Band gap engineering of anatase TiO2 by ambipolar doping: A first principles study

Abstract

Pure Anatase TiO2 is limited to photocatalytic activity only in the UV region of solar energy, (i.e Eg = 3.2 eV and λ = < 388 nm), which utilizes only 5% of the solar spectrum. Adding external impurities to Anatase TiO2 facilitates absorption of the visible spectrum by reducing the band gap of TiO2. Hence, we investigated the effect of Sc and V mono-doping and co-doping on the pure anatase TiO2 by Density Functional Theory (DFT). To elucidate the effect of doping on the electronic structure, the accurate band structure and density of states are derived using the hybrid functional methodology (HSE06). The defect formation energy of the dopants in their different charge states is calculated using the gradient-corrected density functionals using the PBE method. The bonding characteristics were analyzed using the charge density and electron-localization function (ELF) plots, which indicate that the impurities cause a local lattice distortion, which further influences the band features of TiO2. It is observed that the formation of additional energy states by the external impurities below the conduction band minimum, reduces the band gap of the material significantly. The optical absorption analysis shows that Sc and V co-doping not only improves the absorption in the UV region, but also reaches redshift absorption. Hence the ambipolar co-doping by Sc and V to the pure anatase TiO2 makes it a better for visible light active photocatalyst.