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*
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.
