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1. Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms

   https://doi.org/10.1364/PRJ.402411  

   Wang, Yutao ; Quintana, Xavier ; Kim, Jiyun ; Guan, Xinwei ; Hu, Long ; Lin, Chun-Ho ; Jones, Brendon Tyler ; Chen, Weijian ; Wen, Xiaoming ; Gao, Hanwei ; et al ( October 2020 , Photonics Research)

   Halide perovskites, such as methylammonium lead halide perovskites (${\mathrm{MAPbX}}_3$,$\mathrm{X}=\mathrm{I}$, Br, and Cl), are emerging as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes, and photodetectors, due to their superior optoelectronic properties. All-inorganic lead halide perovskites${\mathrm{CsPbX}}_3$are attracting a lot of attention because replacing the organic cations with${\mathrm{Cs}}^{+}$enhances the stability, and its halide-mixing derivatives offer broad bandgap tunability covering nearly the entire visible spectrum. However, there is evidence suggesting that the optical properties of mixed-halide perovskites are influenced by phase segregation under external stimuli, especially illumination, which may negatively impact the performance of optoelectronic devices. It is reported that the mixed-halide perovskites in forms of thin films and nanocrystals are segregated into a low-bandgap I-rich phase and a high-bandgap Br-rich phase. Herein, we present a critical review on the synthesis and basic properties of all-inorganic perovskites, phase-segregation phenomena, plausible mechanisms, and methods to mitigate phase segregation, providing insights on advancing mixed-halide perovskite optoelectronics with reliable performance.

    

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2. Iodine Electrochemistry Dictates Voltage‐Induced Halide Segregation Thresholds in Mixed‐Halide Perovskite Devices

   https://doi.org/10.1002/adfm.202203432  

   Xu, Zhaojian ; Kerner, Ross A. ; Berry, Joseph J. ; Rand, Barry P. ( June 2022 , Advanced Functional Materials)

   Owing to straightforward stoichiometry–bandgap tunability, mixed‐halide perovskites are ideal for many optoelectronic devices. However, unwanted halide segregation under operational conditions, including light illumination and voltage bias, restricts practical use. Additionally, the origin of voltage‐induced halide segregation is still unclear. Herein, a systematic voltage threshold study in mixed bromide/iodide perovskite devices is performed and leads to observation of three distinct voltage thresholds corresponding to the doping of the hole transport material (0.7 ± 0.1 V), halide segregation (0.95 ± 0.05 V), and degradation (1.15 ± 0.05 V) for an optically stable mixed‐halide perovskite composition with a low bromide content (10%). These empirical threshold voltages are minimally affected by composition until very Br‐rich compositions, which reveals the dominant role of iodide/triiodide/iodine electrochemistry in voltage‐induced Br/I phase separation and transport layer doping reactions in halide perovskite devices.

    

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3. Sustainable materials acceleration platform reveals stable and efficient wide-bandgap metal halide perovskite alloys

   https://doi.org/10.1016/j.matt.2023.06.040  

   Wang, Tonghui ; Li, Ruipeng ; Ardekani, Hossein ; Serrano-Luján, Lucía ; Wang, Jiantao ; Ramezani, Mahdi ; Wilmington, Ryan ; Chauhan, Mihirsinh ; Epps, Robert W. ; Darabi, Kasra ; et al ( September 2023 , Matter)

   The vast chemical space of emerging semiconductors, like metal halide perovskites, and their varied requirements for semiconductor applications have rendered trial-and-error environmentally unsustainable. In this work, we demonstrate RoboMapper, a materials acceleration platform (MAP), that achieves 10-fold research acceleration by formulating and palletizing semiconductors on a chip, thereby allowing high-throughput (HT) measurements to generate quantitative structure-property relationships (QSPRs) considerably more efficiently and sustainably. We leverage the RoboMapper to construct QSPR maps for the mixed ion FA 1-y Cs y Pb(I 1-x Br x ) 3 halide perovskite in terms of structure, bandgap, and photostability with respect to its composition. We identify wide-bandgap alloys suitable for perovskite-Si hybrid tandem solar cells exhibiting a pure cubic perovskite phase with favorable defect chemistry while achieving superior stability at the target bandgap of 1.7 eV. RoboMapper’s palletization strategy reduces environmental impacts of data generation in materials research by more than an order of magnitude, paving the way for sustainable data-driven materials research. 

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4. Inorganic CsPb 1− x Sn x IBr 2 for Efficient Wide‐Bandgap Perovskite Solar Cells

   https://doi.org/10.1002/aenm.201800525  

   Li, Nan ; Zhu, Zonglong ; Li, Jiangwei ; Jen, Alex K. ‐Y. ; Wang, Liduo ( May 2018 , Advanced Energy Materials)

   Recently, the stability of organic–inorganic perovskite thin films under thermal, photo, and moisture stresses has become a major concern for further commercialization due to the high volatility of the organic cations in the prototype perovskite composition (CH₃NH₃PbI₃). All inorganic cesium (Cs) based perovskite is an alternative to avoid the release or decomposition of organic cations. Moreover, substituting Pb with Sn in the organic–inorganic lead halide perovskites has been demonstrated to narrow the bandgap to 1.2–1.4 eV for high‐performance perovskite solar cells. In this work, a series of CsPb_1−xSn_xIBr₂perovskite alloys via one‐step antisolvent method is demonstrated. These perovskite films present tunable bandgaps from 2.04 to 1.64 eV. Consequently, the CsPb_0.75Sn_0.25IBr₂with homogeneous and densely crystallized morphology shows a remarkable power conversion efficiency of 11.53% and a highV_ocof 1.21 V with a much improved phase stability and illumination stability. This work provides a possibility for designing and synthesizing novel inorganic halide perovskites as the next generation of photovoltaic materials.

    

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5. Triple-halide wide–band gap perovskites with suppressed phase segregation for efficient tandems

   https://doi.org/10.1126/science.aaz5074  

   Xu, Jixian ; Boyd, Caleb C. ; Yu, Zhengshan J. ; Palmstrom, Axel F. ; Witter, Daniel J. ; Larson, Bryon W. ; France, Ryan M. ; Werner, Jérémie ; Harvey, Steven P. ; Wolf, Eli J. ; et al ( March 2020 , Science)

   Wide–band gap metal halide perovskites are promising semiconductors to pair with silicon in tandem solar cells to pursue the goal of achieving power conversion efficiency (PCE) greater than 30% at low cost. However, wide–band gap perovskite solar cells have been fundamentally limited by photoinduced phase segregation and low open-circuit voltage. We report efficient 1.67–electron volt wide–band gap perovskite top cells using triple-halide alloys (chlorine, bromine, iodine) to tailor the band gap and stabilize the semiconductor under illumination. We show a factor of 2 increase in photocarrier lifetime and charge-carrier mobility that resulted from enhancing the solubility of chlorine by replacing some of the iodine with bromine to shrink the lattice parameter. We observed a suppression of light-induced phase segregation in films even at 100-sun illumination intensity and less than 4% degradation in semitransparent top cells after 1000 hours of maximum power point (MPP) operation at 60°C. By integrating these top cells with silicon bottom cells, we achieved a PCE of 27% in two-terminal monolithic tandems with an area of 1 square centimeter.

    

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