Contacting boron emitters on n-type silicon solar cells with aluminium-free silver screen-printing pastes

Abstract

In the production of n-type Si solar cells, B diffusion is commonly applied to form the p⁺ emitter. Up to now, Ag screen-printing pastes, generally used to contact P emitters, had been incapable of reliably contact B emitters. Therefore, a small amount of Al is generally added to Ag pastes to allow for reasonable contact resistances. The addition of Al, however, results in deep metal spikes growing into the Si surface that can penetrate the emitter. Losses in open-circuit voltage are attributed to these deep metal spikes. In this investigation we demonstrate, that state-of-the-art Al-free Ag screen-printing pastes are capable to contact BBr3-based B emitters covered with different dielectric layers and reach specific contact resistances <1 mΩ cm². Bifacial n-type solar cells with Al-free Ag pastes on both sides show efficiencies of up to 18.3% and series resistances <0.5 Ω cm²