Microstructure analysis of the interaction between watts-type nickel electrolyte and screen printed solar cell contacts

In this work we present the impact of Watts-type nickel electrolytes on the contact microstructure of the screen-printed silver contacts of silicon solar cells. Both an SEM and TEM analysis were used to investigate the reasons for poor contact adhesion following nickel plating. A failing interface was identified and located exactly between the glass frit and the bulk silver inside the contact. A clearly visible gap occurs at this interface due to a chemical dissolution of the boundary layer between the glass and the silver. In TEM measurements, no distinctive features in the elemental composition were identified at the failing interface that might be responsible for the site-specific dissolution. This suggests that the dissolution starts at the very thin oxide layer between the glass and the silver. Furthermore it became clear that the electrolyte reaches the identified failing interface via pores and cavities in the screen-printed silver layer. Closing these cavities prior to nickel electrolyte exposure thus lead to significantly better contact adhesion values.