The most commonly used photovoltaic (PV) encapsulant material is ethylene-vinyl acetate (EVA) co-polymer. To provide the mechanical and electrical protection to the brittle solar cells from different external stresses, the encapsulants need to meet a number of requirements including: adhesion and UV stability, resistance to water/humidity absorption, and high electrical insulation. As an encapsulant, the EVA can be exposed to internal stresses resulting from environmental stresses such as UV exposure, thermal cycles, temperature gradient between the glass side and the silicon wafer side, and moisture ingress. Theses stresses can degrade the performance of EVA leading to a reduced adhesion which will eventually lead to failure of the encapsulation. Measuring the EVA internal stresses can help to understand the failure mechanism of PV modules. In this work, we suggest a novel and non-destructive way to measure the encapsulate materials internal stresses during UV degradation by using Raman spectroscopy. Samples were exposed to NIST SPHERE with UV irradiation, moisture, and elevated temperatures. The internal stresses were monitored by Raman spectroscopy, and the corresponding Raman peak shifts were analyzed. The results have indicated that Raman scattering is sensitive to internal stress state of EVA material. As shown in Figure 1, when EVA was under tensional stresses, the Raman peaks shifted downward; while under compressional stresses, the peaks shifted upward. Aging induced internal stresses will be further discussed..

Using Raman spectroscopy to analyze internal stresses of PV encapsulate materials during UV degradation

248th National Meeting (2014)

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