Abstract: Tri-iodine anion（I3-） is employed as a defect passivator for post-treatment to as-prepared perovskite films,which remarkably improves the interfacial contact between the light-absorbing and the hole transport layer. This strategy on defects is found to significantly enhance power conversion efficiency of planar heterojunction devices to 18.9% by a one-step film deposition method. Meanwhile,the operational stability of PSCs is effectively improved that an efficiency decline of only 5% is observed in the I₃^--treated device after aging for 600 hours. The film morphology,optoelectrical properties,and the effect and mechanism of I₃^-with different concentrations on the device performance are investigated by measurement of phase and optoelectronic. The results show that the defect passivation strategy with post-treatment of I₃^-can benefit preferential growth orientation of the perovskite crystals,reduce trap-state defects,and eliminate the potential energy barrier between the perovskite and the hole transport layer. Furthermore,I₃^-is helpful to form an in-situ protecting layer which prevents the perovskite material from moisture and oxygen attacks.