(167e) Computational and Kinetic Considerations for Morphology Prediction of Donor-Acceptor Oligomers for Organic Photovoltaics

Organic photovoltaic (OPV) solar cells are inexpensive, flexible, lightweight devices for sustainably generating electrical power. The efficiency and stability of OPV devices depends on their morphology, which we currently have poor synthetic control over. In this work, we perform molecular dynamics simulations of neat benzodithiophene-theinopyrrolodione (BDT-TPD) oligomers used in OPVs to evaluate the degree to which current simulation techniques are capable of predicting morphology in BDT-TPD films. The morphologies of simulated BDT-TPD volumes are characterized with simulated grazing-incidence X-ray scattering (GIXS) experiments and compared against experimental GIXS measurements. We find that the morphologies predicted from instantaneously quenched simulations better match experiments than structures that are allowed to equilibrate. This result highlights the competition between thermodynamics and kinetics in the structural evolution of polymer thin films. Further, we find that approximating the aromatic rings in BDT-TPD with rigid bodies rather than combinations of bond, angle, and dihedral constraints, results in better computational efficiency but poorer agreement with experimental structure. We determine the primary structural features in films of BDT-TPD are the stacking of oligomer backbones and the self-organization of backbone stacks into â??ribbonsâ?' with long-range spatial correlations. We conclude with a discussion of the shortcomings of current modeling tools and potential directions for improvement.