Solution-processed perovskite precursors, especially for MAPbBr3-assisted FAPbI3 crystallization, has been noted to achieve high power conversion efficiency (PCE) for perovskite solar cells (PSCs). However, this low-temperature processed (FAPbI3)x(MAPbBr3)1−x typical precursor derived from commercial products (FAI, PbI2, MABr, and PbBr2) suffers from environmental sensitivity, poor film crystallinity and less than ideal device reproducibility. Herein, (FAPbI3)x(MAPbBr3)1–x (0.80 ≤ x ≤ 0.90)-based planar inverted PSCs are fabricated, employing grinded monocrystalline MAPbBr3 and powdered polycrystalline FAPbI3 as precursors. The champion device with optimal molar ratio x = 0.85 comprising highly crystalline larger-grained perovskite film with enhanced carrier transport kinetics and reduced trap-state density exhibits boosted efficiency reaching 20.50%, which shows a 22.90% improvement over typical precursors with a PCE of 16.68%. In addition, the crystal powder precursor yields obvious film stability under ambient conditions (23 °C, 65–85% humidity) for 150 days and improved device storage stability in the glove box within two months. This protocol using stock crystal powders for perovskite precursor formulation provides a relatively facile and reproducible device fabrication route for the commercialization of PSCs.