Unraveling the role of hydrogen bromide in the growth of cesium lead bromide perovskite nanocrystals.

Hydrogen bromide (HBr) could substantially improve the quality of cesium lead bromide perovskite (CsPbBr) nanocrystals (NCs) and greatly enhance their optoelectronic performance. However, clarifying the role of HBr in the growth of CsPbBr NCs has been a substantial challenge thus far. Herein, we design an in situ cryogenic photoluminescence system using liquid nitrogen to unravel the role played by HBr in the growth of CsPbBr NCs. Compared with no HBr (∼40 s), HBr improves the nucleation rate of CsPbBr NCs about two times (∼20 s), and its emission peak also exhibits a redshift of ∼30 nm. Thus, we conclude that HBr accelerates the nucleation rate of CsPbBr NCs and extends their growth stage, affording the generation of large grains. Perovskite light-emitting diodes based on CsPbBr NCs with added HBr also exhibit an outstanding performance. These outcomes provide new insights into the role of HBr in CsPbBr NCs and help prepare high-quality CsPbBr NCs for use in the fabrication of efficient CsPbBr NC-based optoelectronic devices.