Industrial Maturity Of Electrically Conductive Adhesives Demonstrated


The Fraunhofer Institute for Solar Energy Systems ISE and
teamtechnik, report that it is now possible to connect high efficiency solar
cells using electrically conductive adhesives in series production. The results
of the joint research project KleVer show that the adhesive technology is
ready for the market and can be used as an alternative to the widespread soft
soldering interconnection technology. Due to the much lower process
temperatures of this technology compared to soldering, temperature-sensitive
high efficiency solar cells can be connected using adhesives in a gentle and
material-saving process. In industrial production, the throughput is only
slightly lower than with soldering. The reliability of the adhesive connection
was confirmed in tests carried out in a climate chamber.

In the last few years, we were able to greatly expand our
expertise in connecting solar cells using electrically conductive adhesives and
test this process on the laboratory scale. With the stringer unit, we were then
able to further optimize the lead-free interconnection technology on the
industrial scale, explains Dr. Achim Kraft, project manager and team head of
Interconnection Technologies at Fraunhofer ISE. Axel Riethmueller, project
manager and Chief Operating Officer of teamtechnik, is also pleased: »As
manufacturer of high performance stringers, we are proud to hold a front
position in connecting technology for temperature-sensitive heterojunction
solar cells on an industrial scale through the development of this unit. We
already have first orders coming in for the new stringers using this adhesive
technique. This would not have been possible without the joint project with
Fraunhofer ISE.

Within the KleVer project, a stringer with an adhesive
unit was successfully put in operation and tested. On this unit, it was
demonstrated that solar cells as full or half-cells with three, four or five
busbars could be connected using electrically conductive adhesives at a
throughput of ca. 1600 cells per hour. The power of the heterojunction modules
manufactured up to now with the adhesive technology is 320 watts for a standard
size of 60 cells. The process temperature of this technology remains below
180°C, avoiding damage to the hetero layers of the cells. This type of cell,
which currently holds the lead in efficiency, cannot be soldered conventionally
at temperatures over 200°C. Using adhesives greatly reduces the thermal and
mechanical stresses in the cell, resulting in lower material tension.
Therefore, the danger of micro cracks and breakage occurring is also reduced.
The cycle time for cell interconnection in the teamtechnik stringer is less
than 2.3 seconds and is primarily determined by the hardening time of the
adhesive material used.

The KleVer project was financially supported by the German
Federal Ministry for Economic Affairs and Energy BMWi.

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