Gettering improvements of minority-carrier lifetimes in solar grade silicon

The minority-carrier lifetime in p-type solar-grade silicon (SoG-Si) produced by Elkem Solar was investigated after different types of heat treatment. Two groups of samples differing by the as-grown lifetimes were exposed to internal and phosphorus gettering using constant and variable temperature processes. Optimal heat-treatment parameters for each group of samples were then identified which improved the minority-carrier lifetimes to values higher than the minimum value needed for solar cells. Phosphorus gettering using a variable temperature process enhanced in particular the lifetime within each group, increasing in certain cases the lifetime from 3 up to 81 μs.

► Internal and phosphorus gettering considerably enhances the lifetime in Elkem SoG-Si.
► Variable-temperature processes are more effective than constant-temperature ones.
► Lifetime may be increased by a factor of 20 after variable-temperature P-gettering.
► Optimal temperature for constant-temperature processes varies between 800 and 930 °C.
► Maximum temperature for variable-temperature processes is between 1100 and 1200 °C.