Chemical Depth Profiling of Photovoltaic Backsheets after Accelerated Laboratory Weathering

Published

October 8, 2014

Author(s)

Chiao-Chi Lin, Peter J. Krommenhoek, Stephanie S. Watson, Xiaohong Gu

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 SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) with UV irradiance at 170 W/m2 (300 nm-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.

Proceedings Title

Proceedings of SPIE Optics + Photonics 2014

Conference Dates

August 17-21, 2014

Conference Location

San Diego, CA, US

Conference Title

SPIE Optics + Photonics 2014

Pub Type

Conferences

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Keywords

photovoltaic, backsheet, polymeric multilayer, Raman imaging, cross-section, accelerated weathering/aging

Citation

Lin, C. , Krommenhoek, P. , Watson, S. and Gu, X. (2014), Chemical Depth Profiling of Photovoltaic Backsheets after Accelerated Laboratory Weathering, Proceedings of SPIE Optics + Photonics 2014, San Diego, CA, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916475 (Accessed April 19, 2024)