Physical mechanisms of in situ surface gettering of metals in ribbon silicon for solar cells

The authors have employed synchrotron-based x-ray absorption near-edge spectroscopy and x-ray fluorescence microscopy to identify the chemical state and distribution of metals gettered to the surface of String Ribbon silicon grown with CO-ambient gas. Copper and nickel precipitates were observed in their equilibrium silicide phases, indicating a dominant relaxation gettering mechanism. In addition, microwave photoconductive decay measurements show a decrease in bulk iron concentration and a tenfold increase in minority carrier lifetime in CO-ambient grown material. Implications of the observed gettering mechanism on ribbon-type solar cells are discussed.