Nanoscale Phase Separation and High Photovoltaic Efficiency in Solution-Processed, Small-Molecule Bulk Heterojunction Solar Cells

Authors

  • Bright Walker,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
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  • Arnold B. Tamayo,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
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  • Xuan-Dung Dang,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
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  • Peter Zalar,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
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  • Jung Hwa Seo,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
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  • Andres Garcia,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
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  • Mananya Tantiwiwat,

    1. Department of Physics University of California Santa Barbara, CA, 93106 (USA)
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  • Thuc-Quyen Nguyen

    Corresponding author
    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA)
    • Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106 (USA).
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Abstract

Research relating to organic solar cells based on solution-processed, bulk heterojunction (BHJ) films has been dominated by polymeric donor materials, as they typically have better film-forming characteristics and film morphology than their small-molecule counterparts. Despite these morphological advantages, semiconducting polymers suffer from synthetic reproducibility and difficult purification procedures, which hinder their commercial viability. Here, a non-polymeric, diketopyrrolopyrrole-based donor material that can be solution processed with a fullerene acceptor to produce good quality films is reported. Thermal annealing leads to suitable phase separation and material distribution so that highly effective BHJ morphologies are obtained. The frontier orbitals of the material are well aligned with those of the fullerene acceptor, allowing efficient electron transfer and suitable open-circuit voltages, leading to power conversion efficiencies of 4.4 ± 0.4% under AM1.5G illumination (100 mW cm−2). Small molecules can therefore be solution processed to form high-quality BHJ films, which may be used for low-cost, flexible organic solar cells.

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