Impact of Aging Temperatures on the Ostwald Ripening Crystallization and Optical Properties in CsPbBr ₃ Nanocrystals

Despite the exceptional optical properties of CsPbBr₃ (CPB) nanocrystals (NCs), maintaining their long-term colloidal and structural reliability remains a significant barrier to commercialization. The influence of environmental conditions on Ostwald ripening and its effects on the crystal structure and optical behavior of CPB NCs has not been thoroughly investigated. In this work, CPB NCs were synthesized using a high-temperature hot-injection method and dispersed in <i>n</i>-heptane. They were evaluated by integrating population balance theory-based crystallization kinetic studies with experimental measurements over 30 days at aging temperatures of -20, 25, and 70 °C, which represent different storage conditions. The size and crystal lattice of CPB NCs dispersed in <i>n</i>-heptane are influenced by the aging time and temperature, which affect their UV absorbance and photoluminescence spectra. At -20 °C, the NC solutions retained their greenish fluorescence with negligible changes because of the limited crystal growth rate based on population balance kinetic models. However, increasing aging temperatures resulted in an increased crystal growth rate, with significant yellowing observed at 70 °C. Transmission Electron Microscopy, X-ray diffraction, and 3D-tomography studies confirmed that the CPB NCs exhibited 2D crystal growth, which accelerated with increased aging temperature. These findings highlight the nature of thermal degradation mechanisms in CPB NCs as a function of the long-term storage temperature and provide a framework for mitigating such issues.