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Compared to widely adopted low‐dimensional/three‐dimensional (LD/3D) heterostructure, functional organic cation based surface termination on perovskite can not only realize advantage of defect passivation but also prevent potential disadvantage of the heterostructure induced intercalation into 3D perovskite. However, it is still very challenging to controllably construct surface termination on organic–inorganic hybrid perovskite because the functional organic cations' substitution reaction is easy to form LD/3D heterostructure. Here, we report using a novel benzyltrimethylammonium (BTA) functional cation with rational designed steric hindrance to effectively surface terminate onto methylammonium lead triiodide (MAPbI3) perovskite, which is composed of the most unstable MA cations. The BTA cation is difficult to form a specific 1.5‐dimensional perovskite of BTA4Pb3I10 by cation substitution with MA cation, which then provides a wide processing window (around 10 minutes) for surface terminating on MAPbI3 films. Moreover, the BTAI surface terminated BTAI‐MAPbI3 shows better passivation effect than BTA4Pb3I10‐MAPbI3 heterojunction. Finally, BTAI surface terminated solar cell (0.085 cm2) and mini‐module (11.52 cm2) obtained the efficiencies of 22.03 % and 18.57 %, which are among the highest efficiencies for MAPbI3 based ones. [ABSTRACT FROM AUTHOR]

Secondary growth of CsPbI 3 inorganic perovskite film with an in-situ 3D-to-0D phase transformation induced by organic cation is demonstrated. Functional quaternary alkylammonium, benzyldodecyldimethylammonium (BDA+), could react with the surficial layers of CsPbI 3 film for targeted defect passivation. Such surface reconstruction as 0D/3D perovskites can greatly improve both film stability and photovoltaic performance. [Display omitted] Efficiency and stability are the main research focuses for perovskite solar cells. Inorganic perovskites like CsPbI 3 possess higher chemical stability than those with organic A-site cations, while they also exhibit higher defect density. Nonetheless, it is highly challenging to induce orderly secondary arrangement or reconstruction of inorganic perovskites with reduced defects because of their unique chemical properties. In this work, in-situ three-dimension-to-zero-dimension (3D-to-0D) phase transformation and surface reconstruction on CsPbI 3 film is achieved as induced by a functional organic cation, benzyldodecyldimethylammonium (BDA), a process of which that is similar to phase-transfer catalysis. With the help of BDABr salt treatment, 0D Cs 4 PbI 6 perovskites are secondarily formed along CsPbI 3 grain boundaries with Cs-related cationic defects passivated, yielding structures of higher stability. The BDA-CsPbI 3 films exhibit reduced non-radiative recombination and promoted charge transfer, leading to inorganic perovskite solar cells with a high power conversion efficiency of 20.63% and good operational stability. [ABSTRACT FROM AUTHOR]

Although pure formamidinium iodide perovskite (FAPbI3) possesses an optimal gap for photovoltaics, their poor phase stability limits the long-term operational stability of the devices. A promising approach to enhance their phase stability is to incorporate cesium into FAPbI3. However, state-of-the-art formamidinium–cesium (FA–Cs) iodide perovskites demonstrate much worse efficiency compared with FAPbI3, limited by the different crystallization dynamics of formamidinium and cesium, which result in poor composition homogeneity and high trap densities. We develop a novel strategy of crystallization decoupling processes of formamidinium and cesium via a sequential cesium incorporation approach. As such, we obtain highly reproducible, highly efficient and stable solar cells based on FA1–x Cs x PbI3 (x  = 0.05–0.16) films with uniform composition distribution in the nanoscale and low defect densities. We also revealed a new stabilization mechanism for Cs doping to stabilize FAPbI3, i.e. the incorporation of Cs into FAPbI3 significantly reduces the electron–phonon coupling strength to suppress ionic migration, thereby improving the stability of FA–Cs-based devices. [ABSTRACT FROM AUTHOR]

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]

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]

Recently, lead halide perovskite solar cells have become a promising next-generation photovoltaics candidate for large-scale application to realize low-cost renewable electricity generation. Although perovskite solar cells have tremendous advantages such as high photovoltaic performance, low cost and facile solution-based fabrication, the issues involving lead could be one of the main obstacles for its commercialization and large-scale applications. Lead has been widely used in photovoltaics industry, yielding its environmental and health issues of vital importance because of the widespread application of photovoltaics. When the solar cell panels especially perovskite solar cells are damaged, lead would possibly leak into the surrounding environment, causing air, soil and groundwater contamination. Therefore, lots of research efforts have been put into evaluating the lead toxicity and potential leakage issues, as well as studying the encapsulation of lead to deal with leakage issue during fire hazard and precipitation in photovoltaics. In this review, we summarize the latest progress on investigating the lead safety issue on photovoltaics, especially lead halide perovskite solar cells, and the corresponding solutions. We also outlook the future development towards solving the lead safety issues from different aspects. [Display omitted] • Lead in perovskite photovoltaics poses potential risks to human health and ecosystem. • Water-soluble and bioavailable lead that leaks from damaged PSCs is dangerous. • Fail-safe encapsulation and safe device configuration are developed for lead leakage. • End-of-life PSCs as hazardous wastes should be taken into account before commercialization. [ABSTRACT FROM AUTHOR]