Metallization of a Lightly Doped Emitter With Different Industrial Silver Pastes: Performance and Microscopy Analysis

Abstract

Ensuring high-quality front contacts in terms of low contact and line resistance while keeping the recombination losses low in p-type silicon solar cells has been challenging for the development of silver pastes. In this work, three silver pastes were used to create a contact on a lightly doped emitter of 90 Ω/sq, produced in a tube furnace by POCl3 diffusion, with an electrically active phosphorus surface concentration of 8E19 cm–3. The peak firing temperature (Tpeak ) and belt speed (vbelt) of the firing step were varied to study how the silver pastes performed. No shunting was produced after firing as pseudo fill factor exceeded 83%. Efficiencies up to 19% were measured. When firing at higher vbelt, a higher Tpeak permitted higher efficiencies due to better sintering and contact formation as well as a better passivation. A selective etching procedure was applied in order to investigate the contact interface. It was found that contact imprints were preferably located at pyramid tips for all groups. The paste producing larger and deeper contact imprints led to the lowest contact resistance (4 mΩcm2) but higher line resistance (0.46 Ω/cm) and higher saturation current density (30 fA/cm2 above) compared with the other two pastes.