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　　What are the classifications of photovoltaic cells and what are their characteristics?

　　1. Classification of photovoltaic cells

　　1. Monocrystalline silicon photovoltaic cells

　　Monocrystalline silicon photovoltaic cells are a type of photovoltaic cell that was developed earlier, has the highest conversion rate, and has a large output. The conversion efficiency of monocrystalline silicon photovoltaic cells has reached an average of 16.5% in my country, and the highest conversion efficiency recorded in the laboratory exceeds 24.7%. This kind of photovoltaic cell generally uses high-purity monocrystalline silicon rods as raw materials, with a purity requirement of 99.9999%.

　　2. Polycrystalline silicon photovoltaic cells

　　Polycrystalline silicon photovoltaic cells are photovoltaic cells based on polycrystalline silicon materials. Since polycrystalline silicon materials are mostly cast instead of the drawing process of single crystal silicon, the production time is shortened and the manufacturing cost is greatly reduced. In addition, monocrystalline silicon rods are cylindrical, and photovoltaic cells made from them are also wafers, so the plane utilization rate after forming photovoltaic modules is low. Compared with monocrystalline silicon photovoltaic cells, polycrystalline silicon photovoltaic cells appear to have certain competitive advantages.

　　3. Amorphous silicon photovoltaic cells

　　Amorphous silicon photovoltaic cell is a new type of thin film battery made of amorphous silicon as raw material. Amorphous silicon is a semiconductor with an amorphous crystal structure. Photovoltaic cells made with it are only 1 micron thick, equivalent to 1/300 of monocrystalline silicon photovoltaic cells. Compared with monocrystalline silicon and polycrystalline silicon, its manufacturing process is greatly simplified, silicon material consumption is less, and unit power consumption is also reduced a lot.

　　4. Copper indium selenide photovoltaic cells

　　Copper-indium-selenide photovoltaic cells are semiconductor films made of copper, indium and selenium ternary compound semiconductors deposited on glass or other cheap substrates. Due to the good light absorption performance of copper indium selenide cells, the film thickness is only about 1/100 of that of monocrystalline silicon photovoltaic cells.

　　2. Basic characteristics of photovoltaic cells

　　1. Polarity of photovoltaic cells

　　Photovoltaic cells are generally made into P+/N-type structure or N+/P-type structure. P+ and N+ represent the conductivity type of the semiconductor material of the light layer on the front of the photovoltaic cell; N and P represent the conductivity type of the semiconductor material of the back substrate of the photovoltaic cell. The electrical properties of photovoltaic cells are related to the properties of the semiconductor materials used to make the cells.

　　2. Performance parameters of photovoltaic cells

　　The performance parameters of photovoltaic cells consist of open circuit voltage, short circuit current, maximum output power, fill factor, conversion efficiency, etc. These parameters are a measure of the performance of photovoltaic cells.

　　3. Volt-ampere characteristics of photovoltaic cells

　　A P-N junction photovoltaic cell consists of a shallow P-N junction formed on the surface, a strip and finger-shaped front ohmic contact, a back ohmic contact covering the entire back surface, and an anti-reflective layer on the front. When the cell is exposed to the solar spectrum, photons with energy less than the forbidden band width Eg do not contribute to the cell output. Photons with energy greater than the bandgap width Eg will contribute energy Eg to the battery output, and energy less than Eg will be consumed in the form of heat. Therefore, in the design and manufacturing process of photovoltaic cells, the impact of this heat on battery stability, life, etc. must be considered.

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