Temperature Dependence of Photoinduced Phase Segregation in Bromide-Rich Mixed Halide Perovskites

Mixed halide perovskites undergo phase segregation, manifested as the spectral red-shifting of photoluminescence spectra under illumination. In the iodine-bromide-mixed perovskites, the origin of the low-energy luminescence is related to iodine-enriched domain formation. Such domains create favorable bands for the induced carrier to funnel into them. Despite the fact that the phase segregation process is crucial for mixed halide perovskite-based optoelectronics, numerous gaps exist within the understanding of this phenomenon. One such gap pertains to the emergence of temporary and intermediate photoluminescence peaks during the initial stages of phase segregation. However, these peaks appear only within the first few seconds of illumination. Nevertheless, the decreasing temperature may prolong these initial stages. In this work, we carry out a detailed study of the temperature dependence of anion segregation in MAPbBr₂I and MAPbBr_2.5I_0.5 halide perovskites to obtain a deeper comprehension of segregation processes, particularly during their initial stages. The temporal evolution of low-temperature photoluminescence reveals the undergoing of the intermediate stage during the segregation process and the temperature-related phase transition from the orthorhombic to the tetragonal phase. To complement the phase segregation study, the temperature dependence of time-resolved photoluminescence spectroscopy is provided, allowing us to estimate the change in the photoluminescence lifetimes for the initial and segregated peaks with temperature.