Halide perovskites are a new class of functional semiconductor materials from a viewpoint of condensed matter physics. Lead halide perovskites show very sharp absorption edges and extremely efficient luminescence of free carriers and excitons even at room temperatures. Intrinsic optical properties of perovskites can be studied at room temperature. Recent ultrafast optical spectroscopy studies of nonequilibrium photocarrier and exciton dynamics in halide perovskites have provided rich insights into semiconductor photophysics. We clarified the photocarrier dynamics and optical responses in a wide time range from a few femtoseconds to seconds [1-11]: (1) in femtoseconds, ballistic electron motion in the conduction band under laser electric fields and high-order harmonic generation, (2) in picoseconds, hot carrier relaxation and phonon bottleneck effects through strong electron-phonon couplings, and (3) in nanoseconds, radiative recombination of carriers, long-range carrier diffusion, and photon recycling. In addition, low-dimensional nanostructures such as quantum dots and atomically thin layers show the superior luminescence of excitons [12-16]. Biexcitons and trions determine picosecond luminescence and transport properties. In this talk, we discuss the photocarrier dynamics of halide perovskites and the exciton physics in perovskite nanostructures revealed by time-resolved optical spectroscopy.

[1] Y. Yamada, T. Nakamura, M. Endo, A. Wakamiya, and Y. Kanemitsu, J. Am. Chem. Soc. 136, 11610 (2014).
[2] Y. Yamada, T. Yamada, L. Q. Phuong, N. Maruyama, H. Nishimura, A. Wakamiya, Y. Murata, and Y. Kanemitsu, J. Am. Chem. Soc. 137, 10456 (2015).
[3] T. Yamada, Y. Yamada, Y. Nakaike, A. Wakamiya, and Y. Kanemitsu, Phys. Rev. Applied 7, 014001 (2017).
[4] T. Yamada, T. Aharen, and Y. Kanemitsu, Phys. Rev. Lett. 120, 057404 (2018).
[5] K. Ohara, T. Yamada, H. Tahara, T. Aharen, H. Hirori, H. Suzuura, and Y. Kanemitsu, Phys. Rev. Materials 3, 111601(R) (2019).
[6] Y. Sanari, H. Hirori, T. Aharen, H. Tahara, Y. Shinohara, K. L. Ishikawa, T. Otobe, P. Xia, N. Ishii, J. Itatani, S. A. Sato, and Y. Kanemitsu, Phys. Rev. B 102, 041125(R) (2020).
[7] T. Yamada, Y. Yamada, and Y. Kanemitsu, J. Lumin. 220, 116987 (2020).
[8] K. Ohara, T. Yamada, T. Aharen, H. Tahara, H. Hirori, H. Suzuura, and Y. Kanemitsu, Phys. Rev. B 103, L041201 (2021).
[9] F. Sekiguchi, H. Hirori, G. Yumoto, A. Shimazaki, T. Nakamura, A. Wakamiya, and Y. Kanemitsu, Phys. Rev. Lett. 126, 077401 (2021).
[10] Y. Yamada, H. Mino, T. Kawahara, K. Oto, H. Suzuura, and Y. Kanemitsu, Phys. Rev. Lett. 126, 237401 (2021). 
[11] Y. Yamada and Y. Kanemitsu, NPG Asia Materials 14, 48 (2022).
[12] Y. Kanemitsu, J. Chem. Phys. 151, 170902 (2019).
[13] G. Yumoto and Y. Kanemitsu, Phys. Chem. Chem. Phys. 24, 22405 (2022).
[14] G. Yumoto, H. Hirori, F. Sekiguchi, R. Sato, M. Saruyama, T. Teranishi, and Y. Kanemitsu, Nature Commun. 12, 3026 (2021).
[15] G. Yumoto, F. Sekiguchi, R. Hashimoto, T. Nakamura, A. Wakamiya, and Y. Kanemitsu, Sci. Adv. 8, eabp8135 (2022).
[16] E. Kobiyama, H. Tahara, M. Saruyama, R. Sato, T. Teranishi, and Y. Kanemitsu, Appl. Phys. Lett. 122, 252106 (2023). 

Halide perovskite materials find applications in solar cells, X-Ray detectors or memory storage devices. This type of perovskites are mixed electronic and ionic conductors that typically display a strong hysteresis during the electrical characterization. The ionic conductivity is responsible for a memory effect that leads to undesirable hysteresis in the solar cell configuration.² Alternatively, in the resistive memory configuration this hysteresis is a requirement and needs to be well understood to offer a good control of the conductive states. Here, we show that the working mechanism, performance and stability of the solar cells and memory devices can be tuned and improved by a careful selection of each structural layer. Several configurations are  evaluated in which structural layers are modified systematically: formulation of the perovskite³, the nature of the buffer layer⁴  and the nature of the metal contact⁵. Overall, we provide solid understanding on the operational mechanism of halide perovskite electronic devices that unveils the connection between electronic and ionic conduction.

Bandgap tuning is a crucial characteristic of metal-halide perovskites, with benchmark lead-iodide compounds having a bandgap of 1.6 eV. To increase the bandgap up to 2.0 eV a straightforward strategy is to partially substitute iodine with bromine in so-called mixed-halide lead perovskites. Such compounds are prone, however, to defect-induced halide segregation resulting in bandgap instabilities, which limits their application in tandem solar cells and a variety of optoelectronic devices. The optimization of the perovskite composition and surface passivating agents can effectively slow down, but not completely stop, such light-induced instabilities. Here I will show how we identify the defect and the relative intra-gap electronic state/charge carrier dynamics that triggers the material transformation and bandgap shift. It allows us to engineer the perovskite band edge energetics by engineering the chemical composition of the perovskite crystalline unit to radically deactivate the photo-activity of such electronic states and stabilize the perovskite bandgap over the entire spectral range above 1.6 eV. Overall, I will show how the photo-instability of lead based single and mixed halide perovskites, which can been seen as photo-degradation and bandgap photo-destabilization, has the same root. Then, I will conclude my lecture showing how, by halides alloying, we can achieve photo-stable bandgaps in a broad spectral range from NIR to 2 eV, in tin-based perovskites. Here, the defect chemistry modulates the electronic property of the semiconductor switching from a highly p-doped to an intrinsic one.

Our research group focuses on the development of functional polymers and hybrid perovskites for use in various kinds of optoelectronic devices, including thin-film transistor (TFT), (photo-)memory, light-emitting diode (LED), and solar cell devices. We are particularly interested in exploring the structure-performance relationships of polymers and perovskites. In addition to advances in the controlled synthesis of these solution-processable semiconductors, we explore innovative interface and device engineering to optimize device performance. In this presentation, we will share our recent works related to two-dimensional (2D) Sn-based perovskite transistors and the exploration of their memory and synaptic behaviors controlled by bias and/or light. A comprehensive study combining composition tuning, process engineering, and morphology analyses to explore the promise of 2D Sn-based perovskite transistors will be first discussed, with a particular focus on their performance and device stability. Subsequently, we will demonstrate the great potential of 2D Sn-based perovskites for memory and synaptic applications.

In order to fabricate fully-printed carbon-based multi-porous-layered-electrode perovskite solar cells (MPLE-PSCs), a polymer binder thickener had to be added to the carbon paste for the conductive carbon electrode.  The polymer binder thickener is a key material to control the dispersion of carbon particles, viscosity for screen printing, thickness, and porosity of carbon electrode.  In this work, the role and effect of polymer binder thickeners for high-temperature carbon porous electrodes on MPLE-PSCs have been investigated in detail.  Several carbon pastes with/without polymer binder thickeners (4 types of ethyl cellulose and 2 types of hydroxypropyl cellulose, which have different viscosities) were compared.  What we understand in this paper are; [1] Aggregation and dispersion of carbon particles are controlled by the polymer binder thickener (ethyl cellulose and/or hydroxypropyl cellulose); [2] For the porous carbon electrodes, the polymer binder thickeners are carbonized during the sintering procedure at 400 degree C and can be kept on the surface of carbon particles as the additional carbon surface skin, which improve the conductivity; [3] The polymer binder thickeners can help the formation of fine mesoporous structure in the annealed carbon electrodes confirmed.  Combinations of results between viscosity, thermal, and specific surface area analyses revealed the close relationship between device performance and, printability, dispersibility, and porosity brought by the polymer binder thickeners.  As a result, the addition of 20 wt.% polymer binder thickener improved the average power conversion efficiency (PCE) from 9.52 ± 2.04% to 10.86 ± 0.85%, achieving a champion PCE of 12.06%.

Greatcell Solar - Industry talk

I will talk about some of the research activities in my group providing insights into design principles for perovskite solar cells for tandem and space applications. Examples include the roles of ultra-thin layers, e.g., indium tin oxide (ITO), hole transport layer in carrier transport and cell stability.                                                                                                                                                                                                              

In recent years, organic-inorganic halide perovskite solar cells (PSCs) have experienced high-speed developments with the highest power conversion efficiency (PCE) of 26.1%, therefore, the perovskite solar cells (PSCs) have attracted much attention due to their high-energy conversion efficiency and low production cost. However, the problems of stability, toxicity, and scale-up for PSCs are still unresolved. The electron selective layer (ESL) is an indispensable component of perovskite solar cells (PSCs) and is responsible for the collection of photogenerated electrons. Preparing ESL at a low temperature is a key issue for flexible PSCs. While the commonly used electron selective layer (ESL), TiO2, always needs high-temperature post-treatment in its fabrication process, which highly hinder the low-temperature, large-scale and low-cost commercial production of PSCs. Therefore, developing low temperature processable ESLs with high performances can significantly promote the industrialization of PSCs. In this paper, very current results in low temperature processed ESLs, especially non-TiO2 inorganic and organic materials, such as SnO2, SnS2, WOx etc., are described. Their fabrication methods, properties, and applications in PSCs are highlighted. Developing low-temperature processable ESLs will provide more possibilities for designing novel structural PSCs and promoting the commercialization of PSCs. I will also introdue several new Pb-free perovskite materials developed by our group. 

