Defect engineering of codoped visible light photosensitized TiO₂:WN thin-films for efficient electro-photocatalysis

Anionic doping, such as nitrogen doping is widely used to visible-light photosensitize TiO₂. Unfortunately, this promotes the formation of oxygen vacancies (V_O), reducing the per-photon efficiency of TiO₂:N. Herein we propose a solution based on defect engineered acceptor-donor passivation of the electronic defects. This is achieved through the in-situ codoping of TiO₂ by both W and N dopants, using an RF-magnetron sputtering deposition process. Compositional and structural analyses revealed that we were successful in incorporating both dopants in substitutional locations in the TiO₂ lattice. Where nitrogen doping was confirmed to narrow the E_g of the material from 3.2 eV down to ∼2.3eV regardless of doping scheme. Most importantly, high frequency dielectric spectroscopy revealed that codoping greatly reduced V_O concentrations, as tracked by their GHz dielectric contribution. Confirming the passivating interplay between both codopants. Finally, these optoelectronic improvements were shown to directly translate into threefold improved visible-light driven net-photocurrents.