Computational investigation of the structural, electronic and optical properties of co-doped and tri (C, N, Ni) - doped TiO2 for photoelectrochemical applications

Abstract

Titanium dioxide (TiO₂) is efficient in environmental remediation and renewable energy due to its chemical and optical stability. However, its wide bandgap (3.2 eV) is not suitable for absorbing major part of the solar spectrum. Doping with suitable elements can reduce the bandgap and enhance the n-type conductivity. This study explores the impact of substitutional point defect on the TiO₂ photoelectrochemical properties using density functional theory. Different co-doped and tri-doped models significantly reduced the intrinsic band gap of TiO₂. The calculated band gaps are: N, Ni co-doped TiO₂ = 1.81 eV; C, Ni co-doped TiO₂ = 1.42 eV; C, N co-doped TiO₂ = 1.16 eV; and (C, N, Ni) tri-doped TiO₂ = 1.25 eV. The tri-doped system showed the highest conductivity, greater light absorption, and a strong dielectric response, confirming its enhanced interaction with the visible light. The density of states analysis revealed that dopant states successfully changed the band structure making it favorable conditions for photoelectrochemical applications.