Photothermal stability of encapsulated silicon solar cells and encapsulation materials upon accelerated exposures - II

We studied the electrical and optical performance stability of crystalline silicon solar cells that were encapsulated with different types of EVA (ethylene vinyl acetate) between a borosilicate glass superstrate and a glass or white TPT (Tedlar/polyester/Tedlar) substrate. Total internal light reflection from the white TPT layer enhanced the measured cell photocurrent by similar to 20.4% to 23.9% and the efficiency by similar to 17.4% to 20.8%, with a cell-to-sample area ratio of 23.3%. In comparison, the enhancements on the cell photocurrent were from similar to5.0% to 7.0% when the cells were laminated between two borosilicate plates. The samples were exposed under to similar to6.5 UV suns at 65 degreesC or heated in an oven at 105 degreesC and periodically characterized for electrical and optical losses. The results show that, when the samples were measured without black-masking over the non-cell areas, the cell efficiency decreased by similar to0.3% to 8.9% and the fill factor changed by similar to0% to 6.6% after 1133h exposures. When the non-cell areas were masked, the measured cell efficiency losses became 4.1% to 9.0% and the fill factor losses from 0.5% to 5.2%, respectively. The electrical changes are irregular for the sample cells tested and are not proportional to the optical losses of EVA/TPT bi-layer. As an example, a cell's efficiency decreased by 8.9%, whereas its NREL-V11 EVA remained clear; and another cell lost 7.1% efficiency, whereas its slow-cure A9918 EVA browned with a 12.2% loss in integrated transmittance and an increase of 31.85 in yellowness index.