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Issue 4, 2017
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Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

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Abstract

Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. We propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower than most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. Much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.

Graphical abstract: Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

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Publication details

The article was received on 11 Oct 2016, accepted on 03 Jan 2017 and first published on 11 Jan 2017


Article type: Edge Article
DOI: 10.1039/C6SC04547B
Citation: Chem. Sci., 2017,8, 2597-2609
  • Open access: Creative Commons BY-NC license
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    Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

    K. M. Pelzer, Á. Vázquez-Mayagoitia, L. E. Ratcliff, S. Tretiak, R. A. Bair, S. K. Gray, T. Van Voorhis, R. E. Larsen and S. B. Darling, Chem. Sci., 2017, 8, 2597
    DOI: 10.1039/C6SC04547B

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