engleski

In-situ optoelectronic properties of a conducting polymer film studied by means of electrochemical spectroscopic ellipsometry

The dielectric function contains important information about the optical and electronic properties of conducting and semiconducting materials. The aim is to present the experimental dielectric functions of a hydrated poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film, determined from the in-situ measured ellipsometric VIS/NIR spectra under varied conditions of electrochemical doping1. In the experiments, the electrochemical potential of the film was controlled by applying an external equilibrium potential equal to the electromotive force at the PEDOT:PSS thin film electrode in a three electrode cell. The main electronic transition was resolved from the free electron absorption by fitting the Tauc-Lorentz-Drude dielectric function2. The electrical conductivity of the film was calculated from the Drude term, and was drawn into relationship with the main electronic transition by applying a redox isotherm under assumption of a constant density of states. The fitted Nernst slope of only 12 mV is an evidence of very strong electrostatic repulsions between the oxidized EDOT+ sites in doped PEDOT, which is in turn responsible for a low capacitance of the electrical double layer at the PEDOT "surface". The latter gives rise to an electrochemical potential range (about 0.5 V wide) in which PEDOT:PSS exhibits almost exclusively capacitive behavior. This result corroborates the hypothesis that within the above potential regime, the operating mechanism for the organic electrochemical transistors implementing a PEDOT:PSS channel invokes predominately the field effect rather than redox reactions. (1) Pathak, G. ; Krasińska-Krawet, Z. ; Szyk-Warszyńska, L. ; Čakara, D. Thin Solid Films 2018, 651, 31–38. (2) Fujiwara, H. Spectroscopic ellipsometry: principles and applications ; John Wiley & Sons, 2007.

conducting polymer film ; dielectric function ; electrochemical ; doping ; model ; ellipsometry

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