Interfacial modification layer facilitates the preferable contact property between electron transport layer (ETL) and active layer, which is capable of enhancing the performance of inverted polymer solar cells (PSCs). in this study, we use an n -type organic small molecule of N,N-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) as the interfacial modification layer on the top of ZnO ETL by thermal evaporation. We demonstrate that the PTCDI-C8 layer can reduce the work function of ZnO, so that the efficiency of electron transfer is improved, and the recombination of charge carrier on the contact interface is suppressed. As a consequence, the power conversion efficiency (PCE) increases from 8.26% to 9.29%, based on the poly[4,8-bis(5-(2-ethylhexypthiophen-2y1)-benzo[1,2-b:4,5-b]clithiophene-co-3-fluorothieno[3,4-b]-thiophene-2-carboxylate] (PTB7-Th): [6,6]-phenylC-71-butyricacid methyl ester (PC71BM) bulk heterojunction (BHJ) active layer. The enhanced device performance is attributed to the improvement of short-circuit current (J(SC)), open -circuit voltage (V-OC) and fill factor (FF). This work provides an effective approach to reach high performance inverted PSCs.