Solar cells using methylammonium lead perovskite as a solar cell light absorbing material have achieved an astounding 25.5% conversion efficiency improvement, equivalent to silicon solar cells as of 2023. There are concerns about the toxic effects of lead in perovskite solar cell materials on human health and the environment, and there is an urgent need to completely replace lead with a more inert metal. In this study, optical properties and defect structures of double perovskite solar-cell materials in which lead is replaced by tin and germanium are analyzed by first-principles calculations to evaluate and design novel lead-free perovskite materials.

First-principles calculations were performed using the Vienna ab initio package (VASP) with PBE and HSE06 for the functional, a plane wave cutoff energy of 520 eV, and a cell size of 2 × 2 × 2. In order to predict what kind of defects are formed in perovskite crystals, the formation energy of the defect a in charge state was calculated for a series of possible defects, such as vacancies, interstitials and antisite occupations.

In the level diagram of defects of Cs₂SnGeI₆, many defect levels appeared in the band gap, but the formation energies of many of them were found to be high and difficult to generate. The V_Sn(-/0) and V_Ge(-/0) defects appearing near the VBM and CBM are considered to be defects that trap photogenerated carriers and reduce the conversion efficiency (V_Sn(-/0) refers to defect levels that ionize at the Sn vacancy site). The formation energies of these defects are strongly dependent on the chemical potentials of the constituent elements (Sn, Ge, and I), and defect formation can be controlled by changing the crystal growth conditions (chemical potentials). Optical properties of Cs₂SnGeI₆ will be discussed in the poster.

Exceptional optoelectronic properties of metal halide perovskite have skyrocketed the power conversion efficiency of solar cells (HPSCs) by over 26.1%, approaching to Shockley–Queisser limit. Molecular passivation represents a promising avenue for enhancing both the efficiency and operational stability of perovskite solar cells.[1-3] This work reports on the effect of diammonium iodide functional molecules featuring aryl or alkyl cores onto 3D-perovskite surfaces. [1] Our findings revealed the remarkable efficacy of piperazine dihydriodide (PZDI), characterized by an alkyl core and electron-rich -NH terminal, in mitigating surface and bulk defects while modifying surface chemistry. We found that the surface passivation mitigates crystal strain and improves carrier extraction efficiency. These effects resulted in an impressive device efficiency of 23.17% (1 cm² area) with superior long-term stability. Device analysis substantiates that these robust bonding interactions reduce defect densities in the perovskite film and suppress ion migration.[4-7] This report will shed light on the synergetic effect of bifunctional molecules in defect mitigation, opening avenues for design strategies centered on bonding-regulated molecular passivation to enhance solar cell performance and stability.

Charge collection in large-area perovskite solar cells is achieved by using a metallic contact in at least one side of the cell (top or bottom contact), and Ag is often the metal of choice for that purpose [1]. However, this material suffers progressive degradation due to reaction with iodide species from the perovskite layer [2]. It is also detrimental for the device if metal atoms diffuse to the inner layers of the cell. Thus, the metal contact is a component that might also induce instability points in perovskite solar cells. Therefore, the search for a metal that could show adequate cost, electrical conductivity and chemical stability (i.e., less prone to unwanted interactions with other cell components) is imperative for the industrialization this technology. Herein, we investigated a series of different metals typically used in photovoltaic or electronic industries, as bottom contacts in large-are perovskite single cells. Metal grids based on Ag, Al, Au, Cu, Mo, Ni, Pd, Pt or Ta were deposited by sputtering onto 5 x 5 cm2 FTO-glass substrates, and their electrical and morphological characteristics were evaluated in different conditions. Overall, as-deposited grids exhibited good adherence to the substrate, and the grid lines were continuous, without pinholes, as observed by scanning electron microscopy (SEM) and optical microscopy (OM). Then, the grids were subjected to the different steps of a typical n-i-p perovskite cell assembly procedure: a) cleaning step; b) UV-ozone treatment; c) heating at 180 °C for 1 hour (mimicking the treatments applied for the SnO2 ETL deposition); and d) heating at 100 °C for 1h (mimicking the perovskite annealing step). SEM, OM and resistivity data (obtained from 4 point probe measurements) were collected after each step, and after performing a sequence comprising of all 4 steps, which would be used in a complete cell assembly. Afterwards, the stability of the metals when in contact with the SnO2 layer or in direct contact with the perovskite layer was evaluated, by carrying out two types of aging tests. Those experiments were designed to observe what would happen in an operating cell, if the metal component and the perovskite layer come in contact due to the presence of defects in the selective contacts, or by diffusion of the components through the layers. The data gathered reveal that most of the metals suffer some sort of degradation in at least one of the conditions investigated in this work, showing that a careful selection of the metal contact is of utmost importance for long-term stability of these cells.

Perovskite with a bandgap around 1.65-1.70 eV [1] is commonly used for the top cell in silicon/perovskite tandem solar cells. However, because they are often made with mixed-cation, mixed halide compositions, they often suffer from film inhomogeneity and photoinduced halide segregation, which will impact their long-term stability during operation.

We employ benzylamine as a bulk additive to stabilize wide-bandgap mixed halide perovskites. Amines and ammonium halides have often been used to passivate perovskite materials. However, the understanding of how they interact with the perovskite is still limited. In this work, a 1.68 eV wide-bandgap MA-free perovskite is used as an example to show how benzylamine (BnAm) can affect the composition and phases present in the perovskite. We found that depending on the organic cations in the perovskite, the amine reaction can be quite different. In addition, while benzylamine additives cause lower-dimensional phases to form, their corresponding benzyl ammonium halide additives do not. By using BnAm as an additive, the photoluminescence quantum yield (PLQY) and open-circuit voltage of the device were improved. Moreover, compared to the pristine perovskite or BnAm surface-treated perovskite devices, BnAm bulk additive devices achieved a longer T₈₀ stability of 2,460 hours under combined 65°C heat and AM1.5 light stress test. BnAm-modified wide-bandgap perovskite has great potential to be integrated into silicon/perovskite tandem solar cells to improve their overall operational lifetime.

Self-assembled monolayers (SAMs) have emerged as an important area of research for enhancing the efficiency of inverted perovskite solar cells (PVSCs) through improved hole extraction and interfacial passivation. SAMs based on carbazole and various alkyl linkers (e.g., MeO-2PACz and Me-4PACz) have been extensively studied for their potential as commercial SAMs. Recently, researchers have designed innovative SAMs with multifunctionality to enhance charge transport properties and interfacial contacts to simultaneously improve PVSC performance and stability.

In this work, we try to optimize the hole-selective contacts of PVSC by applying and researching two novel SAMs with conjugated linkers and end-group modifications. In this study, two self-assembled monolayers (SAMs) were designed, each featuring a phenyl linker and electron-rich carbazole core and triarylamine end group, respectively. Surprisingly, the PA SAM inhibits excess PbI2 formation and provides efficient hole extraction ability, leading to increasing photoluminescence quantum yield (PLQY), better energy level alignment, and shorter PL lifetime. By applying to inverted PVSC devices, PA exhibited the highest power conversion efficiency (PCE) due to increased Voc & FF. Following effective passivation treatment with phenethylammonium iodide (PEAI), the PVSC with PA SAM achieved a PCE over 23%, and minimal non-radiative recombination loss of less than 100 meV, validated by full energy-loss measurements. In summary, this research explored the structural design of self-assembled monolayers with common functional group moieties and extended conjugation, optimizing hole-selective contacts for efficient inverted PVSCs.

Room-temperature ionic liquids (RTILs) based on bis(trifluoromethylsulfonyl)imide (TFSI) are promising additives for hole transport materials (HTMs) in perovskite solar cells (PSCs) as it does not require lithium (Li) species, which is likely detrimental to the photovoltaic (PV) performances, and can provide additional benefits. However, design of RTILs, especially their cation design, for the PSC application have been limited thus far within the currently major components such as bulky quaternary ammonium-, pyridine-, and imidazole-based cations. Such limitation in RTIL design has confined their functions for the PSC applications, and hence, exploration of RTIL design even different from the current trend yet suitable for a targeted application would allow novel and prominent functions.

In this work, an RTIL comprising aliphatic primary ammonium (i.e., n-octylammonium: OA) cations, which is the archetype RTIL cation found over a century ago (in 1914), and modern TFSI anions [1–3] is proposed and demonstrated as a highly functional additive for Spiro-OMeTAD HTM in PSCs. The OA cations spontaneously and densely passivate the perovskite layer during the HTM deposition process, leading to both suppression of carrier recombination at the HTM/perovskite interface and hydrophobic perovskite surfaces. Meanwhile, the TFSI anions effectively improve the HTM function most likely via efficient stabilization and generation of Spiro-OMeTAD cationic radicals, enhancing hole collection properties in the PSCs. Consequently, with the OA-TFSI additive, PV performances of PSCs involving the long-time stability were improved, comparing to use of conventional Li-TFSI additive.

Light and thermal stability are big concerns for perovskite solar cells (PSCs). To solve the problem of thermal stability MA free PSCs are one of the candidates. For light stability, still research is going on worldwide [1]. Different strategies have been incorporated such as surface passivation, and the inclusion of big organic cation at A position of ABX3 perovskite structure [2]. In this work, we focused on the improvement of light and thermal stability of tin-lead (Sn-Pb) by the introduction of germanium (Ge) into the crystal lattice by adding GeI₂ into the perovskite precursor solution. It is well known that GeI₂ can convert to GeO₄, and can be located at the top of the absorber layer [3]. Different devices with solar cell architecture such as FTO/Hole transport layer/ Sn-Pb-Ge /Electron transport layer/ BCP/ Ag were fabricated. The control device showed a power conversion efficiency (PCE) of 18.68% (Forward) and 19.10%(Reverse). The target devices with Ge_x, where x is the fraction of Ge added into the crystal lattice, exhibited an improved PCE of 20.52%(Forward) and 21.23% (Reverse) as shown in Figure 1. Herein, we further evaluated the thermal and light stability of devices. The experimental results will further be supported by XRD, XPS, SEM, and Impedance spectroscopy analysis.

