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Manipulating the perovskite solidification process, including nucleation and crystal growth, plays a critical role in controlling film morphology and thus affects the resultant device performance. In this work, a facile and effective ethyl alcohol (EtOH) cosolvent strategy is demonstrated with the incorporation of EtOH into perovskite ink for high‐performance room‐temperature blade‐coated perovskite solar cells (PSCs) and modules. Systematic real‐time perovskite crystallization studies uncover the delicate perovskite structural evolutions and phase‐transition pathway. Time‐resolved X‐ray diffraction and density functional theory calculations both demonstrate that EtOH in the mixed‐solvent system significantly promotes the formation of an FA‐based precursor solvate (FA2PbBr4·DMSO) during the trace‐solvent‐assisted transition process, which finely regulates the balance between nucleation and crystal growth to guarantee high‐quality perovskite films. This strategy efficiently suppresses nonradiative recombination and improves efficiencies in both 1.54 (23.19%) and 1.60 eV (22.51%) perovskite systems, which represents one of the highest records for blade‐coated PSCs in both small‐area devices and minimodules. An excellent VOC deficit as low as 335 mV in the 1.54 eV perovskite system, coincident with the measured nonradiative recombination loss of only 77 mV, is achieved. More importantly, significantly enhanced device stability is another signature of this approach.