DECREASE OF RECOMBINATION LOSSES IN BICOMPONENT WO3 TIO2 FILMS PHOTOSENSITIZED WITH CRESYL VIOLET AND THIONINE/

The recombination of photoinjected electrons in semiconducting metal o xide 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 he terogeneous WO3/TiO2 photoelectrodes, was performed for front and back side illumination of the films. A considerably higher photoresponse w as observed for bicomponent WO3/TiO2 films in comparison to single-com ponent films. Employing a porous WO, matrix layer with high open surfa ce area as the substrate for a very thin nanoparticulate TiO2 overlaye r is beneficial for efficient photogeneration for two reasons. First, a lower lying conduction band of the WO3 matrix layer provides the esc ape path for photoinjected electrons from the conduction band of the T iO2 film to the external circuit and prevents the recombination at the TiO2/electrolyte interface. Second, the recombination losses during t he electron transport through grain boundaries in TiO2 film decrease s trongly due to the small film thickness. It has been shown that by emp loying the back side illumination, further decrease in recombination l osses of photoinjected electrons can be achieved.