Investigations of Test Methods, Material Properties, and Processes, for Solar-Cell Encapsulants. Twenty-Second Quarterly Progress Report for Period Ending November 12, 1982

摘要

Investigations were continued into pottants, soil resistant coatings and low cost substrate materials. Two component aliphatic urethane casting syrups for use as solar module pottants were evaluated for suitability on the basis of optical, physical and fabrication characteristics. One formulation was selected as being acceptable for industrial evaluation. This urethane is characterized by high transparency, low mix viscosity, fast cure time and surprising lack of moisture sensitivity that has given trouble with previous urethane compositions. This material is produced with an ultraviolet stabilizer system already blended in. An experimental program was continued to determine the effectiveness of soil resistant coatings. These treatments have been applied to Sunadex glass, Tedlar and oriented acrylic film. The treatments are based on silicone, acrylic and fluorosilane chemistries. Test specimens are being exposed to outdoor soiling conditions with subsequent testing for short circuit-current loss using a standard cell device. After nine months of outdoor exposure, the most effective treatment appears to be a silane modified adduct of perfluorodecanoic acid. The degree of soiling also appears to correlate to the amount of rainfall that results in a natural cleaning of the surface. Wood products, such as hardboard, are potentially the lowest cost candidate substrates identified to date. The difficulty with the use of these materials lies in the very high hygroscopic expansion coefficients. Periods of dryout followed by subsequent moisture regain results in large expansions and contractions that result in cell fracture. Experiments were conducted to determine the effectiveness of occlusive coatings to prevent this effect. Both metal foils and organic films bonded to the hardboard with appropriate adhesives were found to dramatically decrease the hygroscopic response and lower the expansion coefficient by four orders of magnitude. (ERA citation 07:046196)