ZnO/SnO₂ Double Electron Transport Layer Guides Improved Open Circuit Voltage for Highly Efficient CH₃NH₃PbI₃-Based Planar Perovskite Solar Cells

The electron transport layer (ETL), as an important component of planar perovskite solar cells (P-PSCs), can effectively extract photon-generated electrons from perovskites and convey them to the cathode; by this token, its properties directly determine the photovoltaic performances of P-PSCs. Herein, we introduce a ZnO/SnO2 double electron transport layer for CH3NH3PbI3-based P-PSCs, achieving a high open circuit voltage (VOC) of 1.15 V with the power conversion efficiency (PCE) of 19.1% when the SnO2-based devices have a VOC of 1.07 V and a PCE of 18.0%; to the best of our knowledge, this is the highest VOC obtained by using an inorganic electron transport layer for pure CH3NH3PbI3-based P-PSCs so far. This result demonstrates that a higher Fermi energy (EF) and conduction band minimum (ECBM) of ETL could drive a higher VOC and a better PCE.