Accurate Poly(3-hexylthiophene) Forcefield from First-Principle Modeling

A modified version of the dedicated forcefield for poly(3-hexylthiophene) (P3HT) by Marcon and Raos and further optimized by Cheung (MRC) forcefield has been derived from a comparison with ab initio energy minimizations. Our modified version of the forcefield is able to describe more precisely the torsional behavior of thiophene rings in P3HT molecules while retaining the functional forms as well as the original description of Van der Waals, Coulomb, and covalent bond energy contribution of MRC forcefield. Further molecular dynamic (MD) simulations reveal that the modified forcefield yields an optimized structure that agrees more closely with experimental data in term of chain conformation, density and lattice parameters. To further validate the modified forcefield, we compare simulated melting temperatures at different molecular weight against experimentally obtained results, which yields a close agreement especially at the range of molecular weight (> 30,000 g/mol) applied in bulk heterojunction devices. Thereby, the modified forcefield can be used advantageously in MD simulations of P3HT-based bulk-heterojunctions OPV devices, for instance to model the morphology evolution in P3HT:Phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunctions that critically affects device performance.