Materials Science and Engineering B 159–160 (2009) 274–277 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Study of defects and impurities in multicrystalline silicon grown from metallurgical silicon feedstock S. Binetti a,∗ , J. Libal a , M. Acciarri a , M. Di Sabatino b , H. Nordmark c , E.J. Øvrelid b , J.C. Walmsley b,c , R. Holmestad c a University of Milano Bicocca, Department of Materials Science, via Cozzi 53, 20125 Milano, Italy b SINTEF Materials and Chemistry, A. Getz v. 2B, 7465 Trondheim, Norway c Department of Physics, NTNU, NO-7491 Trondheim, Norway article info Article history: Received 29 April 2008 Received in revised form 10 May 2008 Accepted 13 May 2008 Keywords: Metallurgical silicon Impurities Gettering Lifetime EBIC Photoluminescence abstract Nowadays the photovoltaic (PV) market suffers the severe shortage of silicon. One possible solution is to produce SoG-Si via a direct metallurgical route, followed by a final casting step. The use of such lower quality materials in solar cell production depends on the possibility of improving the electrical quality during the cell processing and requires a deep understanding of the interaction between defects. The aim of this work is to study the electrical properties and the minority charge carrier recombination behaviour of extended defects in a mc-Si ingot grown from metallurgical Si produced directly by carbothermic reduction of very pure quartz and carbon. The combined application of photoluminescence, infrared spectroscopy, electron beam induced current technique and transmission electron microscopy succeeded in identifying oxygen precipitates, decorated grain boundaries and dislocations as the defects which limit the quality of the metallurgical mc-Si and, therefore, the efficiency of the related solar cells. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The increasing interest in renewable energy sources with a low environmental impact has given rise to a rapid growth of the pho- tovoltaic (PV) industry. Up to now, the dominant semiconductor material used in PV is silicon and it is expected that silicon will play a fundamental role at least for the next decade. As the electronics sector recovers, and the requirements of the PV industry expand, there has been an increasing need for a dedicated supply of silicon. On the other hand, the severe shortage of the silicon used in the systems threatens to dampen the PV market’s growth. Therefore, a new supply of solar grade silicon (SoG-Si) is crucial. One possible solution is to produce SoG-Si via a direct metallurgical route, fol- lowed by a final casting step. The metallurgical grade silicon made by direct reduction of quartz and carbon black is about 98.5% pure [1], i.e. a purity far from the 8 N pure silicon currently used in PV industry. The possibility of using such contaminated material in solar cell production depends on the following factors: ∗ Corresponding author. Tel.: +39 0264485177; fax: +39 0264485400. E-mail address: simona.binetti@unimib.it (S. Binetti). - using extra pure quartz in order to start with a higher quality material; - improving the electrical quality during the cell processing; - develop of new device process with less dependence on the quality of the material, i.e., on the diffusion length and on dopant/type. The possibility of improving the electrical quality before or dur- ing the cell process requires a deep understanding of the type and concentration of impurity and defect, the presence of complex and cluster, the effect of impurity segregation process on the electrical activity of extended defects, as the solar cell efficiencies attain- able with mc-solar grade Si are determined by all these material properties. This work deals with a complete characterization of the elec- trical properties and the minority charge carrier recombination behaviour of extended defects in mc-Si ingots grown from met- allurgical Si, produced directly by carbothermic reduction of very pure quartz and carbon without subsequent purification processes. The aim of the work is to test the feasibility of using such material in solar cell standard device process and to show how a combined application of different techniques succeeded in the identification 0921-5107/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2008.05.013