Degradation of PERC and Al-BSF Photovoltaic Cells with Differentiated Mini-module Packaging Under Damp Heat Exposure

Monocrystalline PERC and multicrystalline Al-BSF cells were fabricated as 4-cell mini-modules with EVA encapsulant, and low, medium, and high vapor transmission rate (VTR) backsheets. Mini-modules were subjected to a total of 2500 hours of damp heat (85°C, 85%RH) exposure, and characterized with I-V and Suns-Voc every 500 hours. The results show that PERC mini-modules decreased in power by 10.0% through the exposure, while Al-BSF mini-modules lost 12.7% of their initial power. PERC mini-modules did not show increased sensitivity to any particular packaging materials combinations studied here. However, Al-BSF mini-modules exhibited less power loss when made with fluoropolymer coating/PET/PVDF backsheet. Confocal Raman was used to examine the fluorescence background of encapsulants, and an intense fluorescence background can be seen in mini-modules that experienced water condensation during damp heat exposure. Coupons samples made with EVA and POE encapsulants and the same backsheets were also characterized with FTIR step-wise through DH, revealing crystalline phase changes in the PVDF-containing backsheets.