Organic semiconductors have found application in a number of optoelectronic technologies, most notably light emitting diodes (LEDs) and photovoltaics (PV). While organic LEDs (OLEDs) have been in the market for quite some time, organic PV (OPV) is still in its infancy. It is expected that OPV will however find application in a number of emergent applications such as indoor lighting for IoT, aerospace and in agricultural settings (agriPV) due to a number of material and electronic properties (lightweight low-cost materials, high-throughput processing, tuneable electronic properties).[1,2,3] AgriPV in particular is gaining a lot of attention recently thanks to the inherent light-weight and semi-transparent active areas found in OPV, advances in efficiencies and lifetimes, and the inherent ability to tune the bandgap of active layer materials to transmit photons in the photoactive region (PAR) of photosynthesis and absorb light outside of the PAR. [4,5] In this talk I will discuss our initial work in exploring the application of OPV in greenhouse, polytunnel and field applications as well as the challenges involved when scaling ST-OPV devices from the lab to prototype modules.

In addition to OLEDs and OPV, organic semiconductors have been used to fabricate a number of other electronic and optoelectronic devices including photodetectors, transistors, electrochemical transistors, and pseudocapacitors. [6] Organic semiconductors are also emerging as potential materials for neuromorphic computing  applications, and is an area that we have are exploring with great interest. [7] I will highlight our recent work in this area, including a study based on a small-molecule nanowire array that demonstrated multi-state memory, non-volatile memory retention and the ability to write a variety of conductance states. [8] There is great scope to further develop this area of research and I will provide a perspective on how this may be achieved.

Organic solar cells (OSCs) using non-fullerene acceptors (NFAs) have garnered a lot of attention during the past few years and showed dramatic increases in the power conversion efficiency (PCE). PCEs higher than 19% for single-junction systems were achieved. In this talk, I will discuss the current challenges of organic solar cells such as materials reproducibility, green-solvent processing, device stability, and module development. I will highlight the importance of material reproducibility and our effort on understanding the device stability. To accelerate the mass fabrication of OSCs, green solvent processing is crucial to reduce the harmful effect of halogenated solvents to human health and our environment. I will discuss the design, synthesis, and performance of organic semiconductors processed from green solvents such as xylene and 2-methyltetrahydrofuran (2-MeTHF). 2-MeTHF is a biomass-derived (furfural or levulinic acid) and environmentally friendly solvent that is widely used in organic synthesis, which can be produced from low-cost and renewable agriculture feedstock. A combination of characterization methods were employed to gain insight into the film morphology and solar cell performance.

Powerful modulated techniques such as Impedance Spectroscopy (IS), Intensity-Modulated Photocurrent Spectroscopy (IMPS) and Intensity-Modulated Photovoltage Spectroscopy (IMVS) are well-established to characterize optoelectronic devices under operational conditions. They are typically used in an independent way. In this presentation we will show that the combination of the three techniques provides added useful information that helps to select accurate models to fit experimental data and thus to obtain reliable data for the characterization of the physico-chemical properties of the materials these devices are constituted. The theoretical basis of this combination will be described, then several approaches to analyse solar cells and photoelectrodes for water splitting will be shown. We will start using simple elements to estimate the equivalent circuit describing the response of such systems and then evolve towards more complex systems such distributed diffusion and recombination models. Through this analysis the main limitations for the operation of these devices will be identified and, in the particular case of BiVO4 photoelectrodes used for water splitting, the ambipolar response of this electrode for the different illumination side will be unveiled.

Colloidal lead halide perovskite (LHP) nanocrystals (NCs), with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are of immense interest as classical and quantum light sources. Severe challenges LHP NCs form by sub-second fast and hence hard-to-control ionic metathesis reactions, which severely limits the access to size-uniform and shape-regular NCs in the sub-10 nm range. We show that a synthesis path comprising an intricate equilibrium between the precursor (TOPO-PbBr₂ complex) and the [PbBr₃^-] solute for the NC nucleation may circumvent this challenge [1]. This results in a scalable, room-temperature synthesis of monodisperse and isolable CsPbBr₃ NCs, size-tunable in the 3-13 nm range. The methodology is then extended to FAPbBr₃ (FA = formamidinium) and MAPbBr₃ (MA = methylammonium), allowing for thorough experimental comparison and modeling of their physical properties under intermediate quantum confinement. In particular, NCs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation. We then discuss the size-dependent single-photon emission across the LHP NC compositions. We achieve 98% single-photon purity (g(2) (0) as low as 2%) from a cavity-free, nonresonantly excited single 6.6 nm CsPbI₃ NCs, showcasing the great potential of CsPbX₃ NCs as room-temperature highly pure single-photon sources for quantum technologies [2]. In another study, we address the linewidth of the single-photon emission from perovskite NCs at room temperature. By using ab-initio molecular dynamics for simulating exciton-surface-phonon interactions in structurally dynamic CsPbBr₃ NCs, followed by single quantum dot optical spectroscopy, we demonstrate that emission line-broadening in these quantum dots is primarily governed by the coupling of excitons to low-energy surface phonons. Mild adjustments of the surface chemical composition allow for attaining much smaller emission linewidths of 35−65 meV (vs. initial values of 70–120 meV) [3]. NC self-assembly is a versatile platform for materials engineering, particularly for attaining collective phenomena with perovskite NCs, such as superfluorescence [4, 5]. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K. Perovskite SLs exhibit superfluorescence, characterized, at high excitation density, by emission pulses with ultrafast (22 ps) radiative decay and Burnham-Chiao ringing behaviour with a strongly accelerated build-up time.

1. Q. Akkerman et al. Science, 2022, 377, 1406-​1412

2. Chenglial Zhu et al. Nano Lett. 2022, 22, 3751−3760

3. Gabriele Raino et al. Nat. Commun., 2022, 13, 2587

3. Ihor Cherniukh et al. Nature, 2021, 593, 535–542

5. Ihor Cherniukh et al. ACS Nano, 2022, 16, 5, 7210–7232

By 2025 about 75 billion IoT devices will be installed, of which the majority will reside indoors. It is therefore crucial to find an energy source that yields high efficiencies in this environment.^1,2 The ambient photovoltaics will redefine the energy paradigm of the current digital revolution with Internet of Things (IoTs, wireless sensors) as current unsustainable designs are strongly limited by their choice of energy supply. Given the record performance of my hybrid photovoltaics in low and indoor lighting conditions, these devices will be ideal to power smart sensors for the IoTs, making them sustainable and independent from any external power sources.

We address the state-of-the-art materials for indoor photovoltaics, with a particular focus on dye-sensitized solar cells, and their effect on the architecture of next generation IoT devices and sensor networks. Dye-sensitized solar cells (DSCs) are known for efficient conversion of ambient light. Fast charge separation in a variety of organic dyes and tuneable energy levels in the versatile Cu^II/I redox systems combined with negligible recombination processes allow DSCs to maintain a high photovoltage under ambient light.²

We tailored dye-sensitized photovoltaic cells based on a copper (II/I) coordination complexes hole transport material for power generation under ambient lighting with an unprecedented conversion efficiency of PCE 38 %, at 1000 lux from a fluorescent lamp using a novel co-sensitization strategy³ and electrolyte modifications Under 1000 lux lighting, 64 cm² photovoltaic area gives 152 J or 4.41 10²⁰ photons sufficient energy for training and testing of an artificial neural network in less than 24 hours. Ambient light harvesters enable a new generation of self-powered and "smart" IoT device to be powered by a previously untapped energy source.^4,5 The combination of ambient light harvesting with artificial intelligence enables the creation of completely autonomous, self-powered sensor systems for use in industry, healthcare, homes, and smart cities.

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

https://www.tcichemicals.com/JP/en/c/12969

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

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

https://www.tcichemicals.com/JP/en/product/pick/hole_transporting_materials_for_stable_perovskite_solar_cells

Dopants for Organic Electronics Research

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.

Light-weight solar panels have great potentials to increase the installation amount of the solar power generation systems because it can be set-up the photovoltaics to the location of difficult to install, for example, on the wall of building and on the roof of weak building such as carport and prefabricated buildings.

Perovskite solar cells (PSCs) are one of the candidates of the ultra-light photovoltaics from their bendable characteristics of the perovskite layers for potentials of the film-type of solar cells. PSCs also can be manufactured by layering of electron and hole transport materials, and the organic-metal-halide perovskite materials as the intermediate layer by coating and printing. This fabrication processes are expected to lead the low-cost photovoltaics. In addition, higher than 20% power conversion efficiency of PSCs has been reached in the small area cells about 1 cm², and they are expected to become next-generation solar cells that enable high efficiency and low cost. However, the practical application of the perovskite solar cells requires the long-term durability and development of the layers coating processes that enable mass production. In this presentation, it will be introduced that the materials development and interface engineering to overcome the challenges to commercialization of PCS.

