Completely Solar-Driven Photoelectrochemical Water Splitting Using a Neat Polythiophene Film

π-Conjugated polymers are emerging as appealing photoelectrode materials for the photoelectrochemical hydrogen evolution reaction via water splitting, which has otherwise been extensively explored using inorganic semiconductors. Here, we report the performance of a pure organic semiconductor film as a catalyst for hydrogen production via visible light-driven water splitting. The neat and unsubstituted polythiophene film, characterized with a well-filled grain morphology of the crystalline polymer, is prepared by a facile polymerization method. The photovoltage of 1.38 V versus RHE at pH 12 enables solar-driven one-electron-per-photon water splitting in combination with a traditional water-oxidation catalyst to produce hydrogen and oxygen separately. The high photoelectrocatalytic hydrogen evolution rate of 1.02 mol(H2) h−1 g−1 or 0.75 mA/cm2 at 0 V versus RHE is also achieved with high durability. This study may open a new window for π-conjugated polymers for ultimately sustainable hydrogen production.