Giant emission enhancement from Cs₃Bi₂Br₉via oxygen-induced optimization of radiation channels

Among Pb-free perovskite candidates, Bi-based perovskite derivatives show promise as they meet eco-friendly standards and warrant further development. However, the fundamental question of how atmospheric conditions affect the optical performance of Bi-based perovskites, which is closely related to their practical applications, is seldom researched. Here, we observed a significant increase in the light emission from Cs₃Bi₂Br₉ crystals when the reaction was carried out in an oxygen-filled environment, boosting the photoluminescence quantum yield (PLQY) by about 10 times. Through a detailed analysis of the optical properties using X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, it was determined that the oxygen molecules can effectively passivate vacancy defects and suppress nonradiative recombination. In addition, it was found that Cs₃Bi₂Br₉ exhibits a very intense exciton-phonon interaction, with a low thermal activation energy and a high Huang-Rhys factor (S), leading to phonon emission. However, by passivating with oxygen, the exciton-phonon interaction could be regulated, and the radiation channels were optimized for self-trapping emission (STE). These findings could be valuable in gaining a deeper understanding of the impacts of reaction atmosphere, which are often overlooked, on the optical properties of perovskite derivatives.