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 degrees 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 rim. 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. (c) 2006 Elsevier B.V. All rights reserved.