Gettering and hydrogen passivation of edge-defined film-fed grown multicrystalline silicon solar cells by Al diffusion and forming gas anneal

Abstract

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 antireflection-coated edge-defined film-fed grown (EFG) silicon cell efficiency from 7.8% to 14.1%. Front oxide passivation contributed an ∼0.8% increase in absolute cell efficiency, Al diffusion on the back increased the efficiency by 1.4% (absolute), and the forming gas anneal (FGA) after the Al diffusion improved the cell efficiency by an additional 4.1% (absolute). A combination of the above three steps improved the EFG cell efficiency by 6.3%, indicating that the above three effects are complimentary. Oxide passivation reduced front surface recombination velocity and Al diffusion, while FGA improved diffusion length via gettering. We propose that the large increase in cell efficiency produced by the forming gas anneal results from bulk defect passivation by atomic hydrogen generated in the processing.