Physical understanding of the behavior of silver thick-film contacts on n-type silicon under annealing conditions
High-efficiency silicon solar cells with evaporated front contacts and an oxide-passivated rear require post metallization annealing (PMA). In an industrial environment the evaporated front contacts are replaced by screen printed contacts for fast processing and cost reasons. The PMA conditions necessary for optimum rear side passivation can be inferior to such a front side metallization. In order to design a PMA supporting contact in future, this paper investigates what mechanism deteriorates the contact resistance of screen printed front side metallization during nitrogen PMA. Scanning electron microscopy (SEM) on samples with increased contact resistance reveals an altered microstructure at the silver-silicon contact interface that is proposed to impede current flow and hence increases the contact resistance. We present a model that describes the mechanism of contact deterioration during nitrogen PMA.