Surface-driven phase transition of Cs₄PbBr₆ nanocrystals in droplets: a humidity-responsive mechanism and its...

Zero-dimensional perovskite Cs₄PbBr₆ nanocrystals have attracted considerable attention for their potential in optoelectronic and sensing applications due to their excellent optoelectronic properties and environmental stability. However, their non-emissive property has limited their development in luminescent applications. Fortunately, the reversible phase transition between Cs₄PbBr₆ and CsPbBr₃ nanocrystals provides a promising strategy to address this limitation. This study investigates the phase transition mechanism induced by the micro-environment factors, with a particular focus on the evolution of optical properties. Small droplets of Cs₄PbBr₆ nanocrystals were exposed to air, and real-time monitoring of their color changes and photoluminescent emission characteristics was conducted. The results reveal that the large surface area of the droplet facilitates solvent evaporation, which accelerates the phase transition of Cs₄PbBr₆ nanocrystals, leading to a significant enhancement in photoluminescent brightness. By quantitatively correlating environmental humidity with the phase conversion rate, this work highlights the critical role of humidity in modulating the conversion kinetics. Furthermore, the study systematically explores the mechanism of tuning the photoluminescent emission peak by adjusting the surface ligands, which enables the development of an environment-responsive, color-changing optical device based on droplet dynamics.