Role of Water in the Stability and Efficiency of Ionic Liquid-Based Perovskite Solar Cells

The fabrication of perovskite solar cells (PSCs) in ambient air can accelerate their industrialization. However, moisture causes severe decomposition of the perovskite materials, limiting device efficiency. Here, we demonstrate that, compared to traditional <i>N</i>,<i>N</i>-dimethylformamide-based precursor solutions, the ionic liquid methylammonium acetate (MAAc) system forms a protective layer on the perovskite surface due to the C═O···Pb and N-H···I interactions between MAAc and PbI₆^4-, which effectively prevents direct contact between the perovskite components and water. Moreover, we show that a certain level of humidity weakens the interactions between MAAc and PbI₆^4-, promoting the crystallization process and resulting in films with fewer defects. PSCs based on MAAc achieved a power conversion efficiency of 20.73% under optimal water content conditions, and the unencapsulated devices maintained >83% of their initial efficiency after >1300 h in ambient air.