Long-Range Energy Level Shifts Induced by Single Impurity Molecules in C60 Thin Films

ORAL

Abstract

Organic photovoltaics (OPV) is a promising technology for low-cost, flexible solar cells with low embodied energy. However, the efficiency remains low due to high exciton binding energies. The main driving force behind exciton dissociation is the energy landscape around the donor-acceptor interface. To optimize device efficiency, we therefore need to better understand the pathways of exciton dissociation at interfaces in OPV materials and how they correlate with the energy landscape. We use scanning tunneling microscopy and spectroscopy to study model systems consisting of thin films of C60 with single molecules of pure and fluorinated zinc phthalocyanine (ZnPc, F4ZnPc, and F8ZnPc) added. We measure how a molecule affects the energy levels in the surrounding C60 matrix; they shift by up to 150 meV depending on the degree of fluorination of the impurity molecule. This shift prevails over at least several C60 molecules from the impurity. This large and long-range shift induced by the phthalocyanine, and heavily influenced by the fluorine atoms, opens up new possibilities for controlled design of the energy landscape in the OPV heterojunction to optimize charge transfer efficiency.

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Presenters

  • Erik Mårsell

    University of British Columbia

Authors

  • Erik Mårsell

    University of British Columbia

  • Bingkai Yuan

    University of British Columbia

  • Katherine Cochrane

    University of British Columbia, Molecular Foundry, Lawrence Berkeley National Laboratory

  • Miriam D DeJong

    University of British Columbia

  • David J Jones

    University of British Columbia, University of British Colombia, QMI, University of British Columbia, Physics and Astronomy, University of British Columbia, Department of Physics & Astronomy, University of British Columbia

  • Moritz Riede

    University of Oxford

  • Sarah A. Burke

    Department of Physics and Astronomy, University of British Columbia, University of British Columbia, Stewart Blusson Quantum Matter Institute, University of British Columbia