A highly efficient inverted polymer solar cell (PSC) has been successfully demonstrated by utilizing a wide bandgap magnesium oxide (MgO) film and ZnO stacked structure as an effective cathode interfacial layer. The MgO/ZnO bilayer structure is designed to combine the superiorities of both ZnO ETL and MgO film, based on the efficiency comparison of the PSCs without and with MgO interlayer. The ZnO film can serve as an efficient electron transport layer (ETL), while the MgO layer can reduce the surface defects of FTO and block the holes effectively, leading to an elevated electron collection and suppressed carrier recombination at the interface. With the excellent dual functions interface characteristics induced by the MgO/ZnO stacked films, the corresponding inverted PSC device based on the PTB7-Th:PC71BM photoactive layer system presents a superior power conversion efficiency (PCE) of 11.02%, which is higher than that of the PSC without MgO (8.79%). We believe that the MgO/ZnO bilayer structure is a superior interfacial contender for the organic photovoltaics and other photoelectric devices requiring cathode interfacial layers. (C) 2020 Elsevier Inc. All rights reserved.