Pure FAPbI₃ (where FA is formamidinium) based perovskite solar cells (PSCs) have drawn tremendous attention because of their exceptional photovoltaic properties, although long-term stability is still a big challenge. Molecular tailoring is one of the practical approaches to enhancing the stability of FAPbI₃ by passivating the film defects; however, deep understanding of how the molecular configuration affects the adjacent layer in FAPbI₃ PSCs is urgently needed. Herein, we report a strategy of molecularly tailoring the FAPbI₃/SnO₂ interface by employing three Li salts by varying the anion configurations (CO₃^2–, C₂O₄^2–, and HCOO^–). When C–O and C=O groups are in optimal configuration, they will form the strongest bonds with uncoordinated Sn⁴⁺ and FA⁺, respectively, which can increase the formation energy of V_FA defects, release the residual stress of the FAPbI₃ lattice, facilitate the charge transport at the FAPbI₃/SnO₂ interface, and improve the stability of the PSC. Consequently, we obtained a champion device with a power conversion efficiency of 23.5%, and the unencapsulated device can maintain good stability under continuous light illumination.