Thin film TiO2 photoanodes for the photoelectrolysis of water have been deposited onto Ti foil by r.f. reactive sputtering from a 99.97% pure titanium target in a flow-controlled Ar + O-2 gas atmosphere. The influence of the film thickness and temperature on the microstructure and the resulting photoelectrochemical properties has been studied. Donor concentration N-D of the order of 2 x 10(24) m(-3) and the width of the depletion layer W of approximately 60-80 nm have been found to be independent of the film thickness. However, the flat band potential V-Fb and the solar energy conversion efficiency eta(C) can be optimised over the range of thickness d = 200-300 nm. (C) 2003 Elsevier B.V. All rights reserved.