Synergistic Effect to High-Performance Perovskite Solar Cells with Reduced Hysteresis and Improved Stability by the Introduction of Na-Treated TiO₂ and Spraying-Deposited CuI as Transport Layers

For a typical perovskite solar cell (PKSC), both the electron transport layers (ETLs) and hole transport materials (HTMs) play a very important role in improving the device performance and long-term stability. In this paper, we firstly improve the electron transport properties by modification of TiO₂ ETLs with Na species, and an enhanced power conversion efficiency (PCE) of 16.91% has been obtained with less hysteresis. Subsequently, an inorganic CuI film prepared by a facile spray deposition method has been employed to replace the conventional spiro-OMeTAD as the HTM in PKSCs. Because of the improved transport properties at the ETL/perovskite and perovskite/HTM interfaces, a maximum photovoltaic efficiency of 17.6% with reduced hysteresis has been achieved in the PKSC with both the Na-modified TiO₂ ETL and 60 nm-thick CuI layer HTM. To our knowledge, the PCE achieved in this paper is one of the highest values ever reported for the PKSC devices with inorganic HTMs. More significantly, the PKSCs exhibit an outstanding device stability, their PCE remains constant after storage in the dark for 50 days, and they can retain approximately 92% of their initial efficiency after storage even for 90 days.