Distribution and impact of chromium in compensated solar grade silicon

In this study we have investigated two multicrystalline silicon ingots made from a compensated solar grade silicon (SoG-Si) test feedstock. Both ingots were solidified under the same conditions in a pilot-scale directional solidification furnace. In order to study the distribution and the impact of Cr in the compensated SoG-Si feedstock, 50 ppmw Cr (27 ppma) was added to one of the ingots. Electrical properties, such as resistivity and minority carrier lifetime, have been compared for the two ingots. Solar cells performance is also presented. The minority carrier lifetime is significantly reduced by the addition of Cr, being up to 19 μs for the undoped reference ingot, and <1 μs for the Cr-doped material. The maximum solar cell conversion efficiency of the solar cells made from the Cr-doped compensated solar grade silicon in this study is 14.4%, which is similar to the cells made from the ingot with no Cr addition. This work shows that Cr contamination significantly impairs electrical properties but they can, to some degree, be improved by gettering during solar cell processing.

► This work investigates the effect of Cr on a new type of compensated SoG-Si test feedstock. ► Cr significantly reduces the minority carrier lifetime in as-cut material to below 1 μs. ► Lifetime can be enhanced by two orders of magnitude by P-diffusion gettering. ► Solar cells from this test feedstock perform well even with high Cr concentrations. ► The effective segregation coefficient of Cr has been determined.