The accelerated laboratory testing under simultaneous multiple stresses (temperature, moisture, UV radiation) is critical to the development of test methods that correlate to field performance. In this study, the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) was used for accelerated laboratory tests of a number of polymeric materials used in photovoltaics, such as ethylene vinyl acetate (EVA), polyvinyl fluoride/Polyester/EVA (EVA/PET/PVF) backsheet and polyester backsheet materials. Multiscale chemical, optical, mechanical and morphological measurements were carried out to follow changes during accelerated exposures. The effects of the UV irradiance, relative humidity, oxygen and wavelength on degradation mechanisms of these materials were investigated. The results indicated that the UV radiation was the most important factor for the degradation of all studied materials. A synergistic effect between UV and relative humidity was observed for EVA, and PET based backsheet materials. The role of oxygen in the degradation process of UV-stabilized EVA was complex and affected degradation behaviors of the EVA during UV exposure. In addition, advanced cross-sectional characterization techniques combining confocal Raman, atomic force microscopy, and nanoindentation were used to examine chemical, mechanical and structural changes of a multilayered PET-based backsheet before and after exposure. New insights into the effects of accelerated UV and humidity on the innerlayer structures and the properties of PV backsheets will be presented. The implication of this work on the current test standards will be discussed.

Accelerated laboratory test and degradation characterization of polymeric materials used in photoviltaics

248th National Meeting (2014)

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