Benzodithiophene and Imide-Based Copolymers for Photovoltaic Applications
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 Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1043739
- Report Number(s):
- NREL/JA-5200-54080; CMATEX; TRN: US201213%%426
- Journal Information:
- Chemistry of Materials, Vol. 24, Issue 7; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AROMATICS
COPOLYMERS
EFFICIENCY
MODIFICATIONS
MORPHOLOGY
POLYMERS
RESONANCE
SIMULATION
SOLAR CELLS
STABILIZATION
X-RAY DIFFRACTION
pyrroledione
isoindoledione
benzodithiophene
solar cells
low band gap polymer