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Lead-free Solders for Ribbon Interconnection of Crystalline Silicon PERC Solar Cells with Infrared Soldering

: Geipel, Torsten; Eberlein, Dirk; Kraft, Achim

Volltext urn:nbn:de:0011-n-5557646 (9.7 MByte PDF)
MD5 Fingerprint: 276de4bf4507ad94fb03660d26f11979
Erstellt am: 11.10.2019

Präsentation (PDF; )

Metallization & Interconnection Workshop 2019. Online resource : 8th Workshop on Metallization & Interconnection for Crystalline Silicon Solar Cells, Konstanz, May 13-14, 2019
Konstanz, 2019
11 S.
Workshop on Metallization & Interconnection for Crystalline Silicon Solar Cells <8, 2019, Konstanz>
Bundesministerium fur Wirtschaft und Energie BMWi (Deutschland)
0324362; BermUDa
Bleifreies PV-Modul Made in Germany - Umweltimpact, Vermarktung und Demonstration der industriellen Umsetzung
Konferenzbeitrag, Elektronische Publikation
Fraunhofer ISE ()
infrared; interconnection; lead-free; PV module; Ribbons

We report about the analysis of Pb-free, low-temperature solders for the ribbon-interconnection of PERC solar cells with an industrial infrared stringer. Five solders (SnPb, SnBi-A, SnBi-B, SnBiAg and a proprietary lead-free, low-temperature (PLFLT) alloy) are characterized with differential scanning calorimetry to determine the melting and solidification temperature. It is found that SnBi-B, SnBiAg, and the PLFLT composition melt in a temperature range between 137 C to 171 C instead of a single temperature. Solidification occurs at a 3K to 11K lower temperature (undercooling). Mono-crystalline silicon PERC cells are contacted using an industrial stringer. The microstructure of the solder bonds is investigated with scanning electron microscopy. For the SnBi-A-solder, large and brittle Bi-phases are identified. The SnBi-B, SnBiAg and PLFLT solder show a finer grain structure. The added Ag in SnBiAg forms an intermetallic compound of Ag3Sn close to the Cu-core of the ribbon. The peel strength of the connected solar cells with the Pb-free solders is on average 1Nmm􀀀1 or slightly higher. Some bonds show low adhesion. The observed fracture mode is mainly failure at the busbar metallization to solar cell irrespective of the solder type. However, the occasionally observed solder residues on the metallization clearly reveal brittle fracture for the Pb-free solders, which is not observed for SnPb. First reliability tests show similar degradation of 1% to 2% for all solders.