Method for preparing electric-field directional solidification purified polysilicon

Abstract

The invention relates to a method for preparing electric-field directional solidification purified polysilicon. The method comprises the following steps of: adding a silicon material into a graphite crucible of a sealed purifying furnace, purifying the sealed purifying furnace, heating and melting the silicon material in the graphite crucible of the sealed purifying furnace by a heater, completely melting the silicon material and preserving heat; applying an electric field to the completely molten silicon material in the graphite crucible and continuing to preserving heat by the heater for 2-6 hours while acting by the electric field; cooling through the bottom of the graphite crucible to ensure that the silicon material is solidified from the bottom to the top, quickly cooling an obtained silicon ingot after the silicon material is completely solidified, and annealing at 1,350-1,380 DEG C; and taking the silicon ingot out of the furnace, finishing to remove the head and the tail to finish purifying so as to obtain high-purity polysilicon. Compared with the prior art, in the invention, directional solidification is carried out through applying the electric field, which ensures that metal impurities are aggregated to the surface of liquid silicon under the action of the electric field, and most metal impurities are solidified to the surface of the silicon ingot through the directional solidification from the bottom to the top; and finally, the head and the tail of the silicon ingot are removed to obtain the polysilicon with higher purify, thereby the conversion efficiency of a solar battery is improved.

Description

Technical field: [0001] The invention relates to the technical field of silicon and its compounds, in particular to a method for preparing polysilicon by electric field directional solidification and purification. Background technique: [0002] The common problem faced by the purification of solar-grade silicon materials by physical metallurgy is how to purposefully and selectively remove the inherent impurities brought about by the metallurgical method itself. Metal impurities in silicon belong to deep-level impurities, even multiple-level impurities and double deep-level impurities that are donors and acceptors at the same time. The reduction in the effective lifetime of minority carriers in silicon caused by a very small amount of metal impurities will greatly reduce the photoelectric conversion efficiency of the cell. In order to remove metal impurities, the technologies currently used by various scientific research institutions and enterprises are pickling or direction...

AI Technical Summary

Problems solved by technology

The pickling method can remove some active metals, but pickling adds new sources of pollution, and one more process means one more possibility of pollution

Directional solidification is to put the silicon material into the crucible, and under the protection of vacuum or inert gas atmosphere, the silicon material is completely melted by electric heating, and then the temperature is gradually lowered from the bottom to the top, so that the entire silicon liquid will form from the bottom to the top. A certain temperature gradient, so that the silicon liquid will gradually solidify from the bottom to the top, and finally most of the metal impurities with low segregation coefficients will be repelled to the surface of the silicon ingot to be removed, but the removal effect of some metal impurities with large segregation coefficients is not obvious , the existence of this part of metal impurities will reduce the conversion efficiency of polycrystalline silicon solar cells, this problem needs to be solved

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