Electron-withdrawing organic ligand for high-efficiency all-perovskite tandem solar cells

Tin–lead mixed perovskite-based tandem solar cells show promise. However, the inherent oxidation of tin remains a challenge for achieving high power conversion efficiency and device stability. In this study, we present an approach to address this challenge by developing an electron-withdrawing chloromethyl phosphonic acid ligand based on the substituent effect, designed to mitigate tin oxidation in tin–lead mixed perovskite materials. The introduction of this electron-withdrawing ligand improves the redox potential of the tin adduct. Furthermore, it leads to a substantial increase in the ionization potential of the perovskite structure. Through comparative analysis with conventional coordinating molecules, we reveal that the electron-withdrawing ligand is more effective in suppressing tin oxidation and reducing the defect density within the tin-based perovskite film. Using our approach, we demonstrate certified efficiency of 26.96% for all-perovskite tandem solar cells.