In‐Situ Photoluminescence for Perovskite Crystallization: Bridging Mechanistic Insights and Device Engineering Control

Metal halide perovskite solar cells have reached record efficiencies of over 27% within two decades, yet their photovoltaic performance and operational stability remain highly sensitive to the nucleation and crystallization of perovskite films. Conventional characterization techniques capture only static states, overlooking the transient crystallization processes that govern perovskite film quality. In-situ photoluminescence (PL) spectroscopy has emerged as a powerful, non-invasive (under moderate laser illumination) tool for real-time tracking of nucleation, crystal growth, phase transitions, and defect evolution in metal halide perovskites. This review summarizes recent advances in in-situ PL instrumentation, ranging from single-point and multi-probe configurations to multi-channel imaging approaches, and highlights the use of in-situ PL in elucidating crystallization pathways across pure, mixed-cation, and mixed-halide perovskites. We further discuss how in-situ PL reveals the impact of antisolvents, additives, interfacial engineering, and processing conditions on perovskite film formation, and highlight the importance of integrating in-situ PL with complementary in-situ and ex-situ techniques to achieve a comprehensive understanding of perovskite nucleation and crystallization mechanisms. Looking ahead, coupling in-situ PL with machine learning offers an intelligent route toward predictive process control and closed-loop optimization, accelerating the scalable manufacturing with high-quality perovskite films and commercialization of perovskite photovoltaics from lab to fab.