Solvent effects on the charge transport behavior in poly(3,4- ethylenedioxythiophene) synthesized with iron(III)-p-toluenesulfonate

The effects of organic solvent on the charge transport behavior of poly(3,4-ethylenedioxythiophene)/p-toluenesulfonate(PEDOT-OTs) are investigated. The use of different organic solvents during the oxidative chemical polymerization of 3,4-ethylenedioxythiophene(EDOT) with Iron(III)-tosylate can greatly vary the DC conductivity of PEDOT-OTs along with molecular structure and doping concentration. For example, PEDOT-OTs prepared from methanol shows the conductivity of 19.5 S/cm, which is an increase by a factor of 10⁸ compared to PEDOT-OTs prepared from acetone. From the X-ray diffraction (XRD) experiments, it was found that PEDOT-OTs with ketone is amorphous state, while PEDOT-OTs with alcoholic solvent shows the better defined crystalline structure in which the charge transport along and between the PEDOT chains are promoted. Chemical analysis employing X-ray photoelectron spectroscopy (XPS) revealed that the doping concentration of PEDOT-OTs with alcoholic solvent is much higher than that of PEDOT-OTs with ketones. It is proposed that the interactions between the organic solvent and doping anion can cause the variation in doping concentration and, therefore, result in the PEDOT-OTs of different conductivities and chain structures.