Although metal halide perovskites are increasingly popular for the next generation of efficient photovoltaic devices, the inevitable defects from the preparation process have become the notorious barrier to further improvement of performance, which increases non‐radiative recombination and lowers the power conversion efficiency of solar cells. Surface passivation strategies have been affirmed as one of the most practical approaches to suppress these defects. Therefore, it is necessary to have a detailed review on the surface passivation to reveal the improvements of the devices. Herein, the mechanism and recent advances of surface passivation have been systematically summarized with respect to various passivation approaches, including the Lewis acid–base, the low‐dimensional perovskite, inorganic molecules, and polymers. Finally, the review also offers the research trend and prospects of surface passivation.

Flexible perovskite solar cells (f‐PSCs) as a promising power source have grabbed surging attention from academia and industry specialists by integrating with different wearable and portable electronics. With the development of low‐temperature solution preparation technology and the application of different engineering strategies, the power conversion efficiency of f‐PSCs has approached 24%. Due to the inherent properties and application scenarios of f‐PSCs, the study of strain in these devices is recognized as one of the key factors in obtaining ideal devices and promoting commercialization. The strains mainly from the change of bond and lattice volume can promote phase transformation, induce decomposition of perovskite film, decrease mechanical stability, etc. However, the effect of strain on the performance of f‐PSCs has not been systematically summarized yet. Herein, the sources of strain, evaluation methods, impacts on f‐PSCs, and the engineering strategies to modulate strain are summarized. Furthermore, the problems and future challenges in this regard are raised, and solutions and outlooks are offered. This review is dedicated to summarizing and enhancing the research into the strain of f‐PSCs to provide some new insights that can further improve the optoelectronic performance and stability of flexible devices.