Chemical Reaction of FA Cations Enables Efficient and Stable Perovskite Solar Cells

Abstract Organometal halide perovskite solar cells (PSCs) have received great attention owing to a rapid increase in power conversion efficiency (PCE) over the last decade. However, the deficit of long‐term stability is a major obstacle to the implementation of PSCs in commercialization. The defects in perovskite films are considered as one of the primary causes. To address this issue, isocyanic acid (HNCO) is introduced as an additive into the perovskite film, in which the added molecules form covalent bonds with FA cations via a chemical reaction. This chemical reaction gives rise to an efficient passivation on the perovskite film, resulting in an improved film quality, a suppressed non‐radiation recombination, a facilitated carrier transport, and optimization of energy band levels. As a result, the HNCO‐based PSCs achieve a high PCE of 24.41% with excellent storage stability both in an inert atmosphere and in air. Different from conventional passivation methods based on coordination effects, this work presents an alternative chemical reaction for defect passivation, which opens an avenue toward defect‐mitigated PSCs showing enhanced performance and stability.