Molecularly Tailored SnO₂/Perovskite Interface Enabling Efficient and Stable FAPbI₃ Solar Cells

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 (CO32–, C2O42–, 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 VFA 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.