Characterization of Mechanical Strength of Shingle Joints Using Die Shear Tests

Abstract

For shingle interconnection there is no standard method to characterize the mechanical strength of the shingled joints. Therefore, we studied a die shear test for this purpose. In the first part, a single epoxy-based electrically conductive adhesive (ECA) was used in an industrial shingle stringer to produce shingle strings with different ECA printing widths and curing temperatures. It was observed that the printed ECA area increases at higher curing temperatures due to the increased formation of voids. Shear strength increased with elevating the curing temperature. In the second part of the study, three ECAs with varying glass transition temperature (T_g) were analysed with dynamic mechanical analysis (DMA). The shear strength of the ECAs correlates with the flexibility of the materials. ECA A, with the highest T_g, had the highest shear strength with an average of (25 ± 3) MPa, and ECA B with an average of (24 ± 9) MPa while ECA C had the lowest shear strength with an average of (15 ± 9) MPa. After characterising the shingled full-format PV modules produced using the three ECAs with electroluminescence and I–V measurements, it was found that the flexibility of the ECAs and the shear strength of the shingled joints had a very small effect on the module performance after thermal cycling 200 and mechanical load 5400 Pa. The ECAs with higher T_g showed more cell fracture but with negligible power loss. The ECA with the lowest T_g led to subtle joint degradation during the tests.