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Proceedings Paper

Depth profiling of mechanical degradation of PV backsheets after UV exposure
Author(s): Xiaohong Gu; Peter J. Krommenhoek; Chiao-Chi Lin; Li-Chieh Yu; Tinh Nguyen; Stephanie S. Watson
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Paper Abstract

Polymeric multilayer backsheets protect the photovoltaic modules from damage of moisture and ultraviolet (UV) while providing electrical insulation. Due to the multilayer structures, the properties of the inner layers of the backsheets, including their interfaces, during weathering are not well known. In this study, a commercial type of PPE (polyethylene terephthalate (PET)/PET/ethylene vinyl acetate (EVA)) backsheet films was selected as a model system for a depth profiling study of mechanical properties of a backsheet film during UV exposure. The NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) was used for the accelerated laboratory exposure of the materials with UV at 85°C and two relative humidities (RH) of 5 % (dry) and 60 % (humid). Cryomicrotomy was used to obtain cross-sectional PPE samples. Mechanical depth profiling of the cross-sections of aged and unaged samples was conducted by nanoindentation, and a peak-force based quantitative nanomechanical atomic force microscopy (QNM-AFM) mapping techniquewas used to investigate the microstructure and adhesion properties of the adhesive tie layers. The nanoindentation results show the stiffening of the elastic modulus in the PET outer and pigmented EVA layers. From QNM-AFM, the microstructures and adhesion properties of the adhesive layers between PET outer and core layers and between PET core and EVA inner layers are revealed and found to degrade significantly after aging under humidity environment. The results from mechanical depth profiling of the PPE backsheet are further related to the previous chemical depth profiling of the same material, providing new insights into the effects of accelerated UV and humidity on the degradation of multilayer backsheet.

Paper Details

Date Published: 23 September 2015
PDF: 10 pages
Proc. SPIE 9563, Reliability of Photovoltaic Cells, Modules, Components, and Systems VIII, 956305 (23 September 2015); doi: 10.1117/12.2187171
Show Author Affiliations
Xiaohong Gu, National Institute of Standards and Technology (United States)
Peter J. Krommenhoek, National Institute of Standards and Technology (United States)
Chiao-Chi Lin, National Institute of Standards and Technology (United States)
Li-Chieh Yu, National Institute of Standards and Technology (United States)
Tinh Nguyen, National Institute of Standards and Technology (United States)
Stephanie S. Watson, National Institute of Standards and Technology (United States)


Published in SPIE Proceedings Vol. 9563:
Reliability of Photovoltaic Cells, Modules, Components, and Systems VIII
Neelkanth G. Dhere; John H. Wohlgemuth; Rebecca Jones-Albertus, Editor(s)

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