Title: Coarse-Grained Molecular Dynamics Simulations of Thermal Annealing of P3HT:PCBM Bulk Heterojunctions for Organic Photovoltaic Applications
Presenter: Jan Michael Carrillo
Affiliation: Oak Ridge National Laboratory
Abstract: We performed coarse-grained molecular dynamics simulations of the thermal annealing of blends of poly(3-hexylthiophene) (P3HT) and 6,6-phenyl-C61-butyric acid methyl ester (PCBM) at
different weight fractions fm and degrees of polymerization N of the P3HT polymer chains at 423 K based on the force field by Lee, Pao and Chu Lee et al., Energy Environ. Sci., 2011, 4, 4124-4132.
The simulations were performed up to 400 ns in terms of “simulation time” which translates to 0.27 ms in “real time” and one order of magnitude longer than previous MD simulations. The simulation sizes
are comparable to the thickness of the active layer of a bulk heterojunction device which is around 100 nm. We observed that the thermal annealing process proceeds in two stages which is characterized
by the fast evolution of morphological quantities such as the interfacial area to volume ratio ? and the location of the scattering peak qmax and then followed by the slowing down of the evolution of
these quantities. The simulation shows two phases which are the loosely packed PCBM domains and the P3HT matrix with dissolved PCBM and is reflective of the nature of the force field used which implies
that PCBM is immiscible to P3HT. We characterized microscopic properties such as the packing fraction of the P3HT and PCBM beads ?, mean square end-to-end distance of the P3HT chain