Regioselective Multisite Atomic-Chlorine Passivation Enables Efficient and Stable Perovskite Solar Cells

Passivating defects using organic halide salts, especially chlorides, is an effective method to improve power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) arising from the stronger Pb-Cl bonding than Pb-I and Pb-Br bonding. However, Cl- anions with a small radius are prone to incorporation into the perovskite lattice that distorts the lead halide octahedron, degrading the photovoltaic performance. Here, we substitute atomic-Cl-containing organic molecules for widely used ionic-Cl salts, which not only retain the efficient passivation by Cl but also prevent the incorporation of Cl into the bulk lattice, benefiting from the strong covalent bonding between Cl atoms and organic frameworks. We find that only when the distance of Cl atoms in single molecules matches well with the distance of halide ions in perovskites can such a configuration maximize the defect passivation. We thereby optimize the molecular configuration to enable multiple Cl atoms in an optimal spatial position to maximize their binding with surface defects. The resulting PSCs achieve a certified PCE of 25.02%, among the highest PCEs for PSCs, and retain 90% of their initial PCE after 500 h of continuous operation.

Automated summary

Passivation of defects in perovskite solar cells using organic halide salts, particularly chlorides, is an effective method for improving power conversion efficiencies. However, the incorporation of chloride ions into the perovskite lattice can degrade the photovoltaic performance. In this study, we replace ionic chloride salts with atomic-Cl-containing organic molecules, which both retain efficient passivation and prevent chloride incorporation. By optimizing the molecular configuration, the resulting perovskite solar cells achieve a certified power conversion efficiency of 25.02% and maintain 90% of their initial efficiency after 500 hours of continuous operation.