Novel photofunctions of bilayer composed of p-type phthalocyanine and n-type organic semiconductor as photoelectrodes in the water phase

Novel characteristics of p/n organic bilayers as photoelectrodes working in the water phase were reviewed on the basis of recent examples proposed by us. By applying the bilayer to a photoelectrode in water, an organic solid/water interface can perform photoinduced oxidation/reduction coupled with the conduction of the carriers (i.e., holes/electrons) generated in the interior. This characteristic differs explicitly from that of a single layer where carrier generation occurring at the Schottky interface (solid/water interface) is effective; on the basis of this phenomenon, we found that a more efficient and novel photofunctional interface in water can be formed by means of a p/n organic bilayer. Typically, it is noted that the interface of cobalt phthalocyanine (CoPc, a p-type semiconductor)/water in a p/n bilayer can induce the oxidation of water into O2 through hole conduction by the CoPc layer under an irradiation of <750 nm, which successfully leads to the photoelectrochemical splitting of water into O2 and H2. The utilization of a p/n organic bilayer as the photoelectrode could reveal a new aspect of photoelectrochemical research and technology, particularly areas in which few examples of inorganic semiconducting materials have been reported.