In recent years, more and more mysterious dark lines with wide fingers have been distributed on the surface of solar cells. This phenomenon is not really caused by snail crawling, but it is a result of a chemical reaction.

Snail crawl marks usually appear along the micro-crack of the battery, so the micro-crack looks conspicuous, but not all components that have micro-cracks appear stained. According to the current understanding of the problem, the performance degradation of the affected components is not related to the crawl marks of the snail itself. Instead, it is more related to the micro-crack below the crawl mark of the snail. If a crack separates a part of a battery, current cannot flow from the finger electrode to the bus bar. If the so-called battery breaks up to 8 % of the surface area of ​​the battery, it will have an adverse effect on its output - in other words, the larger the "dead zone", the greater the output attenuation. If the battery breaks up to 12%, a linear drop occurs in the relative rupture area of ​​the output. The ISFH Institute in Germany believes that the impact on the output of the module is determined by the number of cells on the broken surface.

Component factories have long believed that snails are caused by micro-cracks that can occur during production, transportation, and installation, or when components are exposed to strong vibrations. The production of components is through the production of solar cells, including silicon ingots, wire cutting, silicon wafer cleaning, diffusion bonding, plasma etching, dephosphorizing silicon glass, anti-reflective film preparation, screen printing, sintering, testing and grading, during this period Due to the single-chip power test and deletion, the probability of cracking is relatively small.

The assembly process is to laminate glass, EVA, solar cells, EVA, and backplanes, and then laminate and cure them. The EVA material is in intimate contact with the cells. Because the EL imaging chart is tested twice during the manufacturing of the assembly, the possibility of cracking of the battery sheet can be eliminated. The laminated assembly passes through the installation frame, the wire box, the silicone, and the surface of the cleaned component. The author believes that the generation of snail lines is not caused by cracking, but during subsequent use, due to the different degree of cross-linking and deformation of EVA materials, the battery slice is broken and the cracks are caused. The silver paste on the surface of the cell sheet is exposed to moisture and The residual peroxide in the EVA is oxidized to produce nano-sized silver oxide, showing a black grain.

What is the difference in the degree of cross-linking and deformation of EVA materials? Because EVA packaging materials become more and more cheaper, the profits of companies producing EVA film are getting lower and lower. To save costs, they will cut and trim the scraps and then perform secondary processing. The EVA film is provided by different manufacturers. EVA rubber particles, coupled with cross-linking agents, antioxidants, coupling agents and other processing agents, in the casting process, will cut off a part of scrap, the leftover material contains different molecular weight, different melting point, a mixture of different VA content , and continue to add it will inevitably lead to different degree of cross-linked film and deformation, just beginning to laminate out without any phenomenon, in the use of the process, after high and low temperature, high voltage, high temperature and humidity applications, due to cross-linking degree Differently, causing thermal expansion and contraction is not the same, breaking the cell chip caused by cracking, the subsequent silver slurry encountered moisture, was formed after the oxidation of nano-black crawl marks.

In order to solve the problem of snail lines, the component factory must eliminate the use of EVA film with recycled materials from the source, carefully test the vulcanization curve of each batch, and ensure the homogeneity of the material. Because quality is the key to business, good materials can ensure the quality of components and are responsible for the power station.

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