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.