Ryan W. Crisp a, Sachin Kinge b, Arjan J. Houtepen a, Laurens D. A. Siebbeles a
Affiliations
a, Department of Chemical Engineering, Delft University of Technology, The Netherlands, Van der Maasweg, 9, Delft, NL
b, Toyota Motor Europe, Hoge Wei 33, B-1930 Zaventem, BE
Abstract

2D semiconductors with tunable band gaps are highly promising materials for ultrathin electronics. Their dimensionality-dependent optoelectronic properties differ significantly from their 0D and 1D counterparts holding high potential for LEDs, photodetectors and solar cells.

2D PbS nanosheets in particular have been investigated due to their thickness-dependent band gap and their increasing carrier multiplication (CM) efficiency with decreasing nanosheet thickness.[1-2] However, up to now, only few colloidal synthesis ways exist to produce 2D PbS with a thickness approaching few atomic layers (1-2 nm).[3-4] We present a low temperature, acetate-free synthesis of colloidal PbS nanoplatelets (thickness 1.5 nm) that exhibit a significantly blue-shifted band gap (683 nm, 1.8 eV) and zero photoluminescence (PL). By surface passivation of the pristine PbS nanoplatelets with different metal halides, we can boost their PL from 705 nm (1.75 eV), only slightly Stokes-shifted to the absorption edge, up to 750 nm (1.65 eV).

We use ultrafast optical-pump terahertz probe spectroscopy to probe the share of excitons and free charges formed under photoexcitation in strongly confined PbS nanoplatelets and to determine if the CM threshold in ultrathin PbS nanoplatelets is decreased as predicted. This would significantly improve the efficiency of CM in 2D PbS structures.

[1] Bielewicz, T.; Dogan, S.; Klinke, C., Small 2015, 11, 826-833.

[2] Aerts, M.; Bielewicz, T.; Klinke, C.; Grozema, F. C.; Houtepen, A. J.; Schins, J. M.; Siebbeles, L. D. A., Nat. Commun. 2014, 5, 3789.

[3] Khan, A. H.; Brescia, R.; Polovitsyn, A.; Angeloni, I.; Martín-García, B.; Moreels, I., Chem. Mater. 2017, 29, 2883-2889.

[4] Lauth, J.; Vázquez, F. M.; Crisp, R. W.; Kinge, S.; Houtepen, A. J.; Siebbeles, L. D. A., in preparation 2017.

15:45 - 16:00
SE2.4-O4
Climente, Juan Ignacio
Department of Physical and Analytical Chemistry, Universitat Jaume I
Excitons in core-only, core-shell and core-crown nanoplatelets: lateral confinement and correlation
Juan Ignacio Climente
Department of Physical and Analytical Chemistry, Universitat Jaume I
Authors
Juan Ignacio Climente a, Fernando Rajadell a, Josep Planelles a, Jose Luis Movilla a
Affiliations
a, Institute of Advanced Materials (INAM), Universitat Jaume I, Avinguda de Vicent Sos Baynat, Castelló de la Plana, ES
Abstract

Semiconductor nanoplatelets are the colloidal analogue of epitaxial quantum wells. Despite several similarities, the opto-electronic properties of nanoplatelets present remarkable differences with respect to those of quantum wells. In this work, we provide theoretical assessment on the main physical factors inducing such differences: (1) the presence of lateral confinement, (2) the presence of an organic environment dielectrically mismatched with the inorganic structure and (3) the possibility of growing heterostructures not only along the direction of strong confinement, but also along the weakly confined directions.

By means of a simple semi-analytical, effective mass method, we calculate exciton emission and binding energies, wave function and radiative lifetime for core-only, core-shell and core-crown nanoplatelets with CdSe core.  In general, the physics is severely dependent on the strength of electron-hole correlation, which in these systems is enhanced by dielectric confinement.

We show that nanoplatelets with lateral dimensions under 20 nm fall in an intermediate confinement regime, where the emission energy can be blueshifted by tens of meV -in agreement with experiments[1]-, and radiative lifetimes are shorter than quantum well expectations.  For typical experimental sizes, we estimate radiative lifetimes of 1 ps or less are feasible, thus supporting related four-wave-mixing experiments.[2]

In core-shell CdSe/CdS nanoplatelets, charge separacion is efficient, but in core-crown ones the strong Coulomb interaction keeps both carriers confined by the core, and the exciton physics resembles that of core-only nanoplatelets, which explains the spectral response resported in Ref.[3].

 

References

[1] Bertrand et al. Chem. Commun. 52, 11975 (2016).

[2] Naeem et al. Phys. Rev. B 91, 121302(R) (2015).

[3] Tessier et al. Nano Lett. 14, 207 (2014).

