Reliability Studies of UV Downshifting Encapsulants after Damp-Heat and UV Weathering

A rigorous degradation analysis of emerging encapsulants containing UV downshifters (DS) was conducted. The encapsulants are based on ethylene vinyl-acetate copolymer (EVA) and a three-layered system, composed of 2 EVAs flanking a polyolefin elastomer (POE) layer, so-called EPE. The UV-downshifting EVA and EPE were exposed to 1000 h damp-heat (DH), 120 kWh UV, and combined DH and UV (100 kWh) accelerated weathering tests and analyzed using a multi-faceted analytical approach. The UV-vis spectroscopy showed degradation of the UV downshifter after the accelerated aging, which was especially pronounced after the UV exposure. The findings were supported by the 2D fluorescence spectroscopy, which also suggested severe changes in the mode of action of the UV downshifter. The changed mode of action led to the reduction in the conversion efficiency by 2 orders of magnitude and shift of the excitation wavelength towards higher values, thus significantly worsening the original functionality. For the first time, encapsulants with UV downshifters were analyzed using pyrolysis-gas-chromatography (Py-GCMS), and the changes of the presumable UV downshifter signal could be directly correlated to the UV-vis and fluorescence spectroscopy results as well as degradation of antioxidant and hindered amine light stabilizer. Building up on the provided results, the degradation analysis will be continued with the encapsulants extracted from the aged minimodules, correlating the material and module degradation. This comprehensive characterization provides insights into the degradation behavior of DS encapsulants under accelerated aging conditions, contributing to a deeper understanding of DS material reliability needed for its PV integration and enabling the development of more robust and efficient PV modules.