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Title: Degradation of thermally-cured silicone encapsulant under terrestrial UV

Concentrator photovoltaic (CPV) modules operate in extreme conditions, including enhanced solar flux, elevated operating temperature, and frequent thermal cycling. Coupled with active environmental species such as oxygen and moisture, the operating conditions pose a unique materials challenge for guaranteeing operational lifetimes of greater than 25 years. Specifically, the encapsulants used in the optical elements are susceptible to environmental degradation during operation. For example, the interfaces must remain in contact to prevent optical attenuation and thermal runaway. We developed fracture mechanics based metrologies to characterize the adhesion of the silicone encapsulant and its adjacent surfaces, as well as the cohesion of the encapsulant. Further, we studied the effects of weathering on adhesion using an outdoor concentrator operating in excess of 1100 times the AM1.5 direct irradiance and in indoor environmental chambers with broadband ultraviolet (UV) irradiation combined with controlled temperature and humidity. We observed a sharp initial increase in adhesion energy followed by a gradual decrease in adhesion as a result of both outdoor concentrator exposure and indoor UV weathering. We characterized changes in mechanical properties and chemical structures using XPS, FTIR, and DMA to understand the fundamental connection between mechanical strength and the degradation of the silicone encapsulant. We developedmore » physics based models to explain the change in adhesion and to predict operational lifetimes of the materials and their interfaces.« less
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Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0927-0248
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Solar Energy Materials and Solar Cells; Journal Volume: 157
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE SunShot Initiative, Physics of Reliability: Evaluating Design Insights for Component Technologies in Solar (PREDICTS) Program
Country of Publication:
United States
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; adhesion; reliability; silicone; UV degradation