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One-Step Macroscopic Alignment of Conjugated Polymer Systems by Epitaxial Crystallization during Spin-Coating

Authors

  • Christian Müller,

    Corresponding author
    1. Institut de Ciència de Materials de, Barcelona (ICMAB-CSIC), Esfera de la UAB, 08193 Bellaterra, Spain
    Current affiliation:
    1. Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, 41296 Göteborg, Sweden
    • Institut de Ciència de Materials de, Barcelona (ICMAB-CSIC), Esfera de la UAB, 08193 Bellaterra, Spain.
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  • Mahdieh Aghamohammadi,

    1. Institut de Ciència de Materials de, Barcelona (ICMAB-CSIC), Esfera de la UAB, 08193 Bellaterra, Spain
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  • Scott Himmelberger,

    1. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
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  • Prashant Sonar,

    1. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 3, Research Link, 117602, Singapore
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  • Miquel Garriga,

    1. Institut de Ciència de Materials de, Barcelona (ICMAB-CSIC), Esfera de la UAB, 08193 Bellaterra, Spain
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  • Alberto Salleo,

    1. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
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  • Mariano Campoy-Quiles

    1. Institut de Ciència de Materials de, Barcelona (ICMAB-CSIC), Esfera de la UAB, 08193 Bellaterra, Spain
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Abstract

The one-step preparation of highly anisotropic polymer semiconductor thin films directly from solution is demonstrated. The conjugated polymer poly(3-hexylthiophene) (P3HT) as well as P3HT:fullerene bulk–heterojunction blends can be spin-coated from a mixture of the crystallizable solvent 1,3,5-trichlorobenzene (TCB) and a second carrier solvent such as chlorobenzene. Solidification is initiated by growth of macroscopic TCB spherulites followed by epitaxial crystallization of P3HT on TCB crystals. Subsequent sublimation of TCB leaves behind a replica of the original TCB spherulites. Thus, highly ordered thin films are obtained, which feature square-centimeter-sized domains that are composed of one spherulite-like structure each. A combination of optical microscopy and polarized photoluminescence spectroscopy reveals radial alignment of the polymer backbone in case of P3HT, whereas P3HT:fullerene blends display a tangential orientation with respect to the center of spherulite-like structures. Moreover, grazing-incidence wide-angle X-ray scattering reveals an increased relative degree of crystallinity and predominantly flat-on conformation of P3HT crystallites in the blend. The use of other processing methods such as dip-coating is also feasible and offers uniaxial orientation of the macromolecule. Finally, the applicability of this method to a variety of other semi-crystalline conjugated polymer systems is established. Those include other poly(3-alkylthiophene)s, two polyfluorenes, the low band-gap polymer PCPDTBT, a diketopyrrolopyrrole (DPP) small molecule as well as a number of polymer:fullerene and polymer:polymer blends.

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