Interplay of Intramolecular Noncovalent Coulomb Interactions for Semicrystalline Photovoltaic Polymers

Mohammad Afsar Uddin, Tack Ho Lee, Shuhao Xu, Song Yi Park, Taehyo Kim, Seyeong Song, Thanh Luan Nguyen, Seo Jin Ko, Sungu Hwang, Jin Young Kim, Han Young Woo

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Abstract

Four different kinds of photovoltaic polymers were synthesized by controlling the intrachain noncovalent coulomb interactions through the incorporation of alkoxy- or alkylthio-substituted phenylene, 4,7-di(furan-2-yl)benzothiadiazole, and 4,7-di(thiophen-2-yl)benzothiadiazole as a building block. Fine modulation of the interplay of dipole-dipole, H-bond, and chalcogen-chalcogen interactions (O...S, O...H, S...S, S...F, etc.) along the polymeric backbone influenced the chain planarity, interchain organization, film morphology, and electrical and photovoltaic properties significantly. By replacing the alkoxy substituents with alkylthio groups, the torsional angle increased (136-168°) due to the absence of an O...S attractive coulomb interaction (and/or increased S...S steric hindrance), enhancing the amorphous nature with hindered interchain packing. The alkoxy-substituted polymers exhibited nanofibrillar structures, showing strong interlamellar scattering peaks up to (300) with tight face-on π-π stacking in grazing incidence X-ray scattering. The measured carrier mobility of the alkoxy-containing polymers was 1-2 orders of magnitude higher than that of the alkylthio-containing polymers. The incident-light-intensity-dependent photovoltaic characteristics clearly suggested efficient charge generation/extraction with less charge recombination for the alkoxy-containing semicrystalline polymers. The resulting photovoltaic energy conversion efficiency of the PPDT2FBT, PPDF2FBT, PPsDF2FBT, and PPsDT2FBT blended devices with PC70BM was measured to be 8.28%, 5.63%, 5.12%, and 0.55%, respectively. This study suggests an important molecular design guideline for the further optimization of photovoltaic polymers and devices by finely controlling the interplay of the weak noncovalent coulomb interactions.

Original languageEnglish
Pages (from-to)5997-6007
Number of pages11
JournalChemistry of Materials
Volume27
Issue number17
DOIs
Publication statusPublished - 2015 Sep 8

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ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

Cite this

Uddin, M. A., Lee, T. H., Xu, S., Park, S. Y., Kim, T., Song, S., Nguyen, T. L., Ko, S. J., Hwang, S., Kim, J. Y., & Woo, H. Y. (2015). Interplay of Intramolecular Noncovalent Coulomb Interactions for Semicrystalline Photovoltaic Polymers. Chemistry of Materials, 27(17), 5997-6007. https://doi.org/10.1021/acs.chemmater.5b02251