Analysis of Ohmic Losses Due to Solder and Pressure Interconnection and Related Interface Resistances for Solar Cells

The interconnection of solar cells is a crucial step during module production. Therefore understanding of the electrical contact mechanism and their degradation behavior is very important. The presented work deals with the results of adapted TLM measurement in order to determine the practical limitation of pressure contacts on cell and module level in regard to the solar cell rear side. The pressure contacts between interconnection ribbon and silver (Ag) show very low contact resistances in contrast to the resistance for pressure contacts to the aluminum (Al) rear side which were found to be at least one magnitude higher. Degradation tests verify that on module level these pressure contacts are not sufficient for reliable cell interconnection, neither to Al nor Ag. Only a solder joint guarantees a reliable interconnection with low ohmic losses. It was also determined that the Ag-Al-interface next to the soldering pad has an unexpectedly high resistance.