The hole-transporting material (HTM) is an important component of perovskite solar cells (PSCs) and the most frequently used HTM is Spiro-OMeTAD. In common, Spiro-OMeTAD requires dopants such as Li(TFSI) to realize high power conversion efficiencies (PCEs). However, these dopants cause severe instability issues in PSCs. To overcome this adverse effect from the dopants in HTM, we collaborate with Nippon Fine Chemical Co.,LTD and developed new HTM, SF48 (figure 1), which do not require the dopants. The PSC with non-doped SF48 exhibited a high PCE of 18%, which was comparable to that of the reference PSCs with doped Spiro-OMeTAD. In addition, the thermal stability of SF48 at 85 °C in air was superior to that of Spiro-OMeTAD, both with and without dopants.[1]

On the other hand, hole transporting self-assembled monolayer (SAM) has been developed and it showed better solar cell performances than the ordinally HTM. SAM has the benefits to prepare hole transport layer on the highly-roughness surfaces and the bended surfaces. To further improve the performance of the PSCs with SAMs, it must investigate that the relationship between molecular structure and solar cell performances. we developed the new SAM materials which including the typical additional groups. Then, the solar cell performances are compared with the SAMs including different structures.

Greatcell Energy - Industry talk

Recently, halide perovskites, a new class of functional materials different from conventional inorganic semiconductors, debuted in the research field of condensed matter physics. Halide perovskites show sharp optical absorption edge and efficient photoluminescence (PL) with no essential Stokes shift even at room temperature. Thus, photocarrier and exciton dynamics can be studied using PL spectroscopy. Two-photon excitation PL spectroscopy clarifies that the photon reabsorption and photon recycle processes occur in halide perovskites [1]. After the first observation [1], by considering photon reabsorption, we successfully explain “anomalous” PL properties of thick samples such as the thickness dependence of the PL spectrum, two peak PL structures at the near band-edge, and the impurity concentration dependence of the PL spectrum [2,3]. Nonlinear optical spectroscopy including two-photon excitation PL measurements is a powerful tool to clarify intrinsic optical processes in halide perovskites. In this talk, we discuss the electronic structures and photocarrier dynamics of halide perovskites revealed by nonlinear optical spectroscopy [4-9].

Hybrid organic / inorganic perovskite have considerably arisen as an efficient active material in the solar community, because of its low cost and its performance's fascinating enhancement in the last decade. Nowadays, the current techniques for depositing the perovskite are essentially based on spin coating in glove box. This method showed good results, but operates with small active areas, limiting the industrialization of perovskite solar cells. Electrodeposition is here investigated as an alternative method to develop large area perovskite active layers for solar device application. Along with the simple MAPbI₃ perovskite, the electrodeposition of mixed MAPbI_3-xCl_x and MA_1-yFA_yPbI_3-xBr_x perovskites will be presented. The present study is one of its kind, since these mixed perovskite were never developed using electrodeposition before. It was observed that using electrodeposition afford enhanced stability compared to spin-coating process, and the different fabricated perovskites were also proved to experience a positive maturation phenomenon during their first 500 hours of life.

Perovskite solar cells and organic thin film solar cells have attracted recent attention as new-generation solar cells. These solar cells consist of three main layers: electron transport layer, hole transport layer, and absorber layer. The electron and hole transport layers play an important role in effective charge separation and enhancing solar energy conversion. The most typical material of the electron transport layer is TiO₂, which is an n-type semiconductor. The TiO₂ layer has often been formed by spray pyrolysis at high temperatures of ~500°C. The necessity of high-temperature deposition is one of the limitations of applying the TiO₂ electron transport layer to flexible solar cells. In this study, an attempt was made to prepare the TiO₂ layer on FTO and ITO transparent conductive oxide substrates by cathode deposition from aqueous electrolytes. The cathodic deposition method has the advantage of the cost-effective preparation of the TiO₂ layer on large conductive substrates at relatively low temperatures. After deposition, hot water treatment was conducted to obtain a crystalline TiO₂ layer at relatively low temperatures.

The cathodic deposition was conducted at a constant current density in aqueous electrolytes containing K₂TiF₆ and K₂SO₄. Hydrogen evolution reaction occurs during the cathodic polarization, and the pH of the electrolyte in the vicinity of the cathode increases. Then, the hydrolysis of TiF₆^2- ions is promoted, inducing the deposition of TiO₂. Thin uniform TiO₂ layers of 20-100 nm thickness were successfully prepared on FTO substrates. The deposited TiO₂ layer was amorphous, but crystallization occurred after hot water treatment at 80°C. When the ITO substrate was used, the colored deposited layer was obtained because of the dispersion of metallic Sn nanoparticles as a consequence of the reduction of ITO. We found that the anodic polarization could effectively remove the metallic nanoparticles, and the deposited layer became colorless.

The deposition involves the hydrogen evolution reaction, often introducing pinhole defects or partial detachment of the TiO₂ layer on the FTO substrate. We introduced a nitrate reduction reaction instead of the hydrogen evolution reaction to increasing the pH in the vicinity of the cathode. Because of the suppression of gas evolution during the deposition, the TiO₂ layer more adherent to the substrate was successfully obtained.

Perovskite solar cells (PSCs) have a photoelectric conversion efficiency of over 20 % and they can be fabricated only by printing and coating processes, so it is expected as next-generation solar cells. However, the back-contact electrode (e.g. Au, Ag) and hole transport materials (e.g. Spiro-OMeTAD) used for PSCs are unstable against water and oxygen, and there is a problem with long-term stability. Therefore, we focused on fully printable carbon-based multi-porous-layered-electrode PSCs (MPLE-PSCs) which have an electron transport layer (mesoporous TiO₂), an insulation layer (mesoporous ZrO₂), and hole transport/back contact electrode layer (carbon) [1-5]. MPLE-PSCs have long-term stability because the thick carbon layer (~15 μm) can be protected the light absorption layer from ambient water and oxygen. However, MPLE-PSCs have a low efficiency of less than ~18%, so it is necessary to aim for higher efficiency for commercialization. In this work, we focus on carbon electrodes, which have roles of hole transport and back contact. Typically, carbon electrodes are made from a mixture of large-sized graphite particles and nano-sized carbon black. However, the role of each material remains unclear. Therefore, carbon electrodes with different mixing ratios of graphite and carbon black are fabricated and compared. This fundamental comparison reveals the role of carbon materials used in MPLE-PSCs.
         A TiO₂ compact layer was deposited by a spray pyrolysis method on patterned FTO glass. Then, porous TiO₂, ZrO₂, and carbon layers were deposited by a screen-printing method, and each layer was sintered at 400 to 500 ºC. Six mixing ratios of graphite and carbon black for carbon electrodes were prepared: 100-0, 80-20, 65-35, 50-50, 20-80, and 0-100. Finally, (5-AVA)_0.05(MA)_0.95PbI₃ perovskite precursor solution was drop-casted and permeated through the carbon layer, and the MPLE-PSCs were completed by removing the solvent and crystallizing the perovskite material by heating and drying. Various measurements were performed on the obtained devices.
         The results show that the mixing ratio of graphite to carbon black has a significant effect on the performance of MPLE-PSC devices. In the graphite-rich, the open-circuit voltage (V_OC) was higher. However, the short-circuit current density (J_SC) and fill factor (FF) were low. On the other hand, increasing the ratio of carbon black decreased V_OC, but improved J_SC and FF. To understand these changes, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) analysis were performed. The results show that carbon black has the effect of promoting hole extraction and graphite has the effect of efficiently transporting the generated charge. In summary, the MPLE-PSC device achieved maximum performance and a champion efficiency of 13% when graphite and carbon black were in a 50-50 or 20-80 ratio. This study is important for realizing inexpensive and sustainable carbon electrodes not only for PSCs but also for various electronic devices.

Carbon as a counter electrode for perovskite solar cells (PSC) has shown the potential towards stable and scalable photovoltaic technology. Traditionally these devices have been developed with TiO₂-based compact and mesoporous electron transport layers (ETL) for high performance. Deposition of TiO₂ layers mainly requires high-temperature Annealing (~450 °C), which can hinder the low-cost manufacturing production or the possibility of PSCs on a flexible substrate. On the other hand, the cerium oxide (CeO_x) as the ETL requires only 150 °C processing temperature, which enhances the pathway for the low-temperature-based fabrication of PSCs. Along with processing temperature, the tunable morphology of nanomaterials can produce a significant variation in performance, as seen in different fields of materials science and technology. In this work, we explored the morphology modification aspect of the CeO_x and derived a rod and a cubical structure for utilization in a perovskite device. The highest power conversion efficiency (PCE) of 14.3% was recorded for the rod structure CeO_x for the carbon-based PSC. Moreover, the rod-shaped CeO_x demonstrated higher interaction with the perovskite layer and a lower charge recombination rate when compared with the cube structure, which demonstrated around 12.3% PCE. [SB1] This work shows the potential to analyze morphology-tuned nanomaterials for PSC as an alternative pathway to enhance their performance. The morphology and photovoltaic correlation can change the future of perovskite photovoltaics due to its many component systems.

Perovskite solar cells (PSCs) are expected to be one of the next generation photovoltaics. However, considerable difficulties in reliable measurements of the power conversion efficiency and prediction for power generation of PSCs are a severe concern for the fair and accurate application of advancements in PSC technologies. 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 in the cells by exposure history (voltage bias, irradiance, and temperature). 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. [1] 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.

