First-Principles investigation of substitutional metallic doping effects on the optical absorption of TiO2 for photovoltaic applications

Titanium dioxide (TiO2), a wide-band gap semiconductor, is transparent to visible light and primarily absorbs ultraviolet radiation. However, its characteristics can be modified by substituting Ti with metallic impurities. This study examines the impact of substitutional doping with Au, Ag, and V on the optical absorption characteristics of TiO2 anatase single crystals using density functional theory (DFT) calculations. To accurately treat electron-electron correlation, the generalized gradient approximation plus U (GGA + U) was employed. Under the constraints of the finite-size supercell model, the band structure, absorption spectra, and energy gaps were determined for each doped system. A key observation was the overall modification of optical properties and the placement of impurity-induced electron states. The results indicate that these substitutional atoms create electronic levels inside pure TiO2’s band gap, thereby extending its absorption into the visible and near-infrared regions. Among the studied dopants, V-doped TiO2 exhibits the most significant enhancement in solar radiation absorption, making it the most promising candidate for photovoltaic applications.