Journal
APPLIED SPECTROSCOPY
Volume 67, Issue 11, Pages 1296-1301Publisher
SOC APPLIED SPECTROSCOPY
DOI: 10.1366/13-07085
Keywords
Vibrational spectroscopy; Raman microscopy; Infrared spectroscopy; Differential scanning calorimetry; DSC; Cross-linking; Ethylene vinyl acetate; EVA; Photovoltaic
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Funding
- European Regional Development Fund (EFRE), Graz University of Technology
- government of Styria
- R&D Program COMET-Competence Centers for Excellent Technologies by the Federal Ministry of Transport, Innovation, and Technology (BMVIT)
- R&D Program COMET-Competence Centers for Excellent Technologies by the Federal Ministry of Economics and Labor (BMWA)
- Austrian Province of Carinthia
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Vibrational spectroscopy was found to be a suitable method for the determination of the degree of cross-linking of ethylene vinyl acetate (EVA) polymers. Spectral changes in the Raman spectra of EVA with increasing lamination time (which equals increasing degree of cross-linking) were mainly detected in the CH vibrational regions, namely, in the relative intensities of the characteristic CH3 and CH2 bands. These spectral regions were chosen for a chemometric evaluation where a calibration was performed with the Raman spectra of reference EVA samples and the results obtained from corresponding thermal analysis (differential scanning calorimetry) and Soxhlet extraction data. These datasets were subsequently used to non-destructively determine the progress of cross-linking in EVA foils, embedded in various mini-modules by Raman microscopy. Thus, we could show that Raman spectroscopy is a highly interesting method for quality control in the production of photovoltaic (PV) modules. However, this approach is valid only for a given grade of EVA, meaning a demand for a new calibration when changing the supplier or the type of EVA used. In addition, the applicability of infrared spectroscopy for the determination of the degree of cross-linking was tested. A good correlation of the decrease in intensity of the characteristic cross-linker infrared bands with increasing progress of the cross-linking was found, as determined by reference methods. However, this analytical method requires taking samples of the EVA foils and is, thus, unsuitable for the non-destructive determination of the degree of cross-linking of the EVA encapsulated within a PV module.
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