 

 

 

16:00 - 16:15
Closing
17:00 - 17:15
Closing
 
Posters
Klaus Boldt, Florian Enders, Peng Zeng, Trevor A. Smith
Ultrafast Carrier Relaxation and Extraction in Semiconductor Nanoheterostructures
Yarimeth A. Alarcón, Oscar A. Jaramillo-Quintero, Marina E. Rincón
Thermographic Analysis of Perovskite Solar Cells Degradation Induced by Light
Michael Nagli, Maytal Caspary-Toroker
M(OH)2 (M = Ni, Fe, Co) two-dimensional materials and investigation of their electronic properties through computational methods
Yannick Gaudy, Stefan Dilger, Steve Landsmann, Ulrich Aschauer, Simone Pokrant, Sophia Haussener
Coupled Experimental-Numerical Analysis of LaTiO2N Particle-Based Water-Splitting Photoelectrodes
Pramod Patil Kunturu, Jurriaan Huskens
Efficient solar water splitting copper(I) oxide photocathodes protected by carbon materials
Daniel Esposito
3D Printed Membraneless Electrolyzers for Hydrogen Production
Wouter Vijselaar, Pieter Westerik, Janneke Veerbeek, Roald Tiggelaar, Erwin Berenschot, Jurriaan Huskens, Han Gardeniers
Spatial Decoupling of Light Absorption and Catalytic Activity of Nickel-Molybdenum on High-Aspect-Ratio Silicon Microwire Arrays
Katsushi Fujii, Takenari Goto, Shinichiro Nakamura, Kayo Koike, Takafumi Yao
In-situ Photoluminescence Observation Trial for Photoelectrochemical Water Splitting using with n-type GaN as an Photoanode
Rotem Strassberg, Yahel Barak, Svas Delikanli, Efrat Lifshitz, Hilmi Volkan Demir
Optically Detected Magnetic Resonance studies of CdSe/CdMnS core/shell colloidal nanoplatelets
Itay Meir, Joanna Dehnel, Efrat Lifshitz
Optical properties of alloyed CdSe/CdS CQDs heterostructure
Huu Chuong Nguyen
Catalytic properties of doped Fe2O3 using DFT+U approach
Juan Ignacio Climente, Josep Planelles, Fernando Rajadell
Quantum Mechanical Origin of Linearly Polarized Emission in CdSe/CdS Dot-in-Rod Heterostructures
Divya Bohra, Wilson Smith
Rational design of carbon dioxide electroreduction catalysts using multiscale modeling
Jannika Lauth, Francisco Manteiga Vázquez, Ryan W. Crisp, Sachin Kinge, Arjan J. Houtepen, Laurens D. A. Siebbeles
Tuning the Photoluminescence and Carrier Multiplication Properties in Ultrathin 2D PbS Nanoplatelets
Satria Zulkarnaen Bisri, Daiki Shin, Sunao Shimizu, Maria Ibanez, Maksym V. Kovalenko, Yoshihiro Iwasa
Charge Carrier Doping Control and Thermoelectricity of Colloidal Nanocrystal Assemblies
Florent Yang, Jan Kugelstadt, Mercedes Alicia Carrillo-Solano, Wouter Maijenburg, Christina Trautmann, Maria Eugenia Toimil-Molares
Cu2O nanowire arrays electrodeposited in etched ion-track membranes as photocathodes for solar water splitting
Ivan Mora-Sero, Bruno Clasen Hames
Perovskite Quantum Dots for LED applications
Nicholas Kirkwood, Francesca Pietra, Luca De Trizio, Anne Hoekstra, Lennart Kleibergen, Rolf Koole, Patrick Baesjou, Nicolas Renaud, Liberato Manna, Arjan Houtepen
Preferential gallium for zinc cation exchange in InZnP nanocrystals leads to photoluminescence enhancement
Solrun Gudjonsdottir, Ward van der Stam, Nick Kirkwood, Wiel Evers, Arjan Houtepen
The role of ion diffusion in electrochemical doping of ZnO Nanocrystal assemblies
Laura Piveteau, Ta-Chung Ong, Brennan J. Walder, Aaron J. Rossini, Dmitry Dirin, Lindon Emsley, Christophe Copéret, Maksym V. Kovalenko
Dynamic Nuclear Polarization NMR Spectroscopy for Atomistic Understanding of Colloidal Nanocrystal Surfaces
Rochan Sinha, Valerio di Palma, Reinoud Lavrijsen, Mariadriana Creatore, Anja Bieberle-Hütter
Improvement In The Water Splitting Activity Of Hematite Thin Films with ZnO Underlayer
Jin-Young Yu, Jin-Young Jung, Jung-Ho Lee
High open-circuit potential obtained by ion-permeable NiOx on n-Si photoanode for efficient water oxidation
