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Bulk lead halide perovskite films with unique optoelectronic properties and facile low‐cost processing methods are promising for various optoelectronic applications including photovoltaics. Solution‐processed colloidal inorganic perovskite nanocrystals with higher crystallinity hold good potential for devices with better stability and optoelectronic properties. To address phase stability and defect passivation issues in black phase FAPbI3 perovskite, all‐inorganic perovskite CsPbBr3 nanocrystals (CPB NCs) are adapted as an effective modifier to form CPB NC‐treated FAPbI3 perovskite films (noted as CPB NC‐FAPbI3). It is identified in this study that, the incorporated CsPbBr3 NCs not only act as surface additives for the bulk perovskite films, but can also serve as ion reservoirs to supply both cation and halide exchanges at the interface. This two‐way ion exchange in CPB NC‐FAPbI3 samples leads to the formation of a compositional gradient as FA1−xCsxPbI3−yBry layers on the bulk perovskite film surface with vertically varied x and y values. Defects at interfaces and grain boundaries are therefore effectively passivated, leading to improved stability and charge carrier dynamics. As a result, the CPB NC‐FAPbI3 perovskite based solar cells exhibit overall enhancements in device efficiency and operational stability. [ABSTRACT FROM AUTHOR]

The photovoltaic performance and long‐term stability of perovskite solar cells (PSCs) are greatly affected by trap states. Herein, a functional ionic liquid of 1‐ethyl‐3‐methylimidazolium trifluoroacetate (EMIMTFA) is introduced, in which the 1‐ethyl‐3‐methylimidazolium cations (EMIM+) can interact with PbI2 to form a stable one‐dimensional (1D) perovskite of EMIMPbI3, and the trifluoroacetic acid anions (TFA−) can passivate the interface between the electron transfer layer and the perovskite layer. Unlike, the widely studied low dimensional perovskite capping layers or quasi‐2D configuration, the EMIM+ cations not only distribute on the top surface and inside the bulk phase, but also accumulate at the buried interface of 3D perovskite film, achieving a multi‐level distribution. The different defect states are successfully passivated by this distribution mode, leading to a significant decrease of non‐radiative recombination. As a result, the methyammonium lead iodide‐based PSCs with the EMIMTFA additive show an enhanced photovoltaic performance with a champion power conversion efficiency up to 22.14% and improved long‐term stability. This work demonstrates that the formation of multilevel low‐dimensional structure is a new strategy for the preparation of efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskites have attracted increasing attention for applications in perovskite solar cells (PSCs) and optoelectronics, including light‐emitting devices (LEDs). Cesium lead halide perovskites with tunable I/Br ratios and a band gap aligning with the sunlight region are promising candidates for PSCs. Although impressive progress has been made to improve device efficiency from the initial 2.9 % with low phase stability to over 20 % with high stability, there are still questions regarding the perovskite crystal growth mechanism, especially at low temperatures. In this Minireview, we summarize recent developments in using an organic matrix, including the addition and use of organic ions, polymers, and solvent molecules, for the crystallization of black phase inorganic perovskites at temperatures lower than the phase transition point. We also discuss possible mechanisms for this low‐temperature crystallization and their effect on the stability of black phase perovskites. We conclude with an outlook and perspective for further fabrication of large‐scale inorganic perovskites for optoelectronic applications. [ABSTRACT FROM AUTHOR]

The in situ formation of reduced dimensional perovskite layer via post‐synthesis ion exchange has been an effective way of passivating organic‐inorganic hybrid perovskites. In contrast, cesium ions in Cs‐based inorganic perovskite with strong ionic binding energy cannot exchange with those well‐known organic cations to form reduced dimensional perovskite. Herein, we demonstrate that tetrabutylammonium (TBA+) cation can intercalate into CsPbI3 to effectively substitute the Cs cation and to form one‐dimensional (1D) TBAPbI3 layer in the post‐synthesis TBAI treatment. Such TBA cation intercalation leads to in situ formation of TBAPbI3 protective layer to heal defects at the surface of inorganic CsPbI3 perovskite. The TBAPbI3‐CsPbI3 perovskite exhibited enhanced stability and lower defect density, and the corresponding perovskite solar cell devices achieved an improved efficiency up to 18.32 % compared to 15.85 % of the control one. [ABSTRACT FROM AUTHOR]

Tin dioxide (SnO 2 ) with high conductivity and low photocatalytic activity has been reported as one of the best candidates for highly efficient electron transport layer (ETL) in perovskite solar cell (PSC). The state-of-the-art SnO 2 layer is achieved by chemical bath deposition with tunable properties, while the commercial SnO 2 nanocrystals (NCs) with low tunability still face the necessity of further improvement. Here, a kind of highly crystallized Cl-doped SnO 2 NCs is reported that can form very stable aqueous dispersion with shelf life up to one year without any stabilizer, which can facilitate the fabrication of PSCs with satisfactory performance. Compared to the commercial SnO 2 NCs regardless of the extrinsic Cl-doping conditions, the intrinsic Cl-doped SnO 2 NCs effectively suppress the energy barrier and reduces the trap state density at the buried interface between perovskite and ETL. Consequently, stable PSCs based on such Cl-doped SnO 2 NCs achieve a champion efficiency up to ≈25% for small cell (0.085 cm 2 ) and ≈20% for mini-module (12.125 cm 2 ), indicating its potential as a promising candidate for ETL in high-performance perovskite photovoltaics., (© 2023 Wiley-VCH GmbH.)

