With the aim of improving the performance and extending the range of applications of mesoporous WO3 films, which were initially developed for the photoelectrochemical oxidation of water, we investigated the effect of a number of dopants (lithium, silicon, ruthenium, molybdenum and tin) upon the transparency, crystallinity, porosity and conductivity of the modified films. Tin, molybdenum and silicon were shown to improve the electrochromic behaviour of the layers whereas ruthenium enhanced considerably the electronic conductivity of the WO3 films. Interestingly, most of the dopants also affected the film morphology and the size of WO3 nanocrystals. X-ray photoelectron spectra revealed absence of significant segregation of doping elements within the film. Raman analyses confirmed that the monoclinic structure of WO3 films does not change upon substitutional cation doping: thus, the crystallinity of WO3 films is maintained. (C) 2009 Elsevier Ltd. All rights reserved.