In situ optical techniques for perovskite crystallization

Solution-processed perovskites have garnered significant attention in photovoltaics owing to their rapid improvement in power conversion efficiency. These advances are largely driven by enhanced film quality enabled by crystallization regulation. However, the roles of various optimization strategies during crystallization remain actively debated, in part because of the lack of reliable approaches to probe the complex, rapid crystallization process. Recently, an increasing number of studies have employed in situ optical techniques to monitor perovskite crystallization. In this review, we provide a systematic overview of the development and application of in situ optical techniques for studying perovskite crystallization. We focus on experimental design considerations, analytical frameworks for correlating time-resolved optical signals with crystallization processes, and representative applications ranging from mechanistic understanding to process optimization. This work aims to offer a comprehensive technical guide for researchers seeking to employ in situ optical methods to investigate perovskite crystallization.