In Situ Characterization of Lifetime and Morphology in Operating Bulk Heterojunction Organic Photovoltaic Devices by Impedance Spectroscopy

Authors

  • Benjamin J. Leever,

    Corresponding author
    1. Department of Materials Science & Engineering and the Argonne-Northwestern Solar Energy Research Institute Northwestern University, 2220 Campus Drive, Evanston, IL, 60208-3108, USA, and Air Force, Research Laboratory 2941 Hobson Way, Wright-Patterson AFB, OH, 45433-7750, USA
    • Department of Materials Science & Engineering and the Argonne-Northwestern Solar Energy Research Institute Northwestern University, 2220 Campus Drive, Evanston, IL, 60208-3108, USA, and Air Force, Research Laboratory 2941 Hobson Way, Wright-Patterson AFB, OH, 45433-7750, USA
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  • Christopher A. Bailey,

    Corresponding author
    1. Air Force Research Laboratory, 2941 Hobson Way, Wright-Patterson AFB, OH, 45433-7750, USA
    • Air Force Research Laboratory, 2941 Hobson Way, Wright-Patterson AFB, OH, 45433-7750, USA
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  • Tobin J. Marks,

    Corresponding author
    1. Department of Chemistry, Department of Materials Science & Engineering, the Materials Research Institute, and the Argonne-Northwestern Solar Energy Research Institute, Northwestern University, 2145 Sheridan Rd, Evanston, IL, 60208-3113, USA
    • Department of Chemistry, Department of Materials Science & Engineering, the Materials Research Institute, and the Argonne-Northwestern Solar Energy Research Institute, Northwestern University, 2145 Sheridan Rd, Evanston, IL, 60208-3113, USA
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  • Mark C. Hersam,

    Corresponding author
    1. Department of Materials Science & Engineering, Department of Chemistry, the Materials Research Institute, and the Argonne-Northwestern Solar Energy Research Institute, Northwestern University, 2220 Campus Dr, Evanston, IL, 60208-3108, USA
    • Department of Materials Science & Engineering, Department of Chemistry, the Materials Research Institute, and the Argonne-Northwestern Solar Energy Research Institute, Northwestern University, 2220 Campus Dr, Evanston, IL, 60208-3108, USA
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  • Michael F. Durstock

    Corresponding author
    1. Air Force Research Laboratory, 2941 Hobson Way, Wright-Patterson AFB, OH, 45433-7750, USA
    • Air Force Research Laboratory, 2941 Hobson Way, Wright-Patterson AFB, OH, 45433-7750, USA.
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Abstract

Time-dependent charge transport in operating poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction organic photovoltaic (OPV) devices has been characterized with impedance spectroscopy. Devices with varied composition and morphology were measured over a range of illumination intensities ranging from dark conditions to 1 sun and applied bias voltages ranging from 0.0 V to 0.75 V. Using an equivalent circuit model, materials properties such as dielectric constant and conductivity were determined and found to be in agreement with values measured by other methods. Average carrier lifetimes were also extracted from the model and found to correlate with measured power conversion efficiencies. At the short circuit condition and ∼1 sun illumination, the average electron lifetime was found to vary from 7.8 to 22 μs for devices with power conversion efficiencies ranging from 2.0 to 2.5%. These results suggest that impedance spectroscopy is an effective tool for predicting how processing parameters can impact device performance in organic bulk heterojunction photovoltaic devices.

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