Comprehensive Study of Material Dependency for Silver based Conductive Glues

This work is related to a comprehensive study on the material dependency for solar cell interconnection by means of epoxy based silver conductive glue (CG) and its effect on module reliability. The effect of power degradation for samples exceeding DH1000 was studied for various ribbon coatings, rear side AlAg silver pad pastes, amount of CG and for different encapsulation materials. We show that the choice of cell and module materials play a significant role in terms of electro-chemical corrosion. Cheap ribbon materials as non-coated copper ribbon were identified which lead to very positive damp heat results if used in combination with the right encapsulation materials. Special Rcontact samples did undergo more than 3000 hours of damp heat and proved that pure Cu ribbons without any coating performed almost the same as Ag coated ribbon and significantly better compared to Sn coated ribbon which typically fails for more than 1200 hours of DH. The speed of moisture ingress strongly impacts the corrosion process, hence specifically the rear contact is prone to degradation. We show that this process is even accelerated for larger amounts of dispensed CG. A study on various encapsulant materials showed that non coated Cu ribbon showed excellent results for TPO, TPO with embedded Al and Ionomer materials and acceptable results for Tectosil and EVA whereas Sn coated ribbon requires a TPO based material. DH testing proved that the choice of AlAg paste has a measurable effect on the electro-chemical corrosion and a minor impact on the CTM losses. Finally results for a new CG product development with superior peel strength and contact behavior are presented.