Rational Design of Additive with Suitable Functional Groups Toward High‐Quality FA0.75MA0.25SnI3 Films and Solar Cells

Stability and efficiency issues are closely related with poor perovskite film quality in perovskite solar cells (PSCs). Herein, 2‐aminophenol (C 6 H 7 NO) and 2‐amino‐4‐fluorophenol (C 6 H 6 FNO) are introduced to improve film quality of FA 0.75 MA 0.25 SnI 3 , both of which consist of —NH 2 and —OH groups, and the latter also contains —F group. The experimental and theoretical analyses show both —NH 2 and —OH groups interact with I of the SnI 6 4− octahedron via hydrogen bond and fluorinated group with low surface energy causes spontaneous migration of C 6 H 6 FNO to solution–air surface and induces initial crystal nucleation and growth from surface, both of which contribute to improved film morphology and crystallinity and suppressed Sn 2+ oxidation via reducing defect‐state density and nonradiative recombination. The F atom of C 6 H 6 FNO facing outward protects FA 0.75 MA 0.25 SnI 3 from water penetration due to its hydrophobic feature. The C 6 H 6 FNO‐doped PSC acquires a champion efficiency of 9.50% and a long‐term stability of >800 h (80% efficiency remained in N 2 ).