1. Principle of the solar cell
Sunlight shines on the p-n junction of the semiconductor to form new hole-electron pairs. Under the action of the electric field of the p-n junction, the holes flow from the n region to the p region. Region. Electrons flow from region p to region n and a current forms once the circuit is connected. This is how photovoltaic solar cells work.
Solar power generation methods There are two solar power generation methods
One is the light-heat-electricity conversion method, and the other is the direct light-to-electricity conversion method.
(1) The light-heat-electricity conversion method uses thermal energy generated by solar radiation to produce electricity. Generally, a solar collector converts the absorbed thermal energy into steam as the working fluid and then drives it away. a turbinefear to produce electricity. The first process is a light-heat conversion process; the second process is a heat-electricity conversion process, which is the same as ordinary thermal power generation. The disadvantages of solar thermal power generation are that its efficiency is very low and its cost is high. Its investment is estimated to be at least higher than that of ordinary thermal power generation. The power plant is 5-10 times more expensive. A 1,000 MW solar thermal power plant requires an investment of 2 to 2.5 billion US dollars. the average investment for 1 kW is 2,000-2,500 US dollars. Therefore, it can only be used on a small scale on special occasions, and large-scale use is not economically profitable and cannot compete with ordinary thermal or nuclear power plants.
(2) Conversion methodn direct light to electricity This method uses the photoelectric effect to directly convert the energy of solar radiation into electrical energy. The basic device for light in electricity. the conversion is the solar cell. A solar cell is a device that directly converts solar energy into electrical energy through the photovoltaic effect. When the sun shines on the photodiode, the photodiode converts light energy from the sun into electrical energy, producing current. When many batteries are connected in series or parallel, a solar cell array with relatively large output power can be formed. Solar cells are a promising new energy source with three major advantages: solar cells have a long lifespan and can be invested once and used for a long time as long as the sun exists, they are different from solar cells.a production of thermal energy; and nuclear energy production. In comparison, solar cells do not cause environmental pollution; Solar cells can be used in both large, medium and small sizes, ranging from a medium-sized power plant with a million kilowatts to a solar battery for one. domestic, which is unmatched by other energy sources.
2. Classification of solar cells
According to the crystallization state, solar cells can be divided into two categories: crystalline thin film type and amorphous thin film type (hereinafter referred to as a -), and the former is divided into single crystal form and polycrystalline form.
According to the material, it can be divided into silicon thin film type, compound semiconductor thin film type and organic film type. The thin film type of compound semiconductor is divided into amorphous type (a-Si:H, a-Si:H:F, a-SixGel-x:H, etc.), Group IIIV (GaAs, InP, etc.), Group IIVI (Cds series) and zinc phosphide (Zn 3 p 2), etc.
According to the different materials used, solar cells can also be divided into: siliconThere are four categories: solar cells, multi-compound thin-film solar cells, polymer multi-layer modified electrode solar cells and nanocrystalline solar cells. Among them, silicon solar cells are currently the most mature and dominate the application.
(1) Silicon solar cells
Silicon solar cells are divided into three types: monocrystalline silicon solar cells, polycrystalline silicon thin film solar cells and polycrystalline silicon thin film solar cells. thin-film amorphous silicon solar cells.
Monocrystalline silicon solar cells have the highest conversion efficiency and the most advanced technologymature. The highest conversion efficiency in the laboratory is 23% and the efficiency in large-scale production is 15%. It still occupies a dominant position in large-scale applications and industrial production. However, due to the high cost and price of monocrystalline silicon, it is difficult to greatly reduce its cost in order to save silicon materials, polycrystalline silicon films and amorphous silicon. films have been developed as monocrystalline silicon solar cells.
Compared to monocrystalline silicon, polycrystalline silicon thin-film solar cells are cheaper and more efficient than amorphous silicon thin-film cells. The maximum conversion efficiency in the laboratory is 18%, and the conversion efficiency in industrial-scale production is 18%. ten%. Therefore, polycrystalline silicon thin film cells dowill soon undermine the solar energy market.
Amorphous silicon thin-film solar cells are inexpensive, lightweight, have high conversion efficiency, are easy to produce on a large scale, and have great potential. However, due to the photoelectric efficiency degradation effect caused by its material, its stability is not high, which directly affects its practical application. If the stability problem and the conversion rate problem can be further solved, then large amorphous silicon solar cells will undoubtedly be one of the main development products of solar cells.
(2) Multi-compound thin-film solar cells
Multi-compound thin-film solar cell materials are inorganic salts, which mainly include arsenide compounds of gallium III-V, cadmium sulfide, cadmium. thin film sulphide batteries andcopper-indium-selenium, etc.
Cadmium sulfide and cadmium telluride polycrystalline thin-film solar cells are more efficient than amorphous silicon thin-film solar cells, less expensive than monocrystalline silicon cells, and are easy to produce in mass. However, cadmium is. highly toxic, will cause serious environmental pollution, so it is not the most ideal substitute for crystalline silicon solar cells.
The conversion efficiency of the III-V gallium arsenide (GaAs) battery can reach 28%. The GaAs compound material has a very ideal optical band gap and high absorption efficiency, and has strong radiation resistance. non-heat sensitive and suitable for manufacturing high efficiency single junction cells. However, the price of GaAs materials is high, which greatly limits the popularity of GaAs batteries.
Copper indium selenide thin film cells (CIS for short) are suitable for photoelectric conversion. There is no photofading problem, and the conversion efficiency is the same as polycrystalline silicon. With the advantages of low price, good performance and simple process, it will become an important direction for the development of solar cells in the future. The only problem lies in the source of the materials. Indium and selenium being relatively rare elements, the development of this type of battery is necessarily limited.
(3) Polymer multilayer modified electrode type Solar cells
Replacing inorganic materials with organic polymers is a research direction in solar cell manufacturing that has just emerged to start. Due to the advantages of organic materials such as flexibility, ease of production, wide sources of material and low cost, they are of great importance for the large-scale use of solar energy and the supply of cheap electricity. However, research into using organic materials to prepare solar cells is only just beginning. Neither the lifespan nor the efficiency of the cells can be compared to that of inorganic materials, especially silicon cells. Whether it can become a product of practical importance remains to be studied and explored in more detail.
(4) Nanocrystalline solar cells
TiO2 crystal nanocrystalline chemical solar cells are newly developed. Their advantages lie in low cost, simple process and stable performance. Its photoelectric efficiency is stable at more than 10%, and its production cost is only 1/5 to 1/10 of that of silicon solar cells. The lifespan can reach more than 20 years.