The quality of the perovskite film is crucial to the technological breakthrough of perovskite solar cells (PSCs). The two‐step method can facilitate the formation of a perovskite film with high quality and reproducibility. Many milestones have been made in the development of hybrid lead halide PSCs by using the two‐step method, which has a significant impact on their practical application. Herein, the reaction mechanism of the two‐step method including two‐step immersion method and two‐step spin coating method is summarized. The strategies such as component engineering, solvent engineering, and additive engineering of the two‐step method in preparing high‐quality films are introduced systematically and in detail. In addition, current issues of the two‐step method and its applications in lead‐free PSCs, all‐inorganic PSCs, large areas, and tandems are introduced and some suggestions are put forward for future research.

Pure FAPbI3 (where FA is formamidinium) based perovskite solar cells (PSCs) have drawn tremendous attention because of their exceptional photovoltaic properties, although long-term stability is still a big challenge. Molecular tailoring is one of the practical approaches to enhancing the stability of FAPbI3 by passivating the film defects; however, deep understanding of how the molecular configuration affects the adjacent layer in FAPbI3 PSCs is urgently needed. Herein, we report a strategy of molecularly tailoring the FAPbI3/SnO2 interface by employing three Li salts by varying the anion configurations (CO3 2–, C2O4 2–, and HCOO–). When C–O and C=O groups are in optimal configuration, they will form the strongest bonds with uncoordinated Sn4+ and FA+, respectively, which can increase the formation energy of VFA defects, release the residual stress of the FAPbI3 lattice, facilitate the charge transport at the FAPbI3/SnO2 interface, and improve the stability of the PSC. Consequently, we obtained a champion device with a power conversion efficiency of 23.5%, and the unencapsulated device can maintain good stability under continuous light illumination.

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Although perovskite solar cells have achieved great breakthroughs in photoelectric conversion efficiency (PCE), some challenges still need to be addressed before commercialization. Lead leakage is harmful to the environment and many methods are developed to prevent lead leakage; among them, chemical adsorption has proved to be an effective way. Herein, a simple and low‐cost strategy that can enhance the device performance and mitigate the lead leakage by applying l‐phenylalanine in the interface of NiOx/perovskite is reported. The results show that this strategy can improve the morphology and conductivity of the NiOx film, optimize the NiOx/perovskite interface energy level, resulting in an efficient and stable device with a PCE of 19.0%. Furthermore, the interface modification improves the stability of the perovskite film through strong interaction with the perovskite, inhibits the decomposition of the film in water, slows down the process of lead leakage, and protects the environment from lead pollution. The devices maintain 86% initial efficiency for 200 h maximum power point measurement and 94% for 2100 h under nitrogen.