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How Does Solar Cells Generate Electricity?
- Aug 06, 2018 -

What is a solar cell?

A solar cell, also known as a solar chip, is an optoelectronic semiconductor chip that directly generates electricity by using sunlight. As long as it satisfies the illumination under certain illumination conditions, it can output voltage instantaneously and generate current in the presence of a loop, which becomes physics. Solar photovoltaic, the current crystalline silicon solar cell operating with photoelectric effect is the mainstream, and the thin film solar cell working with photochemical effect is still in its infancy

How does solar cells generate electricity?

The solar cell consists of seven parts: cell sheet, EVA, silica gel, back sheet, junction box, tempered glass and aluminum alloy frame. It is a kind of photoelectric element that can convert energy. Its basic structure is to use P-type and N-type semiconductor bonding. In the case of sunlight, light energy excites electrons in silicon atoms, and generates convection of electrons and holes. These electrons and holes are affected by built-in potentials, which are respectively N-type and P-type. The type semiconductor attracts and gathers at both ends. At this time, if the external electrodes are connected to form a loop, thereby forming a current, this is the principle of solar cell power generation.

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The solar cell manufacturing materials are mainly semiconductors, mainly including silicon, multi-component compounds, polymer materials and nano-crystals. Currently, monocrystalline silicon solar technology is the most mature, but due to the high cost of monocrystalline silicon, it will gradually be made of polycrystalline silicon thin film solar energy. With the replacement of batteries, nanocrystalline solar cells are gradually entering the field of vision.

Where is the future of solar cars?

Solar energy vehicles are important applications for solar cells. They can solve the problem of automobile fuel pollution and automobile energy shortage. However, solar vehicles still have some technical problems to be solved, as follows (this article belongs to the original, the cat is the first car, please indicate ):

First of all, in order to solve the problem of high cost of silicon solar cells, it is necessary to develop solar cells with lower raw material costs, such as multi-component compounds, polymer materials, and nanocrystalline materials;

Secondly, in order to solve the problem of low photoelectric conversion efficiency, it is necessary to speed up technical research and development in battery material thickness, battery process, battery surface treatment and solar panel angle;

Furthermore, solar cells convert light energy into electrical energy, mostly DC power. Therefore, it is necessary to solve the problem that the direct power is converted into alternating current before being used for automobile driving; the solar battery itself is a power generating device, and is limited by weather factors, and does not have its own The power storage function, if used in conjunction with a lead storage battery, has the problem of weight loss;

summary

A solar cell is a semiconductor wafer that directly generates electricity by using sunlight. Its technical principle is photoelectric effect. Its fabrication materials are mainly semiconductors, which are divided into four categories: silicon, multi-component compounds, polymer materials and nano-crystals. In the field of solar energy vehicles, there is an urgent need to solve the problems of low-cost production materials research, solar energy conversion energy efficiency improvement and solar energy storage technology research and development.

Solar cell principle

The sun shines on the semiconductor p-n junction, forming a new hole-electron pair. Under the action of the built-in electric field of the p-n junction, the photogenerated holes flow to the p region, and the photogenerated electrons flow to the n region, and a current is generated after the circuit is turned on. This is how the photovoltaic effect solar cell works. There are two ways of solar power generation, one is light-heat-electric conversion, and the other is light-electric direct conversion.

Light-thermal-electrical conversion

The light-thermal-electrical conversion method generates electricity by utilizing thermal energy generated by solar radiation, and generally the solar collector collects the absorbed thermal energy into a working medium vapor, and then drives the steam turbine to generate electricity. The former process is the light-to-heat conversion process; the latter process is the thermo-electric conversion process, which is the same as ordinary thermal power generation. The disadvantage of solar thermal power generation is that it is very inefficient and costly. It is estimated that its investment is at least 5 to 10 times more expensive than ordinary thermal power stations. A 1000 MW solar thermal power station requires an investment of 2 to 2.5 billion US dollars, and an average investment of 1 kW is 2,000 to 2,500 US dollars. Therefore, it can only be applied to special occasions on a small scale, and large-scale utilization is economically uneconomical and cannot compete with ordinary thermal power plants or nuclear power plants.

