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Anisotropic Structure and Charge Transport in Highly Strain-Aligned Regioregular Poly(3-hexylthiophene)

Authors

  • Brendan O'Connor,

    1. Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
    Current affiliation:
    1. Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA
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  • R. Joseph Kline,

    1. Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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  • Brad R. Conrad,

    1. Semiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
    Current affiliation:
    1. Department of Physics and Astronomy, Appalachian State University, Boone, NC 28608, USA
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  • Lee J. Richter,

    1. Surface and Microanalysis Division, National Institute and Standards and Technology, Gaithersburg, MD 20899, USA
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  • David Gundlach,

    1. Semiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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  • Michael F. Toney,

    1. Stanford Synchrotron Radiation Lightsource, Menlo Park, CA 94025, USA
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  • Dean M. DeLongchamp

    Corresponding author
    1. Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
    • Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
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Abstract

A novel method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge-mobility anisotropy, where the in-plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two-dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane-on and edge-on packing configurations, as the strain alignment is found to induce a significant face-on orientation of the originally highly edge-on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge-mobility anisotropy of 9, providing a simple and effective method to investigate charge-transport mechanisms in polymer semiconductors.

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