Mixed conductivity of polythiophene-based ionic polymers under controlled conditions

The mixed conductivity behavior of polythiophene-based anionic and cationic polymers is studied under controlled atmospheres in this contribution. The conjugated polyelectrolytes are based on regioregular polythiophene backbones with either pendant sulfonate anions or imidazolium cations with counterbalancing tetrabutylammonium hexafluorophosphate and bromide anions, respectively. Direct current, four-point-probe measurements and impedance spectroscopy are performed to separate electronic and ionic conductivity. Optical absorption spectroscopy is used to make statements about the aggregation of the polymer chains and to visualize the electronic doping behavior. Similar to a pure conjugated polymer such as poly(3-hexylthiophene) the electronic conductivity can be tuned over a wide range from below 10−6 S/cm to 2.2 S/cm by external doping with the strong electron acceptor F4TCNQ by sequential solution doping. The ionic conductivity on the other hand is shown to be strongly dependent on the degree of water uptake. We show that values of up to 10−2 S/cm with effective ionic mobilities in the order of 10−8-10−7 cm2/(Vs) can be reached.