ON THE IMPACT OF GE IN COMPENSATED SOLAR GRADE (SOG) SILICON - A STUDY ON INGOT AND SOLAR CELL LEVEL

摘要

In this study, four dopant compensated silicon ingots grown from solar grade silicon (SoG-Si) feedstock are investigated comparing their properties against a non compensated reference ingot made from polysilicon feedstock. All four SoG ingots are grown from the same feedstock in the same Bridgman furnace under the same conditions using two different compensation scenarios. For two ingots Ge - a metallic impurity - is introduced into the initial melt to study its effects on crystal quality and the possibility of a positive effect on solar cell efficiency as postulated in ref.. Dislocation density maps measured on selected wafers of the different UMG ingots reveal lower dislocation densities for the Ge containing wafers as described in ref.. On solar cell level though, the Ge containing cells show lower conversion efficiencies. High carbon concentrations (6 to 15 ppmw) for all SoG ingots result in SiC precipitation which leads amongst other effects to high rate of wafer breakage and cell shunting.