Determination of the electronic conductivity of polybithiophene films at different doping levels using in situ electrochemical impedance measurements

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Abstract
This letter presents in situ electronic conductivity measurements of polybithiophene films using a twin working electrode in an electrochemical configuration. A twin electrode is made of two metallic stripes which are separated by a few micrometers by an insulating gap. As the polymerdoping level depends on the bias potential maintained between counter- and working electrodes, changes of electronic density of many orders of magnitude (from 10 16 up to 10 20 cm −3 in the potential window investigated) can be achieved using this experimental technique. A simple impedance model based on electronic (polaronic) diffusion between absorbing contacts accounts for the measured impedance spectra. The dependence of low-frequency conductivity σ dc with bias potential E at low doping levels follows the relationship ln σ dc ∝E/2k B T, which allows one to regard it as a double contribution, simultaneously electronic and ionic, to the thermodynamics of doping. It has also been possible to calculate the electronic chemical diffusion coefficient from the diffusioncharacteristic frequency ω d , which results within the range of D e ∼4–1×10 −3 cm 2 s −1 .