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Improved Performance of Molecular Bulk-Heterojunction Photovoltaic Cells through Predictable Selection of Solvent Additives

Authors

  • Kenneth R. Graham,

    1. The George and Josephine Butler, Polymer Research Laboratory, Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, FL 32611-7200, USA
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  • Patrick M. Wieruszewski,

    1. The George and Josephine Butler, Polymer Research Laboratory, Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, FL 32611-7200, USA
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  • Romain Stalder,

    1. The George and Josephine Butler, Polymer Research Laboratory, Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, FL 32611-7200, USA
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  • Michael J. Hartel,

    1. Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA
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  • Jianguo Mei,

    1. The George and Josephine Butler, Polymer Research Laboratory, Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, FL 32611-7200, USA
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  • Franky So,

    1. Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA
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  • John R. Reynolds

    Corresponding author
    1. The George and Josephine Butler, Polymer Research Laboratory, Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, FL 32611-7200, USA
    2. School of Chemistry and Biochemistry, School of Materials Science and Engineering and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
    • The George and Josephine Butler, Polymer Research Laboratory, Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, Gainesville, FL 32611-7200, USA.
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Abstract

Solvent additives provide an effective means to alter the morphology and thereby improve the performance of organic bulk-heterojunction photovoltaics, although guidelines for selecting an appropriate solvent additive remain relatively unclear. Here, a family of solvent additives spanning a wide range of Hansen solubility parameters is applied to a molecular bulk-heterojunction system consisting of an isoindigo and thiophene containing oligomer as the electron donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the electron acceptor. Hansen solubility parameters are calculated using the group contribution method and compared with the measured solubilities for use as a screening method in solvent additive selection. The additives are shown to alter the morphologies in a semipredictable manner, with the poorer solvents generally resulting in decreased domain sizes, increased hole mobilities, and improved photovoltaic performance. The additives with larger hydrogen bonding parameters, namely triethylene glycol (TEG) and N-methyl-2-pyrrolidone (NMP), are demonstrated to increase the open circuit voltage by ~0.2 V. Combining a solvent additive observed to increase short circuit current, poly(dimethylsiloxane), with TEG results in an increase in power conversion efficiency from 1.4 to 3.3%.

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