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.