Systematic reliability studies of back-contact photovoltaic modules

Back-contact module technology offers the advantage of lower yield loss, higher power conversion efficiency, and significantly faster manufacturing as compared to conventional H-pattern modules. In this paper we present results of a systematic accelerated ageing study of ECN back-contact metallization wrap through (MWT) modules. A series of fullsize (6×10 cells) MWT modules based on combinations of four different conductive back-sheet foils, two encapsulants, and two electrically conductive adhesives were manufactured and subjected to the damp heat conditions as defined in the IEC61215 edition 2 standard. Modules that combine conductive back-sheet foil with certain types of isolation lacquer (also referred to as inner layer dielectric, ILD) and EVA showed a high failure rate. It appears that a combined effect of moisture and EVA causes a weakening of adhesion strength at Cu/ILD interface and decisively contributes to delamination at Cu/ILD interface. This delamination puts stress on the interconnection and ultimately results in interconnection failure. Removal of ILD significantly improves the stability of MWT modules in damp heat, as up to 2000 hrs of testing only up to 2.4% relative power loss was observed, and also lowers the foil cost.