“Solar grade silicon” refers to any grade of silicon usable in manufacturing solar cells, including polysilicon and UMG. “Semiconductor grade silicon” refers to the higher purity grades of polysilicon usable in manufacturing semiconductors. 2. Production capacity, supply and demand, price development 2.1. A ten year rollercoaster ride
Solar-grade purity is99.999% (5N) as opposed to electronic-grade silicon purity of up to 99.9999999% (9N). There are three main categories of manufacturing processes, resulting in different purity levels: There are three main steps to produce high-purity polycrystalline silicon.
Purity levels for solar cells do not have to be as high as in chip applications. Solar-grade purity is99.999% (5N) as opposed to electronic-grade silicon purity of up to 99.9999999% (9N). There are three main categories of manufacturing processes, resulting in different purity levels:
Solar grade silicon, as a starting material for crystallization to produce solar cells, is discussed here in terms of impurities whose maximum content is estimated from recent literature and conferences.
Domains of applications High purity silicon is for the manufacture of solar cells further processed into ingot and wafers. The dominant technologies to make ingots are both the single crystal Czochralski/CZ technique and the multicrystalline/m-C directional solidification/DS.
However, the vast majority of solar grade silicon (>90%) is still produced by the historical so called “Siemens” process applying chemical vapor deposition/CVD of high purity trichlorosilane/TCS/SiHCl 3 on a hot filament as this class of process currently is the only one available from technology suppliers and engineering firms.