The effect of aluminum treatment and forming gas anneal on EFG silicon solar cells

The objective of this paper is to investigate and quantify the effects of aluminum treatment, forming gas anneal (FGA), and oxide surface passivation on edge-defined film-fed growth (EFG) silicon solar cells. This study shows for the first time that a combination of Al treatment on the back, oxide passivation on the front, and 400°C forming gas anneal in the presence of Al, raised the double layer AR coated EFG cell efficiency from 7.8% to 14.1%. Oxide passivation on top of the emitter resulted in ~0.8% increase in EFG cell efficiency. Aluminum diffusion at 850°C alone on the back side increased the n ⁺-p-p⁺ EFG cell efficiency by 1.4% (absolute). Finally, a forming gas anneal at 400°C in the presence of aluminum, just after the aluminum diffusion, improved the efficiency by an additional 4.1% (absolute). A combination of the above three steps improved the EFG cell efficiency by 6.3% (absolute) indicating that these effects are complimentary. Oxide passivation reduces surface recombination velocity and Al diffusion improves diffusion length via gettering. The authors propose that the large increase produced by the forming gas anneal results from bulk defect passivation by atomic hydrogen generated in the processing