POLYSILICON VALUE CHAIN
POLYSILICON PRODUCTION(Si >99,9999999%)
The photovoltaic value chain starts from the refining process of metallurgic silicon up to high levels of purification. Metallurgic silicon is mostly produced by the silica gel fusion, which is a mineral who forms about 25% of the entire earth crust. During the purification process, fundamental in order to achieve the best performances in terms of energetic conversion, takes place thanks to Triclorosilane (TCS). This substance is obtained with a reaction of hydrochloric acid on the purified metallurgical silicon from the contaminations of iron, aluminium and boron (impurity in the range of some parts per billion).
MONO-CRYSTALLINE AND POLY-CRYSTALLINE INGOTS PRODUCTION
At this point, the solar grade polysilicon is ready for the next process. In order to produce the photovoltaic cell, it will have to be grown in forms of mono-crystalline or poly-crystalline ingots, that will then be sliced into 125 mm or 156 mm wafers. The growing process of such ingots is divided into Czochralski Crystal Process (CZ) and Directional Solidification System Process (DSS). CZ to obtain mono-crystalline cilindric shape ingots with a variable diameter of 6 inches and 8 inches and DSS in order to obtain poly-crystalline prallelepiped shape ingots.
MONO-CRYSTALLINE AND POLY-CRISTALLINE WAFERS PRODUCTION
The following process is the slicing through wire saw technology, that allows the mono-crystalline and the poly-crystalline ingots cut into bricks and finally into wafers with a range tickness of 180 to 200 micron. This leader technology in the production of wafers for photovoltaic industry allows up to 4 simultaneous bricks slicing, reducing to a minimum level the kerf-loss produced by the
process itself.
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