The most widely studied photovoltaic device in current literature are flexible thin film planar Perovskite Solar Cells (PSCs). Perovskite solar technology has been evolving for over a decade reaching impressive power conversion efficiencies (PCEs) of over 25%. Thin film PSCs are flexible and lightweight, enabling installation upon any type of surface. They are also scalable, being roll-to-roll compatible _[1], enabling the manufacture of such technologies to be rapid and low cost. We introduce a novel thin Back-Contact (BC) Perovskite Solar Micro Module architecture consisting of a series of electrically connected V-shaped microgrooves containing selectively evaporated n- and p-type contacts on each groove wall _[2]. This is followed by scalable deposition of the Perovskite absorbing layer, being in direct contact with the illuminating source allowing for highly conductive n and p type materials to be employed as the requirement for transparent materials is diminished. Some enhancements in planar PSCs performance can be attributed to surface treatments such as UV-Ozone and Oxygen plasma treatments and are commonly employed to improve the bulk and interfacial properties of the as deposited n and p-type materials in isolation. However, with the BC device architecture both n and p-type semiconductors are exposed to surface treatment. A surface treatment enhancing both n and p-type interfacial and semi-conducting properties simultaneously is required to enhance electrical performance. During this work a new treatment method was developed that allows for simultaneous enhancements of both n and p-type materials. It was found that PCEs, open circuit voltage (Voc), short circuit current (Jsc) and fill factor (FF) increases by up to 201%, 26.7%, 94.1% and 22.6% respectively. Analysis has been conducted to explain the mechanisms responsible for electrical performance enhancement. Multiple factors are combined to improve the performance of micro-modules these include surface energy, surface stoichiometry and charge transport capabilities. Contact angle analysis reveals that the wettability of both n and p type surfaces are improved whilst reducing void formation. X-Ray Photoemission Spectroscopy (XPS) analysis indicates improvements in p-type surface chemistry whilst having potential to be detrimental to the n type material. However, through careful control of processing parameters benefits of p type stoichiometry can be maintained whilst having minimal detriment to the n type material. Time resolved Photoluminescence (TRPL) demonstrates that surface enhancements improve charge transport capabilities resulting in the observed photovoltaic performance. 

Perovskite solar cells (PSCs) exhibit not only high efficiency under full AM1.5 sun-light, but also have great potential for applications in dim-light environments. Among the diverse family of ABX₃ perovskites, methylammonium-free mixed halide Cs_xFA_1–xPb(I_1-yBr_y)₃ perovskites appear as attractive light-absorber materials because of their optimum band gap, superior optoelectronic property, and good thermal stability. In this work, we demonstrated wide-band gap (WBG) perovskite photovoltaics with the composition of Cs_0.18FA_0.82Pb(I_0.6Br_0.4)₃ yield high average PCEs of over 17% under AM1.5 sun-light and excellent performances under indoor light. Furthermore, we also fine-tuned the ratio and source of cesium ion to increases the grain size and film quality leading to improved charge mobility, reduced carrier recombination, and enhanced carrier lifetime, as confirmed by FESEM, XRD, PL and photo-CELIV and measurements. These findings showed the importance and potential of mixed cation, mixed-anion perovskite with tailored bandgap and suppressed trap-states in stable and efficient indoor light application.

Perovskite materials have a great potential for high efficiency in photovoltaic devices and the best performances have now exceed 26% in single junction. We now need to further develop perovskite device architectures that combine simple industrial development with effective durability. Recently, a novel type of architecture emerged for which no hole transport layer is needed thanks to carbon electrodes which are able to extract photo-generated holes by themselves. Consequently, the use of carbon-based perovskite solar cells (C-PSC) with inexpensive and stable carbon electrode not only enhances the durability of the devices but also reduces fabrication costs.

In the presented work, the perovskite deposition has been realized using a final perovskite infiltration through a mesoporous scaffold composed of metal oxide and carbon layers, affording a clean industrial process for large-scale and stable perovskite devices. Different variations will be here explored, including the formulation of the perovskite, the technique of infiltration for the perovskite, the implementation of a post-treatment, and the choice of the encapsulation process. A study of the occurring mechanisms will be conducted using a full set of characterization techniques including J-V measurements, UV-visible and photoluminescence (PL) spectroscopies, light-beam induced current (LBIC) and PL imaging mappings, X-ray diffraction (XRD), Scanning electron microscopy  (SEM), Raman spectroscopy and Electrochemical impedance spectroscopy (ESI).

Finally, the impact on the durability of photovoltaic performances of all the selected variations will be investigated in order to define the more promising paths to future industrial applications. A special attention will also be given to the method used to measure performances by analyzing J-V curves at different scan rates. Indeed, this allowed us to define boundary conditions allowing the observation of two different states within our devices (defined as ‘stable’ and ‘metastable’). This behavior was interpreted as a structural transition and can vary upon aging according to the selected device configuration.

Perovskite solar cells (PSCs) are expected to be one of the next-generation photovoltaics. Many companies around the world are competing to put PSCs into practical use. However, considerable difficulties in the reliable measurement of power generation of PSCs are a severe concern for fair and accurate evaluation in PSC developments. These difficulties are regarded to result from a slow current response to the applied voltage and metastability of PSCs. The metastability of the PSCs could mostly be related to changes in the electrical properties (ion migration) in the cells by exposure history (voltage bias, irradiance, time, and temperature) [1]. In the case of PSCs, reproducible I-V curve measurements might be difficult because the cells' electrical properties change during the measurements.

Steady-state measurements of the maximum power may be better than the I-V curve measurements defined in IEC 60904-1 for such metastable photovoltaics. Saito et al. [2] have reported that excellent consistency existed between the steady-state maximum powers obtained by the Maximum Power Point Tracking method (MPPT), steady-state (or stabilized) power output (SPO), and dynamic I-V measurements. In this study, changes in the electrical properties with exposure history will be discussed by using the MPPT method in order to predict the power generation of PSCs for practical use.

　We have conducted a round-robin test of PSC with several institutions, AIST, JET, NREL, JRC, Fraunhofer, and CSIRO. In the round-robin test, each institution measured the maximum power in its own way. Based on those results, we plan to discuss standardization for PSC measurement at IEC-TC82 meeting. In our presentation, we will introduce the result of the round-robin test and our efforts to standardize PSC.

As global energy demands rise with population growth and industrialization, the need for efficient and cost-effective renewable energy sources is urgent. Perovskite solar cells (PSCs) have emerged as a powerful contender with their impressive power conversion efficiency (PCE) exceeding 25%. However, these figures have so far been achieved in laboratory environments using spin-coating method, highlighting a significant gap when it comes to scalable production techniques such as Roll-to-Roll (R2R) deposition, that could feasibly support mass manufacturing. Overcoming this hurdle could revolutionize the renewable energy landscape and help meet the world's energy needs. Yet, its potential remains largely untapped, as coating techniques compatible with R2R, such as slot die coating or blade coating, struggle to meet the high benchmark set by spin-coating methods. This difference roots in a multitude of hurdles, achieving dynamic drying like conventional spin coating, limited oven residence time, solvent toxicity, cost of material and uniform coating at scale. 

To address these challenges, a bottom-up approach is used to identify and reduce performance losses, bridging the gap between state-of-the-art PSCs and R2R deposition. Successful R2R coating of all active layers in a P–I–N PSC stack is demonstrated using a single-step perovskite ink.[1] Optimized drying conditions and multi-solvent blend systems are developed, resulting in a stabilized PCE of 12.2%. To improve this further, a modified architecture is introduced by depositing Poly(triaryl amine) (PTAA) via R2R and using Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as a buffer layer. This approach increases the power conversion efficiency to 15.2%.

Although fully R2R-coated devices were previously difficult to fabricate due to lack of a compatible back electrode, we present a fully R2R printed PSCs employing a compatible and low temperature processed carbon electrode. The n-i-p architecture, SnO₂/MAPbI₃/PEDOT/Carbon effectively addresses interlayer incompatibilities and recombination losses.[2] The results match the performance of evaporated gold electrodes, with small-scale device efficiencies of 13–14%. Our fully R2R-coated perovskite PSC achieved over 10% (10.8) stabilised PCE and demonstrating promising stability by maintaining 84% of its original efficiency over 1000 hours under specified conditions. This represents a significant leap forward in the scalable production of perovskite photovoltaics.

Despite considerable advancements, the performance of R2R fabricated PSCs has also been constrained due to the prevalent use of MAPbI₃ instead of more efficient alternatives. Although certain studies have reported impressive PCE of up to 17.4% using Cs_0.05FA_0.81MA_0.14Pb(I_0.83Br_0.17)[3], these achievements have relied on the use of toxic solvents, such as dimethyl formamide, which greatly limits their scalability. To address this challenge, we introduce an innovative two-step deposition process for efficient and stable FAPbI₃. Our approach involves the utilization of methanol and methylammonium acetate as solvents. This novel method represents a crucial development that marks a significant stride towards the scalable manufacturing of highly efficient PSCs.

Overall, this study aims to comprehensively address the limitations such as substrate roughness, incompatible interlayers, and environment friendly solvents for the continuous manufacturing of R2R slot die coated PSCs.  

