Silicon is the second most common element in the Earth’s crust. According to the Minerals Education Centre, silicon is not found in its pure form, but in compounds with Oxygen. Silica is one of the most abundant compounds which is found in rocks like obsidian, granite, and sandstone. Silicon can also be mined in quartzite, mica, and talc, but is found most abundantly in sand.
Silicon is reduced through a reduction process by heating it with carbon material to remove the Oxygen and leave behind a pure, metallurgical silicon. The silicon is purified into polysilicon which has a purity of over 99 percent.
Various grades of poly silicon can be created through different processes.
For example, electronic grade poly silicon, is extracted by passing poly silicon through hydrogen chloride at extremely high temperatures and then distilled.
To yield solar-grade silicon however, the poly silicon goes through a chemical refinement process. In the process, the silicon is passed through a mixture of gases to remove boron and phosphorus. The process results in pure cylindrical form solar grade silicon called ingots. The ingots are then sliced into small conductive pieces for photovoltaic panels.
