TECC-wire: A new low-temperature technology for the interconnection of solar cells

Abstract

Next-generation solar technologies such as SHJ (silicon heterojunction) and c-Si/perovskite tandem are pushing into the market. Their temperature-sensitivity prevents from using conventional soldering for the interconnection of the solar cells. Current technical solutions such as electrically conductive adhesives show technically challenges for the usage in the widely applied approach of the multi-busbar concepts, and additional high costs. SHJ solar cells and module manufacturers are using the multi-busbar concept with a desire to save on the low-temperature Ag paste and be able to use established machines in the module manufacturing process. The SmartWire concept (by MeyerBurger) is one potential technical solution - but it was withdrawn from the market within future only being used for MeyerBurgeŕs own product lines. These are the main reasons why essentially the SHJ manufacturers, despite its limitations, focus on soldering with low-temperature solder alloys.
We are presenting a new solar cell interconnection technology based on thermoplastically and electrically conductive coated wires (“TECC-Wire”) which combines the advantages of recently established multi-wire approach with low- temperature conductive adhesives. In fact, there are of course solder alloy coated wires and ribbons available on the market - but wires which are pre-coated with electrically conductive adhesives (ECA) for the interconnection of solar cells are new. Copper wires with an electrically conductive thermoplastic coating are attached to the front and the rear side of the solar cells, respectively, similar to conventional stringing. With different chemistries of the coatings a wide variation in process temperature between l30°C - 200°C can be achieved, and the material can be engineered for the respective type of solar cell. The melting temperature of the coating can be adjusted, by using different thermoplastics for the wire coating. First experimental results in terms of mechanical bonding, electroluminescence (EL) imaging and electrical parameters (current; fill factor; power) are very encouraging. We also had the opportunity to conduct a trial run in an industrial multi- wire stringing machine, which was showing that with just small modifications it is possible to use such equipment which is already available in the market. The main application of this new TECC-Wire solar cell interconnection technology results from its compatibility with temperature-sensitive solar cells, with huge advantages for cost savings as it allows new routes for metallization. The main challenges - besides the consistent and precise application of the wires with our lab equipment - are the achievement of a high cell-to-module power coefficient and the verification of the long-term reliability in accelerated tests. However, it has a great potential for the interconnection of future high-efficiency solar cells.