Analysis of chemical stability of printing pastes in electrochemical plating solutions
In the present work, interactions between chemical solutions and contacting pastes for crystalline silicon solar cells are investigated. The same kinds of interaction are assumed to take place during the plating processes of a seed and plate approach for solar cell metallization. Different means of characterizing effects the plating chemistry has on the printed paste were employed. A simple solder and peel test after a dip in the investigated solution gave insight to the effect of the treatment on adhesion. An evaluation of the damage mechanism by optical and SEM inspection allowed conclusions about probable effects. Experiments with different strong acids and bases showed signs of an effect on the glass layer of the printed contact. This assumption could be verified in a second series of experiments, where the bulk silver was removed from the glass, and spots of the glass on the solar cell surface were investigated by SEM before and after a treatment in the same solutions. In some cases, the glass layer was altered considerably. An ICP/OES investigation of solutions that had been in contact with solar cells with a screen printed front grid revealed the presence of dissolved metals, especially lead, after this treatment. It is concluded that the lead glass of the paste is attacked, which weakens the contact adhesion.