Degradation of the encapsulant polymer in outdoor weathered photovoltaic modules: Spatially resolved inspection of EVA ageing by fluorescence and correlation to electroluminescence

Here we report about the use of spatially resolved fluorescence spectroscopy for non-destructive analysis of encapsulants in outdoor weathered commercial PV modules. Photovoltaic modules with crystalline Si-cells of seven German manufacturers were analyzed after 2 years outdoor weathering in four different climates. For the first time spatially resolved images of the polymer fluorescence for complete photovoltaic modules are reported.The presented results show that the fluorescence intensity and distribution is inhomogeneous within any module. The fluorescence intensity and its spatial distribution depend on the climate, particularly the weathering site. Diffusive processes in the polymer layer between glass and silicon cell can be evaluated with this method. Cracks in the wafer, visible with electroluminescence, show up in spatially resolved fluorescence images as well. The diffusion through the cracks influences the spatial distribution of the fluorescence intensity.Compared to averaging methods, detailed information about the impact of the different degradation factors like UV-irradiation and moisture ingress on the degradation processes can only be obtained using spatially resolved fluorescence measurements. For PV-modules investigated in this study areas can be identified and compared where similar degradation parameters can be assumed. This will allow improving to quantitatively interpret measurement results.