We have characterised a dye-sensitised nanoporous nanocrystalline titania film used in prototype photoelectrochemical solar cell production. From transmission electron microscopy the particles were seen as mixtures of tetrahedral and rhombohedral geometries with size distribution in the range between 10 and 25nm. These particles were identified by X-ray diffraction as nanocrystals of anatase and brookite phases. The film was sensitised with a ruthenium (11) based chromophore for different times (between 0.5 and 24h) and the penetration and coverage of the dye was studied using secondary ion mass spectroscopy. The dye was found to percolate through the whole of the titania film and was distributed uniformly. Using Rutherford backscattering, the composition of the film was determined and found to be 1 wt% Ru on maximum sensitisation. The optical properties of the dye-sensitised films were also measured which resulted in an increase of absorbance and a decrease of transmittance for dyeing times up to 8 h. Beyond this time the values remained unchanged and thus a semi-transparent film with luminous transmittance between 0.12 and 0.60 were obtained. (C) 2002 Elsevier Science B.V. All rights reserved.