Bithiopheneimide-dithienosilole/dithienogermole copolymers for efficient solar cells: Information from structure-property-device performance correlations and comparison to thieno[3,4- c ]pyrrole-4,6-Dione analogues

Xugang Guo, Nanjia Zhou, Sylvia J. Lou, Jonathan W. Hennek, Rocío Ponce Ortiz, Melanie R. Butler, Pierre Luc T. Boudreault, Joseph Strzalka, Pierre Olivier Morin, Mario Leclerc, Juan T. López Navarrete, Mark A. Ratner, Lin X. Chen, Robert P.H. Chang, Antonio Facchetti, Tobin J. Marks

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216 Citations (Scopus)

Abstract

Rational creation of polymeric semiconductors from novel building blocks is critical to polymer solar cell (PSC) development. We report a new series of bithiopheneimide-based donor-acceptor copolymers for bulk-heterojunction (BHJ) PSCs. The bithiopheneimide electron-deficiency compresses polymer bandgaps and lowers the HOMOs-essential to maximize power conversion efficiency (PCE). While the dithiophene bridge progression R 2Si→R 2Ge minimally impacts bandgaps, it substantially alters the HOMO energies. Furthermore, imide N-substituent variation has negligible impact on polymer opto-electrical properties, but greatly affects solubility and microstructure. Grazing incidence wide-angle X-ray scattering (GIWAXS) indicates that branched N-alkyl substituents increased polymer π-π spacings vs linear N-alkyl substituents, and the dithienosilole-based PBTISi series exhibits more ordered packing than the dithienogermole-based PBTIGe analogues. Further insights into structure-property-device performance correlations are provided by a thieno[3,4-c]pyrrole-4,6-dione (TPD)-dithienosilole copolymer PTPDSi. DFT computation and optical spectroscopy show that the TPD-based polymers achieve greater subunit-subunit coplanarity via intramolecular (thienyl) S⋯O(carbonyl) interactions, and GIWAXS indicates that PBTISi-C8 has lower lamellar ordering, but closer π-π spacing than does the TPD-based analogue. Inverted BHJ solar cells using bithiopheneimide-based polymer as donor and PC 71BM as acceptor exhibit promising device performance with PCEs up to 6.41% and V oc > 0.80 V. In analogous cells, the TPD analogue exhibits 0.08 V higher V oc with an enhanced PCE of 6.83%, mainly attributable to the lower-lying HOMO induced by the higher imide group density. These results demonstrate the potential of BTI-based polymers for high-performance solar cells, and provide generalizable insights into structure-property relationships in TPD, BTI, and related polymer semiconductors.

Original languageEnglish
Pages (from-to)18427-18439
Number of pages13
JournalJournal of the American Chemical Society
Volume134
Issue number44
DOIs
Publication statusPublished - Nov 7 2012

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Guo, X., Zhou, N., Lou, S. J., Hennek, J. W., Ponce Ortiz, R., Butler, M. R., Boudreault, P. L. T., Strzalka, J., Morin, P. O., Leclerc, M., López Navarrete, J. T., Ratner, M. A., Chen, L. X., Chang, R. P. H., Facchetti, A., & Marks, T. J. (2012). Bithiopheneimide-dithienosilole/dithienogermole copolymers for efficient solar cells: Information from structure-property-device performance correlations and comparison to thieno[3,4- c ]pyrrole-4,6-Dione analogues. Journal of the American Chemical Society, 134(44), 18427-18439. https://doi.org/10.1021/ja3081583