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

Research output: Contribution to journalArticlepeer-review

58 Scopus Citations

Abstract

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 languageAmerican English
Pages (from-to)1346-1356
Number of pages11
JournalChemistry of Materials
Volume24
Issue number7
DOIs
StatePublished - 2012

NREL Publication Number

  • NREL/JA-5200-54080

Keywords

  • benzodithiophene
  • isoindoledione
  • low band gap polymer
  • pyrroledione
  • solar cells

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