In this work, PCBM:SnO electron transport layers (ETLs) were applied in inverted CHNHPbI perovskite solar cells, and a high power conversion efficiency of 19.7% could be obtained. It increased by 49.0% in comparison with the device based on PCBM-only ETL (13.2%). SnO nanocrystals with excellent dispersibility were employed here to fill the pinholes and cover the valleys of PCBM layer, forming smooth and compact PCBM:SnO layers. Simultaneously, the electron traps caused by deep-level native defects of SnO were reduced by PCBM, proved by the space charge limited current analysis. Thus, PCBM:SnO ETLs can inhibit both of the defects in PCBM and SnO layers which contribute to the electron transport improvement and reduce the recombination loss. Moreover, the device stability based on the bilayer was significantly improved in comparison with the PCBM-only device and the performance of 85% could be maintained after 1 month.