Preparation method of polycrystalline silicon

Abstract

The invention discloses a preparation method of polycrystalline silicon. The preparation method of the polycrystalline silicon comprises the following steps: firstly carrying out pre-treatment on a quartz crucible, then paving a crystalline silicon chip material layer at the bottom of the quartz crucible, then placing silicon and mother alloy into the quartz crucible, charging, vacuumizing, and heating to melt silicon; after melting is finished, controlling the temperature of a heater to be 1540-1570 DEG C, lifting a thermal insulation cage until aperture a is 5-20mm, and controlling temperature TC2 to be no more than 1425 DEG C until broken polycrystals at the bottom are just molten, performing a temperature-fall period, and slowly opening the thermal insulation cage while slowly cooling in gradient; finally growing crystals, so that the polycrystalline silicon containing massive twin crystals is formed. A polycrystalline silicon slice prepared by adopting the preparation method is uniform in grain size, the battery efficiency is 0.2-0.3% higher than that of common polycrystalline silicon, the average battery efficiency of the whole silicon slice is more than 17.5%, and ratio of the silicon slice with the efficiency more than 17.4% is more than 65.0%.

Description

technical field [0001] The invention relates to the field of solar cells, in particular to a method for preparing polysilicon. Background technique [0002] Polysilicon ingot technology is one of the mainstream technologies for producing solar crystalline silicon materials. Polycrystalline silicon ingot has surpassed monocrystalline silicon produced by Czochralski method to a large extent because of its large amount of material, simple operation and low cost. At the same time, compared with Czochralski single crystal, the conversion efficiency of polycrystalline silicon solar cells is low and the service life is short. Therefore, by using high-purity (9N grade) silicon materials, or modifying the thermal field structure of the ingot furnace, the number of twins in the silicon wafers can be controlled, or By optimizing the thermal field and process, controlling the defects in silicon crystals to prepare high-quality polysilicon has become the mainstream direction of polysili...

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Problems solved by technology

[0004] (1) Cage semi-melting process: This method is similar to the quasi-single crystal production process. Polysilicon fragments are laid on the bottom of the crucible and a certain amount of fragments are kept when the material is melted. The unmelted fragments are used as seed crystals to grow Polysilicon with uniform and small grains, but this process is complicated to operate, the material yield is low (the red area at the bottom is longer), and because the silicon material is not completely melted, the content of hard spots in the silicon ingot increases;

[0005] (2) Closed cage full melting process: This method is to obtain polycrystalline silicon wafers with uniform and small grains, mainly relying on a high-efficiency crucible with a specially treated bottom (rough treatment at the bottom of the crucible), and nucleation first occurs on the rough surface of the bottom of the crucible , and then use the rough surface of the crucible as the nucleation surface to grow silicon ingots, but experiments have proved that the battery conversion efficiency of this method is 0.05-0.1% lower than that of the open-cage semi-melting process, and the bottom of the crucible will cause cracks in the silicon ingot during the ingot casting process. more likely

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