A comparative MD study of the local structure of polymer semiconductors P3HT and PBTTT

Atomistic molecular dynamics simulations of P3HT and PBTTT-C12 at finite temperatures are carried out to investigate the nanoscale structural properties that lead to higher measured hole mobility in PBTTT versus P3HT field-effect transistors. Simulations of the polymer melts show that the structural properties in PBTTT facilitate both intra-and inter-chain charge transport compared with P3HT due to a greater degree of planarity, closer and more parallel stacking of the thiophene and thienothiophene rings, and possible interdigitation of the dodecyl side chains. The crucial role played by the bulky dodecyl side chain and thienothiophene ring, respectively, in determining intra-chain and inter-chain structural order is clarified.