A comparison of accelerated degradation test by a UV pulse laser and fluorescence tubes for EVA films

Accelerated degradation test by UV pulse laser and fluorescence tubes for ethylene vinyl acetate (EVA) used as encapsulation of PV-cells is compared. Samples of glass/EVA/glass are prepared and irradiated by a UV pulse laser at 355nm with a repetition rate of 10 Hz, 5 ns pulse width and 10 mJ pulse energy. Spot size is expanded to 1×1 cm2 and thus averaged energy density of 1kW/m2 is available. Induced fast change in yellowness index (ΔYi) is compared between UV pulse laser and conventional fluorescence tubes. Our result shows ΔYi of 10 could be achieved in 20 ~30 hours while exposed EVA to a UV pulse laser. However, ΔYi is still less than 2 for the same sample exposed by fluorescence tubes (60°C, 40 W/m2) in a chamber over 600 hours. Both transmittance and Raman spectrum are also investigated. For samples aged by UV pulse laser, although more decay trend could be observed in transmittance spectrum, rare changes, including fluorescence background are measured by Raman spectroscopy. Our result shows essential difference of polymer degradation in EVA films after accelerated tests by two UV methods.