A Diffusion Process That Improves the Minority Carrier Lifetime of Metallurgical-Grade Silicon Wafers

Abstract

The invention relates to a diffusion technology adopted in the process of manufacturing a physical metallurgical silicon solar cell, in particular to a diffusion technology for prolonging the minority carrier lifetime of a metallurgical silicon wafer. The diffusion technology is characterized by comprising the following steps: (1) propelling a quartz boat at the low temperature and raising the temperature preliminarily; (2) introducing nitrogen carried with phosphorus oxychloride and diffusing generated phosphorus atoms; (3) advancing at the constant temperature; (4) cooling and withdrawing the quartz boat. The technology has the benefits as follows: 1, spraying type diffusion is adopted, so as to save the phosphorus source as well as improve the uniformity of diffusion junction depth, and the technology is suitable for high sheet resistance; 2, according to the characteristics of physical metallurgical silicon, two-sided phosphorus is adopted in gettering to enhance the gettering effect and prolong the minority carrier lifetime of the silicon wafer; 3, the diffusion technology is effectively improved via the coordination of temperature and time; 4, the proportions of introduced oxygen and introduced raw material are controlled to reduce the defects caused by direct diffusion and improve the junction depth of a PN junction, the surface passivation effect can be further improved, and the short-circuit current and the open-circuit voltage are increased, so that the conversion efficiency and the yield of the metallurgical silicon solar cell are further improved.

Description

technical field [0001] The invention relates to a diffusion process in the manufacturing process of physical metallurgical-grade silicon solar cells, in particular to a diffusion process that can improve the minority carrier life of metallurgical-grade silicon wafers. Background technique [0002] Diffusion is the core process in the manufacturing process of solar cells. The purpose of diffusion is to form the heart PN junction of solar cells, and at the same time obtain effective bulk carrier life and sheet resistance. The level of bulk carrier life and whether the sheet resistance is uniform directly affect solar energy. Electrical performance parameters such as short-circuit current, open-circuit voltage, and dark current of the cell ultimately affect the efficiency and yield of the cell. However, metallurgical-grade silicon is different from Siemens silicon, which is generally produced by physical purification, and contains a large amount of iron, carbon, boron, oxygen, ...

AI Technical Summary

Problems solved by technology

However, metallurgical-grade silicon is different from Siemens silicon, which is generally produced by physical purification, and contains a large amount of iron, carbon, boron, oxygen, copper and other impurities and lattice defects, while a large amount of iron, carbon, boron, oxygen, copper, etc. The existence of impurities will increase the recombination probability of photogenerated carriers, so that the bulk minority carrier lifetime of the silicon wafer after diffusion to form a PN junction is very low, and the resulting solar cells generally have low efficiency and cannot improve the yield of products

[0003] However, at present, there are only a handful of enterprises in China that use physical methods to produce metallurgical-grade silicon wafers, and there are even fewer enterprises that use metallurgical-grade silicon wafers as raw materials to produce solar cells. Silicon Diffusion Process

In the industry, the liquid phosphorus source diffusion process is generally used to form the PN junction of solar-grade silicon cells. Due to the presence of metal impurities and dislocation defects in the physical metallurgical-grade crystalline silicon raw silicon wafers, the conventional Siemens silicon wafer diffusion process is usually used for diffusion junctions. Although a good PN junction can be formed, the impurity removal effect is not ideal, and the square resistance in the chip is not uniform

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