Benzodithiophene and imide-based copolymers for photovoltaic applications

Wade A. Braunecker*, Zbyslaw R. Owczarczyk, Andres Garcia, Nikos Kopidakis, Ross E. Larsen, Scott R. Hammond, David S. Ginley, Dana C. Olson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)


Conjugated alternating copolymers were designed with low optical band gaps for organic photovoltaic (OPV) applications by considering quinoid resonance stabilization. Copolymers of thienoisoindoledione (TID) and benzodithiophene (BDT) had appreciably lower band gaps (by ∼0.4 eV) than copolymers of thienopyrroledione (TPD) and BDT. In addition to intramolecular charge transfer stabilization (i.e., the "push-pull" effect), the former copolymer's quinoid resonance structure is stabilized by a gain in aromatic resonance energy in the isoindole unit. Additionally, the HOMO levels of the copolymers could be tuned with chemical modifications to the BDT monomer, resulting in open circuit voltages of greater than 1 V in photovoltaic devices. Despite the optimized band gap, TID containing polymers displayed lower photoconductance, as determined by time-resolved microwave conductivity, and decreased device efficiency (2.1% vs 4.8%) as compared with TPD analogues. These results were partially attributed to morphology, as computational modeling suggests TID copolymers have a twisted backbone, and X-ray diffraction data indicate the polymer films do not form ordered domains, whereas TPD copolymers are considerably more planar and are shown to form partially ordered domains.

Original languageEnglish
Pages (from-to)1346-1356
Number of pages11
JournalChemistry of Materials
Issue number7
Publication statusPublished - 2012
Externally publishedYes


  • Benzodithiophene
  • Isoindoledione
  • Low band gap polymer
  • Pyrroledione
  • Solar cell

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