Systematic reliability studies of back-contact photovoltaic modules

Abstract

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.

Reliability of Back-Contact MWT Modules under Hot and Humid Conditions

“…These results show that polyolefin encapsulant in combination with moisture does not induce delamination of the backsheet. Similar results were observed for thermoplastic encapsulants elsewhere [6].…”

“…The initial I-V characteristic remains stable after 1000 hours of DH test. After 2000 hours of damp heat testing, the module M05 is still very stable due to the presence of a moisture blocking Al layer integrated in the backsheet [6]. However, module M06 presents a drop in V oc of 11.43% which induces decrease of FF and P max by respectively 14.7% and 24.6%.…”

“…The back-contact module technology allows a singlestep encapsulation and interconnection process of the back-contact cells. The main distinctive feature of this technology is the use of a full area conductive backsheet foil (typically copper) and a conductive adhesive to connect the cells electrically [6]. The full area conductive backsheet is patterned to interconnect both polarities of the solar cells and the cells can simply be picked and placed by a programmable robot, allowing large flexibility.…”