The gel content of photovoltaic module encapsulation Ethylene-vinyl acetate (EVA) is usually measured by the Soxhlet extraction method. Due to the destructive sample preparation, long turnaround times, hazardous solvents and the limited precision of results, an alternative crosslinking determination technique for the in-line process control is needed.The general capability of Raman spectroscopy as cross-linking determination method was investigated.EVA foils from two different manufactures were cured to different cross-linking degrees. Solvent extraction was used as reference technique. For the Raman spectroscopic investigation of the degree of cross-linking, residual peroxide peaks from the cross-linking agent in EVA were utilized. The intensity of the peroxide peaks appeared to be inversely correlated to the gel content.

The root cause of the photochemical ethylene vinyl acetate (EVA) discoloration in photovoltaic (PV) modules was investigated. Laminates containing EVA foils with a systematic variation of the additive formulation, i.e. the crosslinking agents, ultraviolet (UV) absorber, hindered amine light stabilizers and antioxidants, were subjected to UV aging. The influence of the additive combination on the photochemical aging of EVA was investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and UV/visible spectroscopy. The amount of EVA discoloration was found to be strongly depending on the additive formation. An important impact of the antioxidant in terms of chromophore formation inhibition could be found. Surprisingly, the highly stabilized EVA foils showed higher discoloration rates as well as a more intense fluorescence background in the Raman spectra.

In this study, the influence of the PV laminate design on the silicon cell degradation was investigated. Laminates consisting of two different kinds of encapsulation (EVA and PVB) and three different back-sheet materials (TAPT, PA and a TPT foils) were manufactured. Standard cells with a two and three bus bar design were used as well as MWT cells. The laminates were subjected to a UV, heat and damp-heat aging tests. The degradation of the cell metallization was investigated by means of electroluminescence imaging, the degree of polymeric aging was determined by Raman spectroscopy. Special attention was paid to the spatial distribution of corrosion effects on the cell. A severe influence of the solar cell type, i.e. the metallization paste, could be shown. Furthermore, a strong dependence of the degree of metallization degradation on the type of back-sheet material was found. An extensive UV aging for up to 180 kWh appeared to have no influence on the metallization corrosion.

During the service life of a PV module, various different degradation mechanisms can be induced. Polymer degradation depends strongly on the external conditions, which are determined by the climate and the specific conditions of the module. Nondestructive measurements of the degradation behavior of the PV-module encapsulation material ethylene vinyl acetate (EVA) were performed. We present results of Raman spectroscopic measurements on full-sized PV modules from several different PV module manufacturers, which were exposed outdoors in different climates for up to three years. This way, the different degradation mechanisms that are induced under the influence of different climatic conditions during outdoor exposure could be investigated. It was found that the degradation pattern, detected by Raman spectroscopy, was rather similar for the investigated climates, but the extent of polymer degradation was found to be higher for tropic and arid climates than for moderate or mountain climates.