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Nanostructure and Optoelectronic Characterization of Small Molecule Bulk Heterojunction Solar Cells by Photoconductive Atomic Force Microscopy

Authors

  • Xuan-Dung Dang,

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

    1. Departments of Chemistry & Biochemistry, Department of Materials, Institute for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106 (USA)
    Current affiliation:
    1. Present address: Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401 (USA)
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  • Junghwa Seo,

    1. Departments of Chemistry & Biochemistry, Department of Materials, Institute for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106 (USA)
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  • Corey V. Hoven,

    1. Departments of Chemistry & Biochemistry, Department of Materials, Institute for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106 (USA)
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  • Bright Walker,

    1. Departments of Chemistry & Biochemistry, Department of Materials, Institute for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106 (USA)
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  • Thuc-Quyen Nguyen

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

Photoconductive atomic force microscopy is employed to study the nano­scale morphology and optoelectronic properties of bulk heterojunction solar cells based on small molecules containing a benzofuran substituted diketopyrrolopyrrole (DPP) core (3,6-bis(5-(benzofuran-2-yl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione, DPP(TBFu)2, and [6,6]–phenyl-C71-butyric acid methyl ester (PC71BM), which were recently reported to have power conversion efficiencies of 4.4%. Electron and hole collection networks are visualized for blends with different donor:acceptor ratios. Formation of nanostructures in the blends leads to a higher interfacial area for charge dissociation, while maintaining bicontinuous collection networks; conditions that lead to the high efficiency observed in the devices. An excellent agreement between nanoscale and bulk open-circuit voltage measurements is achieved by surface modification of the indium tin oxide (ITO) substrate by using aminopropyltrimethoxysilane. The local open-circuit voltage is linearly dependent on the cathode work function. These results demonstrate that photoconductive atomic force microscopy coupled with surface modification of ITO substrate can be used to study nanoscale optoelectronic phenomena of organic solar cells.

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