Tandem solar cells that combine perovskite (PVK) top cells and Si, Cu(In,Ga)(Se,S)2 (CIGS), PVK and other bottom cells have attracted much attention for increasing the efficiency of solar cells [1,2]. To use the PVK solar cells (PSC) as the top cells, their metal electrode needs to be replaced with a transparent conductive layer such as indium tin oxide (ITO) deposited by sputtering, however, it is still on discussion about the damage by the sputtering during the deposition to the layers. In this study, double layer ITO of 50 nm for the damage controlling of spatter as first and 250 nm for high conductivity as second were introduced. It was revealed that the effect of ion bombardment during first ITO sputtering on spiro-OMeTAD was not detrimental in the suitable condition of oxygen concentration and sputter power density during the deposition process. The photovoltaics of semi-transparent PVK cells has been developed with less damage and higher conductivity with enough transmittance, then the power conversion efficiency (PCE) of 19.5% (certified 19.3%) was achieved for a 1 cm2 buffer-free semi-transparent PVK cell. Furthermore, mechanically stacked four-terminal PSC / CIGS tandem solar cells showed 26.2% of PCE [3].

References:
[1] Yeom, K. M.; et al., Adv. Mater. 2020, 32, e2002228, 32909335.
[2] Zhu, Z., et al., J. Energy Chem. 2021, 58, 219–232.
[3] M. Nakamura, et al., ACS Appl. Energy Mater. 2022, 5, 8103−8111

Thanks to the emerging non-fullerene acceptors (NFAs), power conversion efficiencies (PCEs) of bulk heterojunction (BHJ) organic solar cells (OSCs) continue increasing towards the 20% milestone. Nevertheless, important factors for industrial application are mostly neglected, such as photostability and cost potential. Single-component organic solar cells (SCOSCs) employing materials with donor and acceptor moieties chemically bonded within one molecule or polymer, successfully overcome the immiscibility between donor and acceptor as well as the resultant self-aggregation under external stress [1]. To inspire a broader interest, in this work, the industrial figure of merit (i-FOM) of OSCs is calculated and analyzed, which includes PCE, photostability, and synthetic complexity (SC) index [2]. Based on the notable advantages of SCOSCs over the correspondent BHJ OSCs, especially the enhanced stability and simplified film processing, we systematically compare the i-FOM values of BHJ OSCs and the corresponding SCOSCs.

SCMs exhibit overall much higher i-FOM values compared with the BHJ OSCs, and the highest value reaches 0.3, which is even higher than the famous PM6:Y6, even though the PCE (8%) is only half of PM6:Y6. With the increase in efficiency, SCOSCs possess the further potential for a higher i-FOM value. Among all factors, the synthetic complexity of SCOSCs is slightly higher than that of the corresponding BHJ OSCs due to the extra synthetic step for connecting donor and acceptor moieties. This feature however overcomes the large-scale phase separation and stability issue for the corresponding BHJ systems [3]. SCOSCs based on dyad 1 exhibit surprisingly high photostability under concentrated light (7.5 suns and 30 suns), corresponding to almost unchanged device stability up to 10,000 hours under 1-sun illumination. For realizing industrial application, SCOSCs have to give a high efficiency comparable to the current high-efficiency BHJ OSCs, while BHJ should be developed in the direction of less complicated synthesis [4]. With joint efforts of researchers from multidiscipline, SCOSCs will see continuing progress in efficiency, reaching an i-FOM value enough for industrial application.

The advantages of organic-inorganic halide perovskites, such as their configurable bandgap, inexpensive material costs, and high charge carrier mobilities, make them intriguing -candidates for next-generation solar cell and opto-electronic applications. Despite tremendous advancements, worries regarding material stability still prevent the widespread use of perovskite-based technology. Using transmission electron microscopy (TEM) and time-resolved photoluminescence (TRPL) techniques, we investigate how environmental factors impact the structural and optical characteristics of thin film perovskites.

The hydrophilic nature of 3D halide perovskites renders them sensitive to temperature and moisture. As a result, the organic cation of 3D halide perovskite can be easily destroyed in an ambient environment. But the stability of 3D halide perovskites can be improved by decreasing the perovskite dimensionality. To create lower dimension perovskites, large organic cations such as phenyl-ethyl ammonium (PEA) are added to the 3D perovskites.

In this work, we compare the stability of 3D perovskite, MAPbI₃ (CH₃NH₃PbI₃) and 2D perovskites, (PEA)₂PbBr₄ against environmental conditions like moisture and air. The characterizations are performed on perovskite thin films exposed to air, nitrogen and vacuum environments, the latter being possible by using dedicated air-free transfer setups, after their fabrication into a nitrogen-filled glovebox. We observe that even less than three minutes air-exposure increases the sensitivity to electron beam deterioration and modifies the structural transformation pathway for 3D MAPbI₃ thin films.

However, in comparison to their 3D counterparts, 2D perovskite films show better stability. Their distinct layered structural layout makes it possible to adjust their physical and chemical properties using organic spacer cations.

The findings pave the way to understand the relationship between the microstructural changes and the optical properties of perovskites when subjected to air-induced degradation.

Perovskite solar cells (PSCs) are suitable candidates as sub cells for tandem solar cell technologies thanks to their bandgap tunability and high efficiency. For an all-thin film tandem solar cell, high-bandgap PSCs can be matched with low-bandgap CIGS. State-of-the-art high-bandgap PSCs last for thousands of hours at standard operating conditions[1], but the required operational stability for the commercialization of such applications is more than 20 years. Therefore, there is the need to optimize the devices for stability under accelerated ageing conditions.
In this study, we tested encapsulated perovskite solar cells of various compositions with bandgaps higher than 1.6eV and an efficiency of up to 20%. The stressing experiments were carried out at different temperatures from 25°C up to 85°C at MPP conditions in air with 1-sun equivalent illumination intensity (ISOS-L1 conditions) using the benchtop instrument Litos. Additionally, by performing in-situ JV scans every 60 minutes, we could follow the evolution of the PV parameters in parallel with stressing. The MPP decay can be fitted with a bi-exponential function, where the first exponent is attributed to a burn-in effect from which the burn-in time is derived. This allows to determine the effective operative lifetime of the device. The decay of the MPP correlates with the short-circuit current decay, thus indicating the development of charge generation and collection issues with ageing. We performed additional characterization techniques before and after the stressing experiments using the Paios measurement platform to gain further insight into the degradation mechanisms. The aged devices present slower current rise and decay dynamics as observed in transient photocurrent (TPC) compared to the pristine devices confirming the appearance of charge transport issues. Following the optimization of the device stability on glass substrates, the ageing tests will be performed for PSCs deposited on flexible substrate.

References:

[1]        X. Zhao et al., “Accelerated aging of all-inorganic, interface-stabilized perovskite solar cells,” Science, vol. 377, no. 6603, pp. 307–310, Jul. 2022, doi: 10.1126/science.abn5679.

Perovskite solar cells (PSCs) have achieved power conversion efficiencies (PCEs) exceeding 25% over the past decade. Effective passivation at the bottom interface with high trap density is challenging yet plays an important role in PSCs.^[1,2] Here, organic molecules with A-D-A structure are studied as passivator. Firstly, we demonstrated that an advantageous molecular geometry and intermolecular ordering, aside from the functional moieties, are of great significance for effective and extensive passivation. Secondly, the passivation molecules spontaneously form a uniform passivation network adjacent to the bottom surface of perovskite films during a top-down crystallization via liquid medium annealing, which greatly reduces defect-assisted recombination throughout the whole perovskite/SnO₂ interface. As a result, we achieved a device PCE over 25%.^[1] Furthermore, we would like to extent the application field of the molecules in flexible PSCs. The investigation highlights a comprehensive understanding of designing passivation materials and provides a new avenue to achieve effective bottom-interface engineering for perovskite photovoltaics.

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells (PSCs) has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.

This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, simple fabrication technologies for realizing large scale perovskite module are introduced and recent effort for achieving high efficiency module is going to be presented. Finally, recent interesting results regarding ultra flexible perovskite cells will be discussed.

Colloidal lead halide perovskite nanocrystals (LHP NCs_, NCs, A=Cs⁺, FA⁺, FA=formamidinium; X=Cl, Br, I) have become a research spotlight owing to their spectrally narrow (<100 meV) fluorescence, tunable over the entire visible spectral region of 400-800 nm, as well as facile colloidal synthesis. These NCs are attractive single-photon emitters as well as make for an attractive building block for creating controlled, aggregated states exhibiting collective luminescence phenomena. Attaining of such states through the spontaneous self-assembly into long-range ordered superlattices (SLs) is a particularly attractive avenue. In this regard also the atomically-flat, sharp cuboic shape of LHP NCs is of interest, because vast majority of prior work had invoked NCs of rather spherical shape. Long-range ordered SLs with the simple cubic packing of cubic perovskite NCs exhibit sharp red-shifted lines in their emission spectra and superfluorescence (a fast collective emission resulting from coherent multi-NCs excited states).

