Benzodithiophene and Imide-Based Copolymers for Photovoltaic Applications

Journal Article · Tue Apr 10 04:00:00 EDT 2012 · Chemistry of Materials

DOI:https://doi.org/10.1021/cm2038427· OSTI ID:1043739

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

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 {approx}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.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1043739
• Report Number(s): NREL/JA-5200-54080
• Journal Information: Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 7 Vol. 24; ISSN CMATEX; ISSN 0897-4756
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AROMATICS
COPOLYMERS
EFFICIENCY
MODIFICATIONS
MORPHOLOGY
POLYMERS
RESONANCE
SIMULATION
SOLAR CELLS
STABILIZATION
X-RAY DIFFRACTION
benzodithiophene
isoindoledione
low band gap polymer
pyrroledione
solar cells