Sn and mixed Sn-Pb iodide perovskites (ASnI₃, ASn_0.5Pb_0.5I₃) provide an excellent opportunity to yield lower toxicity and efficient Pb-free perovskite photovoltaics, close-to-ideal bandgaps in single-junction solar cells and near-infrared absorption in all-perovskite tandem solar cells. Despite a growing interest in these perovskite variants, the sensitivity of Sn(II) to oxidation under operational conditions remains the main challenge towards their widespread adoption. Additionally, their strong p-type character arising from degradation-related defects (i.e., Sn(IV) states, Sn(II) vacancies) further hamper their potential, causing charge carrier losses. It is therefore imperative to gain detailed knowledge of their chemical decomposition pathways to boost their stability, as well as to design strategies to fine-tune their electrical properties. This talk will cover our work on these avenues, unveiling the degradation mechanisms of both Sn and Sn-Pb perovskites under ambient conditions and presenting novel molecular doping routes to harness carrier density in Sn-Pb perovskites.

Firstly, the key role of perovskite native iodine (I₂) on determining stability will be unveiled. Previously, we identified a cyclic degradation pathway where I₂, formed from Sn perovskite exposure to ambient conditions, aggressively degrades the material to SnI₄, which then evolves back to I₂ in the presence of H₂O and O₂.^1,2 We observe this process to govern the degradation of Sn-Pb perovskites as well, highlighting the need to identify perovskite compositions with innate I₂ resilience. Specifically, we reveal the inconspicuous role of A-site cations in these oxidation pathways, finding that Cs-rich compositions present rates of I₂ and SnI₄ generation one order of magnitude lower than their methylammonium (MA)-rich analogues. We ascribe the enhanced resistance of Cs-rich Sn-Pb perovskites against oxidative stress vs MA compositions to stronger I₂ adsorption at the surface of perovskite in the latter, mediated by the polarising power of the MA cation.

Secondly, we address the electrical aspect by providing novel molecular doping design rules based on the crucial role of host-dopant interactions.³ By leveraging an n-type molecule, namely n-DMBI-H, we discern a unique dative bonding mechanism between Sn atoms in Sn-Pb perovskite surfaces and the dopant, followed by the dissociation of an electron-donating hydride from n-DMBI-H. Arising from the higher Lewis acidity of Sn, we find this surface interaction to mediate charge transfer, providing an effective way to compensate the p-type character of Sn-Pb perovskites (nearly one order of magnitude reduction in charge carrier density).

These insights offer a comprehensive roadmap to developing stable, efficient and adaptable Sn and Sn-Pb perovskite solar cells and beyond.

Among the different renewable energy sources, solar energy stands out because of its abundance and global character. The sun delivers more energy to the Earth within one hour than we use in a whole year from fossil, nuclear, and renewable energy combined. Silicon solar cells currently cover 90% of the market, but require a lot of scarce space on rooftops or in solar parcs. Therefore, integration of photovoltaic technologies in building facades is a very interesting and complementary approach. One of these building facades that occupy a great amount of space in modern constructions are windows. Integration of photovoltaics in windows requires visible transparency. To achieve this, the photoactive materials must absorb as little as possible in the visible range (defined as 435‒670 nm). This implies that only the ultraviolet (UV) and near-infrared (NIR) part of the solar spectrum can be employed for energy generation. Since only 2% of the solar energy is located in the UV region, and as much as 51% is NIR light, the focus lies on NIR photon harvesting. As inorganic solar cells have a fixed absorption in the visible area, these are not fitted for this application. In contrast, organic photovoltaics (OPVs) have a tuneable absorption range (Figure 1) and are therefore much more suitable.¹ Recently, several well-performing NIR-absorbing non-fullerene acceptors have become available, such as IEICO-4F, FOIC, and Y6.² NIR-absorbing donor polymers on the other hand are rather scarcely reported. Using the push-pull approach, the absorption can be shifted to the NIR by combining strong electron-donating and strong electron-accepting monomers to obtain an ‘ultra-low’ bandgap conjugated polymer.

In this work, we focus on the synthesis of novel NIR-absorbing donor polymers based on diketopyrrolopyrrole (DPP) as the electron-accepting monomer. Several electron-donating monomers are combined with DPP using Stille cross-coupling polymerization. The polymer with the highest open-circuit voltage was used in an organic solar cell optimization study, incorporated in a transparent device stack (Figure 1), and evaluated on its performance and transparency. Lastly, a new fluorinated DPP polymer was synthesized to red-shift the absorption and enhance the open-circuit voltage.

Perovskite solar cells (PSCs) have been getting significant attention in the photovoltaic community because of their high power conversion efficiency, solution processability, large-area device fabrication, and low production cost [1-3]. Recently, PSC technology is being studied for space applications to overcome its disadvantages in instability in normal terrestrial ambient air conditions containing moisture and oxygen [4]. The superiors combining with their high specific power (power per weight) [5] as well as the facile low-temperature solution processibility for in-situ fabrication in spaceships make PSCs a promising replacement for currently used PV technologies in space applications. However, the space radiation hardness of PSCs should be further studied before they can be applied in space missions.

In this work, PSCs were tested under 10MeV proton radiating from back side of the cells at different fluence of 10¹², 10¹³, 10¹⁴ proton/cm² which equivalents to 1, 10, and 100 years in medium Earth orbit [6]. With >24% initial efficiency of PSCs, this study accurately reflects the behaviour of fresh and state-of-the-art perovskites under proton radiations comparing to far lower initial efficiency in the previous reports. This is important as it isolates the proton-induced degradation of the studying PSCs from storage degradation and high density of existing defects in low efficiency PSCs. Therefore, we could confidently conclude that this experiment shows a high hardness of PSCs under 10MeV proton radiations, in which the samples stand at its ~90% initial efficiency at the highest fluence without any shielding. In terms of radiation-induced additional defect, ToF-SIMS analysis shows movement of gold and lead atoms into further layers after reacting with radiating protons. Additionally, SEM observations witness mechanical damage on surface of perovskite films when exposing proton radiation. These findings are visual evidence of proton-induced damages on materials during radiation. Besides, CL measurement at high resolution SEM images points out that the effect of radiations onto perovskite are uneven among grain and grain boundaries, indicating that there should be different kinds of defects were created during the radiation processes. Finally, the PL and TRPL show that the perovskite quality degrades a lot after being radiated at high fluence of proton. This is consistent with the reduction of Voc and FF observed during J-V characterization while there is a slight drop in terms of Jsc.

Overall, this is the first findings on mechanical interaction between protons and perovskite materials, in which PSCs were subjected to irradiation from the back side. With different fluences of 10MeV proton, PSCs show extremely high tolerance without any shielding, in which the PSCs can stand at its 90% initial efficiency at a fluence equivalents to 100 years in the medium Earth orbit.

The use of molecular dopants is an intriguing strategy for achieving a high power conversion efficiency (PCE) in organic solar cells (OSCs). However, despite its promise, the number of molecular dopants that enhance the PCE of OPVs remains limited. In this study, we introduce two novel n-type dopants, Ethyl Viologen (EV) and Methyl Viologen (MV), into ternary PM6:BTP-eC9-PC₇₁BM bulk heterojunction (BHJ) OPVs and compare their performance with other known n-type dopants. Our findings reveal that the addition of EV and MV results in remarkable enhancements in PCE, reaching maximum values of 19.03% and 18.61%, respectively, along with fill factor (FF) values of 80% and 79.2%, respectively. We demonstrate that EV and MV function as both n-type dopants and microstructure modifiers, inducing enhancements in the absorption coefficient, balancing the charge carrier mobility, increasing the carrier lifetime, and reducing charge carrier recombination. Our results suggest that low concentrations of EV and MV can enhance the performance of highly efficient organic solar cells to levels beyond those achievable by the pristine BHJ.

Recently self-assembled monolayers (SAMs) have found widespread applications in the field of solar cells, particularly in hole-selective SAMs within inverted perovskite solar cells and in tandem solar cell configurations. Compared to conventional charge transport layers (CTLs), SAM-based CTLs offer a multitude of advantages, including cost reduction, minimal energy losses, straightforward deposition processes, and the ease of modifying energy levels and surface characteristics. The combination of various hole-selective SAMs has resulted in the development of highly efficient single-junction solar cells. In this research study, three innovative SAM self-assembled layers were chosen for integration into inverted perovskite solar cells. The study involved observing surface state of SAM by using contact angles, roughness by using Atomic Force Microscopy (AFM), and investigating transport properties of respective device through photoluminescence (PL), transient photovoltage (TPV) and transient photocurrent (TPC). Additionally, Field-Emission Scanning Electron Microscopy (FE-SEM) was utilized to examine the deposition of perovskite layers on top of these three novel SAM layers, thus exploring their potential applications in the context of perovskite solar cells.

Simplifying the manufacturing processes of renewable energy technologies is crucial to lowering the barriers to commercialization. In this context, to improve the manufacturability of PSCs, we have developed a one-step solution-coating procedure in which the hole-selective contact and perovskite light absorber spontaneously form, resulting in efficient inverted PSCs. We observed that phosphonic or carboxylic acids, incorporated into perovskite precursor solutions, self-assemble on the indium tin oxide substrate during perovskite film processing. They form a robust self-assembled monolayer as an excellent hole-selective contact while the perovskite crystallizes. Our approach solves wettability issues and simplifies device fabrication, advancing the manufacturability of PSCs. Our PSC devices with positive–intrinsic–negative (p-i-n) geometry show a power conversion efficiency of 24.5% and retain >90% of their initial efficiency after 1,200 h of operating at the maximum power point under continuous illumination. The approach shows good generality as it is compatible with different self-assembled monolayer molecular systems, perovskites, solvents and processing methods.

