Studies of degradation behaviors of poly (3-hexylthiophene) layers by X-ray photoelectron spectroscopy

Degradation behaviors of poly(3-hexylthiophene-2,5-diyl) (P3HT) layers on NiO in the presence of H₂O at ambient pressure and dark conditions were studied using X-ray photoelectron spectroscopy (XPS). Upon H₂O exposure at 120 °C, partial oxidation of P3HT together with molecular water incorporation, but with the maintained local ring-structure, were deduced by XPS. Valence band spectra of XPS evidenced that the partial oxidation of P3HT local structure could alter π-conjugation systems of P3HT layers, forming additional electronic states close to its original highest occupied molecular orbital. For comparison, P3HT surface was also exposed to O₂, and no change in the S 2p and C 1s spectra was found by O₂ exposure at 120 °C, implying that H₂O plays a major role at the initial stage of P3HT oxidation.