Thin-film solar cells will also play a positive role in promoting the development of PVD vacuum coating(PVD vacuum coating equipment)
In the solar cell industry, crystalline silicon technology has long occupied the mainstream position. Due to the high cost of crystalline silicon technology, the industry has been reducing the cost through technologies such as the improvement of cell conversion efficiency and the reduction of the thickness of silicon wafers; at the same time, thin film solar Due to the advantages of batteries such as good low light performance (that is, strong power generation capacity in cloudy days), low production costs, and easy integration, thin-film solar cells have gradually attracted the attention of the industry and have grown rapidly. In the future, the market share of thin-film solar cells will gradually increase. It will also play a positive role in promoting the development of PVD vacuum coating equipment.
In the process of vacuum coating, spray spots and moist spots (mottling) sometimes occur. These spray spots and moist spots (mottling) greatly affect the quality of the film and reduce the pass rate of the product. This article will discuss the reasons for the formation of spray spots and moist spots (variegations) and how to eliminate them.
1. Reasons for the formation of spray spots
There are several reasons for spray spots during the coating process:
1. The coating material is not high in purity and contains many impurities. These impurities cannot be removed during the pre-melting process. The impurities splash on the surface of the workpiece during the evaporation process to form spray spots.
2. The material is relatively humid. During pre-melting, the electron gun spot cannot melt all the materials on the surface, and it is easy to produce spray spots during the evaporation process (this situation is more likely to occur when using domestic electron guns to plate MgF2 and some directly sublimated materials. ).
3. The pre-melting of the material before coating is not sufficient, and the fine particles in the material splash on the surface of the workpiece during the evaporation process to form spray spots.
4. During the coating process, the spray point caused by the material splash caused by the electron gun beam flow is too large.
2. Reasons for the formation of wet spots:
1. The cleaning solution is not well proportioned and contains a lot of water. After cleaning, there are residues on the surface of the workpiece, and mottling is formed after coating.
2. When the workpiece with more than two sides is plated, one side is finished, and when the second side is cleaned, the side after the plating is contaminated, and mottling is formed after the second side is coated.
3. Moisture contained in the workpiece itself (details in the process of making white pieces of the workpiece) escapes during the baking process before vapor deposition, and moisture spots are formed after vapor deposition.
4. During the baking process, the coating fixture will emit water vapor and other exhaust gas. After evaporation, moisture spots will be formed on the surface of the workpiece and will affect the optical characteristics of the coating.
3. In view of the causes of the above spray spots and moisture spots (variegation), the following measures have been taken in the production to eliminate spray spots and moisture spots (variation):
1. Choose a reliable material supplier and do a test for each batch of purchased materials before putting them into use to determine the reliability of the materials.
2. Standardize the use and storage of materials, (drying tank, desiccant) to ensure that the materials are not damp, and the properties of the materials remain unchanged.
3. Standardize the coating operation and strictly implement the operating procedures of pre-melting and evaporation. The pre-melting of the material before evaporation must be thorough, and the method of multiple pre-melting can be used to eliminate spray spots when plating some thicker layers.
4. Standardize the cleaning operation, strengthen the inspection after cleaning, improve the cleaning quality, and eliminate the moist spots (mottling) caused by cleaning.
5. Adjust the baking temperature to eliminate moisture spots caused by baking.
6. Standardize the management of coating fixtures. Before each use, the fixture needs to be cleaned and baked (300 degrees, more than 3 hours) before it can be put into production.
7. When designing coating fixtures, try to use materials with a small outgassing volume in the vacuum chamber. At the same time, you can use Ni plating on the surface of the fixtures to reduce the outgassing volume of the fixtures and eliminate the resulting moisture spots (variegations).
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