Cationic Lattice Coupling Enables Efficient FAPbI 3 Perovskite Solar Cells

FAPbI 3 is an ideal recipe for single‐junction perovskite solar cells owing to the ideal bandgap, exceptional optical absorption, and weak exciton binding energy. However, charge transport and extraction in polycrystalline FAPbI 3 films are always hindered by structural and energetic mismatches at the top surface and grain boundaries. In this work, we enhance the cation‐lattice coupling by controlling the competitive interaction of formamidinium (FA + ) and isopropyltriphenylphosphonium (TPP + ) with octahedron lattice scaffolds (PbI 6 4− ) to improve carrier behaviors of the FAPbI 3 film. The microscale chemical, electrical, and photophysical mappings are comprehensively investigated to demonstrate the structural and energetic matching of the interfacial heterostructure. By the effective cation‐lattice coupling, the champion mesoporous solar cells achieve a champion power conversion efficiency (PCE) of 25.60%, with a promising photovoltage of 1.18 V and fill factor of 84.68%. Hysteresis issues of the mesoporous devices were alleviated, and the device stability is extended to 1800 h in conditions at 85% of the initial efficiency.