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1. Impact of PbI 2 Passivation and Grain Size Engineering in CH 3 NH 3 PbI 3 Solar Absorbers as Revealed by Carrier‐Resolved Photo‐Hall Technique

   https://doi.org/10.1002/aenm.201902706  

   Euvrard, Julie ; Gunawan, Oki ; Mitzi, David B. ( November 2019 , Advanced Energy Materials)

   With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley‐Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of MASCN (MA = methylammonium) and excess PbI₂have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, a newly developed carrier‐resolved photo‐Hall (CRPH) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n‐type MAPbI₃films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI₂added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120–2100 nm) and MASCN addition induce no significant change in carrier‐related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI₂must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI₃optoelectronic properties as elucidated by the new CRPH approach.

    

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2. Room‐Temperature Partial Conversion of α‐FAPbI 3 Perovskite Phase via PbI 2 Solvation Enables High‐Performance Solar Cells

   https://doi.org/10.1002/adfm.201907442  

   Barrit, Dounya ; Cheng, Peirui ; Darabi, Kasra ; Tang, Ming‐Chun ; Smilgies, Detlef‐M. ; Liu, Shengzhong ; Anthopoulos, Thomas D. ; Zhao, Kui ; Amassian, Aram ( January 2020 , Advanced Functional Materials)

   The two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI₃hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI₃, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI₃, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI₂into the α‐FAPbI₃perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI₂precursor from its different states are compared. α‐FAPbI₃forms spontaneously and efficiently at room temperature from P₂(ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI₂) to 17.23(±0.28)% (from solvated PbI₂) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA⁺cation without the need for Cs⁺or mixed halide formulation.

    

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3. Eco‐Friendly Solvent Engineered CsPbI 2.77 Br 0.23 Ink for Large‐Area and Scalable High Performance Perovskite Solar Cells

   https://doi.org/10.1002/adma.202310279  

   Abate, Seid Yimer ; Qi, Yifang ; Zhang, Qiqi ; Jha, Surabhi ; Zhang, Haixin ; Ma, Guorong ; Gu, Xiaodan ; Wang, Kun ; Patton, Derek ; Dai, Qilin ( December 2023 , Advanced Materials)

   The performance of large‐area perovskite solar cells (PSCs) has been assessed for typical compositions, such as methylammonium lead iodide (MAPbI₃), using a blade coater, slot‐die coater, solution shearing, ink‐jet printing, and thermal evaporation. However, the fabrication of large‐area all‐inorganic perovskite films is not well developed. This study develops, for the first time, an eco‐friendly solvent engineered all‐inorganic perovskite ink of dimethyl sulfoxide (DMSO) as a main solvent with the addition of acetonitrile (ACN), 2‐methoxyethanol (2‐ME), or a mixture of ACN and 2‐ME to fabricate large‐area CsPbI_2.77Br_0.23films with slot‐die coater at low temperatures (40–50 °C). The perovskite phase, morphology, defect density, and optoelectrical properties of prepared with different solvent ratios are thoroughly examined and they are correlated with their respective colloidal size distribution and solar cell performance. The optimized slot‐die‐coated CsPbI_2.77Br_0.23perovskite film, which is prepared from the eco‐friendly binary solvents dimethyl sulfoxide:acetonitrile (0.8:0.2 v/v), demonstrates an impressive power conversion efficiency (PCE) of 19.05%. Moreover, the device maintains ≈91% of its original PCE after 1 month at 20% relative humidity in the dark. It is believed that this study will accelerate the reliable manufacturing of perovskite devices.

    

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4. Inorganic cesium lead mixed halide based perovskite solar materials modified with functional silver iodide

   https://doi.org/10.1038/s41598-022-11729-0  

   Eze, Vincent Obiozo ; Carani, Lucas Braga ; Majumder, Haimanti ; Uddin, M. Jasim ; Okoli, Okenwa I. ( May 2022 , Scientific Reports)

   Inorganic CsPbIBr₂perovskites have recently attracted enormous attention as a viable alternative material for optoelectronic applications due to their higher efficiency, thermal stability, suitable bandgap, and proper optical absorption. However, the CsPbIBr₂perovskite films fabricated using a one-step deposition technique is usually comprised of small grain size with a large number of grain boundaries and compositional defects. In this work, silver iodide (AgI) will be incorporated as an additive into the CsPbIBr₂perovskite precursor solution to prepare the unique perovskite CsI(PbBr₂)_1-x(AgI)_x.The AgI additive in the precursor solution works as a nucleation promoter which will help the perovskite to grow and merge into a continuous film with reduced defects. With detailed characterizations, we found that incorporating AgI additive resulted in a uniform perovskite film with fewer grain boundaries, increased grain size, crystallinity, optical absorption while decreasing carrier recombination and trap density. Using the AgI in an optimum amount, we fabricated CsPbIBr₂perovskite solar cells (PSCs) with a simple structure and achieved a power conversion efficiency (PCE) of 7.2% with a reduced hysteresis index. This work offers an alternative approach towards preparing high-quality CsPbIBr₂perovskite films for solar cells with higher stability and other optoelectronic applications.

    

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5. Boosting Photovoltaic Performance for Lead Halide Perovskites Solar Cells with BF 4 − Anion Substitutions

   https://doi.org/10.1002/adfm.201808833  

   Zhang, Jie ; Wu, Shengfan ; Liu, Tiantian ; Zhu, Zonglong ; Jen, Alex K. ‐Y. ( February 2019 , Advanced Functional Materials)

   Composition engineering is a particularly simple and effective approach especially using mixed cations and halide anions to optimize the morphology, crystallinity, and light absorption of perovskite films. However, there are very few reports on the use of anion substitutions to develop uniform and highly crystalline perovskite films with large grain size and reduced defects. Here, the first report of employing tetrafluoroborate (BF₄⁻) anion substitutions to improve the properties of (FA = formamidinium, MA = methylammonium (FAPbI₃)_0.83(MAPbBr₃)_0.17) perovskite films is demonstrated. The BF₄⁻can be successfully incorporated into a mixed‐ion perovskite crystal frame, leading to lattice relaxation and a longer photoluminescence lifetime, higher recombination resistance, and 1–2 orders magnitude lower trap density in prepared perovskite films and derived solar cells. These advantages benefit the performance of perovskite solar cells (PVSCs), resulting in an improved power conversion efficiency (PCE) of 20.16% from 17.55% due to enhanced open‐circuit voltage (V_OC) and fill factor. This is the highest PCE for BF₄⁻anion substituted lead halide PVSCs reported to date. This work provides insight for further exploration of anion substitutions in perovskites to enhance the performance of PVSCs and other optoelectronic devices.

    

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