Low-temperature Synthesized Nba??doped TiO <sub/>2</sub> Electron Transport Layer enabling High-efficiency Perovskite Solar Cells by Band Alignment Tuning

摘要： An Nb-doped TiO2 (Nb-TiO2) film comprising a double structure stacked with a bottom compact layer and top mesoporous layers was synthesized by treating a Ti precursor-coated substrate using a one-step low-temperature steam-annealing (SA) method. SA-based Nb-TiO2 films possess high crystallinity and conductivity, and that allows better control over the conduction band (CB) of the TiO2 for electron transport layer (ETL) of the perovskite solar cells (PSCs) by the Nb doping level. Optimization of power conversion efficiency (PCE) for the Nb-TiO2 based ETL was combined with CB level tuning of the mixed-halide perovskite by changing the Br/I ratio. This band offset management enabled to establish the most suitable energy levels between ETL and perovskites. This method was applied to reduce the bandgap of perovskite to enhance photocurrent density while maintaining a high open-circuit voltage. As a result, the optimal combination of 5 mol% Nb-TiO2 ETL and 10 mol%-Br in the mixed-halide perovskite exhibited high photovoltaic performance for low-temperature device fabrication, achieving a high yield PCE of 21.3%.