This study examined a water-splitting system comprising a TiO₂ photoanode and an organo-photocathode consisting of a p–n bilayer. Stoichiometric decomposition of water into H₂ and O₂ successfully occurred at bias voltages lower than the theoretical value (i.e. 1.23 V). Compared to the conventional TiO₂ and Pt systems, the proposed water-splitting system demonstrated water splitting without any externally applied bias.