We report the fabrication of self-assembled surface-passivated [CH(NH2)(2)](0.8)Cs0.2PbI3 thin films using a one-step method with a fluorinated polymer (FP) as an additive without post-treatment. The FP phase is separated and aggregated at the top surface of the perovskite layer during film formation. This FP acts as a passivation layer and improves the short-circuit current density and the fill factor. Consequently, the power conversion efficiency increases from 17.2% for the FP-free device to 19.1% for the 4-mg/mL-FP-added device.