Carrier recombination dynamics in [MAPbCl₃][CsPbBr₃]_1- shell-passivated CsPbBr₃ single crystals

As one of the commonly used methods for surface passivation of semiconductors, a heterostructure method was developed in this work to passivate surface traps of CsPbBr₃ single crystals (SCs), and further, this method was correlated with carrier recombination processes. Herein, carrier recombination processes in bare and [MAPbCl₃]_0.34[CsPbBr₃]_0.66-covered CsPbBr₃ SCs were studied using time-resolved spectroscopic techniques, including steady-state and time-resolved photoluminescence (TRPL) spectroscopy and time-resolved microwave photoconductivity (TRMC). By comparing the kinetics of TRPL and TRMC, we concluded that surface hole-trapping process dominates the TRPL kinetics of bare CsPbBr₃ SCs and surface electron-trapping process dominates the slower decay component in TRMC. By studying carrier recombination processes of CsPbBr₃ SCs with and without choline bromide (CB) additives, we found that the use of CB could introduce additional surface electron and hole traps. For CsPbBr₃ SCs with a shell, we observed charge carrier transfer from the shell to the CsPbBr₃ crystal. We found that the [MAPbCl₃]_0.34[CsPbBr₃]_0.66 shell can reduce the electron-trapping and hole-trapping rates by 2.2 times and 5.2 times, respectively, indicating that the [MAPbCl₃]_0.34[CsPbBr₃]_0.66 shell can passivate the surface traps of CsPbBr₃ crystals effectively.