Role of defects in photocatalytic water splitting: Monodoped vs Codoped SrTiO₃

SrTiO₃ is used as a photocatalyst due to its exceptional electronic structure, high stability, non-toxicity, and low cost. However, owing to the wide bandgap (3.2 eV), it could only utilize the UV irradiation. Here we have investigated the role of monodopants (nonmetals (N, S) and metals (Mn, Rh)) and codopants in SrTiO₃ to ameliorate the photocatalytic efficiency for water splitting by reducing its bandgap using hybrid density functional theory (HSE06), many-body perturbation theory approach (viz. G₀W₀@HSE06) and ab initio atomistic thermodynamics. We find that substitutional defect is the most stable defect. Further, monodoping can induce visible light absorption, but not suitable to enhance the photocatalytic activity either due to the formation of recombination centers or lowering of conduction band minimum (CBm). Contrarily, the codopant can be chosen such that the recombination of photogenerated charge carriers is suppressed, and the CBm is not affected much. Our results reveal that Mn_SrN_O (codoping of Mn at Sr site and N at O site) and Mn_TiS_O are the potential candidates for enhancing the photocatalytic activity of SrTiO₃ under visible light.