Self energy and excitonic effect in (un)doped TiO2 anatase: a comparative study of hybrid DFT, GW and BSE to explore optical properties†
TiO2 anatase has significant importance in energy and environmental research. However, the major drawback of this immensely popular semi-conductor is its large bandgap of 3.2 eV. Several non-metals have been doped experimentally for extending the TiO2 photo-absorption to the visible region. Providing in-depth theoretical guidance to the experimentalists to understand the optical properties of the doped system is therefore extremely important. We report here using a state-of-the-art hybrid density functional approach and many body perturbation theory (within the framework of GW and BSE) the optical properties of p-type (S and Se doped) and n-type (N and C doped) TiO2 anatase. The anisotropy present in non-metal doped TiO2 plays a significant role in the optical spectra. The p-type dopants are optically active only for light polarized along the xy direction, whereas the n-type dopants are optically active when light is polarized along the xy and z directions in the low energy region. We find that dopants give rise to new absorption peaks at low energy below 3 eV (i.e. the visible spectral region). This helps to improve the opto-electronic and solar absorption properties. All the calculations are well validated with respect to the available experimental observations on pristine TiO2 anatase.