Contact formation on p-doped Si by screen-printing pure Ag pastes for bifacial n-type Si solar cells

Abstract

n-type solar cell concepts increasingly utilize emitter formation by diffusion from boron doped sources. Combining the advantage of n-type silicon material and bifacial cell architecture enables high-efficiency and versatile photovoltaics. In case of boron emitters, it was standard until now to form a metal-semiconductor contact by screenprinting Al containing Ag pastes. Instead of utilizing Al to enable Ag to form a sufficient contact with the risk in loss of VOC and FF, different glass compositions for pure Ag pastes were developed to form a contact with low impact on cell efficiency. In direct comparison this method in the first try already surpasses the performance of commercial Al containing Ag pastes in direct comparison. The experimental pastes show a distinctive gain in solar cell characteristics in contrast to commercial pure Ag pastes. In this case we reached an overall efficiency of 18.6% using pure Ag pastes. Contact resistivity values thereby range below 1-2 mcm² comparable to pure Ag pastes on n-type emitters and Ag/Al pastes on p-type emitters.