Method for preparing high-purity cadmium telluride

Abstract

The invention discloses a method for preparing high-purity cadmium telluride. The reaction process is carried out in a closed quartz tube with melting point above cadmium and tellurium and after carbon coating treatment, wherein the mass ratio of a 5N cadmium material to a 5N tellurium material is 1: 1.1-1.15. The method comprises the following steps: dividing the weighed tellurium material into N parts according to the charging times N, dividing the weighed cadmium material into N-1 parts, alternately adding each part of tellurium material and each part of cadmium material into the quartz tube and adding the tellurium material into the quartz tube firstly and lastly, removing oxygen after charging, sintering and sealing the tube by using a sealed bulb, and slowly performing high-temperature and high-pressure synthetic reaction. The method has the advantages that the contact area of the raw materials is larger in a molten state, the reaction speed is more sufficient compared with the solid raw material, the micro-sized crushing treatment for the raw materials is avoided, the shape requirement of the raw materials is relaxed, the preparation cost is greatly reduced, the purity of the raw material is ensured, the method is suitable for large-scale production, the synthetic conversion rate of the cadmium telluride can reach 98 to 99.5 percent, and the single-tube yield of 800 to 1,000 grams can be ensured by using the quartz tube with the inside diameter of 32 millimeters under the premise of safety.

Description

technical field [0001] The invention relates to a method for preparing high-purity cadmium telluride, in particular to a method for preparing high-purity cadmium telluride without grinding raw materials, and the reaction process takes place above the melting points of cadmium and tellurium. Background technique [0002] Cadmium telluride is a compound semiconductor whose energy gap width is most suitable for photoelectric energy conversion. A solar cell made of this semiconductor is a device that directly converts light energy into electrical energy, and has a high theoretical photoelectric conversion efficiency. Cadmium telluride can be made into a large-area cadmium telluride film by vapor deposition, and the deposition rate is also high. It is precisely because of the low manufacturing cost and high conversion efficiency of cadmium telluride thin-film solar cells, and its rapid and large-area deposition in a high-temperature environment, it is suitable for commercial mas...

AI Technical Summary

Problems solved by technology

However, its shortcomings are: (1) The mixture needs to be crushed or ground into pellets with a particle size of 8-13 μm, which requires the support of high-end equipment, especially because cadmium is a soft metal, and it is very difficult to grind powder. Grinding to micron-sized particles is close to sky-high cost, which is not suitable for the actual situation of production

(2) In the process of grinding raw materials, it is difficult to avoid the pollution of equipment to raw materials, and it is impossible to prepare 6N or even higher-grade cadmium telluride

But the disadvantages are: (1) This technology is also prepared by powder feeding, the cost of preparing powder raw materials is high, and the requirements for equipment are strict, which will cause pollution to the equipment

(2) The products prepared by this technology are limited to cadmium telluride particles, and it is difficult to guarantee the synthesis rate

The disadvantages are: (1) In order to improve the product purity and increase the synthesis rate, the contact area of ​​the raw materials in the solid state must be increased to make the reaction sufficient, so the mixture must be pulverized or ground into micron-sized granules, resulting in The problem is that it needs the support of higher-end equipment, especially since cadmium is a soft metal, it is very difficult to grind powder, and the cost of grinding to micron-sized particles is almost sky-high, which is not suitable for the actual situation of production

(2) In the process of raw material grinding, it is difficult to avoid the pollution of the grinding equipment to the raw material, and it is impossible to prepare high-purity cadmium telluride

(3) The melting point of cadmium is lower than that of tellurium, and it reacts at the melting point of cadmium. The cadmium material and the tellurium material are both solid, and the reaction is not as good as the reaction between the cadmium material and the tellurium material in the molten liquid state.

[0006] One of the methods to avoid crushing or grinding the raw materials while ensuring sufficient contact between the raw materials is to react the raw materials in a molten state. It is not difficult for those skilled in the art to think of this scheme, and the inventor believes that this scheme should be in a closed It should be carried out in a quartz tube instead of a crucible. The reason is that the synthesis of the crucible is based on the grinding of the raw materials. Only the grinding can realize the synthesis at the melting point of tellurium and cadmium, and avoid steam in a real sense. If you use The crucible is synthesized above the melting point of tellurium and cadmium, and there will be a large raw material vapor. The vacuum environment based on the crucible needs to be sealed. The sealing is difficult, the reliability is poor, and the sealing degree is difficult to guarantee. During the synthesis process, steam will continue to rise , the steam will condense and adhere to the sealing cover after contacting the sealing cover which is always lower than the steam temperature, resulting in the loss of raw materials, and the synthesis rate and purity cannot be guaranteed

Therefore, the synthesis should be carried out in a closed quartz tube, but the technical problems to be solved urgently are: (1) Since the synthesis of cadmium telluride is an exothermic reaction, if the synthesis is carried out above the melting point of the raw material, the reaction will release a large amount of heat so that the inside of the quartz tube The pressure increases rapidly, and the tube is easy to explode

(2) Cadmium vapor will react with the quartz tube, affecting product purity and synthesis rate

(3) Sealing under high temperature and high vacuum conditions is difficult to achieve

These problems directly determine the success or failure of the synthesis and even threaten the safety of personnel, so there are no relevant reports on the successful application of this method to batch synthesis of high-purity cadmium telluride

Images