Decrease of recombination losses in bicomponent WO3/TiO2 films photosensitized with cresyl violet and thionine

The recombination of photoinjected electrons in semiconducting metal oxide films, photosensitized with cresyl violet and thionine, has been investigated. A comparative analysis of photoresponse characteristics for single-component photoelectrodes, WO3 and TiO2, and bicomponent heterogeneous WO3/TiO2 photoelectrodes, was performed for front and back side illumination of the films. A considerably higher photoresponse was observed for bicomponent WO3/TiO2 films in comparison to single-component films. Employing a porous WO, matrix layer with high open surface area as the substrate for a very thin nanoparticulate TiO2 overlayer is beneficial for efficient photogeneration for two reasons. First, a lower lying conduction band of the WO3 matrix layer provides the escape path for photoinjected electrons from the conduction band of the TiO2 film to the external circuit and prevents the recombination at the TiO2/electrolyte interface. Second, the recombination losses during the electron transport through grain boundaries in TiO2 film decrease strongly due to the small film thickness. It has been shown that by employing the back side illumination, further decrease in recombination losses of photoinjected electrons can be achieved.