Lowly-doped compensated solar-grade Cz-silicon for high efficiency solar cell processes

Alternative feedstock production routes avoiding the gaseous phase during silicon purification led up to now to significantly increased boron and phosphorus concentrations. The new generation of SoG ESSTM feedstock of Elkem Solar features reduced dopant concentrations with a net doping concentration similar to standard industrial silicon. Two Cz crystals, one p-type and one n-type doped, from blends with 50% ESSTM feedstock were studied regarding their light-induced degradation behavior and the ability of the p-type silicon to be used in high-efficiency solar cell concepts. For the light-induced degradation in n-type compensated silicon, we can confirm recent results from literature and show in addition the dependence of the defect generation rate and the saturated value of the Cz defect from the oxygen concentration. The potential of the p-type crystal with 50% ESSTM feedstock for solar cell production has been shown by Al-BSF and PERC solar cells. The intrinsic boron-oxygen defect is identified to be the only limiting defect for the p-type materials in the stable degraded state. Furthermore, a lifetime study reveals that there are getterable background impurities in the 50% ESSTM crystal which are proven not to be feedstock-specific as there amount is very similar in the virgin reference crystal.