When CsPbBr₃ NCs are combined with spherical dielectric NCs, perovskite-type ABO₃ binary NC SLs form, wherein CsPbBr₃ nanocubes occupy B- and/or O-sites, while with spherical dielectric Fe₃O₄ or NaGdF₄ NCs reside on A-sites. When truncated-cuboid PbS NCs are added to these systems, ternary ABO₃-phase form (PbS NCs occuoy B-sites). Such ABO₃ SLs, as well as other newly obtained SL structures (binary NaCl, AlB₂- and ABO₆ types, columnar assemblies with disks etc.), exhibit a high degree of orientational ordering of CsPbBr₃ nanocubes. These mesostructures exhibit superfluorescence as well, characterized, at high excitation density, by emission pulses with ultrafast (22 ps) radiative decay and Burnham-Chiao ringing behaviour with a strongly accelerated build-up time. Combining CsPbBr₃ nanocubes with large and thick NaGdF₄ nanodisks results in the orthorhombic SL resembling CaC₂ structure with pairs of CsPbBr₃ NCs on one lattice site. We also implement two substrate-free methods of SL formation. Oil-in-oil templated assembly and self-assembly at the liquid–air interface result in the formation of binary supraparticles. [1]

Photosensitizers yielding superior photocurrents are crucial for copper-electrolyte-based highly efficient dye-sensitized solar cells (DSCs). Herein, we present two molecularly tailored organic sensitizers coded ZS4 and ZS5 through judiciously employing dithieno[3,2-b:2',3'-d]pyrrole (DTP) as the p-linker, and hexyloxy-substituted diphenylquinoxaline (HPQ) or naphthalene-fused-quinoxaline (NFQ) as the auxiliary electron-accepting unit, respectively. Endowed with the HPQ acceptor, ZS4 shows more efficient electron injection and charge collection based on substantially reduced interfacial charge recombination as compared to ZS5. As a result, ZS4-based DSCs achieve a power conversion efficiency (PCE) of 13.2% under standard AM1.5 G sunlight, with a high short-circuit photocurrent density (Jsc) of 16.3 mA cm-2, an open-circuit voltage (Voc) of 1.05 V and a fill factor (FF) of 77.1%. Remarkably, DSCs sensitized by with ZS4 exhibit an outstanding stability, retaining 95% of their initial PCE under continuous light soaking for 1000 h. To the best of our knowledge, this is the record efficiency reported so far for copper-electrolyte-based DSCs using a single sensitizer. Our work highlights the importance of developing molecularly tailored photosensitizers for highly efficient DSCs with copper electrolyte.

One promising third generation photovoltaic technology is Dye-sensitised Solar Cells (DSCs) as they perform well under higher temperature conditions and diffuse light. They have been demonstrated to perform particularly well for indoor applications powering small devices, such as small sensors for the Internet of Things (IoT).^[1] DSCs, although highly tuneable to suit their application, face shortcomings over relatively low power conversion efficiencies and limited durability when utilising a liquid electrolyte.

To overcome the stability issues surrounding the liquid electrolyte, solid-state DSCs (ssDSCs) have been introduced where the liquid electrolyte has been replaced by solid-state alternatives.^[2] To increase the theoretical maximum efficiency, n-p tandem structured DSCs have been designed by sandwiching an n-type DSC (n-DSC) with a p-type DSC (p-DSC) to utilise more of the solar spectrum.^[3]

The focus of this research is on combining the features of both n-p tandem DSCs and solid-state DSCs in attempt to overcome the current problems with traditional DSCs and lay the foundations for a highly efficient, stable solar cell. The presentation will discuss device fabrication and materials deposition, and will include supporting kinetic data as well as other solar cell characterisation.

The recent focus on tandem cell structures has generated a renewed interest in mixed-composition perovskite materials with bandgaps in the range of 1.7–1.9 eV. These wide bandgap absorbers are typically obtained by increasing the fraction of bromide ions present in the X-site of the ABX3 perovskite lattice. Indeed, it is already well established that the perovskite bandgap can be reliably tuned over a wide range by adjusting the Br/I ratio.[1] These early studies also revealed, however, that certain compositions are more stable than others, and, in addition, the homogeneous distribution of I- and Br- ions in the perovskite lattice tended to spontaneously and reversibly de-mix under strong light, an effect that is generally referred to as “halide segregation”.[2]

While it is often suggested that halide segregation presents an intrinsic limit for the performance of wide bandgap perovskite solar cells, recent work by Brinkmann et al., featuring monolayer-based n-i-p devices would contradict this assessment, as they were able to obtain an open circuit voltage of 1.35 eV from a perovskite absorber with a 1.85 eV bandgap and 50% bromide fraction.[3]  In light of these new results, it is useful to re-evaluate the influence of the halide ratio on device performance and operational stability.

In this work, two triple-cation mixed halide lead perovskite absorbers are compared, one with high bromide content (Br/I ratio 1:2, bandgap 1.72 eV, 16.1% power conversion efficiency) and one with low bromide content (Br/I ratio 1:11, bandgap 1.57 eV, 19.1% power conversion efficiency).[4] Both materials demonstrated good stability while operating under simulated sunlight at the maximum power point for 100 h. After 100 h operation, however, the measured device efficiency fell temporarily due to a transient loss of output current before returning to the nominal level after a long recovery period in the dark. These transient losses were more apparent in the wide bandgap device under strong light and were likely caused by light-induced halide segregation. After recovery, however, both devices retained good performance under a wide range of light intensities. Overall, we conclude that the monolayer-based p-i-n device structure with wide bandgap perovskite absorber layers shows great promise for long-term deployment in both solar and ambient-light harvesting applications from the standpoint of both efficiency and operational stability.

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Tin perovskite solar cells (Sn-PVK PVs) have attracted attention as Pb free PVK PVs having the band gap of about 1.3-1.4 eV, which is the best band gap from the viewpoint of Shockley-Queisser limit. One of the alloyed perovskites, Tin Lead perovskite solar cells (SnPb-PVK PV) is a candidate as the bottom layer of the perovskite tandem solar cells(1). We have reported Ge ion doped Sn-PVK solar cells with the efficiency higher than 14% and SnPb alloyed perovskite solar cells with the efficiency higher than 23%. In this talk, we discuss these high efficiencies from the viewpoint of modified hole transport layers. In almost all Sn-PVK PVs, PEDOT-PSS has been employed. We now report the SnOx (x=1.77) as the hole transporting layer. The normal structure with SnOx layer working as ETL did not give sufficiency efficiency which has been already reported by us(2). However, the inverted structure consisting of SnOx working as the hole transporting layer gave the efficiency of 14. 1%(ACS Energy Letters, accepted). The mechanism is discussed in detail. In addition, we report SnPb-PVK PV with 23.3 % efficiency by using mixed 2PACz/methylphosphonic acid hole transport layer, where we aimed at enhanced surface coverage on FTO by mixing small and large phosphonic acids(3).

I will give a quick overview of recent progress and future prospects of perovskite tandem solar cells reported in the literature. I will then talk about some of the research activities in my group. Specifically, We will discuss how our perovskite-Si tandem cell monolithic integration strategy has evolved from interface-layer-free design to ultra-thin interface layer design due to the switch from homo-junction Si cells to hetero-junction Si cells for the bottom stack. Recent results include 27.2% power conversion efficiency with a fill factor of 82.4% on 1.0 cm2; 24.2 % efficient 11.8 cm2 cell; and 21.1 % efficient 65.1 cm2 (~4-inch round) cell. I will also talk about the evolution from p-i-n to n-i-p tandem demonstrations. In addition, I will present our results of 20% 3-junction tandem and recent innovations on low-bandgap and high-bandgap perovskites with very high fill factors for the demonstration of perovskite-perovskite tandems with very good yield.           

Since perovskite solar cell (PSC) achieved high efficiency over 25%, fundamental studies of PSCs have been directed to stability and durability improvement by defect passivation and interfacial modification while efficiency development is becoming a major issue for large area modules and muti-junction tandem cells.¹ We have been tackling interfacial passivation with functional organic molecules, particularly focusing on the method of enabling high voltage output (close to theoretical limit) in photovoltaic performance.² In compositional engineering, inorganic perovskites are promising in the viewpoints of high thermal stability and potentially high stability against light-assisted phase segregation. Besides the perovskite composition, use of diffusible dopants in hole transport materials (HTMs) are responsible for low stability of perovskites at high temperatures (>120^oC). In this respect, use of dopant-free HTMs for all-inorganic perovskite absorbers is highly desired. CsPbI₂Br perovskites in combination of dopant-free polymer HTMs achieved PCEs of >17% under 1 sun and >34% under indoor LED illumination, supported by high V_oc values and low voltage deficits.³ Phase segregation in CsPbI₂Br is less than those for hybrid perovskite and it was not observed under indoor light circumstance. Therefore, inorganic PSCs are promising for applications to the IoT industry. Creation of new inorganic perovskite materials includes lead-free compositions. As a typical composition, Ag-Bi-halide (sulfide) system is an important target for achieving environmentally kind PSCs, where the method to achieve high V_oc by interfacial passivation is the key to high efficiency.⁴

Applications of PSCs in space environments attract attentions because thin perovskite photovoltaic films demonstrate high stability and tolerance against exposure to high energy particle irradiations (proton and electron beams).⁵ Thin absorbers (<500 nm) avoid accumulation of particles and due to intrinsic defect tolerant nature of perovskites, radiation-induced collision damage is highly suppressed. Based on our current R&Ds, future perspectives of perovskite photovoltaics will be presented.

