Abstract2‐Methoxyethanol (2ME), as a more environmentally friendly solvent with a lower boiling point compared to dimethylformamide, is ideal for the fabrication of perovskite solar cells (PSCs). However, when 2ME is used for antisolvent‐free deposition of perovskite films, an uncontrolled nucleation process and an easy phase transition to the δ‐phase often occur. Herein, an ultrafast nucleation process is developed using methylamine chloride (MACl) and n‐butylammonium chloride (BACl) as dual additives in 2ME without further solvent addition. While MACl can rapidly induce MACl‐based nuclei to initiate the nucleation process for formamidinium lead iodide (FAPbI3), the addition of BACl to the precursor with MACl can further increase the nucleation rate and density of nuclei, and bypass the transition from δ‐ to α‐phase during crystal growth to obtain a highly crystalline and pinhole‐free perovskite film. As a result, the FAPbI3 PSCs achieve a power conversion efficiency (PCE) of 23.6%. This work provides a new inspiration for controlling the crystal quality of perovskite thin films via nucleation rate suitable for upscaling.