Surface-modified anodic TiO2 films for visible light photocurrent response

N-doped titania thin films were prepared by anodic oxidation of titanium sheets and subsequent heat treatment in the presence of urea pyrolysis products at 400 °C. The resulting films are modified predominantly at the surface. They exhibited a significant photocurrent response upon visible light irradiation inducing an incident photon-to-current efficiency of 1.5% at 400 nm. The flatband potential was anodically shifted by 0.2 V as compared to the unmodified film. Photocurrent transients revealed that nitrogen-centered intra-bandgap states, responsible for visible light response, induce also enhanced recombination as indicated by a cathodic “overshoot” after turning off the light. This recombination can be inhibited by the presence of iodide.