High efficiency solar cells can be connected by using electrically conductive adhesives in series production. This is the conclusion of a joint research project KleVer carried out by the Fraunhofer Institute for Solar Energy Systems ISE and Germany based PV production equipment supplier teamtechnik.
With KleVer, funded by the German Federal Ministry for Economic Affairs and Energy BMWi, the research project attempts to prove that adhesive technology can be used as an alternative to today's soft soldering cell interconnection technology. The adhesive technology uses much lower temperatures compared to soldering; temperature sensitive high-efficiency solar cells can be connected with adhesives in a gentle and material-saving process.
A stringer with an adhesive unit was tested for the purpose of this research. The experiment determined that solar cells full or half-cells) with three, four or five busbars could be connected using electrically conductive adhesives at a throughout of ca. 1,600 cells per hour. There is no damage to the hetero layers of the cell since temperature in this method is below 180°C. Use of adhesives ensures there is less thermal and mechanical stress in the cell. Hence, there is less material tension that reduces the danger of micro cracks and breakage, according to ISE and teamtechnik
The research team confirmed this in a series of tests conducted in a climate chamber. Throughput of this method is only slightly lower than with the conventional method of soldering in industrial production. The research team claims the technology is ready for the market.
"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 Achim Kraft, project manager and team head of Interconnection Technologies at Fraunhofer ISE.
TaiyangNews published a market survey on cell connection equipment end of 2017, asking manufacturers of stringers about conductive adhesives. While basically every leading company is working on such solutions only one commercial solution was listed in our survey as there is currently no demand (see Market Survey On Cell Interconnection Equipment).
However, the International Roadmap for Photovoltaic 2017 (ITRPV) anticipated that more than 20% of module interconnections will be accomplished using conductive adhesives in 10 years, from a minor presence in today's manufacturing.