The Role of π Bridges in High-Efficiency DSCs Based on Unsymmetrical Squaraines

Authors

  • Dr. Jared H. Delcamp,

    1. Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland), Fax: (+41) 21-693-41-11
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    • These authors contributed equally to this work.

  • Dr. Yanrong Shi,

    1. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400 (USA), Fax: (+01) 404-894-5909
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    • These authors contributed equally to this work.

  • Dr. Jun-Ho Yum,

    1. Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland), Fax: (+41) 21-693-41-11
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  • Dr. Tissa Sajoto,

    1. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400 (USA), Fax: (+01) 404-894-5909
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  • Elisa Dell'Orto,

    1. Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland), Fax: (+41) 21-693-41-11
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  • Dr. Stephen Barlow,

    1. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400 (USA), Fax: (+01) 404-894-5909
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  • Dr. Mohammad K. Nazeeruddin,

    1. Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland), Fax: (+41) 21-693-41-11
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  • Prof. Seth R. Marder,

    Corresponding author
    1. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400 (USA), Fax: (+01) 404-894-5909
    • School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400 (USA), Fax: (+01) 404-894-5909
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  • Prof. Michael Grätzel

    Corresponding author
    1. Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland), Fax: (+41) 21-693-41-11
    • Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne (Switzerland), Fax: (+41) 21-693-41-11
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Abstract

A series of squaraine-based sensitizers with various π bridges and anchors were prepared and examined in dye-sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through π bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4-di-n-hexyl-cyclopentadithiophene group that is directly attached onto the π bridge, JD10, exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem-di-n-hexyl substituents, which extend above and below the π-conjugated dye plane. Dye JD10 demonstrates a power-conversion efficiency of 7.3 % for liquid-electrolyte dye-sensitized solar cells and 7.9 % for cells that are co-sensitized by another metal-free dye, D35, which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident-photon-to-current-conversion efficiency curve is realized for this dye with an excellent short-circuit current of 18.0 mA cm−2. This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5 000 M−1 cm−1 from 400 nm to the long-wavelength onset of 724 nm for dye JD10.

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