Water-Triggered Transformation of Ligand-Free Lead Halide Perovskite Nanocrystal-Embedded Pb(OH)Br with Ultrahigh Stability

Lead halide perovskite (LHP) nanomaterials have attracted tremendous attention owing to their remarkable optoelectronic properties. However, they are extremely unstable under moist environments, high temperatures, and light illumination due to their intrinsic structural lability, which has been the critical unsolved problem for practical applications. To address this issue, we propose a facile and environmentally friendly ligand-free approach to design and synthesize rod-like CsPb₂Br₅-embedded Pb(OH)Br with excellent stability under various harsh environments such as soaking in water, heating, and ultraviolet (UV) illumination. Plate-like CsPbBr₃- and Cs₄PbBr₆-embedded Pb(OH)Br powders are first formed by evaporating the solvent in a dispersion of ethanol (or methanol, isopropanol), Cs₂CO₃, and PbBr₂. Upon soaking in water, the plate-like sample undergoes phase transformation from CsPbBr₃ and Cs₄PbBr₆ to CsPb₂Br₅ and shape conversion from nanoplate to a microrod, leading to the formation of rod-like CsPb₂Br₅-embedded Pb(OH)Br. The stable Pb(OH)Br coating effectively prevents the luminescent CsPb₂Br₅ nanocrystals from reacting with water, leading to extremely high aqueous stability of the CsPb₂Br₅-embedded Pb(OH)Br. The photoluminescence (PL) intensity of the representative CsPb₂Br₅-embedded Pb(OH)Br sample can maintain 92.2% of the initial PL intensity value even after soaking in room-temperature water for 165 days; in the meantime, the phase and shape are preserved. The typical sample also shows outstanding stability under hot water, UV illumination, and annealing conditions. The ultrahigh aqueous stability, thermal stability, and photostability of the CsPb₂Br₅-embedded Pb(OH)Br nanomaterials suggest an effective, facile, and environmentally friendly technique to grow perovskite-based nanomaterials for promising practical applications in the optoelectronic field.