Abstract: Perovskite solar cells (PSCs) based on α-phase FAPbI₃ (α-FAPbI₃) microcrystals precursor outperform those with δ-phase microcrystals due to their superior crystallinity and fewer defects, making α-phase microcrystals precursor more advantageous for high-performance PSCs. However, most reported synthesis methods of perovskite microcrystals, especially for aqueous synthesis, fail to reach the energy threshold required for α-phase transformation and therefore exhibit the δ phase. In this study, we introduce a novel aqueous synthesis method to fabricate α-FAPbI₃ microcrystals. Our approach overcomes the energy barrier by properly heating the reaction system, enabling the direct formation of α-FAPbI₃ in water. This direct one-step aqueous synthesis route yields α-FAPbI₃ microcrystals with superior phase purity, crystallinity, and minimal defect density. Combined with green anti-solvent, the high-quality α-FAPbI₃ microcrystals serving as exceptional precursors endow perovskite films with reduced nonradiative recombination. The PSC achieves a remarkable power conversion efficiency (PCE) of 24.43%, which is one of the highest PCE reports for using the green anti-solvent in ambient air condition. This aqueous synthesis approach shows a significant potential for scalable production of high-performance PSCs.