1. T. Miyasaka, editor, Perovskite Photovoltaics and Optoelectronics ―From Fundamentals to Advanced Applications―, Wiley-VCH, Weinheim, 2021, ISBN: 978-3-527-34748-3.

2. G. M. Kim, H. Sato, Y. Ohkura, A. Ishii, and T. Miyasaka, Adv. Energy Mat. 2022, 12, 2102856.

3. Z. Guo, A. K. Jena, I. Takei, M. Ikegami, A. Ishii, Y. Numata, N. Shibayama, T. Miyasaka, Adv. Func. Mat. 2021, 31, 2103614.

4. T. Miyasaka, A. Kulkarni, Gyu Min Kim, Senol Öz, A. K. Jena, Adv. Energy. Mat. 2019, 1902500.

5. Y. Miyazawa, M. Ikegami, H.-W. Chen, T. Ohshima, M. Imaizumi, K. Hirose, T. Miyasaka, iScience 2018, 2, 148.

With the efficiencies of perovskite solar cells (PSCs) approaching  26%, the focus has turned to the fabrication of long-lasting scaled up devices. In this regard, slot-die coating has emerged as a front runner owing to its large area coating uniformity, high throughput capability, minimal material wastage, as well as compatibility with high volume production. To date, power conversion efficiency (PCE) of the state-of-the-art slot-die coated PSCs is over 20% for small-areas and over 19% for large-areas. As variation of crystallization kinetics and the presence of residual solvents can become more significant in large area coating, there is an urgent need for the development of approaches capable of addressing a wide variety of defects. We utilize a hydrophobic all-organic salt to modify the top surface of large area slot-die coated methylammonium (MA)-free halide perovskite layers. Endowed with anchoring groups capable of exhibiting secondary interactions with the perovskite surfaces, the organic salt acts as a molecular lock by effectively binding to both anion and cation vacancies, substantially enhancing the materials’ intrinsic stability against different stimuli. The treated PSCs demonstrate efficiency of 19.28 % for the corresponding mini-module (active area of 58.5 cm2). In addition to solution processing, deposition of perovskite absorber layers by thermal co-evaporation have gathered considerable interest for both single junction and multi-junction solar cells. The main advantages for thermal evaporation include conformal coatings, control of deposited layer thicknesses, and possibility of multi-layer processing. We have recently demonstrated highly efficient, large area, planar PSCs ranging from 0.16 cm2 to 20 cm2 with high efficiencies. This methodology is also compatible with depositing layers for quantum confinement that is crucial for optoelectronics applications.

In this industrial talk we present LayTec's InspiRe metrology system for in-situ monitoring perovskite formation processes. This system allows to monitor the formation in real-time by means of spectral reflectance measurements. The methodology can be applied for obtaining spectral "fingerprints" during wet-chemical processes such as spin-coating or slot-die-coating as well as during annealing and physical vapor deposition. In this talk, we also show first examples of real time growth rate and film thickness monitoring applied during perovskite evaporation. Here, growth rate and thickness values are obtained by fitting the reflectance signal based on optical models. Finally, we will give an outlook on complementary metrology methods like spectral and time-resolved photoluminescence.

Highly efficient and low-cost perovskite solar cells (PSCs), one of the most promising next-generation photovoltaic technology, triggered intensive research around the world. Up till now, PSCs have achieved the record power conversion efficiency of 25.7% and the device stability has been improved substantially. To push forward the development of PSCs, researchers from home and abroad have been overcoming the obstacles of commercialization. According to our estimation of the levelized cost of electricity, the key to future applications is to reduce the cost of PSCs which strongly depend on high efficiency and long stability. In this presentation, I will introduce our recent works on promoting the efficiency and stability of PSCs from aspects of crystallization, passivation, and ion-migration blocking.

We introduced a perovskite crystal array (PCA) with regular distribution to assist the growth of the perovskite absorption layer. The PCA provided nuclei where the crystallization can commence without overcoming the critical Gibbs free energy for nucleation and induces a controllable bottom-up crystallization process under solvent annealing. As a result, the device achieved power conversion efficiency of over 25.1%. Furthermore, we constructed a composite electrode of copper-nickel (Cu-Ni) alloy stabilized by in situ grown bifacial graphene. The device with the copper-nickel electrode showed an efficiency of 24.34% (1cm²) and stability: 95% of their initial efficiency is retained after 5,000 hours at maximum power point tracking under continuous 1 sun illumination.

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Power conversion efficiency (PCE) of perovskite solar cells (PSCs) has increased dramatically and has reached to 25.7%. For even higher PCE, the increase of open-circuit voltage (Voc) as well as fill factor (FF) will be a main challenge to be solved since the short circuit current density (Jsc) is almost approaching the theoretical limit (i.e., 28.97 mAcm-2). The reason for low Voc and FF must be related with the energy loss of charge carriers which is originated from the recombination through defects, inefficient charge extraction from the absorbers on the surfaces/interfaces, and current leakage through shunt paths. As recent studies reported incorporation of methylammonium chloride (MACl) to stabilize α-FAPbI3, herein, we propose that crystallization process of α-FAPbI3 can be kinetically controlled by adjusting MACl concentration. We examined higher concentration of MACl induces slower crystallization kinetics, resulting in larger grain size and [100] preferred orientation. This indicates the impact of controlling the crystallization kinetics to result a preferred orientation and a large grain size, which leads to high PCEs. Furthermore, we present an amorphous TiO2 and V2O5-x passivation layers, deposited by atomic layer deposition (ALD) at low temperature (< 50 ℃), on Spiro-OMeTAD to prevent metal-induced interfacial degradation while maintaining the overall performance. Finally, we have fabricated perovskite solar cells (FTO/SnO2-based ALD-ETL/FAPbI3/2Dperovskite/Spiro-OMeTAD/Au) and confirmed increased PCE (23.91 %) measured under AM 1.5 G. Not only PCE, but also device stability with ALD-TiO2 and V2O5-x layers was dramatically improved. It was confirmed through ion contents profiling using ToF-SIMS that the improvement of the stability in PSC adopting ALD-TiO2 and V2O5-x comes from preventing the metal ion diffusion. In conclusion, we have demonstrated high PCE and stability of PSCs. 

Recently, photoexcited hot carriers (HCs) relaxation dynamics in halide perovskite materials have attracted much attention since the HCs cooling lifetimes was found to be unusually slow with orders of magnitude longer compared to those of the conventional semiconductor. On the other hand, the HCs cooling in perovskite quantum dots (PQDs) is size-dependent and the cooling time was observed to be around two orders of magnitude longer than that of their bulk counterparts [1], which suggests that the PQDs are promising candidates for hot-carrier solar cells (HCSCs). Therefore, a deeply understanding the hot carrier cooling and extraction dynamics in the PQDs has a profound implication for further developing the disruptive HCSCs. In this talk, we will introduce our recent research results on hot carrier cooling and extraction dynamics in PQDs, including both experimental results obtained using transient absorption (TA) spectroscopy and DFT theoretical calculation. We will discuss on how the A-site cations cross-exchange of the PQDs affects the hot carrier relaxation dynamics, and how about the hot carrier extraction from the PQDs to inorganic metal oxide substrates and fullerene [2-4].

Perovskite solar cells (PSCs) using organic-inorganic halides as a light-absorbing layer exhibit high power conversion efficiencies (PCEs; 25.7%) in small-area solar cells . The film quality dramatically affects the performance of PSCs and depends on the fine structure of the perovskite layers, including the crystallinity, surface coverage, and roughness. Also, Device structure dramatically affects performance, and the use of transparent conductive films with textured structures with light confinement effects effectively improves short-circuit current density. However, it is difficult to form a uniform electron transport layer on a textured structure using a solution method such as spin coating. The spray and chemical bath deposition methods can deposit films on textured structures without defects, but they require high temperatures or long deposition times.

In this study, a uniform electron transport layer was formed on a textured transparent conductive film by the sequential spin casting of positively charged Poly(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFN) and negatively charged colloidal SnO₂ solution, which is applied to perovskite solar cells.

 Uncoated areas were observed around the convexity without PFNs, whereas the SnO₂ coverage increased with PFN. This is thought to be due to the electrostatic effect between PFN and SnO₂ during deposition. FA_1-xCs_xPbI₃ perovskite thin films were deposited on the electron transport layer using high-boiling co-solvent and Lewis bases as additives in a one-step process and without an antisolvent t[1~3]. Spiro-OMeTAD hole transport layer was deposited by spin-coating method, and finally an Ag electrode was formed by vacuum evaporation. The PCE of perovskite solar cells with a single SnO₂ electron transport layer is 16.2% (13.0%) with J_SC = 25.7 (25.7) mA·cm^-2, V_OC = 0.951 (0.874) V, and FF of 65.7% (57.9%) for the RS (FS),whereas the PFN/SnO₂ bilayerd electron transport layer improves all performance factors, resulting in a PCE of 20.5% (20.0%) with J_SC = 26.3 (26.4) mA·cm^-2, V_OC = 1.03(1.03) V, and FF of 75.5% (73.9%) for the RS (FS).

