Direct Heteroarylation Polymerization of Low Bandgap Thiophene-Based Conjugated Polymers
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Direct Heteroarylation Polymerization of Low Bandgap Thiophene-Based Conjugated Polymers Jiyeon Yoon, Se Hyun Jang, Sang Yong Kim, Sun Jae Kwon, Jing Guo and Yong Ku Kwon Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea ABSTRACT Direct heteroarylation polymerization was employed to synthesize a novel low bandgap polymer, used as a p-type material of polymer photovoltaic cells. To achieve low bandgap of conjugated polymers, electron donor-acceptor (D-A) alternating strategy was used. The electron-donating 3alkylthiophene and electron-withdrawing cyanothiophene were coupled to be polymerized via direct heteroarylation polymerization. The cyano moiety of the polymer backbone allowed a strong intermolecular interaction between neighboring chains and improved the structural perfection of the crystal structure on the substrate. The solar cell devices of ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al were fabricated on ITO-coated glass substrate. INTRODUCTION Most conjugated polymers have been synthesized via various cross-coupling methods such as Suzuki, Kumada, Stille and Yamamoto reactions. However, they suffer from a number of disadvantages such as low catalytic activity, high reaction temperature and prolonged reaction time that limit their extensive usage in many industrial applications. Direct heteroarylation polymerization has been recently proposed to offer a facile route to synthesize aromatic polymers in relatively high yields with simple purification of the final polymer product. In this study, this method was employed to synthesize a novel low bandgap polymer that was used as a p-type material in the active layer of polymer photovoltaic cells. The most efficient way to achieve low bandgaps of conjugated polymers has been applied. To reduce the bandgap of poly(3-alkylthiophene) as one of the most well-known, commercialized conjugated polymers, the electron donor-acceptor (D-A) alternating strategy was employed. The electron-withdrawing cyanothiophene and electron-donating 3-alkylthiophene were polymerized via direct heteroarylation polymerization. The cyano group of the polymer backbone allowed the intermolecular interaction between neighboring chains and improved the structural perfection of the crystal structure on the substrate. Since silicon-based inorganic solar cell has many limitations in practical uses, the research on organic solar cell has attracted many researchers. Polymer solar cells have the unique advantages. First, organic compound can produce light and flexible device in a large area via simple solution process. Second, light absorption is over the 1000 times larger than that of inorganic solar cells, so that a very thin thickness (100-150nm) can maximized solar absorption. In addition, the production cost of device is relatively cheaper than that of inorganic devices.
EXPERIMENT 3-Thiophenecarbonitrile (95%), 2,5-dibromo-3-dodecylthiophene (97%), palladium (Ⅱ) acetate (reagent grade, 98%), potassium carbonate (reagent plus, 99%), pivalic acid (99%), N,NDimethylacetamide
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