LR6 battery.Contact cleaning technology alleviates solar cell pollution problems

　　Contact cleaning technology alleviates solar cell pollution problems

　　Frequent and recurring pollution in the production environment seriously affects production efficiency. Using contact cleaning machines in every process where material surface contamination may occur can significantly improve production efficiency and the efficiency of solar cells.

　　Today's photovoltaic cell manufacturers are facing pressure to continuously improve production efficiency and improve the efficiency of their products. In addition, drastic changes in raw material prices also make it imperative. One of the main issues affecting production efficiency and product efficacy improvement is the frequent and recurring pollution in the production environment. If there is contamination on the material surface before the coating, printing or lamination process, production efficiency will be seriously affected.

　　This article will focus on the impact of pollution; the main sources of pollution and the problems they may cause; and propose feasible solutions to reduce pollution problems.

　　How pollution affects solar module production depends on which type of solar module is produced. There are three types of module production:

　　First Generation Solar Cells – Silicon Wafers: Dust and contaminants can affect the screen printing process, causing problems such as ‘tombstoning’, open circuits and short circuits. When contaminants in the soldering joints volatilize and expand rapidly, soldering leaks and dry soldering will occur. The solar cell is then encapsulated in an EVA film. If there are dust or pollution particles between the film and the cell, the final product will be less efficient because it blocks sunlight. Even tiny contamination particles invisible to the naked eye will appear as "fish eyes" on the repressed surface due to the "tent effect", resulting in visually defective products. These are things that manufacturers should try to avoid.

　　Second generation solar cells – vacuum alloy: It is more efficient, but the surface of the substrate must be very clear before entering the deposition process. If there are contamination particles in the wiring circuit, the same problems as the first-generation process will occur, such as 'fish eyes' and 'tombstones'. Likewise, if optimal cell efficiency is to be achieved, the glass or film surface must be cleaned during the packaging stage.

　　Third generation solar cells utilize screen printing technology similar to that used in the electronics industry. These batteries are generally less efficient than first- and second-generation batteries, so the problem of contaminants reducing their efficiency is even more serious. The substrate and stencil must be thoroughly cleaned before each printing step. The substrates generally used for screen printing are plastic materials or metal foils. These substrates arrive directly from the manufacturing plant before coating or deposition, and usually contain contaminant residues. For example, plastic films are generally cut into different sizes according to customer requirements. Debris is likely to remain on the surface of the material, and electrostatic attraction of dust is also a serious problem.

　　Contamination doesn't just cause problems during production. If the contaminant is a conductive material, it will cause corrosion of the finished product, which will most likely only be discovered later in the product life while it is being stored in the warehouse.

　　So where do the sources of pollution in the production process come from?

　　A number of potential sources of contamination include human hair, fabric fibers, exfoliated epidermis (one of the major sources of airborne dust), ceilings, floors, packaging and racks, and even alcohol-based cleaning cloths called 'non-exfoliated fibres'. become a source of pollution. ‘No shed fibers’ means that the fabric does not have fibers that fall off the surface, but when it is used to wipe the battery substrate or template assembly, the fibers are likely to fall off and remain on the surface of the object being cleaned. Static electricity is another major cause of pollution. Generally, battery panels are made of insulating materials and easily contain electrostatic charges. Therefore, loose particles are immediately attracted to the panel surface. Shipping, unpacking, or cleaning panels with a rag can generate static electricity. Especially in processes that require surface treatment such as printing, coating or lamination, a clean substrate is crucial to product quality, reducing waste and downtime, and improving production efficiency and corporate profits.

　　So what can be done to minimize the impact of pollution on solar cells? How can you combat contamination and static electricity and their impact on production? There are currently two methods for surface dust removal and static electricity removal: non-contact and contact dust removal.

　　Non-contact dust removal means that the cleaning equipment does not directly contact the surface of the material being cleaned, such as vacuuming, blowing dust or ultrasonic waves. Combining the anti-static rod and the dust collector, it makes direct mechanical contact with the coil to achieve the dust removal effect. In the case of a vacuum system, the suction force must be evenly distributed over the entire surface. If the seal connecting the object to be cleaned to the vacuum cleaner is not tight, the effectiveness of the cleaning operation will be reduced. Correct positioning and settings are crucial, as well as matching the speed, width and type of material being cleaned to the vacuum output. The disadvantage is that contamination residues around the work environment can be activated during the dust removal process of the vacuum equipment. Similarly, if dust is blown, it is also necessary to ensure that the force of the dust blowing air on the surface of the material is consistent. In addition, the blown pollution particles or dust are likely to be scattered in other places in the production line, or be captured twice by static electricity on the surface of the material. . Non-contact dust removal methods are relatively successful at removing moderate levels of contamination (contaminants around 25 microns). However, nowadays, the quality requirements of solar cell manufacturers and users are constantly increasing, because it is difficult to effectively break through the surface air layer of the material to be cleaned, and can only remove about 25 micron pollutants. Such cleaning performance is obviously not enough. The moving roll or sheet will form an air layer. If you want to achieve efficient cleaning results, you must break through this air layer. Some people believe that high-pressure air must break through this layer and blow away particles on the surface. But in reality this application doesn't work. Because the source of contamination is dispersed in the air and then stops at another point in the cleaned material. Therefore, traditional non-contact cleaning machines such as ultrasonic or airflow types are not the most effective method because they cannot break through the contamination particles captured by the surface air layer of the cleaning material.

　　Another option is to utilize a technology already proven by the semiconductor industry - contact cleaning technology. Contact dust removal technology began in the late 1970s and early 1980s. Teknek in the UK developed and manufactured the world's first contact cleaning machine. Contact cleaning usually uses the physical contact between the cleaning roller and the surface of the object to be cleaned to achieve the purpose of cleaning and dust removal. Contact cleaning rollers are polymer-covered rubber rollers that provide an efficient method of cleaning webs and sheets. When the cleaning roller comes into physical contact with substrate surface contaminants, the contaminants are transferred to the cleaning roller surface. This is a pinch-type method, where the cleaning roller simultaneously squeezes the air layer on the surface of the substrate. The result is highly efficient (over 96%) removal of tiny contaminants (typically less than 10 microns) at high speeds. Unlike brush-type or mechanical brush cleaning systems that can scratch sensitive material surfaces (such as films), rubber rollers will not damage the surface of the panel. The use of contact cleaning equipment can remove loose contamination particles as small as 1 micron on the surface of substrates such as silicon wafers, glass or EVA films without damaging the surface of the substrate. The subsequently removed contamination particles are transferred to sticky paper rolls for further analysis and destruction. After the cleaning process, the cleaned battery panels are immediately passed through the static elimination unit to remove static electricity to prevent re-contamination caused by attracted particles.

　　Using contact cleaning machines in every process where material surface contamination may occur can significantly improve production efficiency and the efficiency of solar cells. Contact cleaning has been proven to be the most efficient method of surface dust removal and cleaning.

　　in conclusion

　　As raw material prices continue to increase, solar cell manufacturers must find their own methods to improve production efficiency and reduce waste. Contaminants have a significant impact on both production efficiency and the efficiency of the solar cells themselves. Contact cleaning technology provides an optimal alternative solution for increasing production and battery efficiency.

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