Synthesis and characterization of thieno[3,2-b]thiophene-isoindigo-based copolymers as electron donor and hole transport materials for bulk-heterojunction polymer solar cells

Authors

  • Xiaofeng Xu,

    1. School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
    Search for more papers by this author
  • Ping Cai,

    1. State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640, China
    Search for more papers by this author
  • Yong Lu,

    1. School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
    Search for more papers by this author
  • Ng Siu Choon,

    Corresponding author
    1. School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
    • School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
    Search for more papers by this author
  • Junwu Chen,

    1. State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640, China
    Search for more papers by this author
  • Xiao Hu,

    1. School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798
    Search for more papers by this author
  • Beng S. Ong

    Corresponding author
    1. School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
    2. Institute of Creativity and Department of Chemistry, Hong Kong Baptist University, Hong Kong, China
    • School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
    Search for more papers by this author

Abstract

A novel class of thieno[3,2-b]thiophene (TT) and isoindigo based copolymers were synthesized and evaluated as electron donor and hole transport materials in bulk-heterojunction polymer solar cells (BHJ PSCs). These π-conjugated donor-acceptor polymers were derived from fused TT and isoindigo structures bridged by thiophene units. The band-gaps and the highest occupied molecular orbital (HOMO) levels of the polymers were tuned using different conjugating lengths of thiophene units on the main chains, providing band-gaps from 1.55 to 1.91 eV and HOMO levels from −5.34 to −5.71 eV, respectively. The corresponding lowest unoccupied molecular orbital (LUMO) levels were appropriately adjusted with the isoindigo units. Conventional BHJ PSCs (ITO/PEDOT:PSS/active layer/interlayer/Al) with an active layer composed of the polymer and PC71BM were fabricated for evaluation. Power conversion efficiency from a low of 1.25% to a high of 4.69% were achieved with the best performing device provided by the D−π−A polymer with a relatively board absorption spectrum, high absorption coefficient, and more uniform blend morphology. These results demonstrate the potential of this class of thieno[3,2-b]thiophene-isoindigo-based polymers as efficient electron donor and hole transport polymers for BHJ PSCs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Ancillary