Surface Chemical Conversion of Residual PbI₂ Enables Efficient and Stable Perovskite Solar Cells by 1,3‐Diphenyl‐benzimidazolium Iodide Treatment

Abstract Perovskite films have long been plagued by defects, mainly located at grain boundaries, leading to device degradation, especially the effects of residual PbI₂. As effective grain boundary passivators, organic ammonium salts are thus extensively investigated. Here, the study introduces a nitrogen heterocyclic molecule, 1,3‐diphenyl‐benzimidazole iodide (DBI), for the post‐treatment of the perovskite film to construct robust one‐dimensional (1D)/three‐dimensional (3D) perovskite structure. The 1D structure of DBPbI₃ formed from the interaction between residual PbI₂ and DBI enables the repair of local defects and enhancement of film stability. Concurrently, the double conjugated benzene and imidazole rings synergistically facilitate charge transfer and promote the optimization of energy levels, thereby boosting charge extraction. The corresponding 1D/3D perovskite solar cells (PSCs) yielded a high efficiency of 25.04% with excellent photo/thermal stabilities. The corresponding perovskite solar module exhibited an efficiency of 21.04% with a total area of 36 cm² with robust long‐term stability.