Serious nonradiative recombination and decomposition of perovskite film exist in MAPbBr₃-based perovskite light-emitting diodes (PeLED) due to the residue of lead atoms from an incomplete reaction, thereby limiting the efficiency of PeLEDs. Excessive Methylammonium bromide (MABr) added into the precursor of methylammonium lead bromide (MAPbBr₃) can solve this problem. However, how the excessive MABr self-passivates perovskite films improves the performance of PeLEDs requires further examination. The self-passivated perovskite film by overdoping MABr was investigated by varying stoichiometric ratios of perovskite precursors. It was found that, as the content of MABr increased, the interaction between free charge and longitudinal optical phonons was enhanced, thus reducing the exciton binding energy, resulting in emission broadening and blue shift of the PL spectra. With the molar ratio of PbBr₂ and MABr of 1:1.315, the PeLED achieved a good trade-off between the brightness and the stability, thus demonstrating a maximum brightness of 9981 cd m ^{− 2} and a lifetime of 14 min, with a maximum current efficiency of 6.59 cd A ^{− 1}.