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Investigating the Influence of Interfacial Contact Properties on Open Circuit Voltages in Organic Photovoltaic Performance: Work Function Versus Selectivity

Authors

  • Erin L. Ratcliff,

    Corresponding author
    1. Department of Chemistry and Biochemistry, University of Arizona, 1306 E. University Blvd, Tucson, AZ 85721, USA
    • Department of Chemistry and Biochemistry, University of Arizona, 1306 E. University Blvd, Tucson, AZ 85721, USA
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  • Andres Garcia,

    1. National Center for Photovoltaics, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA
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  • Sergio A. Paniagua,

    1. Department of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Tech University, 901 Atlantic Drive, Atlanta, GA 30332, USA
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  • Sarah R. Cowan,

    1. National Center for Photovoltaics, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA
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  • Anthony J. Giordano,

    1. Department of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Tech University, 901 Atlantic Drive, Atlanta, GA 30332, USA
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  • David S. Ginley,

    1. National Center for Photovoltaics, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA
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  • Seth R. Marder,

    1. Department of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Tech University, 901 Atlantic Drive, Atlanta, GA 30332, USA
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  • Joseph J. Berry,

    1. National Center for Photovoltaics, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA
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  • Dana C. Olson

    Corresponding author
    1. National Center for Photovoltaics, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA
    • National Center for Photovoltaics, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
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Abstract

The role of work function and thermodynamic selectivity of hole collecting contacts on the origin of open circuit voltage (VOC) in bulk heterojunction organic photovoltaics is examined for poly(N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) and [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) solar cells. In the absence of a charge selective, electron blocking contact, systematic variation of the work function of the contact directly dictates the VOC, as defined by the energetic separation between the relative Fermi levels for holes and electrons, with little change in the observed dark saturation current, J0. Improving the charge selectivity of the contact through an increased barrier to electron injection from the fullerene in the blend into the hole contact results in a decreased reverse saturation current (decreased J0 and increased shunt resistance, RSH) and improved VOC. Based on these observations, we provide a set of contact design criteria for tuning the VOC in bulk heterojunction organic photovoltaics.

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