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

Introduction / project objectives
Transparent conducting oxide (TCO) materials as typically used in thin film front contacts have much
higher resistivity than metallic layers. Therefore fine lines of metal on top of a TCO layer can significantly
reduce the serial resistance of the layer. Printing of such lines on flexible CIGS solar cells was
investigated and optimized for laterally thin but vertically high structures with reasonably low contact
resistance. At the same time, the metal grid structure can be used to improve the resistance of the
serial interconnection of single cells (fig. 1)
Fig. 1: Serial interconnection of single cells to a solar module with higher output voltage.
Work performed and results obtained
Front contact
Absorber
Back contact
Substrate
Back contact patterning was investigated by the use of sputtering masks, lithography,
mechanical scribing or mechanical cutting and reconnection (shingling) and for metal grid connection
of single cells, screen-printing, evaporation and soldering methods were evaluated. Due to simpler
handling of the substrates, the monolithic interconnection technique is the method of choice. The
deposition processes of the solar cell layers were scaled up to 20x20cm 2 (Fig. 2). Demonstrator modules
with various output voltages (aprox. 0.5V per interconnected cell) were manufactured and used
for proof of concept.
Fig. 2: Flexible monolithic demonstrator modules with grid interconnected cells.
National / international collaborations
FLISOM is a spin-off from ETH and has emerged from the thin film physics group of ETH Zurich. Additional
specific know-how is required and is acquired through subcontracting and collaboration with
Swiss and European industries.
Acknowledgement
The support from axpo Naturstrom Fonds is kindly acknowledged [1].
References
[1] Naturstrom-Newsletter, Herbst 07, Axpo Vertrieb AG, Page 5,6
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Development of flexible CIGS solar modules with metal grids, M. Kaelin, FLISOM
2/2