The frequent and repetitive pollution in the production environment seriously affects the production efficiency. The use of contact cleaners in each process where there may be surface contamination of the materials can significantly increase the production efficiency and the efficiency of solar cells.
Today's photovoltaic cell manufacturers are under constant pressure to increase 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 problems affecting the production efficiency and the improvement of product efficacy is the frequent and repetitive pollution in the production environment. If the material surface is contaminated before the coating, printing or laminating process, the production efficiency will be seriously affected.
This article will focus on the impact of pollution; the main sources of pollution and the problems it may cause; and propose feasible solutions to reduce pollution.
How pollution affects the production of solar modules depends on which 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 many problems such as 'tombstoning', open circuits and short circuits. When the volatilization and rapid expansion of the contaminants in the solder joints result in missed and dry soldering. The solar cell is then encapsulated in an EVA film. If there is dust or contaminating particles between the film and the cell, the working efficiency of the final product will be reduced due to the blockage of sunlight. Even tiny particles that are invisible to the naked eye will have a 'fisheye' on the surface of the recompression because of the 'tent effect', creating visual artifacts. These are the factories to try to avoid.
Second Generation Solar Cell - Vacuum Alloy: It is more efficient, but the surface of the substrate must be very clear before entering the deposition process. If there are pollution particles in the wiring circuit, there will be the same problems as the first-generation process, such as 'fish eyes' and 'tombstones'. Also, if the best battery efficiency is to be achieved, the glass or film surface must be cleaned during the packaging phase.
Third-generation solar cells use screen printing technology similar to the electronics industry. Normally these batteries are not as efficient as the first and second generations, so the problem of reducing their efficiency due to contaminants becomes even more serious. The substrate and stencil must be thoroughly cleaned before each printing step. The substrates that are typically used for screen printing are plastic materials or metal foils, and these substrates, which come into the coating or deposition prior to deposition, arrive directly from the manufacturing plant, often with contaminating residues. For example, plastic films are generally cut to 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.
Pollution is not just a problem in the production process. If the contaminant is a conductive material, it will cause the finished product to corrode, and it is likely that it will only be found in the warehouse when it is stored in the warehouse.
Where does the source of pollution in the production process come from?
A large number of potential sources of contamination include human hair, fabric fibers, exfoliated skin (one of the main sources of airborne dust), ceilings, floors, packaging and scaffolds, and even alcohol-based cleaning cloths called 'non-shedding fibers'. Become a source of pollution. 'No shedding fiber' means that the fabric does not have surface-shedding fibers, but when the battery substrate or the stencil assembly is rubbed with it, the fibers are likely to fall off and remain on the surface of the object to be cleaned. Static electricity is another major cause of pollution. The general battery board is made of insulating material and easily contains electrostatic charges. Therefore, loose particles are immediately attracted to the surface of the panel. Transporting, packaging, or cleaning the panel with a rag can generate static electricity. Especially when printing, coating or laminating processes require surface treatment, clean substrates are critical to product quality, reducing waste and downtime, and increasing production efficiency and corporate profits.
So what can we do to minimize the impact of pollution on solar cells? How can we fight pollution and static electricity and their impact on production? There are two methods of dust removal and static elimination currently: non-contact and contact dust removal.
Non-contact dusting means that the cleaning equipment is not in direct contact with the surface of the material being cleaned, such as vacuuming, dust blowing or ultrasonic waves. Combine the electrostatic rod and vacuum to mechanically contact the coil directly to achieve the effect of dust removal. If it is a dust collection system, the suction power on the entire surface must be evenly distributed. If the connection between the object to be cleaned and the vacuum cleaner is not tight, the effectiveness of the cleaning operation will be reduced. The correct position and setting are critical, as are the speed, width, and type of material being cleaned that match the vacuum output. The disadvantage is that the pollution residue around the working environment will be activated during the dust removal process of the vacuum cleaner. Similarly, if the method of dust blowing is to ensure that the dust blowing air power on the surface of the material is the same, in addition, the airborne particles or dust may be scattered on other parts of the production line or trapped by static electricity on the surface of the material. . The non-contact dusting method was relatively successful in removing moderate levels of contamination (about 25 microns in contaminants). However, today's demand for quality in solar cell manufacturing and users continues to increase because it is difficult to effectively break the surface air layer of the material being cleaned, and only about 25 microns of contaminants can be removed. Such clean performance is obviously not enough. The moving web or sheet will form an air layer. If it is to achieve an efficient cleaning effect, it must break through this air layer. Some people believe that the high-pressure air will break through this layer and then blow off the particles on the surface. But in reality this application does not work. Because the source of pollution spreads in the air, then stays at another point of the cleaned material. Therefore, a conventional non-contact cleaner such as an ultrasonic or air flow type is not the most effective method because it cannot break through the contaminant particles captured by the surface air layer of the cleaned material.
Another option is to use the contact-based cleaning technology that has been proven by the semiconductor industry. Contact dust removal technology began in the late 1970s and early 1980s. Teknek in the UK developed and manufactured the world's first contact cleaner. 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 dust removal. The contact cleaner roller is a polymer-coated roller that provides a highly efficient coil and sheet cleaning method. When the cleaning roller physically contacts the surface of the substrate, contaminants are transferred to the surface of the cleaning roller. This is a sandwich-type method in which the cleaning roller simultaneously presses the air layer on the surface of the substrate. The result is the ability to remove small contaminants (usually less than 10 microns) with high efficiency (over 96%) at high speeds. It does not scratch the sensitive material surface (such as a film) like a brush or mechanical brush cleaning system. The rubber roller does not damage the surface of the panel. The use of a contact cleaning device can remove loose contaminant particles as small as 1 micron on the surface of substrates such as silicon wafers, glass or EVA films without damaging the substrate surface. Subsequent removal of the contaminated particles was transferred to a roll of viscous dust for further analysis and destruction. After the cleaning process, the cleaned panel is immediately charged with static electricity through the static elimination unit to prevent re-contamination caused by the attraction of particles.
The use of a contact cleaner in each process where surface contamination of the material may occur can significantly increase production efficiency and the efficiency of solar cells. Contact cleaning has proven to be the most efficient surface dusting and cleaning method.
in conclusion
With the continuous increase in the price of raw materials, solar cell manufacturers must find ways to improve their productivity and reduce waste. Pollutants have an important influence on the production efficiency and the efficiency of the solar cell itself. Contact cleaning technology provides an optimal alternative solution for improving production and battery efficiency.
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