Author: diyan.wang

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

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) was employed to analyze the morphology and dynamics of 2D and 3D perovskite nanostructures in their native colloidal state. Unlike previous studies that attribute CsPbI₃ degradation to delta-phase formation, SWAXS revealed preexisting 2D Cs₇Pb₆I₁₉ nanosheets in pristine CsPbI₃ 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 Cs₇Pb₆I₁₉ 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.

Discovery of a Thermodynamic-Control Two-Dimensional Cs6Pb5I16 Perovskite with a Unique Green Emission Color via Dynamic Structural Transformation

 Yi-Chia Chen, Kuan-Chang Wu, Jou-Chun Lin, Anupriya Singh, Yu-Dian Chen, Hsin-An Chen, Di-Yan Wang*

https://doi.org/10.1021/acs.jpclett.4c02083

New perovskite materials of two-dimensional (2D) all-inorganic Ruddlesden-Popper (RP) perovskite Cs₆Pb₅I₁₆ nanosheets were successfully obtained from the structural transformation of 2D PR-phase Cs₇Pb₆I₁₉ nanosheets. The 2D RP-phase Cs₆Pb₅I₁₆ perovskite nanosheets exhibited a unique green emission light with an emission wavelength of approximately 500 nm. The crystal structure of the 2D RP-phase Cs₆Pb₅I₁₆ perovskite nanosheets was determined by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). The time-dependent PL measurements and XRD spectra were used to observe the optical and structure transformation from 2D Cs₇Pb₆I₁₉ (n = 6) to 2D Cs₆Pb₅I₁₆ (n = 5) perovskites. The in-situ XRD measurements confirmed that there were γ-phase CsPbI₃ released during the structural transformation process. Moreover, temperature-dependent in-situ XRD measurements were employed to examine the kinetic energy involved in the structural transformation from n = 6 to n = 5. Specifically, an intermediate structure from n = 6 to n = 5 was also identified. Most importantly, 2D Cs₆Pb₅I₁₆ (n = 5) demonstrated much better structural stability than 2D Cs₇Pb₆I₁₉ (n = 6) in thermodynamics. This study provides an essential route for the discovery of new types of perovskite structures during the structural transformation process.