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.

In the present study, the chemical interaction between screen-printed solar cell front-side contacts and electrolyte solutions is investigated in detail. Especially the Ni-plating process is known to lower the mechanical adhesion of solar cell contacts significantly. The mechanisms behind this adhesion loss were analyzed by performing contact exposure experiments with and without applied voltage in electrolyte solutions with subsequent characterization of the contact peel-force, complemented with X-ray-diffraction investigations of the material changes in the solid contact compounds. Reaction paths, behind the contact corrosion, as observed in SEM images, were identified: PbO and Ag2O out of the contact react with sulphates and chlorides in the electrolyte, forming lead sulphate and silver chloride. If a voltage is applied to the contacts an alternative more effective reaction path were identified. The voltage offers the possibility to reduce the dissolved lead and silver, and this shifts the equilibrium reactions strongly towards further dissolution. The activity of the reduction was found to depend on the reduction potential of the cations in the used electrolyte solution. The less noble the metal to be deposited on the solar cell contacts, the more difficult it is to achieve the deposition without adhesion loss of the screen-printed solar cell contact