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Tuning the HOMO Energy Levels of Organic Dyes for Dye-Sensitized Solar Cells Based on Br/Br3 Electrolytes

Authors

  • Chao Teng,

    1. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185
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  • Prof. Xichuan Yang,

    Corresponding author
    1. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185
    • State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185

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  • Shifeng Li,

    1. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185
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  • Ming Cheng,

    1. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185
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  • Prof. Anders Hagfeldt,

    1. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185
    2. School of Chemical Science and Engineering, Center of Molecular Devices, Physical Chemistry, Royal Institute of Technology (KTH), Stockholm (Sweden)
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  • Prof. Li-zhu Wu,

    1. Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China)
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  • Prof. Licheng Sun

    Corresponding author
    1. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185
    2. Department of Chemistry, Organic Chemistry, Royal Institute of Technology(KTH), Stockholm (Sweden)
    • State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian (China), Fax: (+86) 411-837-02185

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Abstract

A series of novel metal-free organic dyes TC301TC310 with relatively high HOMO levels were synthesized and applied in dye-sensitized solar cells (DSCs) based on electrolytes that contain Br/Br3 and I/I3. The effects of additive Li+ ions and the HOMO levels of the dyes have an important influence on properties of the dyes and performance of DSCs. The addition of Li+ ions in electrolytes can broaden the absorption spectra of the dyes on TiO2 films and shift both the LUMO levels of the dyes and the conduction band of TiO2, thus leading to the increase of Jsc and the decrease of Voc. Upon using Br/Br3 instead of I/I3, a large increase of Voc is attributed to the enlarged energy difference between the redox potentials of electrolyte and the Fermi level of TiO2, as well as the suppressed electron recombination. Incident photon to current efficiency (IPCE) action spectra, electrochemical impedance spectra, and nanosecond laser transient absorption reveal that both the electron collection yields and the dye regeneration yields (Φr) depend on the potential difference (the driving forces) between the oxidized dyes and the Br/Br3 redox couple. For the dyes for which the HOMO levels are more positive than the redox potential of Br/Br3 sufficient driving forces lead to the longer effective electron-diffusion lengths and almost the same efficient dye regenerations, whereas for the dyes for which the HOMO levels are similar to the redox potential of Br/Br3, insufficient driving forces lead to shorter effective electron-diffusion lengths and inefficient dye regenerations.

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