Vacuum processing is the most established pathway to the commercial production of organic solar cells. However vacuum processed devices currently exhibit much lower device efficiencies than solution processed devices. Despite their commercial success, the underlying charge carrier dynamics determining the efficiency of evaporated, vacuum processed organic solars have received far less attention than those solution processed devices. In my talk, I will focus on these charge carrier dynamics in high performance vacuum processed organic solar cells and photodetectors, and how these compare with those observed in solution processed devices. These studies will include consideration of exciton separation, charge transfer states, charge carrier mobility and non-geminate recombination losses. Studies will address and contrast both planar and bulk heterojuctions devices, as well as the effect of annealing on film nanomorphology. A key consideration will be consideration of molecular energetics in impacting these kinetics, including the impact of molecular quadrupoles and octupoles.

Polymer solar cells have attracted much attention as a next-generation renewable energy source.  Recently, power conversion efficiency has exceeded 19% even for single junction solar cells.  Ternary blending is one of the key approaches in achieving such high-efficiency polymer solar cells.  In this talk, I will discuss how ternary blending of three different materials in the photoactive layer can effectively improve not only light harvesting but also charge transport in polymer solar cells.  In ternary blend polymer solar cells based on a wide-bandgap polymer (P3HT), a fullerene acceptor (PCBM), and a low-bandgap molecule (SiPc), photocurrent can be increased by additional absorption of SiPc and efficient exciton harvesting due to long-range energy transfer from P3HT to SiPc [1].  Interestingly, not only photocurrent but also fill factor is increased effectively in ternary blend polymer solar cells based on a wide-bandgap polymer (PDCBT), a low-bandgap polymer (PTB7-Th), and a fullerene acceptor (PCBM) [2].  In order to discuss the origin of the improved charge transport, we studied charge transport of conjugated polymers blended with an insulating polymer (PS) [3].  As a result, we found most of conjugated polymers exhibited improved hole transport in films blended with PS rather than their neat films.  This finding shows that charge transport can be also improved by using ternary blends. 

Perovskite solar cells have been recognized as a newly emerging solar cell with the potential of achieving high efficiency with a low cost fabrication process. In particular, facile solution processed cell fabrication facilitated rapid development of optimum cell structure and composition. Over the last few years, the cell efficiency has reached 26%.

Highly efficient charge transfer reactions in addition to high charge separation efficiency and swift charge transport with minimum charge recombination are required to improve solar cell performance. Intensive studies  have been focused on monitoring photo-induced exciton formation and charge dissociation, charge transport and interfacial charge transfer dynamics including interfacial charge recombination in perovskite solar cells.[1-5] Several parameters have been identified to influence these charge carrier dynamics, and therefore the solar cell performance.[1-5] Clarifying these parameters is extremely important to understand the charge transfer mechanisms to further improve solar cell performance.

In this presentation, we will present parameters controlling charge dissociation in metal halide perovskites and their charge separation and recombination dynamics at the perovskite interfaces employing a series of transient absorption and emission spectroscopies. Correlation of the key parameters controlling the charge carrier dynamics with the solar cell performance will be discussed [1-5].

References

[1] S. Makuta, M. Liu, M. Endo, H. Nishimura, A. Wakamiya and Y. Tachibana, Chem. Commun., 52 (2016) 673 - 676.

[2] M. Liu, M. Endo, A. Shimazaki, A. Wakamiya and Y. Tachibana, J. Photopolym. Sci. Technol. 30 (2017) 577-582.

[3] M. Liu, M. Endo, A. Shimazaki, A. Wakamiya and Y. Tachibana, J. Photopolym. Sci. Technol., 31 (2018) 633-642.

[4] M. Liu, M. Endo, A. Shimazaki, A. Wakamiya and Y. Tachibana, ACS Appl. Energy Mater., 1 (2018) 3722-3732.

[5] M. Liu, H. Liu, S. R. Padmaperuma, M. Endo, A. Shimazaki, A. Wakamiya and Y. Tachibana, J. Photopolym. Sci. Technol., 32 (2019) 727-733.

Bulk-heterojunction organic photovoltaic cells based on π-conjugated polymers have been intensively investigated in the last few decades. A key to improving the power conversion efficiency is to control the polymer order and morphology as well as the molecular orbital energy levels and the absorption range. Therefore, it is imperative to carefully design the π-conjugated polymers to manage their electronic structures, backbone coplanarity and intermolecular interactions. We have been studying a number of π-conjugated polymers by incorporating various fused heteroaromatic rings into the polymer backbone. In this presentation, I will show the design and synthesis of novel π-conjugated polymers based on newly developed heteroaromatics based on thiazole and thiadiazole moieties. In fact, the power conversion efficiencies of ~12% in the cells based on a fullerene acceptor and ~18% in the cells based on a nonfullerene acceptor was achieved using the newly developed polymers. More importantly, significantly efficient charge generation was realized with small voltage loss. I will discuss how the molecular structure affects the polymer properties and polymer order in the thin film and thereby photovoltaic performances.

Organic photovoltaic (OPV) and photodetector (OPD) devices are attracting significant attention due to their potential to be lightweight, flexible, non-toxic, and compatible with large-scale manufacturing. In particular, the development of the new small molecule-based non-fullerene acceptors (NFAs) has enabled OPVs to show remarkable improvements in device efficiency. Although promising, there is still a lack of clear understanding of the impact of molecular structure and orientation of NFAs on photophysical processes critical for device performance. 

In this talk, I will discuss the two key NFA molecular perspectives for high performance OPV and OPD devices.  First, I will show the molecular-structure dependent photostability, with a particular focus on NFA molecular planarity, rigidity, and end groups [1, 2]. Second, I will show the molecular orientation-dependent energetic shifts in NFAs, demonstrating the impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the OPV and OPD performances [3, 4]. Compared to sublimed small molecules where the molecular orientation control is relatively easy [5], there has been no report, to the best of our knowledge, demonstrating the orientation control of solution-processed NFA molecules leading to an energetic shift large enough to impact exciton separation for free charge generation. As such, it is now critical to understand the molecular origins of OPV/OPD performance in much deeper detail than before to direct synthesis of organic semiconductors in more promising directions.

Tokyo Chemical Industry (TCI) is a global supplier of laboratory chemicals and specialty materials, and also leading the next-generation solar technology by providing high-quality and reliable materials, including metal halide perovskite precursors and materials for carrier transporting.

Metal Halide Perovskite Precursors with High Purity and Product Variety

Organic-Inorganic Perovskite Precursors | Tokyo Chemical Industry Co., Ltd.(JP) (tcichemicals.com) https://www.tcichemicals.com/JP/en/c/12969

Hole Selective Self-Assembled Monolayer (SAM) Forming Agents: PACzs

Self-Assembled Monolayer (SAM) Forming Agents for Enhancing Solar Cell Performance | Tokyo Chemical Industry Co., Ltd.(JP) (tcichemicals.com) https://www.tcichemicals.com/JP/en/product/topics/hole-selective_self-assembled_monolayer-forming_agents

Hole Transport Materials For Stable and Practical Perovskite Solar Cells: TOP-HTMs

New Hole Transport Materials for Highly Stable Perovskite Solar Cells | Tokyo Chemical Industry Co., Ltd.(JP) (tcichemicals.com) https://www.tcichemicals.com/JP/en/product/pick/hole_transporting_materials_for_stable_perovskite_solar_cells

Dopants for Organic Electronics Research

Dopants for Organic Electronics Researches | Tokyo Chemical Industry Co., Ltd.(JP) (tcichemicals.com) https://www.tcichemicals.com/JP/en/product/topics/dopants_for_organic_electronics_research

In this short talk, these highly useful materials will be introduced including most recently commercialized new products.

Metal halide perovskite (PSC) solar cells are emerging with the promise of bringing about a revolution in the solar photovoltaic industry, as their efficiencies are now comparable to those of silicon. This fantastic result was only possible due to precise control and engineering of the morphology, interfaces and the use of multiple cations in the perovskite's A site, such as Rb, Cs, MA (methylammonium) and FA (formamidinium). For tandem perovskite solar cells, a mixture of different anions such as Br and I is also desired to tune the band gap. Such a cocktail of different cations and anions influences the formation of intermediates, new phases, favors the homogenization of halides, etc.; so that in the end, the efficiency of the device is closely related not only to the optical quality of the film, but also to the morphology and composition. We cannot forget how such a multicomponent system also influences degradation mechanisms (still the main problem for PSC!)

In this presentation, we will summarize important results from our group using in situ experiments to probe halide perovskite formation (2D and 3D), crystallization, composition, and stability. We employed several synchrotron techniques as time-resolved grazing incidence wide angle X-ray scattering (GIWAXS), small angle X-ray scattering (SAXS), high-resolution XRD and nano-infrared taken at the Brazilian Synchrotron National Laboratory, SSRL-Stanford and ALS Berkeley.

In situ GIWAXS experiments allowed us to understand the influence of the relative humidity and time to drop the antisolvent during the preparation of perovskite films [1], type of the solvent and deposition method [2] and the influence of additives [3]. It is well known that a 2D layer on the top of a 3D bulk perovskite improves stability and performance. In situ GIWAXS revealed us that during thermal annealing the 2D layer transforms itself into a disorder layer, improving hole transfer and stability [4]. Ex situ and in situ PL spectroscopies acquired during the formation and annealing of such 2D/3D interface showed us the importance of the chemical structure of the long organic cation on formation dynamics and final composition [5].

