Thin films of perovskite deposited from solution inevitably introduce large number of defects,which serve as recombination centers and are detrimental for solar cell performance.Although many small molecules and polymers have been delicately designed to migrate defects of perovskite films,exploiting credible passivation agents based on natural materials would offer an alternative approach.Here,an eco-friendly and cost-effective biomaterial,ploy-L-lysine(PLL),is identified to effectively passivate the defects of perovskite films prepared by blade-coating.It is found that incorporation of a small amount(2.5 mg mL-1)of PLL significantly boosts the performance of printed devices,yielding a high efficiency of 19.45％with an increase in open-circuit voltage by up to 100 mV.Density functional theory calcula-tions combined with X-ray photoelectron spectroscopy reveal that the functional groups(-NH2,—COOH)of PLL effectively migrate the Pb-I antisite defects via Pb-N coordination and suppress the for-mation of metallic Pb in the blade-coated perovskite film.This work suggests a viable avenue to exploit passivation agents from natural materials for preparation of high-quality perovskite layers for optoelec-tronic applications.