Surface Halide Manipulation for Stable Inorganic Perovskite Solar Cells and Modules

Abstract Iodine‐rich inorganic perovskites possessing desirable bandgaps as well as high thermal and chemical stability are facing serious issues of low polymorphic stability, whereas chlorine‐rich inorganic perovskites hold outstanding thermodynamic stability but suffer from low efficiency. Here, we develop function‐gradient inorganic perovskites adopting a surface halide substitution strategy, where a stable chlorine‐rich skin protects efficient iodine‐rich layers, incorporating high stability of chlorine‐rich perovskites with high efficiency of iodine‐rich perovskites. This strategy simultaneously passivates surface defects and stabilizes the photoactive polymorphs of perovskite, leading to a power conversion efficiency of 21.2% for unit cells (0.16 cm 2 ) and 19.2% for solar modules (23.9 cm 2 ). Notably, the compositional gradient mitigates light‐induced ion migration and enhances resistance to environmental erosion. Thus, our devices exhibit negligible efficiency loss after 1000 h storage in air and 3200 h operation under continuous 1‐sun illumination at 40 °C, representing the most stable wide‐bandgap perovskite solar cells reported to date.