Title:	Investigating Long-Term UV Durability of Glass/Transparent Backsheet Laminates for Bifacial Photovoltaics - Cross-sectional Analysis of Backsheet Degradation
Author(s):	X. Gu, S. Smith, S. Mitterhofer, S. Moffitt, S. Jhang, S. Watson, L.P. Sung
Keywords:	Fluorescence, Accelerated Laboratory Testing, bifacial modules, Cross-section, Glass/Transparent Backsheet
Topic:	Photovoltaic Modules and BoS Components
Subtopic:	Materials for PV Modules, Durability, Reliability and Accelerated Testing Methods
Event:	8th World Conference on Photovoltaic Energy Conversion
Session:	3DO.19.1
Pages:	599 - 604
ISBN:	3-936338-86-8
Paper DOI:	10.4229/WCPEC-82022-3DO.19.1
Price:	0,00 EUR
Document(s):	paper

Abstract/Summary:

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Bifacial modules with glass/transparent backsheet (G/CB) structures offer lighter weight and higher hail resistance over traditional glass/glass (G/G) modules. However, research on long-term durability of transparent backsheets and their usage in bifacial modules is lacking. In this study, the G/CB laminated coupons were constructed with polyolefin elastomer encapsulant (POE) and three types of fluoropolymer-based transparent backsheets. The coupons were aged using an integrating sphere-based weathering device at 65 C and 50 % relative humidity (RH) for 3600 h, with an approximately 1800 MJ/m2 UV dose (295 nm to 400 nm), followed by 200 cycles of thermal cycling from 85 C to -40 C. Cross-sectional characterizations of optical, chemical, and mechanical degradation were conducted on the transparent backsheets of the exposed coupons using confocal fluorescence microscopy, microscale infrared spectroscopy, and nanoindentation, respectively. All three types of backsheets show one or more degradation modes including yellowing, surface/bulk cracking, or delamination. The greatest yellowing and cracking are seen on a fluoroethylene vinyl ether (FEVE)/polyethylene terephthalate (PET)/ethylene-vinyl acetate (EVA)-based transparent backsheet. The results also show changes in fluorescence intensity are consistent with chemical and mechanical changes across the thickness of the PET core layer in the FEVE/PET/EVA backsheet.