Phosphorus diffusion and gettering in multi-crystalline silicon solar cell processing

Gettering of mc-Si by P diffusion has been studied in the temperature range 840-990°C, in order to investigate its effect on the minority carrier recombination lifetime. We find that the recombination lifetime increases with both increased diffusion temperature and time. However, by correlating the enhancement in minority carrier lifetime with the sheet resistance of the emitters, we find that phosphorus penetration alone cannot not explain the gettering. It is found that for approximately equal emitter sheet resistances, longer diffusion times at lower temperatures are more efficient for gettering purposes than shorter high temperature diffusions. For successful gettering of non-recombinative traps, however, deep P penetration is required. Finally, by applying a temperature cool down to extend the high temperature processing without altering the emitter sheet resistance, we find that the minority carrier lifetime can be significantly increased, resulting in increased average solar cell efficiency from 12.53% to 13.43%.