Achieving high-performance planar perovskite solar cell with Nb-doped TiO2 compact layer by enhanced electron injection and efficient charge extraction

The power conversion efficiency (PCE) of a planar perovskite solar cell (PSC) is closely associated with the conduction band energy, conductivity and coverage of the compact layer. However, as the most widely used compact layer material, TiO2 has unfavorable electrical properties such as low electron mobility and conductivity; as a result, modifications such as elemental doping are of paramount importance. In this study, Nb-doped TiO2 with improved carrier density and conductivity was prepared via a facile one-pot solution process and applied successfully as a high-quality compact layer for planar PSCs. A positive shift in the flat-band potential (V-fb) and increased conductivity after Nb doping efficiently facilitated photogenerated electron injection and charge extraction from the perovskite film to the 2% Nb-doped TiO2 compact layer, contributing to impressive advances in photovoltaic performance compared with pristine TiO2. Ultimately, a PSC assembled using optimized 2% Nb-doped TiO2 and CH3NH3PbI3 yielded a power conversion efficiency of up to 16.3%.