Comparison of new conductive adhesives based on silver and carbon nanotubes for solar cells interconnection

The interconnection of solar cells is one of the main process steps in photovoltaic module production. Usually solar cells are connected into strings by soldering. Due to cell thickness reduction and substantial changes of solar cell metallization, alternative interconnection techniques are required. The thermomechanically induced stress, caused by high soldering temperature and different coefficients of thermal expansion limits the long term reliability of the modules. The use of conductive adhesive enables the reduction of this thermomechanically induced stress significantly. Furthermore, conductive adhesive enables interconnection of new cells and interconnector concepts, such as heterojunction solar cells with their heat sensitive surface. Relatively costly silver (Ag) based conductive adhesives are commercially available. For cost reduction and for increase in long-term reliability reasons a carbon nanotube (CNT) based conductive adhesive has been produced and investigated. Single cell modules have been built using CNT and Ag based conductive adhesives and compared. Electroluminescence, power measurement, and contact resistance measurement among other tools have been used for evaluation.