Black-phase formamidinium lead iodide (FAPbI 3 ) with narrow bandgap and high thermal stability has emerged as the most promising candidate for highly efficient and stable perovskite photovoltaics. In order to overcome the intrinsic difficulty of black-phase crystallization and to eliminate the lead iodide (PbI 2 ) residue, most sequential deposition methods of FAPbI 3 -based perovskite will introduce external ions like methylammonium (MA + ), cesium (Cs + ), and bromide (Br - ) ions to the perovskite structure. Here a zwitterion-functionalized tin(IV) oxide (SnO 2 ) is introduced as the electron-transport layer (ETL) to induce the crystallization of high-quality black-phase FAPbI 3 . The SnO 2 ETL treated with the zwitterion of formamidine sulfinic acid (FSA) can help rearrange the stack direction, orientation, and distribution of residual PbI 2 in the perovskite layer, which reduces the side effect of the residual PbI 2 . Besides, the FSA functionalization also modifies SnO 2 ETL to suppress deep-level defects at the perovskite/SnO 2 interface. As a result, the FSA-FAPbI 3 -based perovskite solar cells (PSCs) exhibit an excellent power conversion efficiency of up to 24.1% with 1000 h long-term operational stability. These findings provide a new interface engineering strategy on the sequential fabrication of black-phase FAPbI 3 PSCs with improved optoelectronic performance., (© 2022 Wiley-VCH GmbH.)

Perovskite photovoltaics with the advantages of facile fabrication and high efficiency have been the rising star in the field for a decade. Methylammonium lead triiodide (MAPbI 3 ) was the first widely studied perovskite to initiate the boom of perovskite photovoltaics, but it was later considered thermodynamically instable for commercialization. Here, we demonstrate that simple cesium (Cs) doping without any complicated process can form a stable MA-based perovskite with a widened bandgap, which may broaden the application of MA-based perovskites in tandem solar cells. A record-high efficiency of ≤22% is thus achieved for a 1.6 eV bandgap perovskite solar cell. This work not only provides a new stable and efficient pure iodide candidate as a 1.6 eV bandgap perovskite but also reveals that Cs incorporation can help improve the efficiency and stability of MA-based perovskites.

Achieving reduced defect density and efficient charge carrier extraction plays a vital role for efficient and stable perovskite solar cells (PSCs). Over the course of technical development, it is desired to use one single material or approach to synergistically passivate defects and enhance the charge extraction. In this work, we developed an effective strategy for obtaining efficient and stable PSCs via incorporating quasi-monolayer two-dimensional WSe 2 into the MAPbI 3 perovskite layer. The addition of WSe 2 helps with the formation of perovskite film with higher quality and also passivates the Pb-related defects through Pb-Se coordination bonding. MAPbI 3 /WSe 2 shows a more matched energy-level alignment between the perovskite layer and hole transport layer for accelerated hole extraction. Consequently, the performances of PSCs significantly improved with power conversion efficiency increase from 19.2% to 21.2% after the incorporation of WSe 2 . Accordingly, the MAPbI 3 /WSe 2 -based PSCs exhibit well-improved photostability with suppression of Pb 0 defect formation.

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high-efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI 3 with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single-junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI 3 exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI 3 induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI 3 perovskite are presented. The development of various solution chemistry approaches for depositing high-quality phase-pure CsPbI 3 perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI 3 are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI 3 have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI 3 materials will further advance inorganic perovskite for highly stable and efficient photovoltaics., (© 2020 Wiley-VCH GmbH.)

5-Ammonium valeric acid iodide (AVAI) has been widely known as a stabilizer to enhance the stability of MAPbI 3 perovskite, but its role and function is still under exploration. The typical 2D perovskites of AVA 2 PbI 4 have been proposed as the capping layer for stabilization. Here, a novel AVA-MA mixed-cation perovskite of AVAMAPbI 4 is found to show a more even and compact coverage than the typical 2D perovskite of AVA 2 PbI 4 . A simple post-treatment on MAPbI 3 films by using AVAI isopropanol solution can fabricate such a mixed-cation 2D perovskite capping layer on the MAPbI 3 sample. This AVAMAPbI 4 capping layer effectively passivates surface defects of MAPbI 3 perovskite films and reduces the charge-carrier recombination, enabling AVAI-MAPbI 3 perovskite films to exhibit improved stability against thermal and moisture stress. Finally, the AVAI-MAPbI 3 -based perovskite solar cells also show an enhanced photovoltaic performance with a champion PCE up to 20.05% with enhanced stability.