In situ observation of crystallization process and cathodoluminescence origin in Cs–Pb–Br perovskite by environmental SEM

Water vapor plays a pivotal role in both the crystallization of CsPbBr-based perovskites and the operational stability of devices incorporating these materials. However, previous studies on this topic have been limited to indirect ex situ observation. Here, we utilize in situ environmental scanning electron microscopy (ESEM) to directly monitor the dynamic growth of CsPbBr-based perovskite at a water vapor pressure of 609 Pa (equivalent to 75% relative humidity at 4 °C) under a controlled gas atmosphere. Our real-time in situ observation captures the concomitant and direct crystallization of CsPb 2 Br 5 and CsPbBr 3 , challenging the conventional phase-transition-mediated formation pathway. Furthermore, we demonstrate that the dual emission in the mixture of CsPbBr 3 and CsPb 2 Br 5 originates from distinct emissive centers, in contrast to the self-absorption and re-emission mechanism in rod-like CsPbBr 3 . These findings offer direct evidence of water-vapor-mediated crystallization and their impact on material performance, thereby paving the way for both the design of environmentally stable perovskite-based devices and future ESEM investigations into complex multiphase processes.