The Effect of Organic and Metal Oxide Interfacial layers on the Performance of Inverted Organic Photovoltaics

Authors

  • Achilleas Savva,

    1. Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol, 3603, Cyprus
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  • Foteini Petraki,

    1. Department of Chemical Engineering, University of Patras, Patra, 26504 Greece
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  • Polyvios Elefteriou,

    1. Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol, 3603, Cyprus
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  • Lambrini Sygellou,

    1. Department of Chemical Engineering, University of Patras, Patra, 26504 Greece
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  • Monika Voigt,

    1. Department of Physics and Centre for Plastic Electronics, The Blackett Laboratory, Imperial College London, London SW7 2BZ, UK
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  • Myrsini Giannouli,

    1. Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol, 3603, Cyprus
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  • Stella Kennou,

    1. Department of Chemical Engineering, University of Patras, Patra, 26504 Greece
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  • Jenny Nelson,

    1. Department of Physics and Centre for Plastic Electronics, The Blackett Laboratory, Imperial College London, London SW7 2BZ, UK
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  • Donal D. C. Bradley,

    1. Department of Physics and Centre for Plastic Electronics, The Blackett Laboratory, Imperial College London, London SW7 2BZ, UK
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  • Christoph J. Brabec,

    1. Institute for Materials in Electronics and Energy Technology, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, D-91058, Germany
    2. Bavarian Center for Applied Energy Research (ZAE Bayern), Erlangen, D-91058, Germany
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  • Stelios A. Choulis

    Corresponding author
    1. Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol, 3603, Cyprus
    • Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol, 3603, Cyprus.
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Abstract

We study the origin of the improvement of the power conversion efficiency (PCE) of inverted organic solar cells when an interfacial insulating organic layer of polyoxyethylene tridecyl ether (PTE) is introduced between the indium tin oxide (ITO) bottom electrode and the TiOx interfacial layer. XPS and UPS measurements are used to investigate the energy level alignment at the interfaces within the ITO/TiOx and ITO/PTE/TiOx structures and to identify any effects due to chemical interaction and interfacial dipoles. Scanning electron microscopy studies show that the surface structure of the TiOx layer is affected, when it is coated on top of the PTE layer. Surface contact angle measurements show that the incorporated interfacial layer of PTE is more hydrophilic than ITO and thus PTE modified TiOx becomes more hydrophilic. This, in combination with the surface gaps of the PTE interfacial layer, is likely to lead to changed wetting and hydrolysis properties of TiOx when coated on ITO/PTE than on ITO alone. The different TiOx layer quality is reflected in improved electron selectivity, leading to enhanced fill factor, reduced parasitic resistance effects and higher power conversion efficiency for inverted solar cells with a PTE interfacial layer between ITO and TiOx.

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