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Defect passivation is one of the most important strategies to boost both the efficiency and stability of per-ovskite solar cells(PSCs).Here,nontoxic and sustainable forest-based biomaterial,betulin,is first intro-duced into perovskites.The experiments and calculations reveal that betulin can effectively passivate the uncoordinated lead ions in perovskites via sharing the lone pair electrons of hydroxyl group,promoting charge transport.As a result,the power conversion efficiencies of the p-i-n planar PSCs remarkably increase from 19.14％to 21.15％,with the improvement of other parameters.The hydrogen bonds of betu-lin lock methylamine and halogen ions along the grain boundaries and on the film surface and thus sup-press ion migration,further stabilizing perovskite crystal structures.These positive effects enable the PSCs to maintain 90％ of the initial efficiency after 30 days in ambient air with 60％±5％relative humidity,75％after 300 h aging at 85℃,and 55％after 250 h light soaking,respectively.This work opens a new pathway for using nontoxic and low-cost biomaterials from forest to make highly efficient and stable PSCs.