Between Sand and Sun

Quartz sand is the starting material for the production of hyperpure polysilicon, the most important raw material for photovoltaics. Between sand and hyperpure polysilicon lie a number of highly complex and technically sophisticated working steps – and in the case of WACKER over 50 years of experience. All combining to produce the best polysilicon available on the market.

The key stages in the production of hyperpure polysilicon:

1. Quartz Sand

Silicon is the second most abundant element in the earth’s crust. In nature it occurs primarily as silicon dioxide (SiO2) in the form of quartz sand.

2. Metallurgical Silicon

Heating the silicon dioxide (SiO2) with carbon removes the oxygen atoms. This yields metallurgical silicon (Simg), which contains one to two percent impurities – far too much for the production of high-efficiency solar cells. So WACKER employs a tried-and-tested distillation process to purify it even further.

3. Fluidized Bed Reactor

First, the metallurgical silicon (Simg) is transformed in a fluidized-bed reactor into liquid trichlorosilane (HSiCl3) with the aid of hydrogen chloride gas.
Simg + 3 HCl -> SiHCl3 + H2

4. Trichlorosilane Distillation

This liquid is distilled to remove the impurities and generate highly pure trichlorosilane.

5. Silicon Deposition Reactor

The extremely pure trichlorosilane distillate is then heated to 1,000 °C and passed over thin, heated silicon rods.

6. Pure Silicon

The trichlorosilane decomposes, allowing hyperpure silicon to deposit on the surface of the rods.
4 SiHCl3 -> Si + 3 SiCl4+ 2 H2

7. Silicon Chunks

The hyperpure silicon is then chopped up. The resulting chunks are the starting material for solar cells and semiconductor wafers.

The purer the polysilicon, the more efficient is the solar cell.

The polysilicon produced by WACKER is 99.9999999 percent pure. It is an enabler for highly efficient solar cells that deliver a shorter energy payback time, a smaller carbon footprint and ongoing cost reductions. Over the lifetime of a solar cell, a kilogram of hyperpure polysilicon from WACKER can save on more than 7,000 kilograms of CO2 emissions.

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Our hyperpure polysilicon is a key raw material for the photovoltaics and semiconductor industry. For more about the advantages of this high-tech material, visit our product portal.

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