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Chemical Analysis and Proposed Generating Mechanism for Snail Tracks Contamination of EVA Encapsulated Modules
Y.H. Chou, W.Y. Chou, S.-M. Shiu, Y.C. Chien, S.Y. Huang, S. Chi, E. Wang, R. Struwe
Module Manufacturing, PV Materials, Reliability
Components for PV Systems
Subtopic: PV Modules
Event: 27th European Photovoltaic Solar Energy Conference and Exhibition
Session: 4DO.5.3
3132 - 3136
ISBN: 3-936338-28-0
Paper DOI: 10.4229/27thEUPVSEC2012-4DO.5.3
0,00 EUR
Document(s): paper


Problems in PV systems installed for several months have been observed recently. A phenomenon called Snail Tracks, small dark meandering lines becomes visible to the naked eye on affected modules. Snail Tracks have neither been associated with a decrease in performance nor have they caused safety hazards. However, it was observed that this phenomenon correlates with cell micro-cracks. The major object of this study was to determine the chemical reactions that result in the formation of the dark lines by analyzing the chemical structure of affected and non-affected areas. In the formation of snail tracks silver seems to be a key factor. Silver carbonate (Ag2CO3) is detected in the affected snail track areas by XPS measurement. Under UV light a discoloration of the EVA could be observed, which correlates with an organic compound, identified exclusively in the affected areas by Py-GC/MS analysis. This organic compound, observed in the affected EVA areas may be a facilitator for the generation of snail tracks. In the simulation test, we could identify a change in the UV luminescence behavior of the EVA above all cracked wafers and cells, but snail track could not be observed in the wafers without silver. Neither an elevated potential nor a current flow through the module are necessary for the formation of snail tracks.