Electroanalytical features of non-uniformly doped conducting poly-3-(3,4,5-trifluorophenyl)thiophene films

Specially prepared, thin poly-3-(3,4,5-trifluorophenyl)thiophene, PTFPT, films were shown to possess stable p- and, most importantly, n-doping in TEABF₄/sulfolane (SF) solutions. Electrodes comprising PTFPT films were studied by cyclic voltammetry (CV), potentiostatic intermittent titration (PITT), and electrochemical impedance spectroscopy (EIS). A detailed analysis of the shape of the time-dependent current transients during PITT characterization of the PTFPT electrodes has been performed. The non-uniform character of the PTFPT film doping was proved. Plots of dlogl(t)/dlog t vs. t/τ_d were found to be useful for understanding the response of potentiostatic transients. The Cottrell time domain during potentiostatic transients was found to be very narrow, reflecting the drastic effect of the Ohmic potential drops (mainly across the film's bulk) on the semi-infinite diffusion current transient at the shortest times, and a wide distribution of the diffusion time constants. PITT and EIS characterizations provided converging results with respect to the relevant diffusion time constants and the non-uniform character of PTFPT film doping in the SF solution. EIS measurements were found to be very useful for the determination of diffusion time constants, as they allow more effective separation of the medium frequency, Warburg response from the Ohmic and the kinetic high-frequency responses.