Theoretical Studies on Conjugated Phenyl-Cored Thiophene Dendrimers for Photovoltaic Applications
{pi}-Conjugated dendrimers are an important class of materials for optoelectronic devices, especially for light-harvesting systems. We report here a theoretical investigation of the optical response and of the excited-state properties of three-arm and four-arm phenyl-cored dendrimers for photovoltaic applications. A variety of theoretical methods are used and evaluated against each other to calculate vertical transition energies, absorption and excitation spectra with vibronic structure, charge transport, and excitonic behavior upon photoexcitation and photoemission processes. Photophysical phenomena in these dendrimers are, in general, better explained with ab initio methods rather than with semiempirical techniques. Calculated reorganization energies were found to correlate well with the device photocurrent data where available. The excitons formed during photoexcitation are calculated to be more delocalized than the ones formed after vibrational relaxation in the excited states for fluorescence emission. The localization of excitons in emission processes is a result of geometrical changes in the excited state coupled with vibronic modes. Correlated electron-hole pair diagrams illustrate breaking of {pi}-conjugation in three-arm dendrimers due to meta linkage of arms with the core, whereas four-arm dendrimers are not affected by such breaking due to presence of ortho and para branching. Yet, ortho branching causes large twist angles between the core and the arms that are detrimental to {pi}-electron system delocalization over the structure.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 982261
- Journal Information:
- Journal of the American Chemical Society, Vol. 129, Issue 46, 2007; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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36 MATERIALS SCIENCE
ABSORPTION
ALKYL BENZENESULFONATES
ARMS
BEHAVIOR
CHARGE TRANSPORT
DATA
DIAGRAMS
EMISSION
EQUIPMENT
EXCITATION
EXCITED STATES
EXCITONS
FLUORESCENCE
MATERIALS
PHOTOCURRENTS
PHOTOEMISSION
RELAXATION
SPECTRA
THIOPHENE
WELLS
Computational Sciences
Materials Science and Semiconductors
Chemical and Biosciences