Electrical characterization of thermally-formed nickel silicide for nickel-copper plated solar cell contacts

Plated copper is being considered as an alternative to screenprinted silver for the front contacts of crystalline silicon solar cells. Generally, a thin nickel layer, annealed to form nickel silicide is used to improve contact resistance and adhesion of the contact to silicon. Nickel layers can also be used to prevent the detrimental diffusion of copper into the cell. One challenge to the commercialization of plated copper contacts is the potential for this nickel barrier to fail, causing catastrophic local electrical shunts of the cell. In this work, we monitor shunting during a thermal stress test to evaluate the adequacy of nickel diffusion barrier layers and identify different mechanisms by which Ni-Cu plated cells may become shunted.