Abstract
AbstractNew and cheaper refining methods for production of metallurgical silicon are needed to meet the increasing demands for low-cost, high-quality silicon for the solar cell industry. One promising refining method for boron is moist hydrogen treatment. In this work, an evaporation unit has been used to produce wet hydrogen gas, which subsequently has been sparged on top of silicon melts. The effect of temperature and gas composition on boron removal has been studied. The main results show that boron is removed from liquid silicon and the removal rate is controlled by chemical reaction depending on$$ p_{{{\text{H}}_{ 2} {\text{O}}}} $$and$$ p_{{{\text{H}}_{ 2} }} $$. Water vapor treatment of molten silicon can alone remove boron. However, in combination with hydrogen gas, the removal rate is significantly increased. In addition, the rate of boron removal in silicon has been found to decease with increasing temperature.
Highlights
TRADITIONALLY, off-spec polycrystalline silicon from the semiconductor industry, produced through the Siemens process, has been supplying the solar industry.[1]
Many methods have been patented the last decades by companies like Elkem, Fesil/SINTEF, and Kawasaki/NEDO,[4,5,6] where the target has been to produce 6-nines pure solar grade silicon (SoG-Si) at approximately $15 per kg
From the metallurgical production of silicon (MG-Si), approximately 95 pct of the boron put into the process remains in the product, and boron is for the most part linked to the impurity levels in coke (61 pct) and quarts (37 pct)
Summary
TRADITIONALLY, off-spec polycrystalline silicon from the semiconductor industry, produced through the Siemens process, has been supplying the solar industry.[1] This silicon is both costly ( < $35 per kg, 2009) and far purer (9 nines) than that what is needed for PV applications (6 nines).[2] To make solar cells less expensive, it has been necessary to develop production methods for solar silicon that improve cost and efficiency.[3] Many methods have been patented the last decades by companies like Elkem, Fesil/SINTEF, and Kawasaki/NEDO,[4,5,6] where the target has been to produce 6-nines pure solar grade silicon (SoG-Si) at approximately $15 per kg. The effect of temperature and gas composition during gaseous boron removal will be studied
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