Violet/ultraviolet light-induced depassivation in halide perovskite solar cells

Ammonium-terminated ligands, used directly or in the form of two-dimensional perovskites, are leading defect-passivating agents for halide perovskites and have significantly contributed to achieving the highest efficiencies across diverse perovskite solar cells. However, even these state-of-the-art perovskite solar cells suffer from rapid degradation during operation, raising concerns over the durability of the passivation. In this work, we unveil a mechanism of violet/ultraviolet light-induced depassivation that universally affects ammonium ligands. Exposure to violet/ultraviolet light triggers a charge-carrier transition from ammonium-terminated ligands to the halide perovskite framework, leading to the deprotonation of the ammonium group. This deprotonation disrupts the ammonium-perovskite interaction, resulting in depassivated perovskites susceptible to photodegradation, as validated in cells with 26.44% efficiency. This updated understanding surpasses existing ligand failure models limited to thermal intolerance and iodide oxidation, highlighting an essential perspective for enhancing the long-term efficacy of passivating agents.