Passivation Mechanism in Highly Luminescent Nanocomposite‐Based CH₃NH₃PbBr₃ Perovskite Nanocrystals

Water exposure significantly impacts the structure and photoluminescence (PL) of metal halide perovskites. However, humid conditions can enable the in situ synthesis of methylammonium lead bromide (MAPbBr₃) perovskite nanocrystals (NCs) within a nickel acetate matrix, achieving PL quantum yields (PLQY) of up to 80%. The water-driven formation and transformation of MAPbBr₃ is presented, highlighting the crucial role of acetate. Comprehensive optical and structural analyses reveal that low relative humidity (RH < 20%) favors the formation of non-emissive MA₄PbBr₆ (0D) and hydroxide species (PbBrOH, OH^-) . Exposure to higher RH induces a structural reorganization from 0D MA₄PbBr₆ to 3D MAPbBr₃ via a MABr-stripping mechanism, forming NCs with enhanced PLQY. Removing ambient humidity quenches PL, a process that is reversible due to hydroxide-mediated reactions controlled by dual acid-base nature of the acetic acid/acetate system. Unlike previous reports, the findings reveal that hydroxide ions reversibly bind to NCs, passivating traps and improving stability. Acetate's basicity plays a critical role in generating OH^-, promoting the passivation, stability, and enhanced optical properties of the perovskite nanocomposites.