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 (VO), 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 Eg 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 VO 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.