Atomistic Mechanism of Defect Self-Passivation in Metal Halide Perovskites
Pingzhi Zhang, Elizabeth Stippell, Yanhong Chen, Xiaolong Du, Zhufeng Hou, Oleg V. Prezhdo, Wei Li
Abstract
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 (H i –1 ) and bromine (Br i +1 ) interstitials in all-inorganic CsPbBr 3 perovskites. The Br i +1 defect forms a Br 3 – trimer that creates a deep trap state, causing rapid charge recombination within tens of nanoseconds. The isolated H i –1 defect, adopting a Pb–H–Pb bridging configuration, accelerates nonradiative recombination by enhancing thermal disorder and nonadiabatic coupling. However, the Br i +1 /H i –1 complex disrupts the Br 3 – 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.