Modeling cyclic voltammetry and electrochemical impedance spectroscopy measurements of PEDOT:PSS layers with finite density of states

Abstract

This paper examines the impact of a finite density of states on hole transport in conjugated polymers, with a focus on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). To this end, a two-phase drift-diffusion model of PEDOT:PSS is extended to include a Fermi–Dirac, near-equilibrium occupation of the available hole states and a generalized Einstein relation between hole diffusivity and mobility in the PEDOT phase. A dedicated procedure is developed to impose the boundary conditions and to strengthen the convergence of the model equations. Numerical solutions of the extended model are compared to the results that neglect the above-mentioned aspects. We identify those conditions where the limited DoS affects the cyclic voltammetry and the electrochemical impedance spectroscopy response of a circular PEDOT:PSS-coated electrode in contact with an electrolyte. The results provide new insights into the electronic and ionic behavior of these electrodes and can be useful for preventing the inaccurate extraction of PEDOT:PSS properties or even the misinterpretation of cyclic voltammetry and electrochemical impedance spectroscopy experiments.