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Silicon crystallization by Kyropoulos process for photovoltaic applications

Leslie Lhomond 1Guy Chichignoud 1François Lissalde 2Kader Zaidat 1

1. Science et ingénierie des matériaux et des procédés, Elaboration par Procédés Magnétiques (SIMAP-EPM), 1130 rue de la Piscine, Grenoble 38402, France
2. Cyberstar, 1 rue des Tropiques, Grenoble 38435, France

Abstract

Photovoltaic energy is an environmentally friendly way to produce electricity. The efficiency of photovoltaic cells based on silicon depends on the material quality and the crystalline structure. Crystalline structure depends on the crystallization process (mono-crystalline, polycrystalline and quasi-mono). Mono-crystalline silicon has a better efficient than polycrystalline cells because of fewer traps for charge carriers, so their life-time is longer. So far, the main crystallisation process used for mono-crystalline silicon is Czochralski method. Final silicon ingot obtained is cylindrical geometry, raw material has to be cut and lost to manufacture square cells. In the quasi-mono technique, multiple Si single-crystal seed crystals are arranged on the bottom surface of the crucible. The crystallized ingot is then square, matching the crucible geometry. This method is useful for reducing the number of grain boundaries by forming large single-crystal- like grains, but it has still a severe problem that polycrystalline growth from the crucible walls always occurs.  The present work would deals with the adaptation of Kyropoulos process for silicon. Kyropoulos process is well known and used for sapphire. This process should be good for silicon crystallization because of the reduced stress forces applied on the material. The crystal grows naturally in the low-temperature region, then it is slowly pulled upward while ensuring that crystal growth remains in the low-temperature region. This parameter can reduce the number of dislocations. Moreover, in order to reduce the lost raw material, the final ingot should be closed like the crucible geometry (square for standard fused silica crucible). A Cyberstar furnace has been adapted for the Kyropoulos crystallization of silicon.  Experimental studies were carried out to investigate favorable thermal conditions for growth from the seed. As the square geometry highly depends on the control of the radial growth, the effect of seed orientation was also considered.

 

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Related papers

Presentation: Poster at 15th Summer School on Crystal Growth - ISSCG-15, by Leslie Lhomond
See On-line Journal of 15th Summer School on Crystal Growth - ISSCG-15

Submitted: 2013-04-12 16:41
Revised:   2013-04-12 16:41