Method for preparing solar-grade silicon

Abstract

The invention relates to a preparation method of silicon with solar-grade purity, and provides a preparation method of the silicon with total impurity content less than 10ppma, B less than 2ppma, P less than 6ppma and resistivity more than 0.3omega.cm. The method comprises the following steps: taking industrial silicon powder as the raw material; uniformly mixing the silicon powder and remixed fluxing mediums to be filled into a silica pot inside an induction melting furnace after simple chemical pretreatment; blowing protection gas into the melting furnace under micro vacuum or normal pressure; heating by induction until the temperature inside the furnace reaches 1450 DEG C to 1700 DEG C; melting the metal silicon into silicon melt; removing formed slag. The method can effectively reduce the content of B in the silicon, thus leading B to be less than 2ppma and meeting the ordinary demands of silicon materials of the novel process in manufacturing low-cost solar battery. Moreover, the method has the advantages of simple production process, low production cost, easy large-scale production, small investment and short construction period.

Description

Technical field: [0001] The invention relates to a method for preparing solar-grade silicon, which belongs to the technical field of silicon purification. More specifically, the invention relates to a method for removing impurities from molten silicon by slag-forming treatment in an induction melting furnace. Background technique: [0002] The requirement for silicon to be used in solar cells has a purity of 9 to 6 out of 5. The allowable content varies with the elements. Recently, a breakthrough has been made in a new technology for preparing solar cells using metallurgical silicon. The allowable amount of impurity elements in raw silicon is lower than that required for traditional crystalline silicon solar cells. Generally, the total content of impurities in raw silicon is required to be less than 10ppma. B<2ppma, P<6ppma, resistivity>0.3Ω.cm, and the solar cell conversion efficiency can reach 14%, and the solar cell produced by the new process is lower in cost t...

AI Technical Summary

Problems solved by technology

[0004] 1. Process technical parameters, especially its important technical parameters are still uncertain, at least its technology has not been fully disclosed;

[0005] 2. The scale of the embodiment is small, indicating that its technology has not yet reached the level of industrialized production;

[0006] 3. The process is complicated, and plasma and electron beams are used in the process, which consumes a lot of energy and requires high equipment performance;

[0007] 4. In order to achieve the target quality, repeated purification operations are required, which increases the production cost

[0008] The inventor of the present invention has disclosed a production method of ultra-pure metallurgical silicon with the total amount of impurities less than 100ppma in the invention patent "A Preparation Method of Ultra-Pure Metallurgical Silicon" application number 200810068852.9, but it still cannot achieve solar energy The requirements for silicon with high-grade purity, that is, B0.3Ω.cm, and total impurities below 10ppma, the inventor applied No. 200810068852.9 on the basis of further research, improving the process conditions of the original method, using a special slagging agent, using physical metallurgical technology, to produce silicon with a quality that meets the requirements of solar-grade purity