Abstract
To make electrical energy from photovoltaic (PV) silicon (Si) solar cells competitive, the cost in each of the PV manufacturing process steps has to be diminished. Today, high-purity Si is produced by an energy-intensive process exhibiting high irreversible thermodynamic losses. The purity of the product from this process (99,9999999 pct [9 N]) far exceeds what generally is accepted to be the requirements for PV purposes (4 to 6 N). Here we show a novel method for the purification of Si based on the principle of electrochemical refining in a molten high-melting-point fluoride electrolyte at temperatures above the melting point of silicon 1685 K (1412 °C). The method comprised a vertical stack of three molten layers with a metal alloy at the bottom, an intermediate electrolyte layer, and purified metal at the top. The integrity of the layers being secured was through the immiscibility of the liquids and the careful tailoring of the individual densities. Boron (B), exhibiting similar thermodynamic properties to Si, effectively was not removed. A suitable low-B feedstock may be identified in kerf from the sawing of mono- or multicrystalline Si blocks into wafers. To produce purified metal in the 6 N range, practice from electrorefining of aluminum shows that long-term, stable operation in large-scale industrial reactors is needed. The trends and mechanisms observed in the laboratory scale indicate that high purity also can be achieved for Si provided that these criteria can be met.
Similar content being viewed by others
References
A. Luque and S. Hegedus: Handbook of Photovoltaic Science and Engineering, Wiley, Chichester, UK, 2003.
W. Hoopes: Patent US 1 534 318, 1922.
R.A. Gadeau: Patent US 2 034 339, 1933.
A.I. Belyaew, M.B. Rapoport, and L.A. Firsanowa: Metallurgie des Aluminiums—Band II, VEB Verlag Technik, Berlin, Germany, 1973.
T.G. Pearson and H.W.L. Phillips: The Production and Properties of Super-Purity Aluminium, Institute of Metals, London, UK, 1957.
M. Ueda, T. Ohmura, S. Konda, T. Sasaki, T. Ohtsuka, and T. Ishikawa: J. App. Electrochem., 2001, vol. 31, p. 871.
G.Z. Chen and D.J. Fray: J. App. Electrochem., 2001, vol. 31, p. 155.
A. Cox and D.J. Fray: J. Electrochem. Soc., 2003, vol. 150, no. 12, p. D200.
T. Takenaka, S. Isazawa, M. Mishina, Y. Kamo, and M. Kawakami: Mat. Trans., 2003 vol. 44, no. 4, p. 546.
A.A. Andriiko, E.V. Panov, and A.P. Monko: J. Solid State Electrochem., 1998, vol. 2, p. 198.
J. Ackerman, L.S.H. Chow, S.M. McDeavitt, C. Pereira, and R.H. Woodman: J. Metals, 1997, vol. 7, p. 26.
C.C. McPheeters, E.C. Gay, E.J. Karell, and J.P. Ackerman, J. Metals, 1997, vol. 7, p. 22.
S.A. Kuznetsov, H. Hayashi, K. Minato, and M. Gaune-Escard: Electrochimica Acta, 2006, vol. 51, p. 2463.
G. Zwillig: Electrochimica Acta, 1981, vol. 26, p. 637.
D.R. Stull and H. Prophet: JANAF Thermochemical Tables, U.S. Department of Commerce, Washington, DC, 1985.
E. Olsen: Patent Norway 328 263, 2010.
A. Roine, HSC Chemistry for Windows, version 6.12, Outotec Research, Oy, Finland, 2007.
C.W. Bale, P. Chartrand, S.A. Decterov, G. Eriksson, K. Hack, R. Ben Mahfoud, J. Melançon, A.D. Pelton, and S. Petersen: CALPHAD, 2002, vol. 62, p. 189.
T. Yoshikawa and K. Morita: Met. Mat. Trans. B, 2005, vol. 36, p. 731.
The financial support from the Norwegian Research Council through the FORNY program is greatly acknowledged.
Author information
Authors and Affiliations
Corresponding author
Additional information
Manuscript submitted March 30, 2009.
Rights and permissions
About this article
Cite this article
Olsen, E., Rolseth, S. Three-Layer Electrorefining of Silicon. Metall Mater Trans B 41, 295–302 (2010). https://doi.org/10.1007/s11663-010-9362-8
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11663-010-9362-8