Low-temperature processed Tantalum/ Niobium co-doped TiO2 electron transport layer for high-performance planar perovskite solar cells.

Low-temperature preparation process is significant important for scalable and flexible device. However, the serious interface defects between normally used TiO2 electron transport layer (ETL) obtained via low-temperature method and perovskite suppress the further improvement of perovskite solar cells (PSCs). Here, we develop a facile low-temperature chemical bath method to prepare TiO2 ETL with Tantalum (Ta) and Niobium (Nb) co-doping. Systematic investigations indicate that Ta/Nb co-doping could increase the conduction band level of TiO2 and decrease trap state density, boosting electrons injection efficiency and reducing charge recombination between perovskite/ETL interface. The champion power conversion efficiency of 19.44% can be achieved by a planar PSC with Ta/Nb co-doped TiO2 ETL, which is much higher than that (17.60%) of pristine one. Our achievements in this work provide new insights on low-temperature fabrication of low-cost and high-efficient PSCs.