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UV light stability test of c-Si photovoltaic EVA encapsulant modified by organic downshifting additive

Ethylene vinyl acetate copolymer (EVA) is the most commonly used encapsulation material in silicon photovoltaic modules. Its main function is to bond the module components together, to protect the solar cells from mechanical and environmental influences and to insulate them electrically. It is well known that the performance of solar modules (conversion efficiency) decreases when they are operated outdoors. One of the reasons for this is the degradation of the encapsulation material by UV light. To prevent photodegradation, various stabilisers are added to the EVA encapsulation material. However, the effect cannot be completely eliminated and some recent studies suggest that the added stabiliser is involved in the EVA photodegradation (yellowing process). Several new approaches and concepts are proposed as a solution for EVA photodegradation and improving conversion efficiency. One of them is the use of downshifting materials as an additive to EVA encapsulant. Downshifting materials convert photons with higher energy (UV range) into photons with lower energy (in the visible part of the spectrum), where the quantum efficiency of the solar cell is higher. In this way, they protect the c-Si solar cell by blocking the UV light and improving the conversion efficiency. One of the materials with such a function is organic luminescent dyes such as perylene and naphthalimide-based dyes, which have improved photostability under sunlight irradiation. However, several studies have shown that they degrade under UV irradiation below 345 nm. In addition to protecting and improving the efficiency of solar cells, EVA foil modified with organic luminescent dyes can also have an aesthetic function. In recent years, interest in coloured modules has increased. The aim of this work was to investigate the influence of UV irradiation on the performance of silicon solar cells encapsulated with a EVA foil modified with organic luminescent dyes. c-Si mini solar modules (20x20mm) were encapsulated with 4 different encapsulation materials: standard transparent EVA foil, EVA foil with UV cutoff additive, EVA foil modified with red and yellow organic luminescent dyes: Lumogn Red 305 and Lumogen Yellow 087. The degradation of the solar cell parameters was monitored by checking the IV characteristics and the spectral response of the solar cells during longer period of exposure to UV light. We also monitored the transmittance in the UV-Vis region of the EVA encapsulant. c-Si solar modules encapsulated with organic luminescent dyes were also tested under real outdoor conditions on a large scale. We compared and discussed the results for all encapsulation samples used.

c-Si solar cells ; encapsulation ; degradation ; UV light ; luminescence ; downshifting

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