IMPACT OF COMPENSATED SOLAR-GRADE SILICON ON CZOCHRALSKI SILICON WAFERS AND SOLAR CELLS

Elkem Solar AS, Fiskaavn. 100, 4621 Kristiansand, Norway Phone: +49 (0)761 4588 5271, Fax: +49 (0)761 4588 9250, Email: stefan.rein@ise.fraunhofer.de ABSTRACT: Alternative feedstock production routes avoiding the gaseous phase during the purification of the silicon result in significantly increased boron and phosphorus concentrations, which leads to compensation effects in the material. We studied Cz crystals with different mix-in ratios of compensated SoG silicon feedstock from Elkem Solar (100%, 50%, 33% and 0%) regarding the impurity content, the specific resistivity, the effective carrier lifetime, the Cz defect formation and the resulting solar cell parameters of cells processed in an industrial standard screen-printing process. We find that the compensated material is dominantly influenced by the intrinsic metastable Cz defect which is proportional to the net-doping concentration. It is demonstrated that at least up to a mix-in ratio of 33% there are no feedstock-dependent performance losses. There is potential for higher mix-in ratio for this feedstock by lowering the net acceptor dopant concentration. Keywords: Compensated silicon, Czochralski, Defects, Degradation, Electrical properties