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International Journal of Photoenergy
Volume 2014, Article ID 258984, 10 pages
Research Article

Unsymmetrical Heptamethine Dyes for NIR Dye-Sensitized Solar Cells

1Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Functional Polymers, Überlandstrasse 129, 8600 Dübendorf, Switzerland
2Solaronix, Rue de l’Ouriette 129, 1170 Aubonne VD, Switzerland
3Institut des Matériaux, Ecole Polytechnique Fédéral de Lausanne, EPFL Station 12, 1015 Lausanne, Switzerland

Received 9 April 2014; Accepted 8 May 2014; Published 4 June 2014

Academic Editor: Vincenzo Augugliaro

Copyright © 2014 Thomas Geiger et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Seven unsymmetrical heptamethine dyes with carboxylic acid functionality were synthesized and characterized. These near-infrared dyes exhibit outstanding photophysical properties depending on their heterocyclic moieties and molecular structure. As proof of principle, the dyes were used as photosensitizers in dye-sensitized solar cells. Using the most promising dye, an overall conversion efficiency of 1.22% and an almost colorless solar cell were achieved.