Novel NH4+-doped MA1-x(NH4)xPbBr3 perovskite quantum dots were synthesized at room temperature. The introduction of NH4+ results in larger lattice formation energy and better crystallinity of MA1-x(NH4)xPbBr3, which greatly reduces the defect density and inhibits non-radiative recombinations, and thus helps in achieving excellent stability and near unity blue-emitting photoluminescence quantum yields.