Mixed-halide perovskites have emerged as indispensable light-absorbers for high-efficiency tandem photovoltaics, yet their compositional complexity and processing sensitivity demand advanced structural characterization to elucidate film formation, evolution, and degradation across multiple length and time scales. While previous reviews primarily focus on basic tutorials or specific topics like crystallization and degradation, a systematic methodological framework for advanced X-ray platforms remains absent. This review bridges this critical gap by establishing a comprehensive spatiotemporal characterization paradigm, structured along three complementary axes: (i) in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) for resolving crystallization kinetics; (ii) operando multimodal X-ray scattering frameworks for capturing temporal degradation pathways; and (iii) spatially resolved nano-X-ray scattering for decoding structural heterogeneity. Finally, this review highlights future directions, including the integration of AI-assisted automated analysis, upscaled in situ characterization setups, and multimodal characterization. This review aims to equip the community with advanced structural-probing strategies to overcome the bottlenecks of tandem photovoltaics and accelerate their commercialization.
