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

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 polymer doping level depends on the bias potential maintained between counter- and working electrodes, changes of electronic density of many orders of magnitude (from 1016 up to 1020 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 σdc with bias potential E at low doping levels follows the relationship ln σdc∝E/2kBT, 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 diffusion characteristic frequency ωd, which results within the range of De∼4–1×10−3 cm2 s−1.