Fluorinated Methylammonium Cation Containing Perovskite Solar Cells With Over 25% Power Conversion Efficiency

High‐performance perovskite solar cells (PSCs) are typically made using formamidinium CH(NH 2 ) 2 + (FA + ), cesium Cs +, and the thermally unstable methylammonium CH 3 NH 3 + (MA + ) monovalent cations. Excluding unstable MA + leads to perovskite compositions with increased stabilities and decreased bandgaps. This study introduces a novel approach using a simple fluorinated methylammonium CFH 2 NH 3 + (FMA + ) cation capable of doping into the perovskite‐framework. With the addition of an optimized quantity of 0.8 mol% FMAI, perovskite compositions are thermally more stable, enabling more reproducible n‐i‐p PSC performance with a power conversion efficiency of 25.67%. The PSCs exhibit operational stability over 2000 h. Spectroscopic and computational analyses suggest that FMAI may play a dual role as a fluorinated ammonium additive capable of doping into the perovskite and as a chemically non‐innocent precursor producing passivating species.