STABILITY IN Cu(In,Ga)Se{sub}2 SOLAR CELLS WITH EVA ENCAPSULATION IN VARYING DAMP HEAT CONDITIONS

摘要

EVA encapsulated Cu(In,Ga)Se{sub}2 (CIGS) thin-film PV modules have shown stable behaviour in outdoor conditions but the active layers are sensitive to a combination of temperature and humidity. EVA is the encapsulant of choice in the PV industry, but problems with its use for CIGS modules are anticipated since water is readily transported into the polymer. In this study designated test structures are manufactured, so that the cells can be laminated with EVA and still be contacted from the outside. The cells, both bare and encapsulated ones, are subjected to dry heat and damp heat, with different levels of humidity, at 85°C. Cell degradation is evaluated using primarily I-V and QE measurements, and analytical modelling is used as a means of separating degradation effects. The dynamics of water ingression into the EVA layer is studied using a TiO{sub}2 thin-film moisture sensor, on a glass substrate. The typical V{sub}(OC) degradation is clearly present in unencapsulated cells, at the standard conditions (85/85). At a relative humidity below 65%, this effect is not seen. The encapsulated cells are degraded during the lamination process but when exposed to damp heat the effect is considerably less, compared to unencapsulated cells. With EVA encapsulation enhanced Mo back contact corrosion is observed.