HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 264
C126 - Influence of the alkyl chains on the cobalt (II/III) redox-mediated dye
sensitized solar cells
Aswani Yella, Magdalena Marszalek, Micheal Graetzel
Laboratory of Photonics and Interfaces, Ecole Polytechnique Fédérale de Lausanne, Station 6, LPI EPFL, CH-1015, Lausanne ,
Switzerland.
Dye-sensitized solar cell (DSC) technology 1 is under intense investigation owing to its
efficient conversion of sunlight to electricity, while its key active materials and device
processing remain cost-effective in comparison with those of conventional inorganic
semiconductor photovoltaics. Recently we have shown that electrolytes that rely on the
Co(II)/Co(III) redox mediators can produce highhvalues for organic dyes 2 and zinc porphyrins 3 ;
however, a similar performance with Ruthenium-based dyes at full sun has not yet been
demonstrated.
Open-circuit photovoltage (VOC) for devices employing the Co(II)/Co(III) mediator in
conjunction with the Ruthenium dyes is not higher than that for devices using the I3 - /I -
mediator, despite the more positive redox potentials of the Cobalt based redox mediators. This
indicates that with the ruthenium dyes the recombination is faster when using the cobalt
based redox mediator either due to an increased recombination rate constant or due to a
relatively low-lying conduction band edge, which increases electron concentration for any
given cell voltage and thus increasing the recombination flux. Herein we studied the influence
of the alkyl chain barriers on the ruthenium dyes when used in combination with the
ruthenium dyes. As was shown previously for the I3 - /I - based electrolytes, additives can be used
to optimize the electrolyte composition and to improve the solar-cell performance. Effects of
the different additives such as the pyridines and the lithium salts were also studied to see the
influence on the charge recombination.
References
[1] O’Regan, B.; Grätzel, M. Nature 1991, 353, 737– 740
[2] H. N. Tsao, C. Yi, T. Moehl, J.-H. Yum, S. M. Zakeeruddin, M. K. Nazeeruddin,M. Grätzel, ChemSusChem, 2011, 4,
591
[3] Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.;
Zakeeruddin, S. M.; Grätzel, M. Science 2011, 334, 629– 634
© SEFIN 2012