Although antimony selenoiodide (SbSeI) exhibits a suitable bandgap as well as interesting physicochemical properties, it has not been applied to solar cells. Here the fabrication of SbSeI solar cells is reported for the first time using multiple spin-coating cycles of SbI 3 solutions on Sb 2 Se 3 thin layer, which is formed by thermal decomposition after depositing a single-source precursor solution. The performance exhibits a short-circuit current density of 14.8 mA cm −2 , an open-circuit voltage of 473.0 mV, and a fill factor of 58.7%, yielding a power conversion efficiency (PCE) of 4.1% under standard air mass 1.5 global (AM 1.5 G, 100 mW cm −2 ). The cells retain ≈90.0% of the initial PCE even after illuminating under AM 1.5G (100 mW cm −2 ) for 2321 min. Here, a new approach is provided for combining selenide and iodide as anions, to fabricate highly efficient, highly stable, green, and low-cost solar cells.Small effective mass, large dielectric constant, high band dispersion level, and valence band maximum with antibonding states are desirable properties for highly efficient and defect-tolerant light harvesters. [1] Most of the aforementioned properties exist in materials containing metal cations with ns 2 valence electron configuration, [2] owing to their high bandwidth conduction band and high Born effective charge derived from large spin-orbit effects as well as their soft Polaris ability. Popular light harvesters including halides or chalcogenides of Pb 2+ , [3] Sn 2+ , [4] Ge 2+ , [5] Sb 3+ , [6] and Bi 3+[7] contain metal cations with the ns 2 valence electron configuration. However, most of them are affected by one or several issues, such as low efficiency, low stability, toxicity, and high cost. Hence, efficient, stable, green, and low-cost light-harvesters must be developed.As important material exhibiting the ns 2 electronic configuration, metal chalcohalides have received extensive attention owing to their interesting physical and chemical properties. [8] Because of the distinct bonding preferences of chalcogenide and halide atoms, to form stable sites in compounds, the competition among atoms might yield unique structures and properties. [9] Additionally, a wide bandgap range can be obtained in these materials because halide and chalcogenide coexist as anions; hence,