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

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. Here 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 ofmore » polarons in OSCs. In conclusion, 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. Lastly, our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.« less
Authors:
ORCiD logo ; ; ; ; ; ; ; ; ORCiD logo
Publication Date:
Report Number(s):
LA-UR-16-22738; NREL/JA-2C00-68402
Journal ID: ISSN 2041-6520; CSHCBM
Grant/Contract Number:
AC52-06NA25396; AC02-06CH11357; CHE-1464804; AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 8; Journal Issue: 4; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Argonne National Lab. (ANL), Argonne, IL (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Material Science; 14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; organic photovoltaics; charge transport; organic semiconducting materials; Langevin molecular dynamics
OSTI Identifier:
1353009
Alternate Identifier(s):
OSTI ID: 1340928; OSTI ID: 1352608

Pelzer, Kenley M., Vázquez-Mayagoitia, Álvaro, Ratcliff, Laura E., Tretiak, Sergei, Bair, Raymond A., Gray, Stephen K., Van Voorhis, Troy, Larsen, Ross E., and Darling, Seth B.. Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer. United States: N. p., Web. doi:10.1039/c6sc04547b.
Pelzer, Kenley M., Vázquez-Mayagoitia, Álvaro, Ratcliff, Laura E., Tretiak, Sergei, Bair, Raymond A., Gray, Stephen K., Van Voorhis, Troy, Larsen, Ross E., & Darling, Seth B.. Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer. United States. doi:10.1039/c6sc04547b.
Pelzer, Kenley M., Vázquez-Mayagoitia, Álvaro, Ratcliff, Laura E., Tretiak, Sergei, Bair, Raymond A., Gray, Stephen K., Van Voorhis, Troy, Larsen, Ross E., and Darling, Seth B.. 2017. "Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer". United States. doi:10.1039/c6sc04547b. https://www.osti.gov/servlets/purl/1353009.
@article{osti_1353009,
title = {Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer},
author = {Pelzer, Kenley M. and Vázquez-Mayagoitia, Álvaro and Ratcliff, Laura E. and Tretiak, Sergei and Bair, Raymond A. and Gray, Stephen K. and Van Voorhis, Troy and Larsen, Ross E. and Darling, Seth B.},
abstractNote = {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. Here 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. In conclusion, 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. Lastly, our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.},
doi = {10.1039/c6sc04547b},
journal = {Chemical Science},
number = 4,
volume = 8,
place = {United States},
year = {2017},
month = {1}
}

Works referenced in this record:

Conjugated Polymer-Based Organic Solar Cells
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Electron transfer reactions in chemistry. Theory and experiment
journal, July 1993