Initial Stage of Photoinduced Oxidation of Poly(3-hexylthiophene-2,5-diyl) Layers on ZnO under Dry and Humid Air

We studied the initial stage of the oxidation behaviors of poly(3-hexylthiophene-2,5-diyl) (P3HT) layers on ZnO under visible light irradiation using in situ X-ray photoelectron spectroscopy. In the S 2p core-level XPS spectra, partial oxidation of S into sulfoxide was found with a sustained ring structure of P3HT in both humid and dry atmospheric conditions. Much lower increases in the XPS peak intensities were also found for sulfone and other S species related to P3HT ring opening. However, the partial oxidation of the P3HT layers resulted in significant changes in optical properties by disturbing inter- and intra-π-conjugation. P3HT oxidation was more pronounced under humid air conditions. Incorporation of molecular water into the P3HT lattice was also observed.