UV stability and module testing of nonbrowning experimental PV encapsulants

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Abstract
Development work on EVA-based PV encapsulants has yielded three strategies to limit photothermal browning. (1) Use of one of four new EVA-based encapsulants-"standard-cure" X9903P, X9923P, or X9933P, or "fast-cure" X15303P. After 38-42 weeks in a Weather-Ometer, sample laminates using Starphire glass, which is highly transparent in the UV-B region, developed ASTM D-1925 Yellowness Indexes of 2.1-4.5. (2) Use of cerium-oxide-containing glass superstrates, especially with an existing encapsulant, "fast-cure" 15295P. After one year in the Weather-Ometer, sample laminates registered a Yellowness Index of 13. A 15295P control with noncerium glass had an index of 87. Similarly, samples with cerium-oxide-containing glass subjected to 15 months of EMMA accelerated outdoor exposure showed almost no measurable yellowness, while controls had a 4.2 Index. A control prepared with "standard-cure" A9918P and noncerium glass registered a 34.5 Index. (3) Use of an optically transparent, gas-transmissive superstrate in place of glass. After 60 weeks exposure in the Weather-Ometer, a Tefzel/A9918P encapsulant/glass laminate had a Yellowness Index of 2.0. Samples subjected to 15 months of EMMA showed no measurable yellowing. Mini-modules were then prepared, using six different combinations of the four experimental encapsulants, plus controls with low-iron glass, cerium-containing glass, or Tefzel superstrates. These are being aged in the Weather-Ometer, with additional sets sent to Phoenix for EMMA exposure.

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