Titanium dioxide (TiO2) anatase is one of the most abundant, functionally versatile oxide materials, with applications in the field of opto-electronic devices and solar cell conversion efficiency. However, owing to its large bandgap (3.2 eV), the photo-absorption efficiency is limited only in the UV region. Doping-mediated modulation is one of the most pragmatic approaches in the pursuit to improve the photocatalytic and solar energy conversion efficiencies of TiO2. We report here using state-of-the-art hybrid density functional and ab initio atomistic thermodynamics, the thermodynamic (meta-)stability of different non-metal dopants X (X= N, C, S, Se) as a function of charge state at realistic temperature and pressure. We have obtained that charged defects (mainly substitution/interstitial type) play an important role in providing enhanced stability, by carefully analyzing the individual effect of bond-making/breaking and charge carrier trapping energies. Knowing the most stable defects, we aim an accurate theoretical estimation of the optical properties of doped TiO2 for both scientific and practical interest. To do this, we have used many body perturbation theory viz. one particle Green's function (GW) method and higher order Green's function techniques Bethe-Salpeter Equation (BSE). The calculated quasiparticle excitation energies of pristine anatase TiO2 are in good agreement with available photoemission and inverse photo-emission results. Further, our calculations reveal the highly anisotropic nature of the doped TiO2. The n-type doped TiO2 is optically active in both x, z direction, whereas the p-type doped TiO2 is optically inactive along z-direction. The most evident hallmark of the doped system is the appearance of absorption peaks at low energy below 3 eV, to give rise visible-light absorption.

Charged defects in TiO2 anatase: Comparative study of hybrid DFT, GW and BSE to explore optical properties

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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