X-ray study on damp-heat induced cell degradation (DHID)

Ethylene vinyl-acetate (EVA) is a commonly used encapsulation material in the PV industry. Although EVA degrades under various climatic conditions forming acetic acid, its relatively low price and missing experience with alternative materials makes it the predominant choice for encapsulation material. Chemical reactions, which occur during extended damp-heat (DH) conditions (90 °C/85 % r.h.) between the degradation by-products of EVA and other involved components like e.g. the metallic compounds or the glass of the metallisation, may result in metallisation corrosion and in isolated areas of the cell, visible in the electroluminescence images. To evaluate the actually affected components and accelerating conditions to this phenomenon, several parameters of the laminate design, such as number of bus bars (two or three) or the distance from the bus bar to the glass and the back sheet material (TPT, TPAT, PA) were varied. The produced laminates were then exposed under extended DH conditions to reveal the accelerating factors for the metallisation corrosion. In addition to this preliminary work, the herewith presented study of X-ray investigations (X-ray diffraction and EDX spectroscopy studies) were carried out on the metallisation and the degradation products.