Yellowing reaction in encapsulant of photovoltaic modules

To clarify the mechanism of the yellowing reaction in encapsulant used for photovoltaic (PV) modules, a low molecular weight substance in EVA (ethylene vinyl acetate) under accelerated weathering tests (Dew cycle test, 1000 hours) with yellow change and virgin EVA were extracted with methanol. Extracts were chemically analyzed by GCIR (gas chromatography infrared-ray spectroscopic analysis), GC-AED (gas chromatography atomic emission detector), and FDMS (field desorption mass spectroscopy). The conditions of this accelerated test were based on JIS-K9117. The analysis results showed that 2,6 di-t-butyl-4-methyl phenol of antioxidant and 2-hydroxy-4-octoxy-benzophenone of UV absorbent were consumed after the weathering test and that 3,5-di-t-butyl-4-hydroxybenzaldehyde having yellow color was newly produced. A mechanism of the yellowing reaction in encapsulant was presented here that 2,6 di-t-butyl-4-methyl-phenol was oxidized by the N-O from Bis-2,2,6,6-tetramethyl-4-Piperidinyl sebacate to produce 3,5 di-t-butyl-4-hydroxy benzaldehyde