How to Obtain Solderable Al/Ni:V/Ag Contacts

AbstractWe investigate process sequences for obtaining solderable Al/Ni:V/Ag contacts to PERC-type crystalline Si solar cells by in-line Al evaporation. For a high cell efficiency the evaporated aluminum must be annealed at 350°C for about 5min. We find that annealing the Al/Ni:V/Ag metallization stack at temperatures above 150°C destroys the solderability of the wetting layer. A solution for this problem is to first deposit the 2.5μm Al layer by evaporation, then anneal the cell at 350°C for 10min, and finally sputter a double layer of Ni:V/Ag with respective thickness values of 200nm and 25nm. This process leads to a contact resistivity lower than 1 mΩcm2. The solderablility is proven by a peel force greater than 3N/mm. We present a solderable PERC cell with Al/Ni:V/Ag rear side metallization and an efficiency of 18.9%