Spray-Pyrolyzed Tantalium-Doped TiO₂ Compact Electron Transport Layer for UV-Photostable Planar Perovskite Solar Cells Exceeding 20% Efficiency

The electron-transporting layer (ETL) material is one of the critical components of the n-i-p planar perovskite solar cells (PSCs). TiO2 is the most typically used ETL material; however, low electron mobility and conductivity of TiO2 limit the performance of the cells. Ion doping is an effective method for improving the electrical properties of TiO2 films. In this study, pure and tantalum (Ta)-doped TiO2 films, fabricated with the spray pyrolysis method, were employed as the ETL in the n-i-p planar PSCs. Ta doping improved the electrical conductivity and decreased interface defect between the TiO2 electron transport and perovskite layers, promoting efficient electron transfer at the interface. After dopant optimization of transport layers, the overall power conversion efficiency was increased to as high as 20.45% with negligible hysteresis exceeding the previous highest efficiency recorded for Ta-doped TiO2 ETL-based PSCs. More importantly, Ta-doped TiO2 ETL-based PSCs exhibited an admissible photostability under continuous illumination including UV radiation and retained 65% of their initial efficiency over 300 h in the ambient environment, higher than that of 50% for the control device. These findings indicated that spray-pyrolyzed Ta-doped TiO2 films could be a promising compact layer to fabricate highly efficient and UV-stable planar PSCs in large-scale manufacturing.