Raman spectroscopic analysis of encapsulants in aged photovoltaic modules

Abstract

The aging of an encapsulation material of a random copolymer of ethylene and vinyl acetate (EVA), in outdoor-exposed (OE) crystalline-silicon (c-Si) photovoltaic (PV) modules was investigated through nondestructive Raman spectroscopy. The effect of water vapor (WV) on the Raman spectra of EVA encapsulants in c-Si PV modules was also investigated after long-term damp-heat (DH) tests at 85 °C and 85 % relative humidity. The EVA encapsulants in the long-term OE modules showed two different shapes and intensities of broad Raman spectra due to the increased intensity of the fluorescence background (FB). The encapsulants at the center of c-Si solar cells in the long-term OE modules showed a high intensity of FB, which increased with the exposure time. On the other hand, the Raman spectra of the encapsulant at the edge of the c-Si solar cells resembled those of the DH-exposed (DHE) modules, with a similar shape and lower intensity of FB than at the center. The spectral results indicate that the encapsulants at the edge were affected by WV, similar to the same as the DHE condition. The DHE-type Raman spectra for the EVA encapsulants at the edge of c-Si solar cells in OE modules show that the acetic acid may be formed from the EVA encapsulants by WV, resulting in corrosion of finger electrodes on c-Si solar cells and consequently diminishing the performance of the modules.