Solderable PVD Al Back Contacts for the Module Integration of High-Efficiency c-Si Solar Cells

Several high-efficiency solar cell types, such as tunnel oxide passivated contact and SunPower's interdigitaded back contact cells, benefit from physical vapour deposited (PVD) Al on the backside. For cell interconnection, the industry prefers to solder tinned Cu connectors to the cells' metal electrodes, so there is a great need to make the Al solderable. Cost calculations in a previous study have shown that the deposition of only one thin additional metal layer directly after the PVD of Al in the same coating system without interruption of the vacuum is the most cost-effective approach. In this work we introduce sputtered pure Ni as a solderable layer on PVD Al for the connection of c-Si solar cells. Using high-throughput tabber stringers we obtained a very high average normalised 90° interconnector peel force of 3.9 N/mm on our p-type PERC test cells. We also found a very good stability of the manufactured modules in climate tests carried out according to the standard IEC 61215. After double thermal cycling and damp-heat tests, the degradation of the electrical power was < 3 % for an only 100 nm thick pure Ni solderable layer.