Carrier recombination at the interfaces of perovskite solar cells (PSCs) has always been one of the main limitations of device performance. How to restrain the generation of defect state on the perovskite film surface and improve the carrier extraction efficiency are crucial to break the bottleneck. Herein, the influence of an amino acid-based N-(9-fluorenylmethoxycarbonyl)-L-alanine (Fmoc-Ala-OH) molecule on the perovskite surface quality and thus device performance were investigated. Varied concentrations (0 mg/mL, 0.5 mg/mL, 1 mg/mL, 1.5 mg/ mL, 2 mg/mL) of Fmoc-Ala-OH were explored, and 1.5 mg/mL was found to be the optimal passivation concentration for perovskite films. This strategy could reduce PbI₂ impurity, prolong carrier lifetime, and enhance luminescence of perovskite films. Space charge limited current results indicated a lower defect state density on the perovskite film surface. Electrochemical impedance spectroscopy revealed a decreased charge transfer resistance and an increased recombination resistance after amino acid passivation. As a result, a power conversion efficiency of 21.14% with a high V_oc of 1.08 V was obtained for the modified device.