Efficient conversiton of light energy by using funational semiconductor surfaces

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Lihhy rnergy conversion systems based on the semiconductor liquid junctions have been focusing on fuel production as well as electrical energy generation.When a semiconductor electrode receives photons with energy greater than its band gap, electron-hole pairs are generated within a space charge layer. In the case of an n-type semiconductor, electric field existing within the space charge layer drives photo- generated holes toward the interfacial region and electrons toward the interior of the electrode. Thus, by combining a semiconductor electrode with an appropriate counter-electrode, a photo-cell can be constructed.The possibiliy of solar photoelectrolysis of water was demonstrated by us for the first time with a system in which an n-type titanium dioxide electrode was connected to a platinum black electorde, construction of an efficient photoelectrochemical cell in which water is decomposed to H2 and O2, as well as for the construction of an efficient regenerative photovoltaic cell in which a common redox couple is reacting at both the photoanode and the metal cathode.Following three subjects have been studiel.1) Increase of conversion efficiency by using semiconductor surfaces loaded with catalytic metals2) determination of reaction sites of photocatalytic semiconductor surfaces by separation factor method3) surface modification of semiconductor surface with chemical modification and polymer coating.