Template-Assisted Synthesis of CsPbBr₃ Nanocrystals with a Humidity-Induced Fluorescent Response: Mechanism and Sensing Applications

Metal halide perovskites present a vast potential for the development of cutting-edge optoelectronic devices. However, their vulnerability to environmental factors, especially humidity, leads to widely acknowledged stability challenges. On the other hand, such a high sensitivity to water in the atmosphere is an opportunity for humidity sensing applications. In this study, we synthesize lead halide perovskite CsPbBr₃ nanocrystals within CaCO₃ templates with a porous structure (CsPbBr₃@CaCO₃) and investigate the mechanisms underlying the fluorescence response to changes in relative humidity. The reversible transformation of CsPbBr₃ to CsPb₂Br₅ leads to the removal of surface defects, which results in an increase in photoluminescence intensity, thereby enabling the determination of ambient relative humidity levels. Moreover, we investigated a mechanism of CsPbBr₃ degradation driven by CO₂ in humid environments underlying the perovskite transformations. As a proof of concept, we developed a fluorescence-based humidity sensor based on CsPbBr₃@CaCO₃ with rapid response and recovery times, maintaining performance across multiple cycles.