Electrochemical Impedance Spectra of Poly(3-octylthiophene) Films

Charge transfer in poly(3-octylthiophene) films in 0.05–0.5 M LiClO₄ solutions in acetonitrile is studied by an electrochemical impedance method. The resistance to charge transfer R _ct and the capacitance of the electrical double layer C _dl are calculated from the high-frequency semicircle and referred to the film/electrolyte interface. The low-frequency capacitance C _lf and effective diffusion coefficient D _ef are determined by analyzing the region of medium and low frequencies. The discrepancies between potential dependences of C _lf and D _ef derived experimentally and calculated within a simple model for a redox film are analyzed. The assumption is made that additional factors, such as a macroporous character of the films and the change in their properties during oxidation, which results from the film swelling, the change in the film volume and the solvation character, should be taken into account.