Solar cells can be divided into crystalline thin-film type and amorphous thin-film type (hereinafter referred to as a-) according to their crystalline state, and the former is divided into single crystalline and polycrystalline.
According to the material, it can be divided into silicon film, compound semiconductor film and organic film. The compound semiconductor film is divided into amorphous (a-Si: a-Si: H: F, a-SixGe1-x ：H etc.), Ⅲ-V group (GaAs, InP, etc.), Ⅱ-VI group (CdS series) and zinc phosphide (Zn3P2), etc.
According to the different materials used, solar cells in actual use can be divided into four categories:
①Crystalline silicon solar cells, ②Thin film solar cells, ③Organic solar cells, ④Nanocrystalline chemical solar cells (see Table 1). Among them, crystalline silicon solar cells are currently the most mature: they occupy a dominant position in applications, and their current market share exceeds 80%.
After the rapid development of thin-film solar cells in recent years, the cost advantage has made it steadily increase its share in the application.
| species | Material | Conversion efficiency/% | Advantage | Disadvantage |
| Crystalline silicon solar cell | Monocrystalline silicon | 24.7 ± 0.5 | Durable, high conversion efficiency, mature technology, long life | Manufacturing energy consumption is high, cost is high, and the process is complicated |
| Polysilicon | 20.3±0.5 | Low production cost, simple process, suitable for mass production | Lower efficiency than monocrystalline silicon | |
| Thin film solar cell | Amorphous silicon | 11.7 ± 0.4 | Low cost, simple process, can work under low light | The conversion efficiency is low, and there is a problem of light-induced attenuation |
| Gallium Arsenide (GaAs) | 24.5±0.5 | The optical band gap is very ideal, high absorption efficiency, strong anti-radiation ability, and insensitive to heat | Material price is high | |
| Cadmium Telluride (CdTe) | 16.5±0.5 | High efficiency, low cost, stable, easy to scale production | The raw material cadmium is highly toxic | |
| Copper Indium Brocade Selenide (CIGS) | 19.5±0.8 | Low price, good performance, simple process | Indium and selenium are relatively rare | |
| Organic solar cell | Organic matter | 3.0±0.1 | Toughness, low cost, large choice, easy processing, large manufacturing area | Low light absorption rate, resulting in low conversion efficiency |
| Nanocrystalline Chemical Solar Cell | Dye-sensitized TiO2 | 10% | Has high thermal stability and photochemical stability, low cost, simple process | High preparation cost of sensitizer |
(1) Crystalline silicon solar cell
Crystalline silicon solar cells are divided into monocrystalline silicon solar cells and polycrystalline silicon thin film solar cells, which are currently the most mature solar cell technology.
Monocrystalline silicon solar cells have the highest conversion efficiency and the most mature technology. The highest conversion efficiency in the laboratory is 24.7%. The efficiency in mass production has also exceeded 20%. It still occupies a dominant position in large-scale applications and industrial production. However, due to the high cost of monocrystalline silicon, it is difficult to greatly reduce its cost. In order to save silicon materials, develop polycrystalline silicon thin films and amorphous silicon thin films as monocrystalline silicon solar cells. replacement product.
