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Synthesis and characterization of cyclopentadithiophene-based low bandgap copolymers containing electron-deficient benzoselenadiazole derivatives for photovoltaic devices

Authors

  • In Hwan Jung,

    1. Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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  • Hoyeon Kim,

    1. Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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  • Moo-Jin Park,

    1. Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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  • Bongjun Kim,

    1. Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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  • Jong-Hwa Park,

    1. Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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  • Eunjae Jeong,

    1. Department of Nanofusion Engineering (BK21), Pusan National University, Miryang 627-706, Republic of Korea
    2. Department of Cogno-Mechatronics Engineering (WCU), Pusan National University, Miryang 627-706, Republic of Korea
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  • Han Young Woo,

    1. Department of Nanofusion Engineering (BK21), Pusan National University, Miryang 627-706, Republic of Korea
    2. Department of Cogno-Mechatronics Engineering (WCU), Pusan National University, Miryang 627-706, Republic of Korea
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  • Seunghyup Yoo,

    Corresponding author
    1. Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
    • Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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  • Hong-Ku Shim

    Corresponding author
    1. Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
    • Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
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Abstract

We have synthesized two cyclopentadithiophene (CDT)-based low bandgap copolymers, poly[(4,4-bis(2-ethyl-hexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl)-alt-(benzo[c][1,2,5]selenadiazole-4,7-diyl)] (PCBSe) and poly[(4,4-bis(2-ethyl-hexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl)-alt-(4,7-dithiophen-2-yl-benzo[c][1,2,5]selenadiazole-5,5′-diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron-donating CDT unit and the electron-accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37–1.46 eV. The UV–vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor–acceptor (D–A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D–A complex using the ab initio Hartree-Fock method with a split-valence 6-31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC71BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short-circuit current of 6.63 mA/cm2, and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423–1432, 2010

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