Metallization of a lightly doped emitter with different industrial silver pastes: performance and microscopy analysis

Abstract

Ensuring high-quality front contacts in terms of lowcontact and line resistance while keeping the recombination losseslow in p-type silicon solar cells has been challenging for the devel-opment of silver pastes. In this work, three silver pastes were usedto create a contact on a lightly doped emitter of 90Ω/sq, producedinatubefurnacebyPOCl3diffusion, with an electrically activephosphorus surface concentration of 8×1019cm–3. The peak fir-ing temperature (Tpeak) and belt speed (vbelt)ofthefiringstepwere varied to study how the silver pastes performed. No shuntingwas produced after firing as pseudo fill factor exceeded 83%. Effi-ciencies up to 19% were measured. When firing at highervbelt,ahigherTpeakpermitted higher efficiencies due to better sinteringand contact formation as well as a better passivation. A selectiveetching procedure was applied in order to investigate the contactinterface. It was found that contact imprints were preferably lo-cated at pyramid tips for all groups. The paste producing largerand deeper contact imprints led to the lowest contact resistance(4 mΩcm2) but higher line resistance (0.46Ω/cm) and higher satu-ration current density (30 fA/cm2above) compared with the othertwo pastes.