What is a solar cell？

 A solar cell is a new type of material that can convert light energy into electrical energy formed after a silicon wafer is processed by a series of complex production processes.

1. Production process

Silicon wafer inspection - surface texturing and pickling - diffusion junction - dephosphorization silicon glass - plasma etching and pickling - anti-reflection coating - screen printing - rapid sintering, etc.

Silicon wafer inspection: The Silicon wafer is the carrier of solar cells. The silicon wafer's quality directly determines the solar cell's conversion efficiency. The main parameters are wafer surface unevenness, minority carrier lifetime, resistivity, P/N type,  microcracks, etc.

Surface texturing and pickling: The preparation of single-crystal silicon texture is to use anisotropic etching of silicon to form a pyramid structure on every square centimeter of  the silicon surface. In this way, the number of reflections and refractions of light is increased, the absorption of light is strengthened, and the short-circuit current and conversion efficiency of the battery are improved.

Diffusion junction: Conversion of light energy to electrical energy through PN junction

Dephosphorization silicon glass: Remove a layer of Phosphosilicate glass formed on the surface of the silicon wafer after diffusion junction

Plasma etching and pickling： Plasma etching technology is often used to remove the PN junction at the edge of the battery to prevent the formation of short circuits

Anti-reflection coating: The reflectivity of the polished silicon surface is 35%. In order to reduce the surface reflection and improve the conversion efficiency of the cell, it is necessary to deposit a layer of silicon nitride anti-reflection film

Screen printing: Screen printing is the most common production process for making positive and negative electrodes on the battery surface

Rapid sintering: It needs to be quickly sintered in a sintering furnace to burn off the organic resin binder, leaving almost pure silver electrodes that are adhered to the silicon wafer due to the action of glass. When the temperature of the silver electrode and the crystalline silicon reaches the eutectic temperature, the crystalline silicon atoms are integrated into the molten silver electrode material in a certain proportion, thereby forming an ohmic contact between the upper and lower electrodes, and improving the open-circuit voltage and filling factor of the cell. Key parameters to make it resistive to improve cell conversion efficiency

2. Principle of power generation

Put the P-type silicon wafer in the quartz container of the tubular diffusion furnace, and use nitrogen to bring phosphorus oxychloride into the quartz container at a high temperature of 850-900 degrees Celsius, and react with the silicon wafer to obtain phosphorus oxychloride. atom. After a certain period of time, phosphorus atoms enter the surface layer of the silicon wafer from all around. When the P-type and N-type semiconductor materials are combined, the holes (electrons) in the P-type (N-type) material move toward the N-type (P-type) material. Diffusion, the result of diffusion makes the bonding region form a potential barrier, and the resulting internal electric field will prevent the diffusion movement from continuing. When the two reach equilibrium, a depletion region (ie PN junction) is formed on both sides of the PN junction. When the wafer is exposed to light, in the PN junction, the holes of the N-type semiconductor move to the P-type region, while the P-type electrons in the region move toward the N-type region, thereby forming a current from the N-type region to the P-type region. This phenomenon is called the photovoltaic effect, and this is how solar cells generate electricity.

3. The difference between monocrystalline and polycrystalline solar cells

Compared with monocrystalline silicon wafers, crystalline silicon wafers have obvious polycrystalline characteristics, which are mainly distinguished by the grain shape patterns on the surface, while the surface of monocrystalline silicon wafers is uniform. As shown above

Under the electron microscope, the surface of the single crystal shows a uniform pyramid-shaped textured structure, while the polycrystalline surface shows an uneven porous textured surface.

4. Appearance and color types of crystalline silicon solar cells

After the cell is encapsulated, due to the light absorption and refraction of the encapsulation material itself, the dark blue part is visually reflected as black, while the blue and light blue parts are visually displayed as blue.

Due to the uneven difference of its surface grains, polysilicon reflects more light. After coating, the color of the same film thickness will be lighter than that of monocrystalline silicon, so most of them appear blue after packaging

Therefore, the color of the solar panel after encapsulation cannot be used as the only basis for judging single polycrystalline cells.

5. Comparison of common solar cell performance

6. More detailed division of solar cells

In addition to the main name and size description of monocrystalline, polycrystalline, Sunpower, and Taiwan day3 cells in the cell description, there will also be descriptions of the number of front busbars, the number of back backgrounds, the continuity of the background, and the size of single-crystal chamfers.

The 125 sizes single crystal and the 156 sizes single crystal is cut in different ways, such as 101030024 (52*39 polycrystalline cell), 101020027 (monocrystalline cell 78*52 MM), 101020026 (78*26mm single crystal) Cell)

References

Baidu Encyclopedia