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

Fig. 5: J-V curve (left) and external quantum efficiency (right) of the best CIGS solar cell, with 11.9%
efficiency, on flexible polyimide substrates with ITO back contacts.
area
Voc
[mV]
Jsc
[mA/cm 2 ]
FF
[%]
�
[%]
0.582 593 28.1 61.3 10.2
0.307 626 28.9 64.8 11.7
0.187 629 28.0 67.2 11.9
Table 1: Photovoltaic properties of CIGS solar cells on flexible polyimide substrates with ITO back
contacts.
TiN/Ti as alternative back contacts for flexible solar cell on polyimide substrates
In Figure 6 the cross-section of CIGS solar cells with a TiN/Ti bilayer back contact is shown. The TiN
layer and the Mo interface layer is clearly visible and the polycrystalline grains of the CIGS layer form
a good interface to the back contact (the grains have a reasonably large size even at the back-contact
interface) what leads to low recombination at this interface.
We observed a better adhesion of the back contact on the substrate and of the absorber on the back
contact. After the TiN/Ti deposition process optimization also no cracks and no film stress could be
observed, which we attribute to the more suitable thermal expansion coefficient (CTE) with respect to
the CTE of CIGS and the used substrates.
Fig. 6: Cross-section scanning electron microscope image of a CIGS solar cell with TiN/Ti back contact
and a very thin MoSe2 interface layer.
Large Area Flexible CIGS, D. Brémaud, ETH Zurich
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