So, we stopped at an intermediate stage, solar cell production. The original plates have been several successive. chemical treatments. In which the disturbed layer was removed and shaped you want us to micro - texture. Then on the front surface. was formed by diffusion of shallow pn junction. That is the foundation of all products and significantly affecting its future options. Finally, the ends of the plates were. plasma etching. With which they were removed from the parasitic n-layer that is electrically severed the front and the back surface of solar cell. Need to move on.
As you remember, with the texture, we have reduced the reflection from the surface of the plate from 35% to 11%. This means that one tenth of the radiation incident on the surface of a solar still will be reflected back and will not be able to participate in the process of generating an electric current. In order to further reduce these losses, which are classified as optical, the next process step on the working surface of solar cells is applied to the so-called anti-reflective coating ( AOT). Based on the laws of optics, the engineers selected thickness and refractive index coating, so that we can reduce the reflection of up to 1-2 %. And this is a very good indicator.
Today there are so many different types of antireflection coatings that are applied to several different techniques (APCVD, LPCVD, PECVD, and m. n. ). In practice, as the ANC for silicon solar cells are most commonly used titanium oxide film or silicon nitride, with the latter increasingly favored. Silicon nitride is usually applied by PECVD, t. e. accelerated by the plasma chemical deposition from the gas phase, in a special tube furnaces.
PECVD process assumes that the chemical reagent, getting into the zone of the reactor falls under the influence of the plasma temperature and the individual elements, which are then deposited on the surface of the plate and react chemically. As a result, the front surface of the plate, ... Its thickness is about 70 nm, which is much smaller than the microprism texture and allows for the effect antiotrazheniya regardless of the structure of the surface relief.
This method provides a very good uniformity of the coating. Estimate the thickness of the AOP can be quite easy on the eye, even. Optics is that the more unequal thickness, the stronger the color of the plate varies. The same effect can be observed looking at the spilled in a puddle of gasoline - the film shimmers with rainbow colors, letting them know how to change its thickness. Other known methods of applying AOP often require pre- coating the solution onto the surface of the plate, which can not be made uniformly ( a substance will accumulate in the ... This also affects the result in the appearance of the solar cell and impairs its parameters.
After applying AOP silicon plate absorbs most of the solar radiation.
incident on its surface. Moreover, the coating thickness is optimized so that the most effective work in the most effective range of the spectrum. A little later I plan to devote a separate publication of this issue, and now I can only say that it is the blue part of the spectrum. It is because of this, all solar cells have a beautiful, deep dark blue color.
After applying AOP solar cell is almost ready. Under the influence of radiation inside the device is already happening generation of charge carriers, which are then separated and the pn junction is almost ready for further use. But they need to pass in the load circuit, and for this it is necessary to form contacts on the surface of the solar cell. This is what we discuss in an upcoming issue.
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