Metal halide perovskites (MHPs) display a range of superior photophysical properties, rendering them promising as a candidate for the active medium of high-efficiency photovoltaic and electroluminescence devices. In order to maximize their efficacy in photoelectric conversion or light emission, it is essential to regulate the charge separation efficiency of MHPs in a desired manner. Herein, we demonstrate that the extent of charge separation can be effectively manipulated upon thermal annealing treatment on MHPs. As the annealing time is extended from 10 to 30 min, the accumulation of excess lead halides is observed at the boundaries of MHP grains, resulting in the construction of a quasi-Type II band alignment between the lead halide and the MHP. This facilitates the separation of electron-hole pairs, reducing the exciton binding energy from approximately 10