For organic semiconductors, the solid-state packing of the π-conjugated molecules or polymers dictate the material electronic, optical, and mechanical characteristics. Combinations of solution and solid-state investigations are often used to establish structure-function relationships, though these connections are often loosely correlated, and experiments in different laboratories can lead to widely variable interpretations. Hence, there remains a need to develop a deeper, more robust understanding of the connections between molecular and polymer chemistry, structure, processing, solid-state order, and materials properties to enable judicious materials design principles. Towards this goal, we employ fully-atomistic molecular dynamics (MD) simulations of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] (PTB7), a donor-acceptor copolymer that has been widely investigated in the organic solar cell literature, to unravel some of these associations. The MD simulations make use of polymer lengths (molecular weights) and solution concentrations that are consistent with those used in experiment, allowing for a detailed picture to arise as to how variations in the polymer environment can direct polymer structure. Comparisons between experiment and theory suggest that processing history can be an important factor in the polymer structures presumed experimentally that are used to interpret optical and electronic responses. The results of these simulations provide specific information into the behavior of PTB7 under different conditions, and showcase how atomistic MD simulations that approach experimentally relevant sizes can be used to develop broader chemical insight that can aid in the design, processing, and characterization of polymer-based organic semiconductors.
|Number of pages||12|
|Journal||Physical Chemistry Chemical Physics|
|State||Published - 2019|
Bibliographical noteFunding Information:
This work was supported by the Office of Naval Research (Award Number N00014-16-1-2985), and was made possible by the Department of Defense (DoD) Centennial, Hokule’a, Lightning, Onyx, Thunder, and Topaz supercomputing resources through the DoD High Performance Computing Modernization Program (HPCMP; Project Number ONRDC40433481). Additional supercomputing resources on the Lipscomb High Performance Computing Cluster were provided by the University of Kentucky Information Technology Department and Center for Computational Sciences (CCS), and on the Holly computing cluster by the University of Kentucky College of Arts & Sciences. We would like to thank Mr Shi Li for many fruitful discussions on the MD protocols, and Dr Uma Ramasamy for a critical evaluation of this work.
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ASJC Scopus subject areas
- Physics and Astronomy (all)
- Physical and Theoretical Chemistry