The urgent need to mitigate climate change defines a pressing need for new high-performance energy materials and, along with this, new accelerated strategies to discover them. The field of computational materials discovery has picked up significant momentum over the past years and now calls for equally effective methods to experimentally validate their theoretical predictions. In this presentation I will present a new experimental platform, which is in the final stages of assembly at the Mebourne Centre for Nanofabrication (Australia). I will introduce the different tools which will allow us to formulate coating solutions, convert those coating solutions into thin films and subsequently characterise their optical, electrical and structural properties. This process can operate autonomous for 24 hours at a clock -speed of 5 minutes. Machine learning will be a vital tool to help extract valuable information from big data and also to help guide the discovery process. I will present a recent proof-of-concept study where we use machine learning to enhanced the high-throughput fabrication and optimization of quasi-2D Ruddlesden-Popper perovskite solar cells [1] and speak about our plans to integrate this process into our materials discovery strategy.

Organic photovoltaics have the capability to overcome to their inorganic counterparts due to several reasons like low weight, flexibility and low price. Transient Absorption Spectroscopy (TAS) represents the perfect tool to study this kind of devices. TAS is a pump-probe technique, with two different light sources: one excites the sample whereas the other probes the photogenerated excited states. This way, with TAS, we are able to follow the different processes taking place in organic photovoltaics, from charge photogeneration to the different efficiency loss pathways. 

In this work two different systems are presented where unexpected behaviour is obtained. In the first case, DRCN5T is studied. DRCN5T is a well extended material used in binary and ternary solar cells as small molecule donor. In our work, how this molecules is able to generate a large number of triplets is demonstrated, despite being able to obtain large efficencies. In addition, the annealing process is shown that largely increases the number of triplets generated in this material.

The second family to be studied is a range of NDI materials where some substituents is systematically changed in order to stablish a difference between the orthogonality between the core and the substituent. With the help of TAS, it is shown how the orthogonality is associated with an enhancement in the charge generation for these materials. 

Organic-Inorganic Halide Perovskites (OIHPs) represent the big breakthrough of the last decade in low-cost photovoltaics (PV): [1] bulk OIHPs (with general stoichiometry ABX₃, A=organic cation; B=Pb²⁺, Sn²⁺, Ge²⁺; X = halides) are indeed characterized by unique features in solar-to-energy conversion as consequence of a perfect combination of physical and chemical factors.[2,3] Nevertheless, the presence of residual, non-trivial, issues yet prevents their exploitation in solar device mass production. In particular, the hydrophilic organic moiety present in the A-site of OIHPs (methylammonium, CH₃NH₃⁺, and also formamidinium,⁺HC(NH₂)₂) and Pb in the B-site of the most representative compound of the class, i.e. CH₃NH₃PbX₃, represent serious limitations for the applicability in devices. 

An ideal solution for overcoming this latter issue is replacing Pb with other, more environmental friendly, cations.[4]

On the other hand, plausible solution for the former is the replacement, total or partial, of methylammonium cations with other organic, hydrophobic, aromatic or aliphatic, long chain cations. Such cations (mainly, buthylammonium and phenethylammonium) are indeed able to stabilize the final compound against heat and moisture, a stabilization which is accompanied by a reduction in the dimensionality of the final systems. These so-called mixed 2D/3D Ruddlesden-Popper (RPPs) and Dion-Jacobson (DJ) perovskites have been recently suggested as a viable alternative to 3D bulk OIHPs for their photochemical stability coupled with high-performance optoelectronic properties.

A large number of experimental papers has appeared in literature witnessing the interest of the community towards this class of materials.[5] At the same time ab-initio studies focusing on the role of many-body effects are still very limited and the results in this sense are not yet conclusive.

In the present contribution, after a short introduction about the general properties of the 3D bulk organic-inorganic halide perovskites, we will discuss the optoelectronic properties of some Pb-free 3D bulk systems and of dimensionally confined Ruddlesden-Popper perovskites, as a result of the combination of Density Functional and Many-Body Perturbation Theory analysis. With a keen eye on the A-site and B-site cation replacement, we will discuss the excitonic features in 2D and in mixed 2D/3D halide, hybrid and full-inorganic, perovskites in Pb-based,[6] Pb-less,[7] and Pb-free [8] systems. Finally, in the framework of Pb-free systems, we will show some results of the most recent analysis of interfaces formed by Sn/Ge-alloyed OIHPs and GeI₂/GeO₂ in terms of structural, electronic, and optical features, focusing on pros and cons of such passivating mechanism.

Tin-based perovskite solar cells are the most promising alternative to their toxic lead counterparts, due to their outstanding optoelectronic properties, i.e. high charge carrier mobility, and narrower bandgap, closer to the optimal range^[1]. Nevertheless, their efficiency currently lags behind, with the highest power conversion efficiency (PCE) approaching 15%^[2]. The efficiency limitation is attributed to electronic defects primarily due to the facile oxidation of Sn²⁺ to Sn⁴⁺ resulting in a self-p-doping effect^[3]. Additionally, the stereochemical activity of the Sn²⁺ lone pair leads to an off-centring of the metal and, consequently, to a distortion of the SnI₆ octahedron^[4]. In this study, we explore the influence of Sr²⁺ doping on lattice distortion in perovskite materials and on its optoelectronic properties. Through a comprehensive approach involving calculations based on density functional theory (DFT) and practical experiments, we demonstrate the beneficial impact of doping in the tin perovskite structure. The Sr²⁺ tends to fill tin vacancies, reducing the hole concentration and decreasing the microstrain of the crystal structure. Consequently, device performance improves, particularly in terms of open-circuit voltage (V_OC) and fill factor (FF). Our approach opens a path to control the tin off-centring and the self-p-doping to obtain highly efficient and stable tin halide perovskite solar cells.

Sn-based PSCs (14.6% PCE) are primary candidates to usurp their toxic Pb-based counterparts (26.1% PCE) [1,2].
However, they are currently limited by facile oxidation inhibiting stability, and lower PCEs due to energetic mis-
matches [3]. We have recently published a a study detailing the rapid, auto-catalytic oxidation of Sn(II) to Sn(IV) by
demonstrating the detrimental consequences of iodine generation in Sn PSCs [4]. These ideas are expanded upon in a
follow up discussion highlighting the important relationship between hole extraction and device stability, providing
motivation for in-depth studies of the HTL/perovskite interface [5].
This study builds upon the importance of fast hole extraction via the optimisation of energy levels at the
HTL/perovskite interface. We will discuss strategies to improve hole extraction through compositional tuning and
due consideration of HTL energetics. These strategies to remove free holes subsequently can be related to suppressed
Sn(II) oxidation. Preliminary results show substitution of Br– ions with I– ions widen the band gap and deepen the
valence band, allowing us to demonstrate the importance of good energetic alignment. We use this knowledge to
screen HTLs (both established and unreported) in the relatively unexplored N-I-P tin architecture. From this analysis, we
offer design criteria into the optimal HTL/perovskite interface for N-I-P architecture with regards to performance and
stability.

Lead- based perovskite materials are a braking trough technology in the use of optoelectronics devices, which in particularly for solar cells have achieved an efficiency close to 26 % for lab scale devices. However, the toxicity of Pb to the environment and human health, hampers the commercialization of this technology. Therefore, other non-toxic elements have been employed to substitute the highly hazardous Pb in the perovskite structure. Among the candidates, tin-based perovskites (Sn-PS) are the promising alternatives for the development of highly efficient and low-cost photovoltaics based on low-toxicity materials. However, one of the main limitations for Sn-PS is the easy oxidation of Sn⁺² into Sn⁺⁴ upon the exposure to ambient conditions and even during the film and device preparation, which promotes degradation mechanisms and compromises the quality and long-term stability of the material.

Besides this intrinsic challenge, most studies have focused on spin coating as the main deposition method for the absorber layer, which is not compatible with large area manufacturing techniques like roll-to-roll or sheet-to-sheet. In this work, we have successfully deposited Sn-PS films trough bladecoating technic; ink engineering of the solvent system and additives were used as a strategy to control the crystallization dynamics and nucleation to obtain pinhole-free films on flexible substrates. This strategy allows us to deposit successfully uniform FASnI₃ films onto polyethylene terephthalate (PET) sheets up to 700 cm². Our findings demonstrate how to upscale Tin-based perovskites with a simple method; thinking on how to commercialize lead-free perovskites.

To develop a highly efficient solar cell using organometal halide perovskites, precise control over its micro-scale structure emerges as a critical factor. This is because the existence of macrostructural boundaries within the organometal halide perovskite proves detrimental to the flow of charge carriers, thereby compromising device performance.

In our investigation, we utilized transmission electron microscopy (TEM) analysis to confirm the presence of a tetragonal/cubic superlattice within the grain of a methyl ammonium iodide (MAPbI₃, where MA = CH₃NH₃) perovskite. Our findings revealed that the nano-sized domains hinder charge carrier flow in the MAPbI₃ perovskite. To mitigate the adverse effects of these nano-sized domains, we introduced 5% potassium, aiming to reduce the junction domain and tried to enhance the cubic phase proportion through macrostructural phase control using liquid nitrogen.

Through meticulous micro-structural phase control of the MAPbI₃ perovskite, we successfully reduced grain boundaries and minimized physical gaps. This resulted in a noteworthy achievement, as we attained a power conversion efficiency (PCE) of 20.23% with a single cation MAPbI₃ perovskite solar cell.

The high electricity consumption and limited size of multifunctional wearable electronics for health monitoring, telecommunication, and personal drug-delivering have induced new challenges for the device's operating life span. The conventional rigid and bulky photovoltaics (PVs) have restricted their integration with wearable devices and have hindered their niche applications in portable, lightweight, and flexible electronics. Organic photovoltaics (OPVs), with their flexibility, excellent mechanical robustness, high power-per-weight ratios, and economical fabrication processes, have aroused attention in the field. OPVs are born to bring energy supplies to a versatile selection of substrates as portable power sources. In the past two decades, the efficiency of OPVs has come from below 5% to approaching 20%. However, in the race of power conversion efficiency (PCE), the emphasis is mainly on the design of active layers and the related device architecture. The uniqueness of OPVs: the side-group tunability of the donor-acceptor materials allows OPVs a selective absorption for solar conversion either in UV or NIR range. This provides OPVs a wearable way of solar harvesting and a visible light transparent/ semitransparent fashion. This opens a window for playing around with the incoming and penetrating photons. In this work, the focus is on light environment management enhanced PCE for wearable PVs via the luminescent solar concentrator (LSC) add-ons, using amphiphilic polymer conetworks (APCNs).

