Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

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Figure 4: Maximum achievable short circuit current of the two sub-cells in a tandem setup. The white
line shows the region of current matching.
One of the goals of this project is to build a tandem solar cell which has two active layers that absorb
in a different part of the electromagnetic spectrum. It is desired to achieve current matching, where
both subcells generate the same amount of current. From the optical point of view one can calculate
the maximum achievable short circuit current with different thicknesses of the two subcells. Such a
calculation can be seen in figure 4, where the thickness of each subcell has been varied from 0 to 300 nm
and the maximum achievable short circuit current of each cell is shown. The intersection of the two
surfaces show where current matching is achieved.
The result in figure 4 is derived from a purely optical calculation. As a next step we will perform
coupled opto-electronic simulation for the whole stack. The improvement, especially the drift diffusion
part, of the used simulation model is a high priority to understand the operating principles and
limitations of organic solar cells. The priority lies in the implementation of the dissociation mechanism
at the donor-acceptor interface. The theoretical description of this mechanism has been developed by
L. Onsager and additions have been made by C. L. Braun [4].
References
[1] J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J. Heeger, G. C. Bazan, Nature Mater. 2007, 6, 497.
[2] J. Y. Kim, S. H. Kim, H.-H. Lee, K. Lee, W. Ma, X. Gong, and A. J. Heeger, Adv. Mater. 2006, 18, 572.
[3] J. Gilot, I. Barbu, M. M. Wienk, R. A. J. Janssen, Appl. Phys. Lett. 2007, 91, 113502.
[4] C. L. Braun. J. Chem. Phys. 1984, 80 (9), 4157
APOLLO, B. Ruhstaller, ICP ZHAW
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