Surface optimization by poly(α-methylstyrene) as additive in the antisolution to enhance lead-free Sn-based perovskite solar cells

•Poly(α-methylstyrene) is used as additive to modify the property of the antisolvent.•Poly(α-methylstyrene) can significantly influence the surface morphology of the perovskite layer.•The enhancement of PCE by almost 70% is achieved based on FASnI3 perovskite solar cells.