A preparation method of semi-melting high-efficiency ingot and semi-melting high-efficiency seed crystal retention auxiliary plate

Abstract

The invention discloses a semi-molten high-efficiency ingot preparation method comprising the following steps: (1) a semi-molten high-efficiency seed crystal retention auxiliary board is arranged at the bottom of a crucible; (2) a layer of seed crystal is laid on the crucible bottom with the semi-molten high-efficiency seed crystal retention auxiliary board, such that a seed crystal layer is formed; and a block original silicon material is arranged above the seed crystal layer; (3) heating is carried out, such that the silicon material above the seed crystal layer is completely molten while the seed crystal layer is partially molten; (4) the temperature gradient in the crucible is controlled, such that a vertical temperature gradient from bottom to top is formed in the crucible; the molten silicon material grows into semi-molten high-efficiency silicon chips with the induction of the seed crystal layer arranged on the bottom. According to the invention, with the semi-molten high-efficiency seed crystal retention auxiliary board arranged on the bottom of the crucible, a seed crystal retention height in a semi-molten high-efficiency central zone is greatly reduced from 15-20nm of common semi-molten high-efficiency polycrystalline to 5-10mm, such that single-ingot silicon material one-time utilization rate is greatly improved.

Description

technical field [0001] The invention relates to a method for retaining seed crystals during high-efficiency polycrystalline silicon ingot casting, and belongs to the field of polycrystalline silicon ingot casting. Background technique [0002] At present, the preparation method of polycrystalline silicon ingots is mainly carried out by using the directional solidification system provided by GT Solar, which usually includes steps such as heating, melting, crystal growth, annealing and cooling. During the solidification and crystal growth process, the temperature of the top and the opening of the side insulation cover are controlled so that the molten silicon liquid can obtain sufficient supercooling at the bottom of the crucible to solidify and crystallize. However, since the bottom of the crucible has an isotropic structure in the initial stage of crystal growth, the initial nucleation cannot be effectively controlled during the crystallization of silicon liquid, and there a...

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Problems solved by technology

[0004] Although semi-melted high-efficiency polycrystalline silicon wafers have the advantages of lower ingot cost and higher photoelectric conversion efficiency than ordinary silicon wafers compared with "similar single crystal" silicon wafers, they also have the following disadvantages: 1) Due to the It is the top and side heating mode, so the side silicon material is easier to melt than the center silicon material during the melting process, and it is easy to form a convex melting interface with a high center and low sides when melting, and the height difference between the center and side melting interface reaches 10-20mm, it is difficult to retain the seed crystal of the side crystal brick, resulting in a decrease in the overall efficiency of the silicon ingot; 2) In order to ensure that the side crystal brick can effectively retain the seed crystal, manufacturers generally increase the retention height of the central seed crystal to achieve This purpose, but will cause the problem of low utilization rate of silicon material and high cost of casting ingot; 3) Since the purpose of retaining the side seed crystals is achieved by increasing the height of the center seed crystal retention, a large amount of pore reclaimed material will be caused at the bottom. Type recycled materials have the problems of high recycling difficulty and large recycling loss, which greatly increases the casting production cost of high-efficiency silicon ingots, which is not conducive to the further reduction of photovoltaic product production costs and the realization of the goal of photovoltaic grid parity

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