In Situ Raman Spectroscopic Studies of Thermal Stability of All-Inorganic Cesium Lead Halide (CsPbX, X = Cl, Br, I) Perovskite Nanocrystals.

Thermal degradation becomes the main obstacle for industrial applications of all-inorganic cesium lead halide (CsPbX, X = Cl, Br, I) perovskite optoelectronic devices. A complete understanding of thermal degradation of CsPbX perovskites is required but greatly challenging for achieving optoelectronic devices with long-term stability, particularly under extreme settings. Herein, we present an in situ spectroscopic study of thermal stability of CsPbX nanocrystals between the cryogenic temperature and high temperature. The low-frequency Raman signatures of CsPbX nanocrystals dramatically evolve but differentiate from the halogen atoms at elevated temperatures, acting as potent indicators of their crystalline structures and phase transitions. The merging of doublet Raman bands of CsPbX nanocrystals indicates their high-temperature phase transitions. CsPbX (X = Br, I) nanocrystals undergo a state of high degree of disorder with featureless Raman spectra before being thermally decomposed. Such understanding is of particular importance for future design and optimization of high-performance CsPbX perovskite devices with long-term stability under extreme settings.