Water-induced degradation mechanism of metal halide perovskite nanocrystals

Metal halide perovskites have emerged as promising materials for diverse optoelectronic devices due to their superior optical properties. However, their instability in moisture hinders practical use, highlighting the need for an atomic-scale understanding of their degradation mechanism. Here, we uncover water-induced degradation pathways of perovskite nanocrystals using in situ liquid-phase transmission electron microscopy, revealing a distinctive dissolution process driven by ion solvation. The dissolution rates vary according to crystallographic direction, influenced by the surface polarity of different crystal facets, leading to a shape transformation from nanocubes to nanospheres. These observations are further supported by in situ X-ray scattering analysis. Notably, surface passivation of perovskite nanocrystals with halide ion pair ligands provides effective edge passivation, alters the degradation trajectories by preserving their cubic shape during the initial stages, and significantly reduces the overall degradation rate. This study offers critical insights into the water-induced degradation mechanisms of perovskite nanocrystals, potentially guiding strategies to enhance their stability.