Characterization of Encapsulant Degradation in Accelerated UV Stressed Mini-Modules with UV-cut and UV-pass EVA

Encapsulant browning and delamination are two common degradation modes in the crystalline silicon field exposed modules with ethyl vinyl acetate (EVA) as the encapsulant. Six mini-modules with two types of encapsulants: UV-cut (UVC) EVA and UV-pass (UVP) EVA, were exposed to an accelerated UV testing with total UV dosage of 800 kWh/m
²
(between 300 nm - 400 nm) at different temperatures. The UVC mini-modules were maintained at 61°C, 66°C, and 73°C and the UVP mini-modules were maintained at 61°C, 67°C, and 70°C. UV fluorescence (UVF) imaging, cell-level I
_sc
measurements, yellowness index measurements and reflectance measurements were performed intermittently to evaluate the cell performance. UVF images show an increased extent and intensity of browning in UVC mini-modules. The UVP mini-modules show delamination but no browning. The average Isc drop for three UVC and three UVP mini-modules were 2.0%, 3.7%, and 4.2%, and 3.1%, 4.4%, and 4.9%, respectively. Correspondingly, a yellowness index increase of 9.5, 12.4, and 17.2 for UVC and 0.28, 1.02, and 0.32 for UVP mini-modules was measured. The reflectance of UVC mini-modules showed an increase in the 500 nm - 700 nm wavelength range. The characterization results indicate that the EVA browning and delamination are the main degradation modes in UVC and UVP mini-modules, respectively.