Origin of corrosion effects in solar cell contacts during electrochemical nickel deposition

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 Ag 2 O 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.