Niobium Doping Effects on TiO2 Mesoscopic Electron Transport Layer-Based Perovskite Solar Cells

Perovskite solar cells (PSCs) are the most promising candidates as next‐generation solar energy conversion systems. To design a highly efficient PSC, understanding electronic properties of mesoporous metal oxides is essential. Herein, we explore the effect of Nb doping of TiO2 on electronic structure and photovoltaic properties of PSCs. Light Nb doping (0.5 and 1.0 at %) increased the optical band gap slightly, but heavy doping (5.0 at %) distinctively decreased it. The relative Fermi level position of the conduction band is similar for the lightly Nb‐doped TiO2 (NTO) and the undoped TiO2 whereas that of the heavy doped NTO decreased by as much as ∼0.3 eV. The lightly doped NTO‐based PSCs exhibit 10 % higher efficiency than PSCs based on undoped TiO2 (from 12.2 % to 13.4 %) and 52 % higher than the PSCs utilizing heavy doped NTO (from 8.8 % to 13.4 %), which is attributed to fast electron injection/transport and preserved electron lifetime, verified by transient photocurrent decay and impedance studies. Nb‐doped TiO2 nanoparticles for perovskite solar cell: TiO2 nanoparticles doped with n‐type Nb5+ have a diameter of 30 nm and a pure anatase phase; they are used for fabricating perovskite solar cells. Light doping increases the photovoltaic energy conversion efficiency by 10 % due to improved electron injection/transport properties of the nanoparticle‐based electron transport layer.