Directional Strength of Al-BSF Solar Cells with Continuous Busbars

© Fraunhofer CSP

Im 4-Punkt-Biegeversuch zeigte sich eine unterschiedliche Festigkeit vollflächiger Al-BSF Solarzellen mit durchgängigen Busbars in Abhängigkeit der Belastungsrichtung.

The strength of full Al-BSF solar cells with continuous busbars strongly was tested systematically in 4-point bending tests. The strength or breakage stress depends on the tested surface (back or sunny side) and the direction of loading related to the busbars. On the sunny side the strength is independent of the loading direction or the presence of a busbar inside the tested area in 4-point bending. On the back side the strength is significant lower when the busbar is loaded parallel compared to the load across to the busbar. If there is no busbar inside the tested area, the strength is even higher. This difference in strength is caused by different defect types and intrinsic stresses in silicon in the metallization regions while the back side metallization with overlapping Al and Ag metallization shows the strongest influence on strength.

In other cell layouts the strength behavior can change due to differences in the metallization concept, e.g. different busbar/pad layouts or laser processing. With these detailed strength characterizations of solar cells the breakage risk can be estimated for manufacturing and PV module lifetime.