ITO and electron transport layer-free planar perovskite solar cells on transparent Nb-doped anatase TiO_2-x electrodes

Here, we reported on planar perovskite solar cells (PSCs) which are free of the indium tin oxide (ITO) and electron transport layer (ETL) directly prepared on Nb-doped TiO_2-x (NTO) electrodes. By rapid thermal annealing of NTO film at a temperature of 600 °C under vacuum ambient, we obtained conductive anatase NTO electrodes that act as transparent electrodes and ETL simultaneously in ITO and ETL-free PSCs. The sputtered NTO electrode showed decreasing resistivity with decreasing temperature, indicating metallic conductivity. A planar NTO∖(FAPbI₃)_1-x(MAPbBr₃)_x∖Spiro-MeOTAD∖Au cell showed a power conversion efficiency of 12.50% and open-circuit voltage of 1.08 V in spite of the absence of ETL. The ITO and ETL-free PSC with an NTO electrode exhibited a higher open-circuit voltage of 1.08 V than did an ETL-free PSC with ITO electrode because of effective hole blocking by the NTO electrodes. Our results suggest that sputtered NTO film is a promising multi-functional electrode acting as ETL and transparent electrode simultaneously for achieving simply fabricated and cost-effective PSCs.