In our previous work [1,2,3], APCNs are employed as polymer matrices for wearable LSCs owing to their flexibility and wearability. Furthermore, with the assistance of APCNs’ nanophase-separated hydrophobic and hydrophilic domains, hydrophobic (Lumogen Red, acceptor) and hydrophilic (fluorescein, donor) luminescent materials are loaded in adjacent nanometer-separated domains. This results in high ET rates and broadens the acceptor’s absorption range, rendering a more efficient down-conversion emission. We could achieve high ET rates between dye pairs via FRET and photon recycling with a straightforward synthesis procedure. These two energy transfer mechanisms were confirmed by steady-state and dynamic photoluminescence methods, showing a ~100% total ET between donors and acceptors. The developed nanostructure-assisted ET system is not limited to the dyes investigated here but can be directly extended to a wide variety of dyes (Rhodamine B, HPTS, DCM, and Lumogen Yellow) and quantum dots (CsPbBr3 and CdSe/ZnS).

In this work, we take a step further by introducing APCNs into optoelectronic devices. The OPVs donor-acceptor polymers/small molecules and luminescent dyes are loaded into the hydrophobic and hydrophilic domains of APCNs, respectively. Depending on the spectral responsiveness of the selected OPVs active materials, the LSCs dye is then picked for optimal emission wavelength with the absorption of OPVs. With this geometry, each system (OPVs and LSCs) is located in the isolated/ individual domain of APCNs, rendering a brand-new architecture of combining OPVs with the relevant LSCs to boost device efficiency in a single polymeric matrix while preventing the intersystem interpretation and quenching. This delivers an efficient and novel architecture wearable solar energy harvester that utilizes APCNs biphasic nature and wearability.

The covalent connection of donor (D) and acceptor (A) materials as conjugated block copolymers (CBCs) has attracted increasing attention in recent years. When used individually as the photoactive material in organic photovoltaics (OPVs), CBCs can exhibit several advantages, such as excellent mechanical properties and superior long-term stability, as compared to the typical bulk-heterojunction (BHJ) blends. However, relevant studies to date mainly focus on clarifying the device performance difference between CBCs and the blend systems based on the commensurate D and A segments. To the best of our knowledge, the influence of the D-A segment ratios for CBCs on the device performance has not been investigated yet.

In this context, we herein synthesize a series of CBCs based on an n-type PNDI2T and a p-type PBDB-T segments with three different D-A ratios (P1-P3) and introduce these CBCs separately as the single-component photoactive materials in OPVs to scrutinize their photovoltaic performance (Figure 1, left). Compared to P2 and P3, the P1 device with a higher content of PNDI2T exhibits superior exciton dissociation and charge transfer behaviors, leading to the highest power conversion efficiency (PCE). This is due to the more dominant face-on orientation of P1 than the others. On the other hand, the n-type block is revealed to play a more critical role in the inter/intra-chain charge transfer than the p-type block. Finally, we show that the P1 device also possesses the lowest energy loss as a result of the suppressed non-radiative energy loss. This result provides the first discussion on the impact of the segment ratio for a CBC on the resultant chain stacking behavior that would pave the way for the future development of single-component OPVs.

Besides being employed as single-component photoactive materials, CBCs can also serve as compatibilizers for modifying the morphology of BHJ. Typically, BHJ in high-performance OPVs based on non-fullerene small molecular acceptors (NFAs) suffer from insufficient long-term stability due to the higher diffusion coefficient of NFAs compared with polymer donors. Furthermore, the NFAs in the BHJ blends tend to aggregate, forming a larger pure domain region, which can significantly impact the charge dissociation/transfer efficiency and the BHJ morphology stability. To address this issue, we develop PM6-b-PYIT, which possesses an analogous structure of PM6 and Y-series NFAs, and we introduce it as compatibilizers into BHJ blends to optimize their morphology (Figure 1b, right). As a result, adding 0.5 wt% of PM6-PYIT into PM6:L8-BO system can obtain over 18% of PCE, making it the best performance for the inverted OPV device we are aware of. Moreover, adding PM6-PYIT optimizes the morphology of BHJ and thus enhances charge transport properties. Compared with PM6 and Y-series NFA materials, the analogous structure of PM6-PYIT could fix initial morphology through van der Waals force, leading to superior long-term stability and mechanical properties.

  Achieving a relatively high power-to-conversion efficiency (PCE) in all-polymer solar cells remains a significant challenge. Precisely controlling the phase separation between polymers to attain an ideal film morphology is a topic that requires in-depth exploration. Numerous studies have found that optimization through various processes, including the choice of porcessing solution, the use of additives, the method of film deposition, and the control of film thermal annealing procedures, can enhance device performance. In this work, it will focus on the selection of different porcessing solutions and the use of additives to regulate film morphology. By employing these two methods to control the film morphology and further improve the miscibility between polymers leads to a tighter and more regular polymer packing. Benefitting from the ideal film morphology, it facilitates efficient charge separation and conduction, reducing unnecessary charge carrier losses, and ultimately enhancing the overall efficiency. In this work, we introduce a strategy involving the use of a mixed solution. In addition to the original chloroform precursor solution, a high-boiling-point green solution have been incorporated. The addition of the high-boiling-point solution alters the overall volatility of the solution, thereby influencing the solution-to-film forming rate. This also leads to changes in the polymer domain size within the active layer. In addition to employing the aforementioned strategy, we have also added the common volatile solid additive DTT to polymer solution. In this work, we use a more efficient all-polymer blend system, PM6:PY-IT.  The PM6:PY-IT devices based on all mixed solvent systems deliver a very high PCE of >17%. 

The emergence of nonfullerene acceptors (NFAs) has triggered a rapid advance in the performance of organic solar cells (OSCs), endowing OSCs to arise as a promising contender for 3^rd generation photovoltaic technologies. Meanwhile, the ultimate goal of OSCs is to deliver cheap, stable, efficient, scalable, and eco-friendly solar-to-power products contributing to global carbon neutrality. However, simultaneously balancing these five critical factors of OSCs toward commercialization is extremely challenging. In this presentation, I will show the self-assembly strategy we developed to reduce the gap of high power conversion efficiency (PCE), long-term stability, green-solvent-processibility, scalability, and low cost of OSCs and demonstrate our green-solvent-processable and open-air-printable OSCs with simultaneously simplified device architecture and enhanced PCE, shelf, thermal as well as light illumination stability. Further, I will present our recent results on the outdoor degradation mechanism study in top-performing systems. Finally, I will summarize our findings on enhancing the commercial viability of OSCs toward commercialized cheap, stable, efficient, scalable, and eco-friendly OSCs.

Tin-based (Sn) halide perovskites have become one of the most prospective photovoltaic materials due to their optoelectronic properties, high photoconversion efficiency and relatively low toxicity.[1][2] Nevertheless, the rapid crystallization of tin-based perovskite and the easy oxidation of Sn²⁺ to Sn⁴⁺ under ambient conditions increases the interest of the scientific community.[3] To avoid these undesirable processes, we will address by two different methods, for instance, (i) organic cations engineering in Sn-based halide perovskite microcrystals, and (ii) adding reducing agents in three dimensional perovskite thin film.

On the one hand, Sn-based halide perovskite microcrystals have been synthetized by hot-injection method to control the dimensionality by changes the concentration of reactants. The physical properties suggest high photoluminescence quantum yield (PLQY) of 75% and 25% for chloride-based and bromide-based, respectively, and almost negligible for 2D Sn-based microcrystals. Increasing the dimensionality, we suggest adding a variety of additives that act as reducing agents with different nature in thin film. The addition of these novel materials into the FASnI₃ (FA is formamidinium) perovskite solution controlled the oxidation reaction and improved the surface morphology. An inverted perovskite solar cell was prepared and characterized. Due to the Sn⁴⁺ concentration is reduced in the Sn-based perovskite layer, the power conversion efficiency in a solar cell and the cell stability under ambient conditions are improved notably in comparison with the pure FASnI₃.

The metal halide perovskite solar cell has been progressively attaining the appreciable value of efficiency but it is not environment friendly due to the toxic nature of Pb. Similarly, Si solar cell has high production cost so alternative cheap, environment-friendly, and earth-abundant material is needed to mitigate the energy crisis for human civilization. The bismuth sulfide-based material could be the alternative solution to fulfill today’s energy demand because of its wide range of features in optoelectronics and photovoltaics. Among them, Bi-S-O compounds are recently studied in very few numbers in electrocatalytic, humidity sensing [1,2]. In our work, for the first time, we have studied the photovoltaic properties of the new bismuth oxysulfate compound by simple spin coating deposition method and compared it with those of Bi₂S₃ material. There are numerous factors to enhance the performance of the solar cell, annealing temperature is one of the important factors to change the morphology, optical, electrical, and structure of the thin film material.

