Revealing Perovskite Crystallization and Degradation With Grazing‐Incidence Wide‐Angle X‐Ray Scattering: Kinetics, Phase Analysis and Modulation Strategies

ABSTRACT Perovskite solar cells have achieved power conversion efficiencies exceeding 27%, positioning them among the most promising next‐generation photovoltaic technologies. However, the formation of high‐quality perovskite films remains challenging due to complex crystallization processes involving transient intermediate phases, composition‐dependent phase transitions, and depth‐dependent structural heterogeneity. Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) has emerged as an indispensable characterization technique for bridging microscopic structural evolution with macroscopic device performance. This review establishes the theoretical framework of GIWAXS geometry and highlights its unique capability for probing perovskite crystallization dynamics. Recent advances in GIWAXS studies are systematically summarized, including investigations of lattice orientation, compositional gradients, phase segregation, and impurity‐phase formation in perovskite thin films. In situ GIWAXS studies revealing crystallization pathways across diverse fabrication methods and low‐dimensional perovskites are then discussed. Emphasis is devoted to intermediate‐phase identification and modulation strategies enabled by additive engineering, cation design, and compositional optimization. Building upon the crystallization kinetics, the degradation mechanisms triggered by moisture, thermal stress, and light illumination are systematically reviewed. Finally, current challenges and future opportunities are critically examined, including the integration of GIWAXS with complementary characterization techniques and the establishment of standardized analysis protocols. These perspectives provide guidance for leveraging structural insights toward scalable manufacturing and commercialization of perovskite photovoltaics.