Abstract
The energy crisis has stimulated a rapid growth of developments in the photovoltaic industry in recent years. To reduce the high cost and the toxicity of classical metallurgical routes, new methods, such as vacuum refining of silicon, have been developed. Moreover, at the industry level, parameters such as the porosity in crucibles and dies are not controlled, so wettability, infiltration, and reaction between silicon and graphite are the key factors in the purification process. In this work, the behavior of several refractory substrates against melted silicon was studied by the classic sessile drop method. The most important phenomena, i.e., wettability and infiltration, were compared with the properties of the substrates. According to the results, for the carbonaceous materials, the reaction of triple line silicon-graphite manages these phenomena, whereas for alumina, a passive layer is formed due to the presence of oxygen, which is subsequently eliminated by the chemical reactions, delaying the process. Regarding the contact angle and infiltration behavior, alumina showed the best results, but due to its reactivity, it contaminates Si, so that this material is not recommended for solar silicon application. However, composite 2 is compatible with the application, as it shows good results in comparison with the other materials.
Highlights
In recent years, there has been a rapid growth in the development of the photovoltaic industry (PV)
The purpose of this paper is to investigate and understand the interaction processes between molten silicon and different substrates through the analysis of wetting and infiltration processes
Regarding the top and side views of the carbonaceous substrates, the results suggest that the more the silicon spreads, the less the substrates will be infiltrated, independent of the roughness, porosity, or average pore diameter
Summary
There has been a rapid growth in the development of the photovoltaic industry (PV). Photovoltaic energy is considered as a main renewable electric source, and silicon is considered as the dominant material for the fabrication of solar cells, so that solar-grade silicon (SGS) feedstock is more and more needed [1,2]. The photovoltaic properties of silicon depend on the concentration of individual impurities, so the acceptable levels are defined by the conversion efficiency of solar cells. Depending on the degree of purity, silicon is classified into three main groups: electronic grade silicon (EGS) (10−4 –10−5 ppm impurities), solar grade silicon (SGS) (10−1 –10−2 ppm impurities), and metallurgical grade silicon (MGS) (~103 ppm impurities) [3]. The main routes to obtain SGS from MGS are chemical and metallurgical processes. The metallurgical route combines different metallurgical methods to obtain the required purity grade [3]
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