Poly(3‐hexylthiophene) film coated on plastic substrate as an organic photoanode for water oxidation/oxygen evolution with light illumination

Poly(3‐hexylthiophene) (P3HT) film was applied as a photoanode on an electron‐extracting layer‐coated upon a current‐collecting plastic substrate. The film soaked in an aqueous solution (pH 12) exhibited an enhanced anodic current with light illumination, and the photocurrent density (J) reached almost 100 μA/cm2 for its wound cylinder, which was accompanied by oxygen bubble evolution. The light ON/OFF response, light‐intensity proportion, and wavelength‐dependency of the J value supported the photo‐electrolytic function of the P3HT film. The hole‐injection efficiency of the film estimated for water oxidation using a solution involving a sacrificial reagent, was relatively high in the range of 46%–86%. Although an apparent activation energy of 39 kJ/mol for the electrolytic water oxidation in the dark suggested a chemical but catalytic pathway for the film anode, the temperature independence of the photocurrent indicated direct hole‐injection into water or hydroxide ions. The photoanode performance of the P3HT film for water oxidation was discussed in relation to the energy diagram including the highest occupied molecular orbital level.