Unveiling the Mysterious Structure Growth of 2D and 3D All‐Inorganic Perovskite Nanocrystals in Solution Phase Dynamically by Using Small‐Wide Angle X‐Ray Scattering Spectroscopy

Abstract Real‐time analysis of the structural formation of 2D and 3D perovskites in solution is challenging due to the sensitivity of perovskite intermediates to environmental conditions and their rapid growth. Conventional techniques often require stringent sample preparation, limiting the ability to study dynamic behaviors in solution. In this study, small‐ and wide‐angle X‐ray scattering (SWAXS) is employed to analyze the morphology and dynamics of 2D and 3D perovskite nanostructures in their native colloidal state. Unlike previous studies that attribute CsPbI 3 degradation to delta‐phase formation, SWAXS revealed preexisting 2D Cs 7 Pb 6 I 19 nanosheets in pristine CsPbI 3 colloidal solutions. In situ SWAXS tracked the dynamic transformation of these structures during recrystallization in diluted solutions. Adding bis(trimethylsilyl)sulfide (TMS) disassembled the 2D nanosheets, while subsequent recrystallization in a poor solvent formed highly crystalline Cs 7 Pb 6 I 19 nanosheets. The recrystallization dynamics aligned with crystal growth theory, with TMS concentration playing a critical role. Higher TMS concentrations slowed recrystallization, promoting stable lattice formation and enhanced crystallinity, resulting in bright yellow emission. Conversely, lower concentrations accelerated recrystallization, causing structural damage and limiting high‐crystallinity growth. This study highlights the importance of controlling recrystallization rates through TMS concentration to optimize the crystallinity and optoelectronic properties of perovskites, offering insights into improving their performance.