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Development and Testing of an All-Atom Force Field for Diketopyrrolopyrrole Polymers with Conjugated Substituents

preprint
submitted on 24.07.2020 and posted on 24.07.2020 by Vivek Sundaram, Alexey V. Lyulin, Björn Baumeier
We develop an all-atom force field for a series of diketopyrrolopyrrole polymers with two aromatic pyridine substituents and variable number of pi-conjugated thiophene units in the backbone, used as donor material in organic photovoltaic devices. Available intra-fragment parameterizations of the individual fragment building blocks are combined with inter-fragment bonded and non-bonded parameters explicitly derived from density-functional theory calculations. To validate the force field we perform classical molecular dynamics simulations of single polymer chains with 1, 2, and 3 thiophenes in good and bad solvents, and of melts. We observe the expected dependence of the chain conformation on the solvent quality, with the chain collapsing in water, and swelling in chloroform. The glass transition temperature for the polymer melts is found to be in the range of 340K to 370K. Analysis of the mobility of the conjugated segments in the polymer backbone reveals two relaxation processes: a fast one with a characteristic time at room temperature on the order of 10ps associated with nearly harmonic vibrations and a slow one on the order of 100 associated with temperature activated cis-trans transitions.

Funding

Netherlands Organisation for Scientific Research (NWO) and the Netherlands eScience Center project number 027.017.G15, within the Joint CSER and eScience program for Energy Research (JCER 2017)

Innovational Research Incentives Scheme Vidi of the NWO with project number 723.016.002

History

Email Address of Submitting Author

b.baumeier@tue.nl

Institution

Eindhoven University of Technology

Country

Netherlands

ORCID For Submitting Author

0000-0002-6077-0467

Declaration of Conflict of Interest

None

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