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Observation of a Charge Transfer State in Low-Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

Authors

  • Yi Zhou,

    1. Biomolecular and Organic Electronics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden)
    2. Center of Organic Electronics (COE) Linköping University 581 83 Linköping (Sweden)
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  • Kristofer Tvingstedt,

    1. Biomolecular and Organic Electronics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden)
    2. Center of Organic Electronics (COE) Linköping University 581 83 Linköping (Sweden)
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  • Fengling Zhang,

    1. Biomolecular and Organic Electronics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden)
    2. Center of Organic Electronics (COE) Linköping University 581 83 Linköping (Sweden)
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  • Chunxia Du,

    1. Surface and Semiconductor Physics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden)
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  • Wei-Xin Ni,

    1. Surface and Semiconductor Physics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden)
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  • Mats R. Andersson,

    1. Center of Organic Electronics (COE) Linköping University 581 83 Linköping (Sweden)
    2. Polymer Technology Department of Chemical and Biological Engineering Chalmers University of Technology 412 96 Göteborg (Sweden)
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  • Olle Inganäs

    Corresponding author
    1. Biomolecular and Organic Electronics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden)
    2. Center of Organic Electronics (COE) Linköping University 581 83 Linköping (Sweden)
    • Biomolecular and Organic Electronics Department of Physics, Chemistry and Biology (IFM) Linköping University 581 83 Linköping (Sweden).
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Abstract

The presence of charge transfer states generated by the interaction between the fullerene acceptor PCBM and two alternating copolymers of fluorene with donor–acceptor–donor comonomers are reported; the generation leads to modifications in the polymer bandgap and electronic structure. In one of polymer/fullerene blends, the driving force for photocurrent generation, i.e., the gap between the lowest unoccupied molecular orbitals of the donor and acceptor, is only 0.1 eV, but photocurrent is generated. It is shown that the presence of a charge transfer state is more important than the driving force. The charge transfer states are visible through new emission peaks in the photoluminescence spectra and through electroluminescence at a forward bias. The photoluminescence can be quenched under reverse bias, and can be directly correlated to the mechanism of photocurrent generation. The excited charge transfer state is easily dissociated into free charge carriers, and is an important intermediate state through which free charge carriers are generated.

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