We study Ni:Si as a barrier material for the PVD metallization of silicon solar cells and investigate the long term solderability of Al/Ni:Si/Ag metal stacks in terms of peel forces and contact resistances. For this purpose, solar cell connectors are soldered on the Al/Ni:Si/Ag stacks in three different aging states: directly after metallization, after accelerated storage and after storage for six months. The thickness of the Ni:Si layer is varied in these tests. Furthermore we measure the contact resistance between cell interconnect ribbons and the test stack. To assess possible contamination of the Si by the metals we measure the effective lifetime of electron hole pairs during a regularly interrupted thermal treatment procedure. The samples with 200 nm or thicker Ni:Si layers soldered with the lead-containing solder and the flux 952S perform best and pass all tests.