Sputtered Phosphorus‐Doped poly‐Si on Oxide Contacts for Screen‐Printed Si Solar Cells

The impact of the phosphorus doping density in direct current‐sputtered polysilicon layers on surface passivation and contact resistance by fabricating polysilicon on oxide (POLO) contacts is studied, when applying doping densities ranging from 3 × 1019to 4 × 1020 cm−3. Hydrogenation is performed either via a hydrogen‐releasing AlOxlayer and postdeposition anneals in forming gas using a tube furnace at 400 °C, or by rapid firing of an AlOx/SiNystack in a conveyor belt furnace at 810 °C. The study shows that the forming gas anneal of the weakly in situ phosphorus‐doped poly‐Si layers with AlOxenables a passivation quality with an implied open‐circuit voltage of up to 734 mV and a recombination current density down to 1.8 fA cm−2. For fast firing, a high phosphorus concentration of 4 × 1020 cm−3is required for comparably high passivation quality with a recombination current density down to 1.3 fA cm−2. A p‐type POLO back‐junction solar cell featuring such ex situ doped sputtered POLO contacts with a cell efficiency of 22.4% and an open‐circuit voltage of 714 mV is fabricated. To our knowledge, this is the highest open‐circuit voltage published so far with sputtered POLO contacts.