The nucleation stage has an important influence on the lead halide perovskite film morphology, and therefore the solar cell performance. Here, we introduce a facile temperature-assisted rapid nucleation (TRN) method to improve the film crystallization process and the film morphology. By employing low temperature anti-solvents (diethyl ether, chlorobenzene and toluene), we stimulate homogeneous nuclei growth, resulting in a highly dense perovskite thin layer. The TRN method prepared (FAPbI₃)_0.85(MAPbBr₃)_0.15 devices exhibit a power conversion efficiency up to 19.2% and maintain over 85% of the original efficiency after 40 days of storage at room temperature under a relative humidity of 10–40%.