Growth of perovskite CsPbBr₃ nanocrystals and their formed superstructures revealed by in situ spectroscopy

Metal halide perovskites have attracted substantial interest because of their promising properties for optoelectronic applications. Despite much progress made in the field, the exact growth mechanism of perovskite nanocrystals (e.g., CsPbBr₃) remains elusive and further improvement of their controllable synthesis is challenging. Herein, we point out different phenomena during the processes of growth, cooling, and purification of high-quality CsPbBr₃ nanocrystals using in situ photoluminescence spectroscopy. The as-synthesized materials have been further characterized by time-resolved transient differential transmission and photoluminescence spectroscopies. Using X-ray scattering, we confirm that nanocrystals form superstructures during the process of cooling already in dispersion, which is frequently ignored. The purification process is explained using a proposed model based on the self-size-selection. On the one hand, such superstructures pave a potential pathway to the fabrication of high-quality devices such as light-emitting devices. On the other hand, the approach to reveal their formation process benefits the comparison and understanding of the difference between nanocrystals and supercrystals. The fact that superstructures form already during synthesis may also apply to the different perovskite systems and thus help to improve the quality of the as-prepared nanocrystals.