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Raman Spectroscopy Application to Characterize EVA after UV Exposure

Published online by Cambridge University Press:  06 January 2016

Sari Katz*
Affiliation:
On Sabbatical leave from Soreq NRC, Yavne 81800, Israel.
Aaron Urbas
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899-8615, U.S.A.
Stephanie S. Watson
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899-8615, U.S.A.
Xiaohong Gu
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899-8615, U.S.A.
*
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Abstract

Ethylene-vinyl acetate (EVA) is the most commonly used photovoltaic (PV) encapsulant material. As such, it is exposed to UV, thermal cycles, temperature gradients between the glass side and the silicon wafer side, and moisture ingress. The combined effect of all these may lead to different physical and chemical changes of EVA including polymer chain alignment, crystallinity, and crosslinking density, as well as the mechanical stresses resulting from coefficient of thermal expansion (CTE) and aging, thus, reducing the adhesion of EVA and eventually lead to failure of the encapsulation. Measuring the effects of UV exposure on EVA can help in understanding the failure mechanism of PV modules. In this work, we suggest a novel and non-destructive way to measure EVA degradation after UV exposure by using Raman spectroscopy (RS). Samples were exposed to NIST SPHERE with UV irradiation, moisture, and elevated temperatures. The physical and chemical changes as well as the internal stresses were monitored by RS, and the intensities of the corresponding Raman peaks ratio were analyzed. The results have indicated that Raman scattering is a sensitive tool to study EVA encapsulant degradation.

Type
Articles
Copyright
Copyright © Materials Research Society 2016 

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References

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