The term snails trails refers to localized discolorations that can be observed on the solar cells along the contact fingers and become visible as dark streaks. Numerous PV modules are affected after a few months of operation. Within the scope of the analysis carried out at Fraunhofer CSP, silver nanoparticles could be identified as the reason for this brownish discolouration. Certain additives of the films used in the module are the hotbed for the formation of these nanoparticles which accumulate in the encapsulation film above the contact fingers.
On the basis of these results, we could develop a laboratory test method that allows the fast and reliable testing of films and complete modules on the susceptibility to slippery slough.