Gallium-doped polycrystalline silicon ingot and preparation method thereof

Abstract

The invention discloses a preparation method of a gallium-doped polycrystalline silicon ingot. The preparation method comprises the following steps: (1) forming a silicon nitride coating on the inner wall of a crucible; (2) putting the polycrystalline silicon material and a gallium dopant in the crucible to obtain a mixture; (3) putting the crucible filled with the mixture into an ingot furnace, vacuumizing, and heating so that the mixture is gradually melted from top to bottom; (4) at the crystal growth stage, adjusting the temperature of a temperature control thermocouple in the ingot furnace and the upward moving rate of a side thermal insulating cage so that heat radiates downwards and consequently, and the molten silicon grows from bottom to top under a vertically upward temperature gradient; (5) annealing and cooling, thereby obtaining the gallium-doped polycrystalline silicon ingot. Experiments prove that the polycrystalline silicon ingot is long in minority carrier lifetime and low in dislocation density, a polycrystalline silicon solar cell prepared from the polycrystalline silicon ingot is capable of obtaining relatively high photoelectric conversion efficiency, and more importantly, the cell prepared from the polycrystalline silicon is free of light-induced degradation phenomenon.

Description

technical field [0001] The invention relates to the field of semiconductor manufacturing, in particular to a gallium-doped polycrystalline silicon ingot and a preparation method thereof. Background technique [0002] Since entering this century, the photovoltaic industry has become the fastest growing high-tech industry in the world. Among all kinds of solar cells, crystalline silicon (single crystal, polycrystalline) solar cells occupy an extremely important position, and currently occupy more than 75% of the photovoltaic market. Crystalline silicon solar cells use the photovoltaic effect of the p-n junction to realize photoelectric conversion. From the perspective of development, crystalline silicon solar cells will still occupy a dominant position for a long time in the future. [0003] At present, the types of solar cells continue to increase, among which polycrystalline silicon solar cells will still occupy a dominant position in the future due to their lower cost and ...

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Problems solved by technology

[0004] However, the formation of B-O complexes between dopant boron (B) and oxygen (O) in polysilicon ingots under light conditions will cause light-induced attenuation, which reduces the conversion efficiency of the cell; in addition, boron (B) in silicon is easily The formation of Fe-B pairs with other impurities in the silicon ingot such as iron (Fe) deteriorates the minority carrier lifetime of the silicon ingot, thereby reducing the conversion efficiency of the cell

[0005] In the prior art, N-type silicon ingots are produced by doping donor impurities such as VI element phosphorus (P), but the segregation coefficient of phosphorus (P) in silicon is 0.35, and the distribution in silicon ingots is uneven, and the resistivity The difference is large, resulting in low ingot yield; on the other hand, the vapor partial pressure of phosphorus is low, and the volatilization amount is more during the crystal growth process, so the doping amount should not be controlled.

There are also some technical solutions that propose a resistivity compensation doping method when doping gallium (Ga), that is, doping the main dopant gallium (Ga) when charging, and doping donor impurities to balance the main dopant during the crystal growth process. The resistivity drop caused by excessive dopant concentration makes the resistivity meet the requirements; however, although the resistivity meets the requirements in this method, the impurity concentration of the silicon ingot is too high, which is not conducive to the improvement of cell efficiency

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