Fluorescence imaging on the cross-section of photovoltaic laminates aged under different UV intensities

Fluorescence imaging is used to investigate the degradation depth-profile of multilayer glass/EVA/backsheet laminates for photovoltaic (PV) applications. Samples were aged on the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) at 85 °C ± 0.5 °C and 0 % RH ± 5 % RH under different UV light intensities. Based on fluorescence imaging results, non-uniform distribution of degradation species along the thickness direction is observed for EVA encapsulant and EVA middle layer in the backsheet for all exposed specimens. Two adhesive layers in backsheet also show fluorescence emission, implying the degradation of these adhesives and the propensity of the delamination within backsheet layers. It is also found that the fluorescence results are consistent with the changes in the yellowing index by micro-UV-Vis spectroscopy and the modulus by atomic force microscopy-based quantitative nanomechanical mapping (QNM-AFM). This study shows that fluorescence imaging is effective in the characterization of degradation gradient of packaging materials for PV as a function of depth.