Highly performing mixed tin-lead perovskite materials are among the most promising options as an alternative active layer in perovskite solar cells to reduce Pb content. Moreover, these compounds open the possibility of fabricating full perovskite tandem devices, owing to their reduced band gap. The most efficient single junction mixed Sn/Pb perovskite solar cells have been fabricated using methylammonium cations (MA⁺), and a p-i-n structure where poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) is implemented as hole transport layer (HTL).^[1] The record devices were reported to show limited stability, this can be attributed to two major reasons: i) MA⁺ cations easily desorb at high temperature (85 C°) from the perovskite surface, introducing MA vacancies; ii) PEDOT: PSS, due to its hygroscopic and acid nature, reacts with the perovskite active layer, affecting the long-term stability.

In this work we employed a MA⁺ free perovskite composition, namely, Cs_0.25FA_0.75Sn_0.5Pb_0.5I₃ and 2-(9H-carbazol-9-yl) ethyl) phosphonic acid (2-PACz), and [2-(3, 6-dibromo-9H-carbazol-9-yl) ethyl] phosphonic acid (Br-2PACz) as hole transport layers, with the aim of replacing PEDOT: PSS. Moreover, the fact that 2PACz and Br-2PACz can form a monolayer may allow reducing parasitic recombination.

Cs_0.25FA_0.75Sn_0.5Pb_0.5I₃ deposited on SAMs showed absence of pinholes, higher crystallinity (XRD), and larger grain size (SEM) when compared with the layers of PEDOT: PSS.

The fabricated solar cells using PEDOT: PSS as HTL exhibited a champion device efficiency of 16.33%, while devices fabricated on 2PACz and Br-2PACz showed an improved efficiency of 18.44% and 19.57%, respectively. The 19.57% efficiency is the record for the aforementioned perovskite composition.

It furthermore interesting to note that encapsulated Br-2PACz based solar cells retained 80% of the initial efficiency after 230 hours under continuous working condition, while device fabricated on PEDOT: PSS maintained 79% only for 72 hours. In addition, the shelf-life test in N₂ atmosphere showed much more stable devices when using Br-2PACz, with 89% of the initial efficiency after 42 days, when compared to PEDOT: PSS based devices, which solely preserve the 71% of the initial PCE. Moreover, the Br-2PACz-based device retained the 80% of the initial efficiency after 138 days in N₂ atmosphere.

                        The Effect of Phenylethylammonium Halides Additives for Lead-Free Perovskite Solar Cells

Fatemeh Zargar¹, Derese Desta¹, Momo Safari¹, An Hardy¹, Julia Zillner², Erik Ahlswede², Koen Vandewal¹, Melissa Van Landeghem¹, Philip Schulz³, Javid Hajhemati³, Hans-Gerd Boyen¹

           1 Hasselt University, Institute for Material Research (IMO), Wetenschapspark 1, 3590 Diepenbeek, Belgium

           2 Center for Solar energy and Hydrogen Research Baden-Württemberg Meitnerstraße 1, 70563 Stuttgart, Germany

           3 IPVF, Institut Photovoltaïque d'Ile-de-France, Palaiseau, France

Abstract

Tin-based perovskites solar cells (PSCs) have attracted much interest as a promising alternative to traditional PSCs, which usually contain toxic lead. Nevertheless, the fast reaction of Sn²⁺ with moisture to form Sn⁴⁺ leads to a significant loss of open circuit voltage (Voc) in the device. Another critical challenge, which causes low photovoltaic performance of Sn-based PSCs, is uncontrolled and rapid crystallization. Among various approaches suggested to overcome oxidation and non-uniform morphology of Sn-based PSCs, additive engineering is the most effective. Adding bulky organic cations such as phenylethylammonium (PEA) to form two-dimensional (2D) perovskite phases not only helps to improve the stability of Sn-based PSCs against oxygen because of their hydrophobic nature but also induces better crystallinity and well-defined orientation, which results in suppressing tin oxidation and reducing the number of tin vacancies[1]. Although many researchers have demonstrated the positive effect of PEA on the performance of Sn-based PSCs, the knowledge about the underlying cause is still largely unknown.

In this work, we incorporated PEA into perovskite precursor solutions to fabricate PEA_xFA_1-xSnI₃ and PEA_xFA_1-xSnI_3-xBr_x -based perovskite solar cells. Perovskite films were fabricated with a solvent engineering approach using an antisolvent. Inverted planar PSCs show a champion conversion efficiency of 9.09 %, along with enhancements in open circuit voltage, short circuit current I_SC, and fill factor FF. The introduction of Br not only improves the orientation and the crystallinity of the perovskite films but also increases Voc and the band gap of the absorber material.

Title: Grain Engineering for Improved Charge Carrier Transport in Two-Dimensional Lead-Free Perovskite Field-Effect Transistors

Authors: Shuanglong Wang¹, Sabine Frisch², Heng Zhang¹, Okan Yildiz¹, Mukunda Mandal¹, Naz Ugur¹, Beomjin Jeong¹, Charusheela Ramanan^1,3, Denis Andrienko¹, Hai Wang¹, Mischa Bonn¹, Paul W. M. Blom¹, Milan Kivala², Wojciech Pisula,^1,4,* and Tomasz Marszalek^1,4,*

Address: ¹Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

² Organisch-Chemisches Institut, Centre for Advanced Materials, Ruprecht-Karls-Universität Heidelberg, 69120 Heidelberg, Germany

³ Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, Netherlands

⁴ Department of Molecular Physics, Faculty of Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland

Email: wangs2@mpip-mainz.mpg.de, pisula@mpip-mainz.mpg.de, marszalek@mpip-mainz.mpg.de

Controlling crystal growth and reducing number of grain boundaries are crucial to maximize the charge carrier transport in polycrystalline perovskites field-effect transistors (FETs). Herein, the crystallization and growth kinetics of Sn(II)-based 2D perovskite, using 2-thiopheneethylammonium (TEA) as the organic cation spacer, was effectively regulated by the hot-casting method. With increasing crystalline grain size, the local charge carrier mobility is found to increase moderately from 13 cm²V^–1s^–1 to 16 cm²V^–1s^–1, as inferred from terahertz (THz) spectroscopy. In contrast, the FET operation parameters, including mobility, threshold voltage, hysteresis, and subthreshold swing improve substantially with increasing grain size, especially for large channel lengths. This behavior is mainly attributed to screening of the applied electric fields by ion migration that becomes severe for small grain sizes and high densities of grain boundaries. Electrical characterization at various temperatures (from 295K to 100K) presents an influence of the ion migration on the charge carrier transport in transistors architecture. Moreover, it is confirmed by grazing incident wide angle x-ray scattering and theoretical unit cell prediction that hot-casting method does not change the molecular organization in deposited thin films but only reduce the number of grain boundaries. The optimized 2D (TEA)₂SnI₄ transistor exhibits hole mobility of up to 0.34 cm²V⁻¹s⁻¹ at 295 K and higher value of 1.8 cm²V⁻¹s⁻¹ at 100 K. These insights provide important guidance for the grain engineering for high-performance 2D perovskite FETs.

Organolead halide perovskite solar cells have been attracting enormous attention as high efficiency and cost-effective solar cells. However, they suffer from low stability under heat, light, and humid condition due to instability of organic hole-transport materials such as spiro-OMeTAD. To address this issue, robust inorganic CuSCN as an alternative hole-transport material has been developed. The solution-processed CuSCN-based perovskite solar cells exhibit low efficiency compared to conventional spiro-OMeTAD-based solar cells owing to low crystallinity and ununiform morphology of the CuSCN layers. Here in this study, we demonstrate crystal control of CuSCN layers by tuning atmospheric condition during the aging process and post-treatment. The enhanced crystallinity of CuSCN layers at high humidity exhibits higher photovoltaic performance than the layers formed by conventional coating condition. Post-treatment with various solvents to CuSCN further improved crystallinity and yielded the layers of flat and uniform morphology resulting in high power conversion efficiency and high stability of solar cells.

Perovskite solar cells (PSCs) with state-of-the-art efficiencies consist of thermally unstable methylammonium (MA). Though the MA-free perovskite has superior thermal stability, there is a challenge to control the formation of the δ-perovskite phase which decreases device performance. This work reports on the surface passivation method with multifunctional fluoroarene molecule which suppresses the formation of PbI₂ and δ-perovskite phase in MA/Br-free perovskite film. [1]  We found that the fluoroarene passivation has significantly impacted the morphology, interface chemistry, and optoelectronic properties of HaP films. The fluoroarene hydrazine passivation effectively mitigates the defects at surface or grain boundaries in perovskite film with fluoroarene-embedded interfacial layer due to stronger halogen bonding with fluoroarene moieties. Therefore, the PSC achieved superior operational stability and a power conversion efficiency (PCE) exceeding 22 % with a large area of ~1 cm² which is a record-level PCE for MA/Br-free inverted PSCs. [1] This approach is also equally effective in improving the PCE of both narrow and wide bandgap perovskite systems by lowering the open-circuit voltage deficit. [1-4] This report will shed light on the synergetic effect of fluoroarene molecular passivation in film growth and photo-physics of PSCs. [2,5]

Several short and long-term effects in perovskite solar cells, such as the hysteresis in the current-voltage (IV) curve,[1] partial performance recovery during interrupted operation[2] and permanent cell degradation are assigned to the presence of mobile ionic charge carriers. Their characterization in full devices is therefore of outmost importance to improve this type of solar cell.

