Synthesis and Thin Film Morphology of Rod-Rod Polythiophene-b-Polyfluorene Conjugated Copolymers

Wednesday, November 10, 2010: 5:20 PM
250 C Room (Salt Palace Convention Center)
Rafael Verduzco1, Seth B. Darling2, Ioan Botiz2, Deanna Pickel3, Kunlun Hong3 and S. Michael Kilbey4, (1)Chemical and Biomolecular Engineering, Rice University, Houston, TX, (2)Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, (3)Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, (4)Departments of Chemistry and of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN

Polymer solar cells generally lack well-ordered active layers for the conversion of light to electricity. Ideally, the active layer should consist of well-organized p- and n-type regions with long-range order and dimensions not significantly larger than 10 nm. Block copolymer self-assembly can achieve ordered nanoscale domains, but the study of all conjugated block copolymers for photovoltaics is limited. Here, we present the synthesis and characterization of rod-rod all-conjugated block copolymers using a combination of Grignard metathesis (GRIM) polymerization and Suzuki polymerization. GRIM is used to prepare an end-functionalized poly(3-hexylthiophene) polymer. A Suzuki polycondensation of a fluorenyl monomer is subsequently carried out in the presence of the end-functionalized polythiophene to prepare a mixture of block copolymers and homopolymers. The copolymer can be isolated using solvent extraction and column chromatography. NMR, SEC-RI, and SEC-UV/Vis show that the final products contain the desired block copolymers with little or no homopolymer impurities. Futhermore, comonomers such as benzothiadiazole can be incorporated into the Suzuki polycondensation step to tune the optoelectronic properties of the resulting copolymer. We will present the synthesis and characterization of the copolymers as well as preliminary AFM and transient photoabsorption studies on polymeric thin films. We will also discuss the potential for the use of related block copolymers in polymeric OPVs.

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