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Syntheses and characterization of carbazole based new low-band gap copolymers containing highly soluble benzimidazole derivatives for solar cell application

Authors

  • Jaehong Kim,

    1. Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
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  • Sung Heum Park,

    1. Department of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea
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  • Jinwoo Kim,

    1. Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
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  • Shinuk Cho,

    1. Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106
    Current affiliation:
    1. Department of Physics, University of Ulsan, Ulsan 680-749, Korea
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  • Youngeup Jin,

    1. Department of Industrial Chemistry, Pukyong National University, Busan 608-739, Korea
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  • Joo Young Shim,

    1. Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
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  • Hyunmin Shin,

    1. Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
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  • Sooncheol Kwon,

    1. Department of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea
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  • Il Kim,

    1. The WCU Center for Synthetic Polymer Bioconjugate Hybrid Materials, Department of polymer Science and Engineering, Pusan National University, Busan 609-735, Korea
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  • Kwanghee Lee,

    1. Department of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea
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  • Alan J. Heeger,

    1. Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106
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  • Hongsuk Suh

    Corresponding author
    1. Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
    • Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
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Abstract

Newly designed 2H-benzimidazole derivatives which have solubility groups at 2-position have been synthesized and incorporated into two highly soluble carbazole based alternating copolymers, poly[2,7-(9-(1′-octylnonyl)-9H-carbazole)-alt-5,5-(4′,7′-di(thien-2-yl)-2H-benzimidazole-2′-spirocyclohexane)] (PCDTCHBI) and poly[2,7-(9-(1′-octylnonyl)-9H-carbazole)-alt-5,5-(4′,7′-di(thien-2-yl)-2H-benzimidazole-2′-spiro-4′′-((2′′′-ethylhexyl)oxy)-cyclohexane)] (PCDTEHOCHBI) for photovoltaic application. These alternating copolymers show low-band gap properties caused by internal charge transfer from an electron-rich unit to an electron-deficient moiety. HOMO and LUMO levels are –5.53 and –3.86 eV for PCDTCHBI, and –5.49 and –3.84 eV for PCDTEHOCHBI, respectively. Optical band gaps of PCDTCHBI and PCDTEHOCHBI are 1.67 and 1.65 eV, respectively. The new carbazole based the 2H-benzimidazole polymers show 0.11–0.13 eV lower values of band gaps as compared to that of carbazole based benzothiadiazole polymer, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), while keeping nearly the same deep HOMO levels. The power conversion efficiencies of PCDTCHBI and PCDTEHOCHBI blended with [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) are 1.03 and 1.15%, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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