The N and O atoms in the bidentate ligand 8-hydroxyquinoline (8-HQ) can simultaneously coordinate with Sn²⁺, which greatly inhibits the oxidation of Sn²⁺. The formation of complexes improves the quality of FASnI₃ films and reduces defect states, resulting in improvements in the efficiency and stability of FASnI₃-based perovskite solar cells.