Synthesis and characterization of indeno[1,2-b]fluorene-based low bandgap copolymers for photovoltaic cells

Jinseck Kim, Sun Hee Kim, In Hwan Jung, Eunjae Jeong, Yangjun Xia, Shinuk Cho, In Wook Hwang, Kwanghee Lee, Hongsuk Suh, Hong Ku Shim, Han Young Woo

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43 Citations (Scopus)


Two types of indenofluorene-based low bandgap conjugated polymers, poly(6,6′,12,12′-tetraoctylindeno[1,2-b]fluorene-co-4, 7-bis(2-thienyl)-2,1,3-benzothiadiazole) (PIF-DBT) and poly(6,6′,12, 12′-tetraoctylindeno[1,2-b]fluorene-co-5,7-dithien-2-yl-thieno[3,4-b] pyrazine) (PIF-DTP), were synthesized and characterized for use in plastic solar cells. The optical, electrochemical, charge carrier mobility, morphological and photovoltaic characteristics were investigated. The number-average molecular weights of the polymers measured by gel permeation chromatography ranged from 19000 to 27000 g mol-1. The polymers were fairly soluble in common organic solvents and formed optical-quality films by spin casting. Photophysical studies revealed a low bandgap of ∼1.9 eV for PIF-DBT and ∼1.6 eV for PIF-DTP, respectively, which could harvest the broad solar spectrum covering from 300 nm to 650 nm (PIF-DBT), and from 300 nm to 800 nm (PIF-DTP) in film. An electrochemical study confirmed the desirable HOMO/LUMO levels of the copolymers, which enable efficient electron transfer and a high open circuit voltage when blending them with fullerene derivatives. The field effect mobility measurements showed a hole mobility of 10-5∼10-3 cm2 V-1 s-1 for the copolymers. The film surface morphology was also studied by atomic force microscopy. Among the polyindenofluorene copolymers, PIF-DBT50 (containing 50 mol% DBT) showed the best photovoltaic performance with an open circuit voltage of 0.77 V, a short circuit current of 5.50 mA cm-2 and a power conversion efficiency of 1.70% when the polymers were blended with PC71BM, under air mass 1.5 global (AM 1.5G, 100 mW cm-2) illumination conditions.

Original languageEnglish
Pages (from-to)1577-1586
Number of pages10
JournalJournal of Materials Chemistry
Issue number8
Publication statusPublished - 2010
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Chemistry


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