Atomistic Mechanism of Defect Self-Passivation in Metal Halide Perovskites

Passivating detrimental defects is essential for improving perovskite solar cells (PSCs) performance. While hydrogen interstitials are often considered harmful, their role in defect passivation remains unclear. Using ab initio nonadiabatic molecular dynamics, we uncover a self-passivation mechanism between hydrogen (Hi-1) and bromine (Bri+1) interstitials in all-inorganic CsPbBr3 perovskites. The Bri+1 defect forms a Br3- trimer that creates a deep trap state, causing rapid charge recombination within tens of nanoseconds. The isolated Hi-1 defect, adopting a Pb-H-Pb bridging configuration, accelerates nonradiative recombination by enhancing thermal disorder and nonadiabatic coupling. However, the Bri+1/Hi-1 complex disrupts the Br3- trimer and restores the local coordination, eliminating the deep trap and extending the carrier lifetime to tens of microseconds. The improvement arises from symmetry breaking, vibrational anharmonicity, and longitudinal Br displacements that localize the band edge states. Our results reveal an intrinsic self-passivation pathway and provide microscopic insight into hydrogen-assisted stability in PSCs.