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Light-to-electric direct conversion

Solar cell power generation is based on the optoelectronic properties of a particular material. Black bodies (such as the sun) radiate electromagnetic waves of different wavelengths (corresponding to different frequencies), such as infrared, ultraviolet, visible, and the like. When these rays are irradiated on different conductors or semiconductors, the photons react with free electrons in the conductor or semiconductor to generate an electric current. The shorter the wavelength of the ray, the higher the frequency, the higher the energy, for example, the energy of ultraviolet light is much higher than that of infrared ray. However, not all wavelengths of energy can be converted into electrical energy. It is worth noting that the photoelectric effect is independent of the intensity of the radiation. Current can only be generated when the frequency reaches or exceeds the threshold at which the photoelectric effect can be produced. The maximum wavelength of light capable of causing a photoelectric effect of a semiconductor is related to the forbidden band width of the semiconductor. For example, the forbidden band width of crystalline silicon is about 1.155 eV at room temperature, so that light having a wavelength of less than 1100 nm is required to cause photoelectric effect of crystalline silicon. . Solar cell power generation is a renewable and environmentally friendly way of generating electricity. It does not generate greenhouse gases such as carbon dioxide during power generation and does not pollute the environment. According to the production materials, it is classified into a silicon-based semiconductor battery, a CdTe thin film battery, a CIGS thin film battery, a dye-sensitized thin film battery, an organic material battery, and the like. Among them, silicon batteries are further classified into single crystal batteries, polycrystalline batteries, and amorphous silicon thin film batteries. The most important parameter for solar cells is conversion efficiency. In the silicon-based solar cells developed by the laboratory, the efficiency of single crystal silicon cells is 25.0%, the efficiency of polycrystalline silicon cells is 20.4%, and the efficiency of CIGS thin film cells is 19.6%. CdTe The efficiency of the thin film battery is 16.7%, and the efficiency of the amorphous silicon (amorphous silicon) thin film battery is 10.1%.

A solar cell is a photovoltaic element that can convert energy, and its basic structure is formed by bonding a P-type and an N-type semiconductor. The most basic material of a semiconductor is "silicon", which is non-conductive, but if a different impurity is incorporated into the semiconductor, a P-type and an N-type semiconductor can be formed, and a P-type semiconductor has a hole (P type). The semiconductor has one negatively charged electron, which can be regarded as a positive charge. It has a potential difference of free electrons with the N-type semiconductor to generate current, so when the sunlight is irradiated, the light energy will be in the silicon atom. The electrons are excited to generate convection of electrons and holes, which are affected by built-in potentials, which are attracted by N-type and P-type semiconductors, respectively, and gather at both ends. At this time, if the external electrodes are connected to form a circuit, this is the principle of solar cell power generation.

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To put it simply, the principle of solar photovoltaic power generation is a power generation method that uses solar cells to absorb sunlight of wavelengths from 0.4 μm to 1.1 μm (for silicon crystals) and converts light energy directly into electrical energy output.

Since the electricity generated by the solar cell is direct current, if it is necessary to supply power to household appliances or various types of electrical appliances, it is necessary to install a direct/alternating current converter and replace it with alternating current to supply electricity to household electricity or industrial electricity.

Solar cell charging development Solar cells are used in consumer goods. Most of them have charging problems. In the past, general charging objects used nickel-metal hydride or nickel-cadmium dry batteries, but nickel-hydrogen dry batteries could not resist high temperature, and nickel-cadmium dry batteries had environmental pollution problems. Supercapacitors are developing rapidly, with large capacity, shrinking area, and low price. Therefore, some solar products have begun to adopt supercapacitors as charging targets, thus improving many problems of solar charging:

Charging faster,

Life is more than 5 times longer,

Wide range of charging temperatures,

Reduce solar cell usage (can be charged at low voltage)

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