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Issue 30, 2009
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Low-bandgap thiophene dendrimers for improved light harvesting

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Abstract

This article follows our previous work on the synthesis and characterization of pi-conjugated dendrimers for use in organic solar cells. Here we discuss five new thiophene-based dendrimers that were synthesized in order to study the relationship between their chemical structures and electronic properties. Three of these dendrimers incorporate acetylene spacers, included to relieve steric strain, between the thiophene arms and phenyl cores used in previous studies. Only a small effect on the electronic properties is observed upon inclusion of the acetylene spacer in the three-arm dendrimer, 3G1-2S-Ac. In contrast, a decrease in the bandgap is observed for the four-arm dendrimer, 4G1-2S-Ac, due to a reduction of interactions between the arms in the more sterically congested 1,2,4,5-arrangement around the phenyl core, resulting in delocalization of the exciton through the phenyl core. Incorporation of electron-withdrawing cyano groups on the phenyl core of the three-arm dendrimer, 3G1-2S-CN, resulted in a very large (∼0.5 eV) decrease in the bandgap, due to stabilization of the lowest unoccupied molecular orbital, and the low energy absorption band in this material is attributed to a transition with significant intramolecular charge-transfer character. The electronic properties of three- and four-arm dendrimers with electron-donating dibutylaniline moieties attached to the end of the thiophene dendron, 3G1-2S-N and 4G1-2S-N respectively, are almost identical, indicating that they are dominated by the arms, with no through-core communication allowed, even for the para-linked arms of 4G1-2S-N. However, there is a significant increase in the molar absorptivity of these materials, concomitant with significant broadening of the absorption spectrum, which is an important attribute in light-harvesting applications.

Graphical abstract: Low-bandgap thiophene dendrimers for improved light harvesting

  • This article is part of the themed collection: Solar cells
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Supplementary files

Article information


Submitted
18 Feb 2009
Accepted
23 Apr 2009
First published
09 Jun 2009

J. Mater. Chem., 2009,19, 5311-5324
Article type
Paper

Low-bandgap thiophene dendrimers for improved light harvesting

B. L. Rupert, W. J. Mitchell, A. J. Ferguson, M. E. Köse, W. L. Rance, G. Rumbles, D. S. Ginley, S. E. Shaheen and N. Kopidakis, J. Mater. Chem., 2009, 19, 5311
DOI: 10.1039/B903427G

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