Synthesis and characterization of benzodithiophene and benzotriazole-based polymers for photovoltaic applications.

Desta Gedefaw, Marta Tessarolo, Margherita Bolognesi, Mario Prosa, Renee Kroon, Wenliu Zhuang, Patrik Henriksson, Kim Bini, Ergang Wang, Michele Muccini, Mirko Seri, Mats R. Andersson

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    Abstract

    Two high bandgap benzodithiophene-benzotriazole-based polymers were synthesized via palladium-catalysed Stille coupling reaction. In order to compare the effect of the side chains on the opto-electronic and photovoltaic properties of the resulting polymers, the benzodithiophene monomers were substituted with either octylthienyl (PTzBDT-1) or dihexylthienyl (PTzBDT-2) as side groups, while the benzotriazole unit was maintained unaltered. The optical characterization, both in solution and thin-film, indicated that PTzBDT-1 has a red-shifted optical absorption compared to PTzBDT-2, likely due to a more planar conformation of the polymer backbone promoted by the lower content of alkyl side chains. The different aggregation in the solid state also affects the energetic properties of the polymers, resulting in a lower highest occupied molecular orbital (HOMO) for PTzBDT-1 with respect to PTzBDT-2. However, an unexpected behaviour is observed when the two polymers are used as a donor material, in combination with PC61BM as acceptor, in bulk heterojunction solar cells. Even though PTzBDT-1 showed favourable optical and electrochemical properties, the devices based on this polymer present a power conversion efficiency of 3.3%, considerably lower than the efficiency of 4.7% obtained for the analogous solar cells based on PTzBDT-2. The lower performance is presumably attributed to the limited solubility of the PTzBDT-1 in organic solvents resulting in enhanced aggregation and poor intermixing with the acceptor material in the active layer.

    Original languageEnglish
    Pages (from-to)1629-1637
    Number of pages9
    JournalBeilstein Journal of Organic Chemistry
    Volume12
    DOIs
    Publication statusPublished - 2016

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  • Cite this

    Gedefaw, D., Tessarolo, M., Bolognesi, M., Prosa, M., Kroon, R., Zhuang, W., Henriksson, P., Bini, K., Wang, E., Muccini, M., Seri, M., & Andersson, M. R. (2016). Synthesis and characterization of benzodithiophene and benzotriazole-based polymers for photovoltaic applications. Beilstein Journal of Organic Chemistry, 12, 1629-1637. https://doi.org/10.3762/bjoc.12.160