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Proceedings Paper

Chemical depth profiling of photovoltaic backsheets after accelerated laboratory weathering
Author(s): Chiao-Chi Lin; Peter J. Krommenhoek; Stephanie S. Watson; Xiaohong Gu
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Paper Abstract

Polymeric multilayer backsheets provide protection for the backside of photovoltaic (PV) module from the damage of moisture and ultraviolet (UV). Due to the nature of multilayer films, certain material property characterization of a backsheet could only be studied by examining its cross-section parallel to the thickness direction of the film. In this study, commercial PPE (polyethylene terephthalate (PET)/PET/ethylene vinyl acetate (EVA)) backsheet films were aged on the NIST (National Institute of Standards and Technology) SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) with UV irradiance at 170 W/m2 (300 nm to 400 nm) under accelerated weathering conditions of 85°C and two relative humidity (R.H.) levels of 5% (low) and 60% (high). Cryo-microtomy was used to obtain cross-sectional PPE samples with a flat surface parallel to the thickness direction, and chemical depth profiling of multilayers was conducted by Raman microscopic mapping. Atomic force microscopy with peak force tapping mode was used complementarily for cross-sectional imaging. The results revealed that the PPE backsheet films were comprised of five main layers, including pigmented-PET, core PET, inner EVA, pigmented-EVA and outer EVA, along with their interfacial regions and two adhesive layers. UV and moisture degradation on the outer pigmented PET layer was clearly observed; while the damage on the core PET layer was less significance, indicating that the outer pigmented PET layer effectively reduced the damage from UV. In high R.H. exposure, both adhesive layers were severely deteriorated. It was found that the EVA layers were susceptible to moisture at elevated temperature, especially for the pigmented-EVA. Based on the results of accelerated weathering, this depth profiling study brings new understanding to the mechanisms of failure observed in polymeric multilayer backsheets during field exposure.

Paper Details

Date Published: 8 October 2014
PDF: 12 pages
Proc. SPIE 9179, Reliability of Photovoltaic Cells, Modules, Components, and Systems VII, 91790R (8 October 2014); doi: 10.1117/12.2066400
Show Author Affiliations
Chiao-Chi Lin, National Institute of Standards and Technology (United States)
Peter J. Krommenhoek, National Institute of Standards and Technology (United States)
Stephanie S. Watson, National Institute of Standards and Technology (United States)
Xiaohong Gu, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 9179:
Reliability of Photovoltaic Cells, Modules, Components, and Systems VII
Neelkanth G. Dhere, Editor(s)

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