An organic bilayer composed of 3,4,9,10-peryienetetracarboxyl-bisbenzimidazole (PTCBI, n-type semiconductor) and 29H, 31H-phthalocyanine (H2PC, p-type semiconductor) works as a photoanode capable of O-2 evolution in the water phase especially when the outer surface of H2PC is coated with an IrO2, catalyst. A typical photoelectrode is characterized by the fact that a wide and efficient visible light absorption of < 750 nm by only the PTCBI induces the generation of the photocurrent involving water oxidation at the IrO2/water interface, which is based on the photophysical character of the bilayer. The exciton formed in PTCBI bulk can contribute to carrier generation through its charge separation at the p/n interface, with which the O-2 evolution takes place at the IrO2/water interface coupled with the hole-conducting H2PC layer. (c) 2005 Elsevier B.V. All rights reserved.