The generation of hydrogen peroxide (H₂O₂) from water and dioxygen by sunlight-driven heterogeneous photocatalysis is a promising method for the artificial photosynthesis of a liquid solar fuel. We previously found that resorcinol–formaldehyde (RF) resin powders prepared by high-temperature hydrothermal synthesis act as highly active semiconductor photocatalysts for H₂O₂ generation. Herein, we report that RF resin powders doped with poly(3-hexylthiophene-2,5-diyl) (RF/P3HT) exhibit enhanced photocatalytic activities. The highly dispersed P3HT within the resin particles created charge transfer complexes with the conduction band of the resin via electron donation, facilitating efficient transfer of the photogenerated conduction band electrons through P3HT. This enhanced charge separation promoted efficient water oxidation and O₂ reduction. The solar-to-chemical conversion efficiency for H₂O₂ generation on the RF/P3HT resin in water under simulated sunlight irradiation with atmospheric pressure of O₂ was ∼1.0%, which is the highest efficiency reported for powder catalysts in artificial photosynthesis.