Ionic conductivity in cationic polythiophenes

Recently, there has been considerable interest in developing materials that combine electronic with ionic conduction. Herein, we designed novel single ion conductors, based on cationic polythiophenes. They consist of a polythiophene backbone, a side group with a cation covalently bonded and a mobile anion. We report on the ionic conductivity (with Dielectric Spectroscopy) as a function of backbone molecular weight, side group length, and anion size. The side group length varies from four to ten methylene units and increases the room temperature conductivity by four orders of magnitude (internal plasticization). The anion size (anionic radii from 0.19 nm to 0.44 nm) affects both the structure (lamellar to amorphous by increasing anion radius as evidenced by WAXS) and the measured conductivity. The dc-conductivity increases by six orders of magnitude by increasing anion size at ambient temperature. As a result, conductivities as high as 2 × 10^-3 S/cm could be measured at high temperatures. Differences in dc - conductivity are discussed in terms of changes in glass temperature that is increasing with increasing anion size. On top of this, there is a weak dependence of conductivity on the side group length and anion size as evidenced by the different fragilities