Evaluation of welded interconnects on thermally cycled silicon solar cells

To determine the suitability of new welding processes for interconnecting solar cells, space power cells with welded interconnects were cycled between temperatures representative of those expected on-orbit. The welds were then evaluated using scanning electron microscopy (SEM). It was possible to quickly distinguish between weld failures due to thermal fatigue and ductile overload incurred during destructive physical tests. Significant differences were revealed in the weld survivability depending on both the exact welding process and the interconnect material. Variations in weld quality directly affected weld survival rates. Welds with evidence of melting, as opposed to incomplete thermal compression bonding, were more apt to survive thermal cycling. Interconnects using silver (Ag)-plated Invar, because of lower thermal strains and inherently better weld quality, successfully survived the thermal cycling, while those interconnects using an all-Ag interconnect failed