Electron Transporting Bilayer of SnO2 and TiO2 Nanocolloid Enables Highly Efficient Planar Perovskite Solar Cells

Herein, commercially accessible SnO 2 and home‐made TiO 2 nanoparticles as a combined electron transporting bilayer (ETBL) are applied to achieve highly efficient planar perovskite solar cells (PSCs). With the formed cascade‐aligned energy levels from the proper stacking of SnO 2 and TiO 2 layers and the excellent defect‐passivation ability of TiO 2 , SnO 2 /TiO 2 ETBLs effectively reduce energy loss and inhibit defects formation both at the electron transporting layers (ETL)/perovskite interfaces 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 power conversion efficiency (PCE) of 20.50% with a V oc of 1.10 V, a J sc of 24.2 mA cm −2 and an fill factor of 77%, which are superior to the values of the control device based on single SnO 2 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 TiO 2 layer. Herein, it is demonstrated 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.