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Electronic Trap States in Methanofullerenes

Authors

  • Julia Schafferhans,

    Corresponding author
    1. Experimental Physics VI, Faculty of Physics and Astronomy, Julius-Maximilian-University of Würzburg, Am Hubland, 97074 Würzburg, Germany
    • Experimental Physics VI, Faculty of Physics and Astronomy, Julius-Maximilian-University of Würzburg, Am Hubland, 97074 Würzburg, Germany.
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  • Carsten Deibel,

    1. Experimental Physics VI, Faculty of Physics and Astronomy, Julius-Maximilian-University of Würzburg, Am Hubland, 97074 Würzburg, Germany
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  • Vladimir Dyakonov

    Corresponding author
    1. Experimental Physics VI, Faculty of Physics and Astronomy, Julius-Maximilian-University of Würzburg, Am Hubland, 97074 Würzburg, Germany
    2. Bavarian Center of Applied Energy Research e.V. (ZAE Bayern), Am Hubland, 97074 Würzburg, Germany
    • Experimental Physics VI, Faculty of Physics and Astronomy, Julius-Maximilian-University of Würzburg, Am Hubland, 97074 Würzburg, Germany.
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Abstract

The trap states in three fullerene derivatives, namely PC61BM ([6,6]-phenyl C61 butyric acid methyl ester), bisPC61BM (bis[6,6]-phenyl C61 butyric acid methyl ester) and PC71BM ([6,6]-phenyl C71 butyric acid methyl ester), are investigated by means of thermally stimulated current measurements (TSC). Thereby, the lower limit of the trap densities for all studied methanofullerenes is on the order of 1022 m−3, with the highest trap density in bisPC61BM and the lowest in PC61BM. Fractional TSC measurements on PC61BM reveal a broad trap distribution instead of discrete trap levels, with activation energies ranging from 15 meV to 270 meV and the maximum at about 75 meV. The activation energies of the most prominent traps in the other two fullerene derivatives are significantly higher, at 96 meV and 223 meV for PC71BM and 184 meV for bisPC61BM, respectively. The influence of these findings on the performance of organic solar cells is discussed.

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