摘要： Here, we applied the commercially accessible SnO2 and home-made TiO2 NPs as a combined electron transporting bilayer (ETBL) to achieve a highly efficient planar perovskite solar cell (PSC). The formed cascade-aligned energy levels from the proper stacking of SnO2 and TiO2 layers and the excellent defect-passivation ability of TiO2, SnO2/TiO2 ETBLs effectively reduced energy loss and inhibited defects formation both at the ETL/perovskite interface and within the bulk of perovskite layer as revealed by a comprehensive analysis of photoelectric characteristic analysis, including ultraviolet photoelectron spectroscopy, photoluminescence and electrochemical impedance spectroscopy. Consequently, the PSC devices acquired a high PCE of 20.50% with a Voc of 1.10 V, a Jsc of 24.2 mA/cm2 and an FF of 77%, which are superior to the values of the control device based on single SnO2 layer with a PCE of 18.09% (a 13.3% boosting on PCE). Moreover, there was no degradation after 49 days, indicating the great stability after adding TiO2 layer. Our work demonstrates that the cascaded alignment of energy levels between the electrode and perovskite layer by ETBLs could be an effective approach to improve the photovoltaic performance of the PSCs with excellent long-term stability.