Compared with monocrystalline silicon, polycrystalline silicon solar cells have low cost. The maximum conversion efficiency of the laboratory is 20%, and the conversion efficiency of industrial-scale production is about 15%. With the development of technologies such as heterojunction structures, the efficiency of polycrystalline silicon solar cells has been greatly improved, and they have a certain share in the solar cell market. So far, after continuous efforts, the energy conversion efficiency of polycrystalline silicon solar cells is basically the same order of magnitude as that of monocrystalline silicon solar cells. In particular, the polysilicon thin film can be made into a square shape, and the area utilization rate is high when the solar cell module is made. Considering that the power consumption of the LED solar lighting system is more than one-third lower than that of the original system, the use of polysilicon solar cells can effectively reduce the cost of the system and is more conducive to the promotion of LED lighting in power-deficient areas
(2) Thin film solar cells
Thin-film solar cells have the advantages of light weight, simple process and low cost, so they are developing very rapidly. Amorphous silicon thin-film solar cells have low cost, light weight, high conversion efficiency, are convenient for mass production, and have great application potential. Since amorphous silicon does not have the periodic atomic arrangement required by crystals, the lattice mismatch between the material and the substrate that must be considered for crystal preparation can be ignored. So it can be deposited on almost any substrate, such as stainless steel, plastic or even glass substrates. However, due to the photoelectric efficiency decay effect caused by its materials, the stability is not high, which directly affects its practical application. If the stability problem can be further solved and the conversion rate can be improved, amorphous silicon solar cells will undoubtedly be one of the main development products of solar cells. Polycrystalline silicon thin film solar cells not only have the characteristics of crystalline cells, but also have the advantages of low cost, simple equipment and large-scale preparation of amorphous silicon cells. The substrate is cheap, the amount of silicon material is small, and there is no light attenuation problem. It combines the advantages of crystalline silicon and amorphous silicon materials. However, due to the small crystal grains, its photoelectric conversion efficiency is still low, and there is no large-scale application at present. . If the low-cost and high-quality growth process of polycrystalline silicon thin film can be solved, and the controllability and repeatability of the electrical performance of polycrystalline silicon thin film can be improved, polycrystalline silicon thin film solar cells will become a new generation of solar photovoltaic materials.
At present, the more mature thin film solar cells are mainly multi-compound thin film solar cells. The materials are inorganic salts, including gallium arsenide III-V compounds, cadmium sulfide, cadmium associative and copper indium selenium thin film batteries. The efficiency of cadmium sulfide and cadmium telluride polycrystalline silicon thin-film solar cells is higher than that of amorphous silicon thin-film solar cells, and the cost is lower than that of monocrystalline silicon cells. They are also easy to produce on a large scale, but because cadmium is highly toxic, it will cause serious pollution to the environment. Therefore, it is not the most ideal substitute for crystalline silicon solar cells. The conversion efficiency of gallium arsenide (GaAs) III-V compound battery can reach 28%. The GaAs compound material has a very ideal optical band gap and high absorption efficiency, strong resistance to radiation, and is not sensitive to heat. It is suitable for Manufacturing high-efficiency single-junction batteries. However, the high price of GaAs materials limits the popularity of GaAs batteries to a large extent. Copper-indium-selenium thin-film batteries (CIS for short) are suitable for photoelectric conversion and do not have the problem of light degradation. The conversion efficiency is the same as that of polysilicon. It has 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. However, because steel and selenium are relatively rare elements, the development of this type of battery is bound to be limited by the scarcity of materials.
(3) Organic solar cells
Organic solar cells, as the name suggests, are solar cells whose core part is composed of organic materials. Organic materials have large chemical variability, a wide range of raw materials, easy processing, large-area film formation, diversified battery production, low price, relatively simple synthesis processes for organic dyes, polymer semiconductors, etc., such as phthalocyanine dyes have already been industrialized. Therefore, the cost is low. Replacing inorganic materials with organic polymers is a research direction in solar cell manufacturing that has just begun. Because organic materials have the advantages of good flexibility, easy production, wide material sources, and low cost, they are of great significance for large-scale use of solar energy and low-cost electricity. Compared with inorganic silicon solar cells, organic solar cells need to be improved in terms of conversion efficiency, spectral response range, and battery stability. In solar LED lighting, low-power applications can be realized by using organic solar battery systems, which have greater advantages in terms of cost and installation methods.
(4) Nanocrystalline solar cells
Nano-TiO2 crystal chemical energy solar cells are newly developed, and the advantages are their low cost, simple process and stable performance. Its photoelectric efficiency is stable above 10%, the production cost is only 1/5~1/10 of the silicon solar cell, and the life span can reach more than 20 years. However, since the research and development of such batteries have just started, it is estimated that they will gradually enter the market in the near future.
