In this paper, the corrosion mechanism behind damp heat-induced degradation of screen-printed silver front-side contacts of silicon solar cells due to the presence of acetic acid, which is known to be a decomposition product of the most common module encapsulation material ethylene vinyl acetate, is investigated. Scanning electron microscope (SEM) investigations and solder and peel-tests show that the interaction between screen-printed contacts and acetic acid results in a significant adhesion loss of the front-side metallization due to the corrosion of the glass layer inside the contacts. The application of a reductive potential to the front contact accelerates this process considerably and enables it at lower acetic acid concentrations.
The analysis of the dissolved corrosion products of the contact (lead, silver) by chemical trace analysis (inductively coupled plasma optical emission spectrometry) and the generation of Pourbaix diagrams of lead in acetic acid enable the elaboration of a detailed model, which suggests a cycle of dissolution and subsequent reduction of the dissolved species as the mechanism behind the corrosion of the contacts in the model experiment and most probably in module application. Cyclic voltammetry measurements with acetic acid dipping solutions support this conclusion.