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Copolymers Comprising 2,7-Carbazole and Bis-benzothiadiazole Units for Bulk-Heterojunction Solar Cells

Authors

  • Jonggi Kim,

    1. Interdisciplinary School of Green Energy and KIER-UNIST, Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon-ri, Eonyang-eup, Ulju-gu, Ulsan, 689-798 (South Korea), Fax: (+82) 52-217-2909
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  • Myoung Hee Yun,

    1. Interdisciplinary School of Green Energy and KIER-UNIST, Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon-ri, Eonyang-eup, Ulju-gu, Ulsan, 689-798 (South Korea), Fax: (+82) 52-217-2909
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  • Piyush Anant,

    1. Centre for Polymer Science and Engineering, Indian Institute of Technology (IIT), Hauz Khas, New Delhi (India)
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  • Prof. Shinuk Cho,

    1. Department of Physics and EHSRC, University of Ulsan, Ulsan 680-749 (South Korea)
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  • Dr. Josemon Jacob,

    1. Centre for Polymer Science and Engineering, Indian Institute of Technology (IIT), Hauz Khas, New Delhi (India)
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  • Prof. Jin Young Kim,

    1. Interdisciplinary School of Green Energy and KIER-UNIST, Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon-ri, Eonyang-eup, Ulju-gu, Ulsan, 689-798 (South Korea), Fax: (+82) 52-217-2909
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  • Prof. Changduk Yang

    Corresponding author
    1. Interdisciplinary School of Green Energy and KIER-UNIST, Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon-ri, Eonyang-eup, Ulju-gu, Ulsan, 689-798 (South Korea), Fax: (+82) 52-217-2909
    • Interdisciplinary School of Green Energy and KIER-UNIST, Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon-ri, Eonyang-eup, Ulju-gu, Ulsan, 689-798 (South Korea), Fax: (+82) 52-217-2909
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Abstract

On the basis of theoretical considerations of the intramolecular charge transfer (ICT) effect, we have designed a series of donor (D)–acceptor (A) conjugated polymers based on bis-benzothiadiazole (BBT). A PPP-type copolymer of electron-rich 2,7-carbazole (CZ) and electron-deficient BBT units poly[N-(2-decyltetradecyl)-2,7-carbazole-co-7,7′-{4,4′-bis-(2,1,3-benzothiadiazole)}] (PCZ-BBT), a PPV-type copolymer poly[N-(2-decyltetradecyl)-2,7-carbazolevinylene-co-7,7′-{4,4′-bis-(2,1,3-benzothiadiazolevinylene)}] (PCZV-BBTV), and a tercopolymer based on carbazole, thiophene, and BBT poly[N-(2-decyltetradecyl)-2,7-(di-2-thienyl)carbazole-co-7,7′-{4,4′-bis-(2,1,3-benzothiadiazole)}] (PDTCZ-BBT) have been synthesized to understand the influence of BBT acceptor structure and linkage on the photovoltaic characteristics of the resulting materials. Both the HOMO and LUMO of the resulting polymers are found to be deeper-lying than those of benzothiadiazole-based polymers. The measured electrochemical band gaps (eV) are in the following order: PDTCZ-BBT (1.65 eV) < PCZV-BBTV (1.69 eV) < PCZ-BBT (1.75 eV). All the polymers provide a photovoltaic response when blended with a fullerene derivative as an electron acceptor. The best cell reaches a power conversion efficiency of 2.07 % estimated under standard solar light conditions (AM1.5G, 100 mW cm−2). We demonstrate for the first time that BBT-based polymers are promising materials for use in bulk-heterojunction solar cells.

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