Aqueous photocathode activity of regioregular poly(3-hexylthiophene)

The aqueous photocathode activity of regioregular poly(3-hexylthiophene), a p-type organic semiconductor, is presented. Photocurrents up to 20 mu A cm(-2) under 100 mW cm(-2) AM 1.5D irradiation were observed. The highest photon-to-current conversion efficiency was produced for the thinnest films studied (40 nm), attaining a value of 0.55%, which is 10 times greater than reported for regiorandom P3HT. Increasing the thickness of the polymer increased the photocurrent but decreased the photoconversion efficiency. UV-vis absorption and fluorescence spectroscopy indicates protonation is restricted to the surface of the films in aqueous acid. A mechanism for the photocathode activity involving reduction of surface-protonated P3HT is proposed.