Reducing impurities of multicrystalline silicon in a unidirectional solidification furnace for solar cells

Abstract

How would you……describe the overall significance of this paper? This paper proposed some methods to reduce the impurities of carbon and oxygen during the production of multicrystalline silicon. Therefore, high-quality and high-efficiency multicrystalline silicon can be obtained by the present solutions.…describe this work to a materials science and engineering professional with no experience in your technical specialty? We theoretically analyzed the incorporation mechanism of impurities of carbon and oxygen, and proposed to use a crucible cover to effectively reduce the carbon and oxygen impurities. Impurities can be further reduced if a reaction between the crucible and the graphite susceptor is prohibited.…describe this work to a layperson? Multicrystalline silicon has now become the main material in the photovoltaic market because of its low production cost and because of the relative high conversion efficiency of solar cells made from this material. The impurities of carbon and oxygen can markedly damage the quality and conversion efficiency of multicrystalline silicon. This paper mainly deals with the purification of carbon and oxygen impurities during production.Multicrystalline silicon has now become the main material in the photovoltaic market because of its low production cost and the relative high conversion efficiency of solar cells made from this material. Effective control of carbon and oxygen impurities in the crystal is required for the production of a high-quality component. In order to reduce impurity levels in a unidirectional solidification furnace, it is proposed to add a crucible cover to the casting process. Results from numerical simulations indicate a marked reduction of carbon impurity in a multicrystalline silicon ingot. The effect of crucible cover material on impurities in multicrystalline silicon was also investigated. These results show that the carbon concentration within the silicon ingot can be reduced by 10 times if the cover is made from carbon and by 1,000 times if the cover is made from tungsten. These results show that an effective and economical method for designing a cover is to use carbon and deposit a thin layer of tungsten on it. Experimental tests have also been carried out by placing a tungsten cover above the crucible. Results indicated that the carbon impurity has significantly decreased; however, the measured carbon concentration in the crystal is larger than the theoretically predicted value, despite the use of a crucible cover. A theoretical analysis has shown that this difference is due to a reaction between the crucible and the graphite susceptor. Furthermore, global simulations have shown that this reaction has a marked effect on carbon and oxygen impurities. When the carbon activity on the surface of the graphite susceptor increases, both oxygen and carbon impurities in crystal increase rapidly. Therefore, the production of high-purity multicrystalline silicon can be improved by designing a crucible cover with a thin layer of tungsten on it and by setting a fr...

Analysis of the Effect of a Vertical Magnetic Field on Melt Convection and Oxygen Transport During Directional Solidification of Multi-Crystalline Silicon by Numerical Simulation

“…Impurities such as oxygen, carbon, and metals will be inevitably introduced during directional solidification in silicon. The content of impurities effects seriously on the generation of defects such as dislocations in silicon ingot [2,3]. Controlling the content of impurities in the polysilicon can improve the properties of the silicon wafers [2,4].…”

“…The content of impurities effects seriously on the generation of defects such as dislocations in silicon ingot [2,3]. Controlling the content of impurities in the polysilicon can improve the properties of the silicon wafers [2,4]. Recently, lots of studies have indicated that optimizing the solidification process can reduce the impurity in polysilicon [5][6][7][8][9][10][11][12].…”

Effect of grain boundary grooves at the crystal/melt interface on impurity accumulation during the unidirectional growth of multicrystalline silicon

“…In the casting of multicrystalline Si (mc-Si) ingots for solar cells, metallic impurities, oxygen, and carbon are incorporated into the ingot from the crucible, which is usually coated with Si 3 N 4 powder, and from the atmosphere [1][2][3][4][5][6][7][8][9]. If low-grade raw materials, also called metallurgical silicon or solar-grade silicon, are used for the growth, a variety of metallic impurities will be present in the melt.…”