The effect of accelerated aging tests on the optical properties of silicone and EVA encapsulants

The absorption coefficient of three silicones and EVA is measured before and after exposure to three accelerated aging tests: (i) ~2000 hours under Xe-arc lamp exposure at room temperature, (ii) 1200 hours at 85% relative humidity and 85 °C, and (iii) six months at the focal point of a 30× linear tracker. The first exposure satisfied the IEC’s UV conditioning test but with the samples at room temperature rather than at 60 °C (approximate IEC test temperature), the second satisfied the IEEE’s damp-heat test and the damp-heat component of the UL and IEC’s humidity-freeze tests, and the third is a stringent but non-conventional test available at the Australian National University. The most stable encapsulant was found to be polydimethylsiloxane (PDMS) silicone. The EVA was stable under the UV illumination but yellowed under damp-heat exposure and was decimated by the 30× concentrated sunlight. We found the EVA to have the greatest tendency to absorb moisture, a feature that increases scattering and reduces transmission.