Bismuth nitrate and thiourea were dissolved in 2-methoxyethanol and the thin films were synthesized via the spin coating method with changing annealing temperature. The annealing temperature changes the Bi₂S₃ thin film of low band gap to the bismuth oxysulfate material of high band gap along with the advancement of both open voltage and current. The structure change was confirmed by the XRD and UV-vis spectrometer. A similar kind of topological change from Bi₂S₃ precursor to bismuth oxysulfate is reported by Runze Ye et al. [1]. The thin film of Bi₂S₃ material is formed up to 360⁰C annealing temperature and above this temperature material is changed into the new family of bismuth oxysulfate material. The morphology and structure are also changed such as at low annealing temperature nanowires of Bi₂S₃ are found but at 360⁰C and higher temperature slightly thinner nanowires of bismuth oxysulfate are observed which are shown in Fig. 1. The structure of the solar cell is shown in Fig. 3. At 420⁰C annealing temperature, the open voltage is appreciably increased to as high as 0.75 V [Fig. 2] however PCE is low due to the high band gap and some other defects. Many electrical and optical properties of this family of new compound bismuth oxysulfate are still under deep observation and calculation. SEM image and EDS analysis confirmed the formation of the derivative of bismuth sulfide material at the higher annealing temperature. Hence, bismuth sulfide-based material could be an important promising material optoelectronic technology in the future era.

Metal halide perovskites have attracted the attention of many scientists for their excellent optoelectronic properties. However, considering the environmental issues, the use of Pb in metal halide perovskites is not a good choice to be widely used in our daily life. Therefore, in recent years, Sn-based perovskites and other kinds of Pb-free perovskites have aroused great interest among scientists. It is hoped that the harm to the environment can be reduced. Among them, 2D Sn-based perovskites have been studied in the application of perovskite light-emitting diodes (PeLEDs). However, the easy oxidation of Sn from Sn²⁺ to Sn⁴⁺ tends to form detrimental Sn vacancies, which limits the efficiency of 2D Sn-based PeLEDs. In this study, we consider not only the solution to the problems associated with Sn-based perovskites, but also environmental concerns. Considering a more environmentally friendly process, we first investigated a series of natural antioxidants and then selected ascorbic acid (Vit C) as an additive to effectively inhibit the oxidation of Sn. In addition, we added the cyclic molecule 18-Crown-6 to trap excess ions and form a synergistic effect with VitC to significantly inhibit the defective state in PEA₂SnI₄ films. Finally, we demonstrate efficient 2D Sn-based PeLEDs with an emission wavelength centered at 630 nm and a maximum external quantum efficiency of 1.87%. This work provides a way to improve the performance of 2D Sn-based PeLEDs by adding natural antioxidants, thus further promoting the development of environmentally friendly PeLEDs.

As the front runner among emerging photovoltaic technologies, perovskite solar cells (PSCs) with certified power conversion efficiencies (PCEs) over 26% show great promise for scale-up and future commercialization due to relatively simple and low-cost solution processes. However, the disordered stoichiometric compositions at surfaces generate abundant defects in the solution-processed perovskite films, particularly at surfaces and grain boundaries. Such defects shorten the carrier lifetime and limit photovoltaic performance. Moreover, these defects are responsible for accelerated ion migration and the initial invasion of moisture or oxygen, ultimately causing device instability. The defects also hinder the scale-up of PSCs, thus restricting commercialization. Efficient and stable PSCs with a simple active layer are desirable for manufacturing. Organic halide salt passivation is considered to be an essential strategy to reduce defects in state-of-the-art PSCs. This strategy, however, suffers from the inevitable formation of in-plane favored two-dimensional (2D) perovskite layers with impaired charge transport, especially under thermal conditions, impeding photovoltaic performance and device scale-up. In this talk, several molecular approaches toward passivated defective states leading to stabilized perovskite devices will be presented.

Firstly, the energy barrier of 2D perovskite formation from ortho-, meta- and para-isomers of (phenylene)di(ethylammonium) iodide (PDEAI2) that were designed for tailored defect passivation was studied.[1] Treatment with the most sterically hindered ortho-isomer not only prevents the formation of surficial 2D perovskite film, even at elevated temperatures but also maximizes the passivation effect on both shallow- and deep-level defects. The ensuing PSCs achieve an efficiency of 23.9% with long-term operational stability (over 1000 hours). Importantly, an efficiency of 21.4% for the perovskite module with an active area of 26 cm2 was achieved.

Secondly, as a follow-up, passivating salts based on the ortho-methylammonium iodide functional units were molecularly engineered to study the steric hindrance-driven passivation effect further. The incorporation of the fluorine atoms in passivating agents is beneficial not only for maximized defects passivation effect ensuring improved charge transport but also for significantly enhanced hydrophobicity of the perovskite film leading to enhanced device stability. The highest power conversion efficiency (PCE) of over 24% has been achieved on surficial passivated PSCs based on fluorinated cation PFPDMAI₂. Importantly, long-term operational stability over 1500 h is demonstrated showing a great prospect of a simple passivation strategy forming a thin organic halide salt layer instead of a 2D perovskite layer on the surface.
 

Solution-processed organometallic halide perovskites have been widely explored for various optoelectronic applications due to excellent wavelength tunability, high absorption/emission efficiency, easy and low fabrication cost. Optically pumped amplified stimulated emission (ASE) and lasing have been demonstrated in a variety of media such as 3D, 2D, 1D, and 0D perovskites and in a number of cavity configurations. Despite these advances, solution-processed, cavity-free perovskite thin films generally demonstrate lasing with relatively high thresholds and moderate gain values due to optical losses from scattering and non-radiative recombination which originate mainly from the defect states at the surface/bulk of the perovskite materials and their irregular morphology due to grain boundaries and sample inhomogeneity.

In this work, we prepared highly uniform Cs_0.25FA₀.₇₅Pb(I_0.8Br_0.2)₃ thin films doped with various amounts of MDACl₂ that has been known to stabilize the α-phase of FAPbI₃, reduce the lattice strain, and minimize the density of defect centers and traps. Photoluminescence (PL) imaging and steady-state and time-resolved (TRPL) measurements, together with density functional theory (DFT) calculations and secondary ion mass spectrometry (SIMS), reveal that Cl interstitials replace iodine (I) interstitials within the perovskite layer, with some excessive chlorine accumulating near (20-25 nm) the surface. The removal of detrimental non-radiative recombination centers associated with iodine interstitials leads to dramatic improvement of the luminescent properties and stability of the material. We found that the ASE threshold is reduced by 30 times from ~ 200 μJ/cm² to <6 μJ/cm² while the maximum modal gain value is record-highest for the cavity-free configuration at g = 937 ± 91 cm⁻¹ for ultrathin (T = 200 nm) spin-cast films doped with 5% of MDACl₂. ASE did not degrade for over five hours of continuous measurements in the ambient environment. Ultrafast transient absorption (TA) measurements indicate that lasing originates from localized states concentrating towards the surface. [1]

Exploring light-emitting (LED) applications, we designed a novel solvent engineering method to incorporate highly luminescent fully inorganic 0D Cs₄PbBr₆ nanocrystals (PNCs) into a 3D CsPbBr₃ film, forming the active emissive layer in single-layer perovskite light-emitting electrochemical cells. We observed a dramatic increase of the maximum external quantum efficiency (EQE) and luminance from 2.7% and 6050 cd/m² for a 3D-only PeLEC to 8.3% and 11200 cd/m² for a 3D-0D PNC device with only 7% by weight of 0D PNCs. The majority of this increase is driven by efficient inherent emission of 0D nanocrystals, while the concomitant morphology improvement also contributes to reduced leakage current, reduced hysteresis, and enhanced operational lifetime (half-life of 127 h), making this one of the best performing LECs reported so far. [2] These results pave the way for a rational incorporation of the extrinsic elements into perovskite materials to dramatically enhance their optical and lasing properties.

Perovskite solar cells attract attention as promising cost-effective next generation printable photovoltaics. The power conversion efficiencies (PCEs) have been substantially increased in a short period, based on the improvements of the fabrication protocols for the perovskite layer, and the development of new materials for passivation of the surface or efficient charge collection, etc.

Our research approaches for lead and lead-free perovskite solar cells are as follows.

-Development of highly purified perovskite precursor materials: We synthesis a series of complexes of lead halides or tin halides as purified precursor for perovskite materials.

-Development of fabrication methods for perovskite layer by solution process: We focus on the intermediates formed during the solution process and develop efficient fabrication methods.[1-3]

In this presentation, our recent progress of perovskite solar cells will be introduced.

Based on our "dipole strategy", the method and effects of our surface structure modification of perovskite film on solar cells will be shown.[4-7]

We also designed and synthesized novel pi-conjugated materials, including PATAT,[8] in terms of control of the energy level of frontier orbitals, molecular orientation, and interface between perovskite layer. The performance of perovskite solar cells and modules using these materials will be discussed.

Organometal halide perovskite is a promising material for the light-weight and high-efficiency solar cells. In this lecture, current situation and future prospects of the high performance perovskite solar cells and modules are summarized. Through the many studies related to the organometal halide perovskite solar cells (PSCs), the composition of the organometal halide perovskite is recognised as one of the key factors in the improvement of the stability and efficiency. Many groups investigated mixed cation and mixed halogen perovskite absorber toward the high efficiency, whereas unexpected ion migration and/or phase segregation were observed. For the improvement of the stability, several approaches have been investigated. In our study, K+-doped perovskite is good for the stabilization with keeping relatively high performance. It can be stabilized to some extent where it is not decomposed after 10, 000 h of heating. The crystal lattice structure of the organometal halide perovskite is also important for both absorption and photophysics of them, whereas the micro-structural aspects within the simple organometal halide perovskite are still controversial issue. In our study, direct observation of the microstructure of the thin film organometal halide perovskite using transmission electron microscopy was investigated. Unlike previous reports, it is identified that the tetragonal and cubic phases coexist at room temperature, and it is confirmed that superlattices composed of a mixture of tetragonal and cubic phases are selforganized without a compositional change. The organometal halide perovskite self-adjusts the configuration of phases and automatically organizes a buffer layer at boundaries by introducing a superlattice. These results show the fundamental crystallographic information for the organometal halide perovskite and demonstrates new possibilities toward high performance perovskite solar cells.