In this study, we first discuss the characteristics of formamidinium-based perovskite solar cells with non-stochiometric compositions. It is found that a 1-1.5% excess of formamidinium precursor (FAI) leads to an improved stabilized device performance while further increasing the FAI excess detrimentally affects the fill factor. Through electrical impedance spectroscopy measurements, it is revealed that the increased FAI excess leads to a higher ionic conductivity. In order to further distinguish between the density and mobility of the ions, we simulate IV and impedance data with the simulation software Setfos.[3] The experimental trends with increasing FAI excess can only be reproduced with an increased density of ions in the simulation.[4]

In general, one would like to distinguish directly between ionic mobility and density in a single solar cell. A method that has been introduced decades ago[5] and was applied recently to perovskite solar cells is the transient ion drift measurement.[6] The analytical model describing the capacitance over time is based on several assumptions that are not necessarily fulfilled in a perovskite devices. We use drift-diffusion simulations in Setfos to model the transient ion drift experiment and thereby confirm the limitations of the analytical model. We further show that those limitations can be overcome by combining measurement and simulations, allowing the application of the method to a broader set of devices.

The Internet of Things comprises a billion smart wireless objects that share data in real-time via sensors and collaborate to achieve common goals, creating a new technology revolution. Although IoT devices typically use modest power (µW to mW), securing a reliable energy supply is a significant challenge. In addition to high maintenance and limited placement options, using wired or battery systems limits energy use. With the IoT ecosystem's exponential expansion, millions of batteries will need to be replaced regularly.[1]

The energy provided by most indoor lightbulbs has the potential to power small IoT devices and replace batteries. It is possible to design near-perpetual intelligent IoT devices with lifetimes of 10–20 years exploiting ambient light collected by Indoor Photovoltaic devices (IPVs) tailored explicitly for ambient light. The spectra of most interior illumination lamps, such as CFL or LED bulbs, range between 380 and 780 nm.[2] This spectral area supplies widely available, untapped energy. Dye-sensitized solar cells (DSC) are the best at capturing ambient light. PCEs up to 34%,[3] outperforming the established silicon technology and thin-film solar cells made from toxic materials. Fast charge separation in sensitizers, tuneable energy levels in copper complexes, and low recombination allow DSCs to sustain a high photovoltage near 1 V under ambient light.

We designed and implemented a photocapacitor architecture for ambient light harvesting, which powers wireless IoT devices. The photocapacitor has a DSC and a double-layer capacitor (EDLC). The EDLC supercapacitors can store intermittent energy with fast charge-discharge processes, high specific power, and long life cycles.[4][5] Organic conductive materials, such as Polyaniline (PANI) and Polypyrrole (PPy), have previously demonstrated excellent charge-storing properties as electrodes in symmetrical supercapacitors separated by a Nafion ion exchange membrane.[6][7] We have developed new highly stable electrodes with organic polycationic polymers known as polyviologens, which have previously demonstrated excellent capabilities for charge storage.[8] The novel polyviologen systems were deposited into poly 3,4-ethylenedioxythiophene (PEDOT) electrodeposited onto FTO substrates. PEDOT acts as a thin-porous layer to increase the polymer material's mass-loading and generate a pseudocapacitive response to delay capacitor discharge. To create a full photocapacitor, the supercapacitors based on polyviologens will be coupled to DSCs using copper complexes as hole transporter materials (HTM). This project intends to overcome the gap in energy supply availability during day-night cycles by storing surplus charges converted by the DSC in polyviologen supercapacitors.

Perovskite solar cells have attracted much attention due to its high power conversion efficiency and low cost processability. Thanks to the band gap tunability of perovskite compounds, perovskite solar cells are available under various light sources which have different spectrum. For example, perovskite solar cells show high power conversion efficiency even under indoor lightings [1]. A power conversion efficiency of over 40% has been achieved under 824.5 lx LED illumination [2]. Although perovskite solar cells are one of a promising candidates for indoor energy harvesting as above, they show quite large hysteresis under low illuminance conditions even there are no hysteresis under 1 sun condition. Here, we investigated the origin of large hysteresis under low illuminance conditions. Through the characterization of each component of perovskite solar cells under various conditions, we assumed defects in perovskite layer is one of a key factors to reduce the hysteresis under low illuminance conditions. We achieved hysteresis free perovskite solar cells even under 200 lx LED illumination by modification.

Organic–inorganic hybrid lead halide perovskite solar cells (Pb-PSC) have attracted considerable attention as low-cost, lightweight, and versatile next-generation solar cells, and their PCEs have been increased to more than 25% in the last decade. Nonetheless, the use of hazardous Pb is a significant concern in commercialization, and drove the development of Pb-free PSCs, in particular, Sn-based PSCs (Sn-PSC). However, the spontaneous degradation of tin perovskites requires special measurement protocols; therefore, numerous experiments should be performed to ensure result reliability. Herein, we report a multivariate analysis for exploring A-site organic cation mixing in tin iodide perovskite (ASnI3) solar cells (PSC), which are the most suitable Pb-free PSC candidates.[1] To address the common drawbacks of Sn perovskites (facile oxidation of Sn2+ to Sn4+ and large degree of mixing), we proposed an efficient experimental screening method (time-resolved microwave conductivity: TRMC[2] etc) using 133 types of environmentally stable A2Sn(IV)I6 zero-dimensional pseudo-perovskites to predict the PCE of ASn(II)I3, in which A is a ternary or quaternary mixed organic cation (namely metylammonium, formamidinium (FA), dimethylammonium, guanidinium, ethylammonium, acetamidinium, trimethylammonium, imidazolium, or phenylethylammonium (PEA)).[4] The high correlation coefficient of our model (0.953) and experimental validation (0.982) allowed us to identify a new (FA0.92IM0.08)0.9PEA0.1SnI3 Sn-PSC with a PCE of 7.22%. Our results provide a basis for exploring A-site cation mixing in Sn-PSCs for improving their performance.

In recent years, the hybrid organic-inorganic trihalide perovskites compounds have attracted numerous attentions and remarkable performance as active layers in the fabrication of highly efficient solar cells, photonics, and other optoelectronic devices. Extensive efforts on the controlled synthesis of perovskite nanostructures have been made towards potential device applications. As well, a simple established strategy of chemical doping has been used to achieve the highest efficiency and high stability perovskite-based solar cells. The band gap engineering in perovskites tuning its electronic and optical properties, which is one of the key factors to make an efficient and multifunctional optoelectronic device. In this work, the effect of Mn doping in organic-inorganic perovskite CsFAMA (Cs_0.05[MA_0.17FA_0.83Pb(I_0.85Br_0.15)₃]_0.95) has been studied with a power conversion efficiency over 20%. The rational design and fabrication of CsFAMA lead to the enhancements of all the photovoltaic parameters, such as charge and electron transport. To incorporate Mn can effectively eliminate the trap-assist and bi-molecular recombination. Particularly, the occurrence of magnetism in CsFAMA has been studied and confirmed from magnetization measurements. The influence of Mn doping in CsFAMA films, structural and morphological has been analyzed in detail. Due to the eminent double exchange and super exchange interactions in between the Mn²⁺-I^--Mn³⁺ ions in Mn doped CsFAMA giving rise to the charge/spin transport in perovskite based photovoltaic devices. We explicitly determined the role of intrinsic spin–orbit coupling (SOC) in Mn-doped CsFAMA perovskites.  Our finding offers an alternative pathway for spintronic, light controlled magnetic and photovoltaic devices.

Reference:

[1] R. Prasanna, R; Parker, AG; Leijtens, T; Conings, B; Babayigit, A; Boyen, HG; Toney, MF; McGehee, MD. Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics. J. Am. Chem. Soc., 2017, 139, 11117–11124.

 [2] Phung, N; Felix, R; Meggiolaro, D et al. The Doping Mechanism of Halide Perovskite Unveiled by Alkaline Earth Metals. J. Am. Chem. Soc. 2020, 142, 2364–2374.

[3] Deng, L; Yang, H; Pan, R; Yu, H; Li, J; Xu, L; Wang, K. Achieving 20% photovoltaic efficiency by manganese doped methylammonium lead halide perovskites. J. Energy Chem. 2021, 60, 376-383.

