Contact Formation on 100 Ω/sq Emitter by Screen Printed Silver Paste

We present a macroscopic and microscopic analysis of the contact formation of two different commercially available silver screen printing pastes (A and B) for contacting lowly doped phosphorus emitters on crystalline silicon solar cells. The new paste B shows lower contact resistance than paste A on conventional emitters of sheet resistances Rsh = 60 w/sq and 100 w/sq as well as for selective emitters with Rsh,se = 20 w/sq. Paste B achieves a contact resistance ρc = 3 mwcm2 on high ohmic emitters with Rsh = 100 w/sq. Initial investigations demonstrate different contact formations for the two pastes. Paste B shows a higher density of silver crystallites grown in the silicon emitter compared to paste A for the lowly doped emitter with Rsh = 100 w/sq. Additionally, the glass layer at the interface between the front grid of paste B and the investigated emitters contains a high density of silver colloids. The high density of Ag-crystallites and Ag-colloids, the weaker glass frits aggressivity, as well as the different formation of glass layer accompany the better contacting features of paste B on high ohmic emitters.