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

: Geipel, T.; Eberlein, D.; Kraft, A.

Postprint urn:nbn:de:0011-n-5655073 (9.7 MByte PDF)
MD5 Fingerprint: e47fcfd88ef407de5781aa9c6739e0e6
Copyright AIP
Erstellt am: 30.11.2019

Tous, L. ; American Institute of Physics -AIP-, New York:
8th Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells 2019. Proceedings : 13-14 May 2019, Konstanz, Germany
Woodbury, N.Y.: AIP, 2019 (AIP Conference Proceedings 2156)
ISBN: 978-0-7354-1901-8
Art. 020015, 11 S.
Workshop on Metallization & Interconnection for Crystalline Silicon Solar Cells <8, 2019, Konstanz>
Konferenzbeitrag, Elektronische Publikation
Fraunhofer ISE ()
Photovoltaik; Photovoltaische Module und Kraftwerke; Modultechnologie; 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 3 K to 11 K 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 1 N mm−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.