Doping level change of polythiophene film during its electrochemical growth process

Polythiophene (Pth) films have been electrochemically deposited on mirror-like stainless steel (SS) (or gold) electrode surfaces by direct oxidation of thiophene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.3 V (vs. Ag/AgCl). The Raman spectra of Pth films have been investigated by excitation with a 514, 633 or 785 nm laser beam. The 633 nm laser beam was found to be the best among the three excitation lights tried for studying the doping level change of Pth film. The overall features of 633 nm excited resonance Raman spectra of as-grown Pth films depend strongly on film thickness. Raman and X-ray photoelectron energy spectroscopic (XPS) results and electrochemical studies demonstrated that the doping level of the Pth film increased with the increase of film thickness. Furthermore, successive cyclic voltammetric scanning was found to be a more effective approach than applying a constant positive potential for doping a thin compact conducting polymer film.