Since passivated emitter and rear cells (PERC) and other silicon solar cell concepts with evaporated aluminum (Al) as rear metallization are incompatible with a common solder process, in this work an annealing stable,solderable and long-term stable metallization scheme deposited by physical vapor deposition (PVD) is developed. The solder stack that complements the Al metallization consists of sputter deposited TiN/Ti/Ag or TiN/NiV/Ag, whereby the TiN layer serves as a diffusion barrier against Al. It is therefore optimized by varying sputter parameters and by stuffing the grain boundaries with oxygen. On the optimized stack a cell-interconnector can be conventionally soldered even after a strong annealing step of 15 min at 425 °C, which sets this concept apart from other PVD metallization approaches. Cell efficiency is not influenced by the solder stack compared to a reference rear metallization by plain evaporated Al. Additionally, long-term stability of the solder-joints on the metallization schemeis investigated by thermal aging of solder-joints and thermal cycling of demo moduleswith PERC cells.
Kumm, J., Chacko, R. V., Samadi, H., Hartmann, P., Eberlein, D., & Wolf, A. (2015). Long-term and Annealing Stable, Solderable PVD Metallization with Optimized Al Diffusion Barrier. In Energy Procedia (Vol. 77, pp. 374–381). Elsevier Ltd. https://doi.org/10.1016/j.egypro.2015.07.052