To fabricate efficient formamidinium tin iodide (FASnI(3)) 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 FASnI(3) 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.