Abstract Interface engineering has been regarded as an effective and noninvasive means to optimize the performance of perovskite solar cells (PSCs). Here, doping engineering of a ZnO electron transport layer (ETL) and CsPbI₃/ZnO interface engineering via introduction of an interfacial layer are employed to improve the performances of CsPbI₃-based PSCs. The results show that when introducing a TiO₂ buffer layer while increasing the ZnO layer doping concentration, the open-circuit voltage, power conversion efficiency, and fill factor of the CsPbI₃-based PSCs can be improved to 1.31 V, 21.06%, and 74.07%, respectively, which are superior to those of PSCs only modified by the TiO₂ buffer layer or high-concentration doping of ZnO layer. On the one hand, the buffer layer relieves the band bending and structural disorder of CsPbI₃. On the other hand, the increased doping concentration of the ZnO layer improves the conductivity of the TiO₂/ZnO bilayer ETL because of the strong interaction between the TiO₂ and ZnO layers. However, such phenomena are not observed for those of a PCBM/ZnO bilayer ETL because of the weak interlayer interaction of the PCBM/ZnO interface. These results provide a comprehensive understanding of the CsPbI₃/ZnO interface and suggest a guideline to design high-performance PSCs.