Configurationally Random Polythiophene for Improved Polymer Ordering and Charge-Transporting Ability

Random polythiophene polymers are characterized by the arbitrary sequences of monomeric units along polymer backbones. These untailored orientations generally result in the twisting of thiophene rings out of the conjugation planarity in addition to steric repulsions experienced among substituted alkyl chains. These tendencies have limited close polymer packing, which has been detrimental to charge transport in these moieties. To ameliorate charge transport in these classes of polymers, we make use of simple Stille coupling polymerization to synthesize highly random polythiophene polymers. We induced a positive microstructural change between polymer chains by attuning the ratio between alkyl-substituted and nonalkyl-substituted monomer units along the backbones. The optimized random polythiophene was found to have enhanced intermolecular interaction, increased size of crystallites, and stronger tendency to take edge orientation compared with both regiorandom and regioregular poly(3-hexylthiophene) polymers. Incorporation of the optimized random polythiophene as an active material in solid-state electrolyte-gated organic field-effect transistors exhibited better performance than the control device using regioregular poly(3-hexylthiophene), with a high hole mobility up to 4.52 cm² V^-1 s^-1 in ambient conditions.