To fabricate efficient formamidinium tin iodide (FASnI₃) perovskite solar cells (PSCs), it is essential to deposit uniform and dense perovskite layers and reduce Sn⁴⁺ content. Here we used solvent-engineering and nonsolvent dripping process with SnF₂ as an inhibitor of Sn⁴⁺. However, excess SnF₂ induces phase separation on the surface of the perovskite film. In this work, we report the homogeneous dispersion of SnF₂ via the formation of the SnF₂–pyrazine complex. Consequently, we fabricated FASnI₃ PSCs with high reproducibility, achieving a high power conversion efficiency of 4.8%. Furthermore, the encapsulated device showed a stable performance for over 100 days, maintaining 98% of its initial efficiency.