The processing of tempered glass can be divided into ：physical tempering method and chemical tempering method.
Physical tempered glass, also known as quenched tempered glass, is based on the principle that the glass is heated above the softening point temperature, and a large compressive stress is caused on the surface by rapid and uniform quenching, so as to improve the ability to resist external forces;
Chemical tempering, also known as ion exchange strengthening method, is based on the principle that glass changes the surface composition of glass through ion exchange in molten salt, which enhances the stress of glass and thus improves the stability and mechanical properties of glass.
Thin glass tempered by chemical method is better than that tempered by physical method in flatness and mechanical strength, but the broken state of thin glass tempered by chemical method is needle-like and unsafe. In terms of production, compared with chemical method, physical method has the advantages of low cost, high production efficiency and pollution-free waste discharge.
At present, the tempered glass in solar cell module adopts physical tempering method, and the strength after tempering can reach 4~6 times that of ordinary flat glass; Moreover, tempered glass immediately breaks into small particles without sharp corners, which is the most commonly used safety glass.
The coating process is to deposit an antireflection film on the glass surface, thus reducing the reflectivity of light on the glass surface and improving the transmittance. Practice has proved that the use of antireflection coated glass can improve the power generation efficiency of photovoltaic modules by 2.5%, which is a cheap and effective means to improve the power generation efficiency of photovoltaic modules. The deposition of antireflection film on photovoltaic glass is mainly produced by sol-gel method.
At present, there are two main routes for deep processing in the industry: one is to coat the film first and then toughen it, that is, to coat the silica sol on the surface of the original glass, and then go into the tempering furnace for tempering after drying and curing. The coated glass produced by this process has high surface hardness, but the surface is easy to absorb water and be stained with dust; The other is tempering first and then coating, that is, tempering the original glass, then coating silica sol on the glass surface, and drying and curing. The produced coated glass surface contains a small amount of organic matter and has certain hydrophobicity and antifouling performance, but this kind of coated glass has low hardness, poor film adhesion and is easy to be scratched. With the improvement of technology, at present, the process of coating first and then tempering is mostly adopted.
According to the national standard for ultra-white embossed glass (GV/T30984.1-2015), on the one hand, it is light transmittance, and the photovoltaic transmittance of 3.2mm uncoated photovoltaic glass is required to be greater than 91.5%, and greater than 93% after coating; On the other hand, it is impact resistance, which needs to pass the test of more than ten kinds of impact resistance such as physics, heat, pressure, friction and bad weather, so the quality control of the original film production and the subsequent tempering steps are essential.
