Contamination and gettering evaluation by lifetime measurements during single crystal cell processing

Abstract

In this work, the effects of contamination and gettering through two fabrication processes of monocrystalline Si solar cells are evaluated using lifetime measurements. The processes characterized were developed to produce n/sup +/pp/sup +/ and p/sup +/nn/sup +/ solar cells with phosphorus/aluminum and boron/phosphorus. The experiments indicate that in our laboratory environment, the lifetime degradation is influenced by the number of thermal processes. The gettering produced by aluminum in n/sup +/pp/sup +/ cell processing and by phosphorus (with heavy doping) in p/sup +/nn/sup +/ cell processing enhances the base lifetime. Slight phosphorus diffusion without supersaturation conditions, performed in the n/sup +/pp/sup +/ process, does not produce sufficient gettering and has lower effect on the lifetime than boron diffusions that produce some gettering too. Also, we discovered that gettering is strongly reduced when local aluminum back surface field regions are formed in the rear face in a failed attempt of reducing the BSF recombination.