The electronic structure of poly(3,4-ethylene-dioxythiophene): studied by XPS and UPS

The electronic structure of poly(3,4-ethylene-dioxythiophene) (PEDOT) has been investigated by X-ray and ultraviolet photoelectron spectroscopies as well as quantum chemical calculations. Significant differences have been observed in the photoelectron spectra between as-prepared chemically neutralized and anion-doped PEDOT thin films. The electronic structures of as-prepared neutral and doped PEDOT obtained from the photoelectron spectra are in good agreement with the results of new quantum chemical electronic structure calculations. No significant thermal-induced effects have been detected for either as-prepared neutral or doped PEDOT films. The concentration of anions on the polymer surface depends upon the size of the anion, with large anions, like polystyrene sulfonate (PSS−) base, being much more likely to cover the surface of a PEDOT film than small anion, such as tosylate(p-methyl benzyl sulfonate). This surface concentration effect probably makes the large-anion-doped polymer a more suitable candidate as an electrode in polymer light-emitting diodes (LEDs) than the small-anion-doped polymer.