  Recently, all-polymer solar cells consisting of donor- and acceptor- conjugated polymers have become a promising next-generation energy source with various advantages such as, flexibility, lightweight, high thermal stability, and cost-saving by solution processes.  Despite of these advantages, all-polymer solar cells still lag behind compared to conventional silicon solar cells or perovskite solar cells in terms of power conversion efficiency (PCE).  For further improvement in PCE, short-circuit current density (J_SC) should be increased.  It is therefore essential to fabricate all-polymer solar cells with a thick active layer.  Unfortunately, however, it is known that as the active layer thickness increases, bimolecular charge recombination becomes dominant rather than charge collection, resulting in a decrease in the fill factor (FF).  In other words, there is a trade-off relationship between J_SC and FF.  Here, we have focused on all-polymer solar cells based on crystalline donor polymers with different side chains (J51, J61, and J71) and a naphthalene diimide-based acceptor polymer (N2200) to discuss how charge collection and recombination impact on FF in the all-polymer solar cells with different active layer thicknesses.  For the J51:N2200 and J61:N2200 devices, FF was drastically degraded down to 0.4 with increasing active layer thickness.  For the J71:N2200 device, on the other hand, FF was only slightly decreased and maintained as high as 0.6 even for thicker active layers.
  To get further insight into the origin of such a different tendency in FF, we analyzed the charge recombination dynamics measured by transient photovoltage/photocurrent (TPV/TPC) and charge extraction (CE) for these devices.  On the basis of experimental data obtained, we estimated the reduction factor for charge recombination, which is defined by ζ = k_rec/k_L where k_rec is bimolecular recombination rate constant and k_L is the diffusion-limited Langevin recombination rate constant.  For all the devices, ζ was evaluated to be about 10⁻² order, suggesting suppressed bimolecular recombination compared to the diffusion-limited Langevin recombination.
  Subsequently, we simulated the J–V curve using the recombination kinetic parameters obtained in order to examine how recombination dynamics impacts on FF.  Assuming that the bimolecular recombination is a dominant current loss, the J–V curve can be represented by J(V) = J_GEN(V) + J_BR(V) where J_GEN(V) is photogenerated current density and J_BR(V) is the current density loss caused by bimolecular recombination. The simulation result shows that only J71:N2200 device is in good agreement with the experimental J–V curve, indicating that the decrease in FF is mainly derived by bimolecular recombination.  In stark contrast, for the J51:N2200 and J61:N2200 devices, the simulated J–V curve is not in agreement with the experimental one.  This is because the charge carrier density is underestimated in these devices.  Interestingly, the J–V curve is well reproduced by considering additional charge carriers, suggesting that there is an additional recombination driven by isolated charge carriers.  On the basis of the figure of merit α, proposed by Neher et al.,^[1] we conclude that high FF observed for the J71:N2200 device is due to charge collection 2500 times faster than charge recombination.

Tin halide perovskites, ASnX₃ (A = CH₃NH₃⁺ (MA⁺), (NH₂)₂CH⁺ (FA⁺), Cs⁺ ; X = I^–, Br^–, Cl^–), are promising light absorbers in environmentally-friendly, solution-processed solar cells. The wide bandgaps of bromide-containing tin perovskites, ASnI_3–xBr_x, make them attractive materials for use as the top-layer absorber in tandem solar cells, as well as in single junction solar cells for indoor applications.

In the present work, a series of ASnI_3–xBr_x films was systematically fabricated by varying the A-site (FA⁺, MA⁺, Cs⁺) and X-site (I^–, Br^–) ions. The use of solvent-coordinated SnBr₂ complex [1] as a high purity source of bromide combined with Sn(IV) scavenging treatment [2] help to ensure that the optimal film quality across the compositional space is realized. The energy levels and electronic properties of the films were characterized by photoluminescence (PL) and photoemission yield spectroscopy (PYS) measurements. The films with high PL lifetime and favorable energy level alignment resulted in superior device efficiency when evaluated in standard single junction solar cells. The best power conversion efficiency of 7.74% was obtained when the composition was FA_0.75MA_0.25SnI_2.25Br_0.75 [3].

The inverted p-i-n structured perovskite solar cells (PSCs) using the charge-selective contacts with less sensitivity to ambient condition is regarded as a viable route to fabricate high-performance PSCs with better environmental stability, and nickel oxide (NiO_x) is the most frequently used hole-selective contact at the illumination side due to its high carrier mobility, low cost, and high transparency. However, the lifetime of NiO_x-based inverted PSCs is still relatively short (around 1000 hours), and further enhancement of their long-term operational stability is largely limited by the light-induced degradation at the NiO_x-perovskite heterojunction. In this regard, a simple strategy based on construction of a stable buffer layer that can synergistically eliminate the light-induced degradation and minimize the charge recombination loss in NiO_x-based inverted PSCs is highly desirable, and the development of in-situ characterization techniques are urgently needed to identify the degradation products and further clarify the degradation mechanism. In this work, we used time-resolved quadrupole mass spectrometry (MS) technique to reveal the degradation mechanism of NiO_x-FAMAPbI₃  (formamidinium-methylammonium iodide) perovskite heterojunction under operational condition: 1) generation of iodine vapor and free proton via the oxidation and deprotonation reactions; 2) formation of volatile products under elevated temperature, including hydrogen cyanide, methyliodide, and ammonia; 3) formation of condensation product, N-methyl formamidine, with the increased vapor pressures of dissociated FA and MA molecules. Inspired by the aprotic nature, good phototability, suitable size of trimethylsulfonium (TMS⁺), and the high oxidation potential of Br^-, we introduced a novel TMSBr buffer layer between NiO_x and perovskite to eliminate these multi-step photochemical reactions. Consequently, the TMSBr-stabilized inverted PSCs (1.53-eV bandgap) exhibited a promising efficiency of 22.1% with an open-circuit voltage of 1.18 V, and could retain approximately 82.8% of the initial efficiency after 2000-hour operation under AM1.5G light illumination, which translates into an estimated T80 lifetime of 2310 hours (the time over which the efficiency reduces to 80% of its initial value), which is among the highest operational lifetimes reported for NiO_x-based PSCs.

Even though the performance of tin perovskite solar cell (TPSC) has been reported to attain PCE 14.8%,¹ the hole-transport layer was based on a hydrophilic polymer, PEDOT:PSS, and this is the case for most TPSC reported in the literature. PEDOT:PSS is hygroscopic and this could easily degrade the device performance due to moisture penetration. Other HTM has not been reported in the literature until recently. This is because the reaction of SnI₂ with FAI to form FASnI₃ is a much more rapid process than for its lead analogue, control of crystal growth and nucleation rates are important factors to be considered. The traditional one-step method did not work for other hydrophobic HTM because of the poor hydrophilic nature of the film that enables retarded nucleation comparable to the crystal growth. We therefore developed a two-step method² with the procedure to deposit SnI₂ first for its rapid and smooth nucleation and to retard the crystal growth in the second step using an appropriate solvent and additive. This is a very important development for tin PSC because of the versality of the two-step method which can be applied for all the charge-transport materials developed elsewhere. For example, it is possible to fabricate a HTM-free tin-based PSC using the concept of a self-assembled monolayer (SAM) to modify the ITO surface with tin perovskite layer deposition in a two-step approach.³ We also deposited a smooth and uniform tin-perovskite layer on a hydrophobic conducting polymer, (bis (4-phenyl) (2,4,6-trimethylphenylamine) (PTAA), on modification of the PTAA surface with an organic ammonium salt, phenylethylammonium iodide (PEAI), according to a two-step approach.⁴ Our approach is also applicable to other prospective HTL materials to match the energy levels between perovskite and HTL so as to enhance further the performance of the device in the future.

References:

[1] B. B. Yu, Z. Chen, Y. Zhu, Y. Wang, B. Han, G. Chen, X. Zhang, Z. Du and Z. He, Adv. Mater. 2021, 33, 2102055.

[2] S. Shahbazi, M.-Y. Li, A. Fathi and E. W.-G. Diau, ACS Energy Lett. 2020, 5, 2508-2511.

[3] D. Song, S. Narra, M.-Y. Li, J.-S. Lin and E. W.-G. Diau, ACS Energy Lett. 2021, 6, 4179-4186.

[4] C.-H. Kuan, G.-S. Luo, S. Narra, S. Maity, H. Hiramatsu, Y.-W. Tsai, J.-M. Lin, C.-H. Hou, J.-J. Shyue and E. W.-G. Diau, Chem. Eng. J. 2022, 450, 138037.

Since the ground-breaking report of the 9.7% efficient and 500 h-stable solid-state perovskite solar cell (PSC) in 2012 based on methylammonium lead iodide (MAPbI3), perovskite photovoltaics have been surged swiftly due to high power conversion efficiency (PCE) obtainable via facile fabrication procedure. As a result, a PCE of 25.7% was recorded in 2022. According to Web of Science, number of publications on PSCs increases exponentially since 2012, leading to the accumulated publications of more than 28,000 as of June, 2022. PSC is regarded as a game changer in photovoltaics because of low-cost and high efficiency surpassing the conventional high efficiency thin film technologies. High photovoltaic performance was realized by compositional engineering, device architecture and fabrication methodologies for the past 10 years. Toward theoretical efficiency over 30% along with long-term stability, exquisite control of light absorptivity and photo-excited charges is highly required, along with thermodynamic phase stability of alpha phase formamidinium lead iodide (FAPbI3). In this talk, light-morphology relation is discussed, where a specific crystal facet is found to have strong interaction with photon, leading to high photocurrent. Compressive strain via wrinkling process is found to control the top surface tensile strain of perovskite film, which is beneficial to charge carrier transport and lifetime. As a result, we could achieve a QSS-measured PCE approaching 25%  under one sun illumination.