Perovskite solar cells (PSCs) show excellent power conversion efficiencies, long carrier diffusion lengths and low recombination rates. This encourages a view that intragrain defects are electronically benign with little impact on device performance. Here we vary methylammonium (MA)/ formamidinium (FA) composition in MA1-xFAxPbI3 (x=0-1), and compare the structure and density of intragrain planar defects with the device performance, otherwise keeping the device nominally the same. We find charge carrier lifetime, open-circuit voltage-deficit, and current-voltage hysteresis correlate with the density and structure of {111}c planar defects (x=0.5-1) and {112}t twin boundaries (x=0-0.1). The best performance parameters are found when essentially no intragrain planar defects are evident (x=0.2).Similarly, reducing the density of {111}c planar defects using , also improved performance. These observations suggest that intragrain defect control can provide an important route for improving PSCs' performance, in addition to wellestablished parameters, such as grain boundaries and heterojunction interfaces.
The commercialization of perovskite photovoltaic technology is dependent on the development of high‐efficiency, stable, and large‐area solar modules. Despite the rapid rise in efficiencies of laboratory‐scale perovskite solar cells (PSCs), there is still a big gap in the transition from small‐area devices to large‐area perovskite solar modules (PSMs). Herein, recent progresses on scaling‐up PSMs are reviewed: first, multifarious scalable preparation methods, solvent engineering, and corresponding morphology control strategies for large‐area homogeneous perovskite films are summarized. Various charge carrier transport materials, electrode materials, and their scaling methods for high‐efficiency and stable PSMs are then outlined and the device structure design of PSMs is discussed. Finally, the current strategies for optimizing the environmental stability of devices are highlighted, and packaging for reducing lead leakage during operation is discussed.
The sol−gel method exhibits the advantages of simple preparation, low cost, and easy control of stoichiometry, which is widely used for the fabrication of BiFeO 3 -based perovskite ferroelectric films. However, because of the volatilization of organic solvents during the annealing process, voids will inevitably be formed. In this article, high-quality BiFeO 3 -based thin films (with or without La doping) were prepared by physical vapor deposition methods, namely as magnetron sputtering and pulsed laser deposition, respectively. The deposition procedure of gas particles and the annealing process of thin films could be performed simultaneously by pulsed laser deposition, while is impossible by magnetron sputtering. As a result, pulsed laser deposition is considered as a more suitable approach for ferroelectric thin films fabrication. Besides the adoption of the pulsed laser deposition approach for the fabrication of highly dense thin films, the integration of electron transport layers (SnO 2 , TiO 2 , and ZnO) and La 3+ doping is demonstrated to help to alleviate the problem of high electron−hole recombination rate, which then increases the photovoltaic conversion efficiency. In this contribution, planar solar cells, which were fabricated by the pulsed laser deposition approach with TiO 2 as the electron transport layer, exhibited the best efficiency of 5.62% with a reduced leakage current density. This work provides a promising paradigm for the further development of high-performance BiFeO 3 -based perovskite solar cells through the modulation of fabrication process and introduction of electron transport layers.
A deep understanding of the fine structure at the atomic scale of halide perovskite materials has been limited by their sensitivity to the electron beam that is widely used for structural characterization. The sensitivity of a γ-CsPbIBr 2 perovskite thin film under electron beam irradiation is revealed by scanning transmission electron microscopy (STEM) through a universal large-range electron dose measurement, which is based on discrete single-electron events in the STEM mode. Our research indicates that the γ-CsPbIBr 2 thin film undergoes structural changes with increasing electron overall dose (e − •Å −2 ) rather than dose rate (e − •Å −2 •s −1 ), which suggests that overall dose is the key operative parameter. The electron beam-induced structural evolution of γ-CsPbIBr 2 is monitored by fine control of the electron beam dose, together with the analysis of high-resolution (S)TEM, diffraction, and energy-dispersive X-ray spectroscopy. Our results show that the γ-CsPbIBr 2 phase first forms an intermediate phase [e.g., CsPb (1−x) (IBr) (3−y) ] with a superstructure of ordered vacancies in the pristine unit cell, while a fraction of Pb 2+ is reduced to Pb 0 . As the electron dose increases, Pb nanoparticles precipitate, while the remaining framework forms the Cs 2 IBr phase, accompanied by some amorphization. This work provides guidelines to minimize electron beam irradiation artifacts for atomic-resolution imaging on CsPbIBr 2 thin films.
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