Advances in Single‐Halogen Wide‐Bandgap Perovskite Solar Cells

Abstract Wide‐bandgap (WBG) (E_g ≥ 1.65 eV) perovskite solar cells (PSCs) made from mixed‐halide strategy experience severe photo‐induced halide segregation, leading to detrimental effects on the long‐term operational stability. Developing single‐halogen WBG perovskites can be the fundamental solution to prevent halide segregation. In this review, the recent advances in single‐halogen WBG PSCs, focusing on the cesium (Cs)‐based pure‐iodide (I) perovskite and all the pure‐bromine (Br) perovskite species is summarized. A detailed discussion is conducted on the crystallization dynamics of different perovskite systems. The key challenge for all single‐halogen WBG PSCs is the huge energy loss due to inferior interfacial energy level alignment and high defect density in perovskite films, which greatly hinders efficiency improvement. To this end, it is systematically discuss optimization strategies, including regulating crystallization, passivating defects, achieving aligned energy levels, and eliminating interfacial microstrain, to enhance the photovoltaic performance of solar cells. Furthermore, it is highlighted that Cs‐based pure‐I WBG perovskites encounter significant stability issue due to their low structural tolerance factor, warranting substantial attention. Finally, perspectives are outlined to suggest ways to further advance the development and application of single‐halogen WBG PSCs.