Fabio Gabelloni, Giulia Andreotti, Francesco Biccari, Massimo Gurioli, Marco Pagliai, Alessio Milanesi, Nicola Calisi, Stefano Caporali, Anna Vinattieri
Anomalous increase of the photoluminescence decay time with the temperature in CsPbBr3 nanocrystals: role of the thermally activated transfer from the surface states
Nienke Firet, Wilson Smith
The role of crystal structure in oxide-derived Ag catalysts for CO2 reduction
Yuya Uzumaki, Yoko Ono, Kazuhide Kumakura, Takeshi Komatsu
Impedance Analysis of Water Oxidation Reaction with a GaN-based Photoanode for Artificial Photosynthesis
Santanu Jana, Patrick Davidson, Benjamin Abécassis
2D CdSe Nanoplatelets – Self-assembly and Living polymerization
Yoko Ono, Yuya Uzumaki, Kazuhide Kumakura, Takeshi Komatsu
Suppresion of Photocurrent Degradation in an Artificial Photosynthesis System with GaN-based Anode by NiO Protective Layer
Dennis Friedrich, Mario Borgwardt, Sönke Müller, Hannes Hempel, Roel van de Krol, Rainer Eichberger
Carrier dynamics in metal oxide absorbers for solar fuel production
Pieter Schiettecatte, Pengshang Zhou, Shalini Singh, José Martins, Zeger Hens
Surface chemistry of molybdenum disulfide nanosheets
Willem Walravens, Jolien Dendooven, Eduardo Solano, Athmane Tadjine, Christophe Delerue, Christophe Detavernier, Zeger Hens
In-gap Minibands in Epitaxial Quantum Dot Superlattices
Bartek J. Trześniewski, Ibadillah A. Digdaya, Sandheep P. Ravishankar, Isaac Herraiz-Cardona, Sixto Gimenez, Wilson A. Smith
Photocharged BiVO4 photoanodes for solar water splitting
Shababa Selim, Laia Francas, Andreas Kafizas, James Durrant
Charge carrier separation in the BiVO4/WO3 heterojunction
Serena Berardi, Michele Orlandi, Alberto Mazzi, Nicola Bazzanella, Antonio Miotello, Stefano Caramori, Carlo Alberto Bignozzi
Nickel-Iron oxide-modified Hematites as efficient earth-abundant photoanodes
Dmitry Dirin, Ryan Dragoman, Marcel Grogg, Maryna Bodnarchuk, Peter Tiefenboeck, Donald Hilvert, Maksym Kovalenko
Surface-engineered cationic nanocrystals stable in high ionic strength solutions
Ludmilla Steier, Matthew Mayer, Sebastiano Bellani, Hansel Comas, Laia Francas, James Durrant, Maria-Rosa Antognazza, Michael Grätzel
Low-temperature Atomic Layer Deposition of TiO2 for Stable High-performance Organic Photocathodes
Kai Liu, Ming Ma, Sixto Gimenez Julia, Wilson Smith
Au-Cu bimetallic thin film for CO2 reduction
Mona Rafipoor, Rieke koll, Jan Niehaus, Horst Weller, Holger Lange
Auger Recombination and Charge Transfer in CdSe/CdS Core/Shell Quantum Dot/Quantum Rod ensembles
Sacha Corby, Laia Francas Forcada, Andreas Kafizas, James Durrant
Evaluation of water oxidation kinetics and charge trapping in nanostructured WO3 photoanodes
Valeriia Grigel, Laxmi Kishore Sagar, Kim De Nolf, Jonathan De Roo, Qiang Zhao, Andre Vantomme, Zeger Hens
The surface chemistry of HgSe Quantum Dots
Dong-Hyung Kim, Sambhaji S Shinde, Jin-Young Jung, Jin-Young Yu, Sung-Hae Kim, Jung-Ho Lee
Noble metal free Co-Sn-Sx chalcogel hybrids for high performance hydrogen evolution
Gianluca Grimaldi, Ryan Crisp, Nick Kirkwood, NIcolas Renaud, Sachin Kinge, Harjan Houtepen, Laurens Siebbeles
Hot electron transfer in bi-component Quantum-Dot solids
Jin-Young Jung, Jin-Young Yoo, Jung-Ho Lee
Photoelectrochemical hydrogen evolution reactions using electrolyte-permeable NiOx coated Si photocathodes
Bruno Clasen Hames, Rafael Sánchez, Iván Mora-Seró
A Study of the Device Performance and Light Characteristics Stability of Quantum Dot Based White Light Emitting Diodes
Simon C. Boehme, Frank C.M Spoor, Wiel H. Ever, Elizabeth von Hauff, Ivan Infante, Arjan Houtepen
How can we dispose of heat in semiconductor nanocrystals?
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