Laser-weld qualification methods for Al foil interconnection of back-contacted cells to predict module reliability

Conductive backsheet modules have been fabricated using inexpensive Al foil, where the bond between foil and cells are made using a laser-welding process. The durability of this interconnection has been proven via thermocycling (TC) on a millisecond laser in the past. However, this laser is too slow for large-scale manufacturing, so a faster nanosecond laser needs to be proven still. A laser-shunted module demonstrated a durable interconnection that can pass TC, but it resulted in an upfront power loss of 34% from the laser-processing. Microscopy demonstrated that the laser-welding ablated the Ag contact down to the Si surface, causing a shunt of the n-type contact. Quality welds only interact with the surface of the Ag to promote adhesion without damaging the cell performance.