Characterization of electrically conductive adhesives

In today's module production the interconnection of the solar cells is done by leaded soldering. Electrically conductive adhesives are a promising alternative to standard soldering as they are lead-free and enable a gentle interconnection[1]. The low-stress interconnection is required for recent cell improvements such as finer contact structures, fragile cells and cells with all contacts on the rear side. We investigate three different types of electrically conductive adhesives on a standard industrial solar cell: an epoxy-based one-component adhesive, an acrylate-based snap-curable adhesive and an anisotropic epoxy-based adhesive. A tin-silver solder serves as a lead-free reference interconnection. Our analysis includes the processability, the adhesion to the cell metallization, the contact resistance, the property changes after heat treatment and the performance of mini-modules. We find the epoxy-based adhesives to exhibit a low adhesion of 0.25 N/mm. The conductivity of the adhesives is lower than for the lead-free solder reference. In aging at 130 degrees C under nitrogen atmosphere the adhesion of the acrylate adhesive increases which may result from post curing or embrittlement. With our processing parameters the anisotropic adhesive suffers from unsuitably high contact resistance due to a high processed thickness while the epoxy-based one-component adhesive provides sufficient conductivity. (C) 2012 Published by Elsevier Ltd. Selection and peer-review under responsibility of the scientific committee of the SiliconPV 2012 conference.