Strain Regulation via Pseudo Halide‐Based Ionic Liquid toward Efficient and Stable α‐FAPbI3 Inverted Perovskite Solar Cells

Abstract Inverted (p‐i‐n) perovskite solar cells have drawn great attention due to their outstanding stability and low‐temperature processibility. However, their power conversion efficiency (PCE) still lags behind conventional (n‐i‐p) devices mainly due to the lack of strategies to stabilize α ‐FAPbI 3 without changing the bandgap. In this work, a facile and effective strategy is reported to regulate the residual strain via pseudo halide‐based ionic liquids incorporation to stabilize α ‐FAPbI 3 perovskite in inverted perovskite solar cells (PVSCs). The employment of methylamine formate (MAFa) ionic liquid enables a homogenously stronger compressive strain to restrain the transition of shared‐corner PbI 6 octahedron into shared‐face δ ‐FAPbI 3 , as well as affecting the dynamic behavior of carriers and defects to achieve a record PCE (24.08%) among the reported inverted FAPbI 3 perovskite solar cells up to now. In addition, the MAFa incorporation results in enhanced device stability, unencapsulated PVSC retains over 90% of its initial efficiency after stored in ambient environment (RH:30 ± 5%) for 1000 h. This work provides an efficient strategy to realize efficient and stable α ‐FAPbI 3 based inverted PVSCs to further catch up with the conventional ones.