• A novel aqueous synthesis method enables direct formation of α-FAPbI3 microcrystals by heating the reaction system, overcoming the energy barrier that typically yields δ-phase.
• The resulting α-FAPbI3 microcrystals exhibit superior phase purity, crystallinity, and minimal defect density, serving as high-quality precursors for perovskite films.
• Combining these microcrystals with a green anti-solvent reduces nonradiative recombination, achieving a power conversion efficiency of 24.43% in ambient air.
• This eco-friendly aqueous route offers significant potential for scalable, low-cost production of high-performance perovskite solar cells.