ABSTRACT

There is a general perception that electronic structure, and speci›cally the energy band gap, is the key performance-related property of semiconductors for solar energy conversion. Therefore, the main stream of research on the development of high-performance TiO2-based photosensitive semiconductors is concentrated on reduction of the band gap [1,2]. It has been shown, however, that while the performance of TiO2-based semiconductors depends critically on their electronic structure, the remaining performance-related properties, including (1) charge transport, (2) surface structure (responsible for the charge transfer accompanying the reactions at the solid/liquid interface), and (3) electric ›eld (required for light-induced charge separation), are of equal importance [2]. Moreover, all these functional properties are interrelated. Consequently, the procedures aiming at reduction of band gap result in a change of the remaining performance-related properties as well. Awareness is growing, however, that the local semiconducting properties of the surface layer, including TiO2, differ from those of the bulk phase. So far, little is known on these properties.