Principle of solar cell

The sun shines on the semiconductor p-n junction to form a new hole-electron pair. Under the effect of the built-in electric field in the p-n junction, the photo-generated holes flow to the p region, and the photo-generated electrons flow to the n region. After the circuit is connected, the current is generated. This is the working principle of photoelectric effect solar cells.
There are two ways of solar power generation, one is light-heat-electricity conversion, and the other is light-electricity direct conversion.
Photothermal-electrical conversion
The light-heat-electricity conversion mode generates electricity by using the heat energy generated by the solar radiation. Generally, the absorbed heat energy is converted into the steam of working medium by the solar collector, and then the steam turbine is driven to generate electricity. The former process is the light-heat conversion process; The latter process is the heat-electricity conversion process, which is the same as the ordinary thermal power generation. The disadvantage of solar thermal power generation is that its efficiency is very low and its cost is very high. It is estimated that its investment is at least 5 to 10 times higher than that of ordinary thermal power stations. A 1000MW solar thermal power plant needs to invest 2 to 2.5 billion US dollars, with an average investment of 1 kW of 2000 to 2500 US dollars. Therefore, it can only be applied to special occasions on a small scale, while large-scale utilization is not economical and can not compete with ordinary thermal power plants or nuclear power plants.
Direct optical-electric conversion
Solar cell power generation is made according to the photoelectric properties of specific materials. Blackbodies (such as the sun) radiate electromagnetic waves of different wavelengths (corresponding to different frequencies), such as infrared, ultraviolet, visible light, etc. When these rays are irradiated on different conductors or semiconductors, photons interact with free electrons in the conductors or semiconductors to generate current. The shorter the wavelength and the higher the frequency of the ray, the higher the energy it has. For example, the energy of ultraviolet ray is much higher than that of infrared ray. However, the energy of rays of all wavelengths can not be converted into electrical energy. It is worth noting that the photovoltaic effect is independent of the intensity of the rays. The current can only be generated when the frequency reaches or exceeds the threshold that can produce the photovoltaic effect. The maximum wavelength of the light that can make the semiconductor produce photovoltaic effect is related to the band gap width of the semiconductor. For example, the band gap width of crystalline silicon is about 1.155eV at room temperature. Therefore, only the light with wavelength less than 1100nm can make the crystalline silicon produce photovoltaic effect. Solar cell power generation is a renewable and environmentally friendly power generation method. It will not produce greenhouse gases such as carbon dioxide and will not pollute the environment. According to the production materials, it can be divided into silicon-based semiconductor battery, CdTe thin film battery, CIGS thin film battery, dye-sensitized thin film battery, organic material battery, etc. Among them, silicon cells are divided into single crystal cells, polycrystalline cells and amorphous silicon thin film cells. The most important parameter for solar cells is the conversion efficiency. Among the silicon-based solar cells developed in the laboratory, the efficiency of monocrystalline silicon cells is 25.0%, the efficiency of polycrystalline silicon cells is 20.4%, the efficiency of CIGS thin film cells is 19.6%, the efficiency of CdTe thin film cells is 16.7%, and the efficiency of amorphous silicon (amorphous silicon) thin film cells is 10.1%
The solar cell is a kind of photoelectric element that can convert energy. Its basic structure is made by combining P-type and N-type semiconductors. The most basic material of semiconductors is "silicon", which is non-conductive. However, if different impurities are mixed in the semiconductors, they can be made into P-type and N-type semiconductors. Then, P-type semiconductors have a hole (P-type semiconductors have one less electron with negative charge, which can be regarded as one more positive charge), and N-type semiconductors have one more free electron potential difference to generate current, so when the sun shines, The light energy excites the electrons in the silicon atom to produce the convection of electrons and holes. These electrons and holes will be affected by the built-in potential, and will be attracted by N-type and P-type semiconductors respectively, and will gather at both ends. At this time, if the outside is connected with electrodes to form a circuit, this is the principle of solar cell power generation.
In short, the principle of solar photovoltaic power generation is to use solar cells to absorb 0.4 μ m～1.1 μ M wavelength (for silicon crystal) sunlight, which directly converts light energy into electrical energy output.
Since the electricity generated by solar cells is direct current, if it is necessary to provide power to household appliances or various electrical appliances, it is necessary to install a DC/AC converter to replace it with AC power before it can be supplied to household or industrial power.
The charging development of solar cells The application of solar cells in consumer goods mostly has the problem of charging. In the past, the general charging objects used NiMH or NiCd dry cells, but NiMH dry cells cannot resist high temperature, and NiCd dry cells have the problem of environmental pollution. With the rapid development of supercapacitors, large capacity, anti-shrinking area and low price, some solar products began to use supercapacitors as charging objects, thus improving many problems of solar charging:
Fast charging,
The service life is more than 5 times longer,
The charging temperature range is wide,
Reduce the consumption of solar cells (can be charged at low voltage)