Method for casting high efficiency polycrystalline silicon ingots

Abstract

The invention discloses a method for casting high efficiency polycrystalline silicon ingots. The method comprises the following steps: (1) preparing a nucleating agent, namely mixing germanium powder with silicon nitride powder, adding pure water and an organic solvent, uniformly stirring to obtain a nucleating agent suspension liquid and spraying the nucleating agent onto the bottom of a quartz crucible, wherein the mass percentage of the germanium powder is 20%-80% and the mass percentage of the silicon nitride powder is 80%-20%; (2) preserving heat of the quartz crucible at 20-100 DEG C till the nucleating agent in the step (1) is completely dried; and (3) increasing the temperature difference between the top and the bottom of the quartz crucible to ensure that the whole furnace of silicon materials are molten starting from the upper part till totally molten, and carrying out crystal growth and cooling on the molten silicon materials to complete the ingot casting. The ingot casting method disclosed by the invention has the advantages that the crystal grain structure is optimized, so that the crystal defect density in polycrystalline silicon is reduced, the silicon wafer crystal defect is less and the minority carrier lifetime is longer; and compared with conventional polycrystalline silicon wafers, the polycrystalline silicon ingots have the advantage that the efficiency of polycrystalline silicon batteries adopting the polycrystalline silicon ingots is increased by 0.3-0.5%.

Description

technical field [0001] The invention belongs to the technical field of photovoltaics, and in particular relates to an ingot casting method for improving the photoelectric conversion efficiency of a polycrystalline silicon solar cell. Background technique [0002] Today, with the gradual depletion of fossil energy and the deteriorating environment, solar power generation has become the hope of human beings to replace energy in the future. Crystalline silicon solar cells have become the most advantageous solar power generation device due to their high efficiency and high stability. Among them, polycrystalline silicon solar cells have a high cost performance and occupy more than 80% of the current market share. However, the current solar cell technology is not yet Mature, low photoelectric conversion efficiency, high power generation costs and other short boards restrict the large-scale promotion and application of solar cells. Therefore, improving the photoelectric conversion...

AI Technical Summary

Problems solved by technology

However, after the silicon nitride coating is sprayed on the roughened crucible, the silicon nitride coating is in direct contact with the silicon liquid. Since the silicon nitride coating has no wettability with the silicon liquid, it cannot play the role of a nucleation center. Therefore, This method is not ideal for improving the grain morphology

[0005] Patent CN102776557A proposes a method of casting polysilicon ingots using broken silicon chips as seed crystals. The broken silicon material is spread on the bottom of the crucible as the seed crystal to promote nucleation. After the silicon material is melted, the process is adjusted to keep the broken silicon material partially melted. The crystal grows upward with the unmelted silicon material as the seed crystal to obtain high-quality silicon ingots. However, due to the unmelted silicon material at the bottom of this method, the impurity rate of the silicon ingot is high, and the yield of the ingot is low, and this method requires Precisely control the remaining amount of seed crystals. At present, automatic control cannot be realized. It can only be detected manually with quartz rods. The control of the remaining amount of seed crystals is unstable, and it is difficult to achieve comprehensive promotion.