Refining of Solar Cell Silicon Through Metallurgical Routes

摘要

The study of photovoltaics (PV) has shown that we could provide clean, renewable, and sustainable energy without burning fossil fuels or running nuclear fission reactors. When Kvithyld1 introduced for the first time in 2009 the concept of "sun rush," she was referring to the industry rush towards PV production. At that time, the PV industry was experiencing an increase of about 30% to 40% annually driven by the subsidies mostly in European countries. Well, 3 years later, the situation does not seem to have changed that much; the PV industry is still growing at the same pace, notwithstanding the recent financial problems and economic recessions in southern Europe. Now, about 90% of the PVs utilize silicon as a semiconductor to absorb the energy from the sun and to transform it to electricity. However, unfortunately the energy produced by PVs is still more costly than the energy produced by other conventional ways. Production of solar grade silicon (SG-Si), which is silicon material with sufficient purity for use in PVs, adds a considerable amount to the cost. Silicon production distinguishes between two main technologies, a chemical route where the most prominent technologies are Siemens and fluidized bed reactor and a metallurgical route that is based on metallurgical refining of the silicon metal produced by carbothermic reduction of quartz and silica. This is called metallurgical-grade silicon (MG-Si). The chemical routes involve production and handling of chemicals that are highly volatile, corrosive, toxic, and explosive in the presence of water. These routs are avoided in the case of metallurgical refining of silicon.3 Refining of MG-Si to produce SG-Si has many benefits. It has been seen as a promising route not only to supply the growing demand for silicon but also to provide cheap silicon that consumes only a fraction of the energy required for silicon production by the chemical routes. Both routes are important for a sustainable PV technology. However, this section of JOM is dedicated to refining of silicon by metallurgical routes.