Triplet Formation in Fullerene Multi-Adduct Blends for Organic Solar Cells and Its Influence on Device Performance

Authors

  • Clare Dyer-Smith,

    1. Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (UK)
    2. Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ (UK)
    3. Grantham Institute for Climate Change, Imperial College London, South Kensington Campus, London, SW7 2AZ (UK)
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  • Luke X. Reynolds,

    1. Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ (UK)
    2. Grantham Institute for Climate Change, Imperial College London, South Kensington Campus, London, SW7 2AZ (UK)
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  • Annalisa Bruno,

    1. Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ (UK)
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  • Donal D. C. Bradley,

    1. Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (UK)
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  • Saif A. Haque,

    1. Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ (UK)
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  • Jenny Nelson

    Corresponding author
    1. Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (UK)
    • Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (UK).
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Abstract

In organic solar cells, high open circuit voltages may be obtained by choosing materials with a high offset between the donor highest occupied molecular orbital (HOMO) and acceptor lowest unoccupied molecular orbital (LUMO). However, increasing this energy offset can also lead to photophysical processes that compete with charge separation. In this paper the formation of triplet states is addressed in blends of polyfluorene polymers with a series of PCBM multi-adducts. Specifically, it is demonstrated that the formation of such triplets occurs when the offset energy between donor ionization potential and acceptor electron affinity is ∼1.6 eV or greater. Spectroscopic measurements support a mechanism of resonance energy transfer for triplet formation, influenced by the energy levels of the materials, but also demonstrate that the competition between processes at the donor–acceptor interface is strongly influenced by morphology.

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