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.