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

*Corresponding author for this work

Research output: Contribution to journalArticle

216 Scopus citations

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 (US)
Pages (from-to)18427-18439
Number of pages13
JournalJournal of the American Chemical Society
Volume134
Issue number44
DOIs
StatePublished - Nov 7 2012

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ASJC Scopus subject areas

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

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