Synthesis and modeling of new biomimetic redox systems, and their application in Dye Sensitized Solar Cells
Natalie Flores a b, Leslie Pineda a b, Guy Lamoureux a c
a Escuela de Química, Universidad de Costa Rica, Apartado 2060, San José
b Centro de Electroquímica y Energía Química, CELEQ, San Pedro, Ciudad de la Investigación, Universidad de Costa Rica, Costa Rica
c Centro de de Investigación en Productos Naturales, CIPRONA, San Pedro, Ciudad de la Investigación, Universidad de Costa Rica, Costa Rica
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Poster, Natalie Flores, 237
Publication date: 1st March 2014

Dye Sensitized Solar Cells (DSSCs) are a very promising alternative to first and second generation solar cells. The best efficiencies for laboratory cells range from 12-13%, generally using electrolytes withI-/I3- as a redox couple(1). This redox couple has shown the best performance among other redox pairs, because it presents very low back electron transfer rates (recombination), and this results in long electron diffusion lengths(2). However, electrolytes based on iodide present various problems, such as leaking, evaporation, visible light absorption, corrosiveness, etc., that decrease the efficiency, and limit the lifetime of the cell(3). A redox couple of hydroquinone/benzoquinone (HQ/BQ) was reported in 2012 by Cheng and collaborators reaching an efficiency of 8.4% in a cell sensitized with N719, and has also been tested with different counter electrodes and using acetic acid to enhance the stability, showing promising results(4)(5). Our research focuses on the synthesis and molecular modeling of redox couples based on modified hydroquinones/quinones that also have ionic liquid properties. With these derivatives we avoid the problems mentioned above, and simplify the electrolyte cocktail. Finally we will characterize the DSSC using the quinonic redox couples. The natural product Lawsone has been used as a starting point (Figure 1), using different bases to deprotonate the OH group. The protonated base acts as the cation of the ionic liquid; the best results have been obtained using DBU as the base, forming a room temperature liquid. Hydroquinone has also been used and, with DBU as the base, it formed an almost colorless ionic liquid. We are synthesizing substituted hydroquinones and our future work is to form an ionic liquid redox couple, to model the energy levels and to characterize the resulting DSSC.

Figure 1. Representation of the quinonic redox system
(1)Upadhyaya, H. M.; Senthilarasu, S.; Hsu, M. H.; & Kumar, D. K. Recent progress and the status of dye-sensitised solar cell (DSSC) technology with state-of-the-art conversion efficiencies. Solar Energy Materials and Solar Cells, 2013, 119, 291–295. (2)Ondersma, J. W & Hamann. T. W. Recombination and redox couples in dye-sensitized solar cells. Coord. Chem. Rev. 2013, 257, 1533-1543. (3)Cheng, M.; Yang, X.; Zhang, F.; Zhao, J.; & Sun, L. Efficient Dye-Sensitized Solar Cells Based on Hydroquinone/Benzoquinone as a Bioinspired Redox Couple. Angewandte Chemie International Edition. 2012, 51(39), 9896-9899. (4)Cheng, M.; Yang, X.; Chen, C.; Zhao, J.; Zhang, F.; & Sun, L. Dye-sensitized solar cells based on hydroquinone/benzoquinone as bio-inspired redox couple with Different Counter Electrodes. Phys. Chem. Chem. Phys. 2013, 15(36), 15146-15152. (5)Yu, Z.; Bu, C.; Zhou, Z.; Liu, Y.; Huang, N.; Bai, S.; Fu, H.; Guo, S.; & Zhao, X. Effect of HAc Treatment on an Open-environment Prepared Organic Redox Couple Based on Hydroquinone/Benzoquinone and its Application in Dye-sensitized Solar Cells. Electrochimica Acta. 2013, 107, 695-700.
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