GETTERING AND HYDROGEN PASSIVATION OF EDGE-DEFINED FILM-FED GROWN MULTICRYSTALLINE SILICON SOLAR-CELLS BY AL DIFFUSION AND FORMING GAS ANNEAL

This study shows for the first time that a combination of Al treatment on the back, oxide passivation on the front, and 400-degrees-C formin g gas anneal in the presence of Al, raised the double-layer antireflec tion-coated edge-defined film-fed grown (EFG) silicon cell efficiency from 7.8% to 14.1%. Front oxide passivation contributed an approximate ly 0.8% increase in absolute cell efficiency, Al diffusion on the back increased the efficiency by 1.4% (absolute), and the forming gas anne al (FGA) after the Al diffusion improved the cell efficiency by an add itional 4.1% (absolute). A combination of the above three steps improv ed the EFG cell efficiency by 6.3%, indicating that the above three ef fects are complimentary. Oxide passivation reduced front surface recom bination velocity and Al diffusion, while FGA improved diffusion lengt h via gettering. We propose that the large increase in cell efficiency produced by the forming gas anneal results from bulk defect passivati on by atomic hydrogen generated in the processing.