Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE

Introduction / Project Goals
Thin film solar cells (also often known as 2 nd generation solar cells) are attributed important cost reduction
potential over today’s mono- and polycrystalline silicon cells (often called 1 st generation). Due
to the low material usage, large area deposition of layers with in-line methods and monolithic interconnection
the processing costs of thin film solar modules will be significantly lower and energy pay-back
times in the order of a few months can be achieved. Using flexible substrate materials allows further
cost cutting by roll-to-roll manufacturing. The use of highly efficient thin film solar absorbers as
Cu(In,Ga)Se2 (called CIGS) will increase the energy output per area which is of crucial importance for
most applications.
In this project the necessary concepts for producing flexible prototype module demonstrators for different
voltages and a module areas will be established using metal grid interconnection of solar cells
(See figure 1).
� Evaluation of possible Mo patterning technologies
� Evaluation of grid interconnection configurations
� Design and optimization of grid pattern
� Module production of different sizes and of various output voltages
� Up-scaling of CIGS deposition process on home-build customised equipment
Fig. 1: Interconnection of solar cells with metal grid connections
Work and results
Front contact
Absorber
Back contact
Substrate
For Mo scribing a variety of patterning technologies as the use of sputtering mask, lithography,
mechanical scribing or mechanical cutting and reconnection are explored to identify the best method.
Metal grid connection of single cells is done by evaluating screen-printing, evaporation and soldering
methods. The metal grid pattern which connects a cells front contact to an adjacent cells back contact
has to be designed for efficient current collection and minimum interconnection resistance as well as
minimum covered sample area. The deposition step of the Cu(In,Ga)Se2 layer on the substrate material
is a key factor for efficient solar cell production. Through this project evaporation components for
homogeneous deposition on large areas are developed and installed to the home-build equipment to
improve the processes. Process control for continuous deposition is tested and evaluated.
National and international collaboration
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
Seite 106 von 288
Development of flexible CIGS solar modules with metal grids, M. Kaelin, FLISOM
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