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Analysis of Reasons for Leakage of Crystalline Photovoltaic Cells
- May 30, 2018 -

Solar cells were first introduced as monocrystalline silicon solar cells. Silicon is an extremely rich element on the earth. Almost everywhere there is silicon, which can be said to be inexhaustible. The use of silicon to make solar cells has no shortage of raw materials. However, it is not easy to refine it, so while people are producing monocrystalline silicon solar cells, they have also studied polycrystalline silicon solar cells and amorphous silicon solar cells. So far, commercial-scale solar cells have not jumped out of the series of silicon.


In fact, there are many semiconductor materials available for the manufacture of solar cells. With the development of the material industry, there will be more and more varieties of solar cells. Solar cells that have been researched and trial-produced at present have many types of solar cells such as cadmium sulfide, gallium arsenide, and copper indium selenide in addition to the silicon series. There are many types of solar cells. Here are some of the more common silicon-based solar cells.


Monocrystalline silicon solar cells


Monocrystalline silicon solar cells are one of the fastest-growing solar cells currently in development. Their composition and production processes have been established. Products have been widely used in space and ground facilities. This kind of solar cell uses high-purity single-crystal silicon rod as raw material, and its purity is 99.9999%. In order to reduce production costs, solar-powered single-crystal silicon rods are now being used for surface solar cells, and the material performance indicators have been relaxed. Some can also use semiconductor devices to process the head and tail materials and waste secondary single crystal silicon materials, and after being double-pulled into single-crystal silicon rods for solar cells. Single crystal silicon rods are cut into pieces, typically about 0.3 mm thick. After the silicon wafer is shaped, polished, cleaned, and other processes, the raw silicon wafer to be processed is made.


Processing solar cells, first of all doped and diffused on the silicon, the general dopant is a trace of boron, phosphorus, antimony and so on. Diffusion is performed in a high-temperature diffusion furnace made of a quartz tube. This forms a P/N junction on the silicon wafer. Then, using a screen printing method, a silver paste is printed on a silicon wafer to form a gate line, and after sintering, a back electrode is formed at the same time, and an anti-reflection source is coated on the surface of the gate line to prevent a large number of photons. The surface of the silicon wafer is reflected off the surface. At this point, the monocrystalline silicon monocrystalline solar cell is made.


Monolithic chips can be assembled into solar modules (solar panels) according to the required specifications after random inspection and inspection. The output voltage and current are determined in series and in parallel, and finally assembled with the frame and packaging material. According to the system design, the user can compose the solar battery components into a variety of solar cell arrays of different sizes, also known as solar arrays. The average photoelectric conversion efficiency of monocrystalline silicon solar cells currently on the market is about 19%, and new products recently introduced by individual companies generally exceed this value. Laboratory results are generally above 20%. There are up to 50% more solar panels for the space station.


Polycrystalline silicon solar cells


The production of monocrystalline silicon solar cells consumes a large amount of high-purity silicon materials, and the manufacturing process of these materials is complicated and consumes a lot of electricity. The total cost of solar cells has exceeded one-half, plus the monocrystalline silicon rods that are produced. Cylindrical, slicing solar cells is also a wafer, the composition of the solar component plane utilization is low. Therefore, since the 1980s, some European and American countries have invested in the development of polycrystalline silicon solar cells.


At present, the polysilicon materials used in solar cells are mostly aggregates containing a large number of single-crystal particles, or are melted and cast from scrap secondary single-crystal silicon materials and metallurgical-grade silicon materials. The process is to select a polycrystalline silicon block or single crystal silicon tailings with a resistivity of 100-300 ohm centimeters, broken, and then etched with a 1:5 mixture of hydrofluoric acid and nitric acid, and then deionized. The water rinse is neutral and dried. Quartz is used to pack polysilicon material, add appropriate amounts of borosilicate, put the casting furnace, heat and melt in a vacuum state. After melting, it should be kept in heat for about 20 minutes, and then injected into the graphite mold. After solidification and cooling, polycrystalline silicon ingots are obtained. This silicon ingot can be cast into cubes for slicing into square solar cells, which improves material utilization and facilitates assembly.


The manufacturing process of polycrystalline silicon solar cells is similar to that of monocrystalline silicon solar cells, and its photoelectric conversion efficiency is about 12%, which is slightly lower than that of monocrystalline silicon solar cells. However, the material is simple to manufacture, saves power consumption, and the total production cost is low. A lot of development. With the improvement of technology, the conversion efficiency of polysilicon can reach 18%.


Amorphous silicon solar cells


Amorphous silicon solar cells are new thin film solar cells that appeared in 1976. They are completely different from the single crystal silicon and polycrystalline silicon solar cells. They consume very little silicon and consume less power. They are very attractive. There are various methods for manufacturing amorphous silicon solar cells, the most common of which are glow discharge methods, reactive sputtering methods, chemical vapor deposition methods, electron beam evaporation methods, and thermal decomposition silane methods. In the glow discharge method, a quartz vessel is evacuated and filled with hydrogen or argon diluted silane and heated with a radio frequency power supply to ionize the silane to form a plasma. An amorphous silicon film is deposited on the heated substrate. If an appropriate amount of hydrogenated phosphorus or boron hydride is added to the silane, an N-type or P-type amorphous silicon film can be obtained. The substrate material is generally glass or stainless steel. The process for preparing amorphous silicon thin films mainly depends on strict control of air pressure, flow rate, and RF power, and is also important for the temperature of the substrate.


Amorphous silicon solar cells have a variety of different structures, among which there is a better structure called the PiN cell, which is a layer of phosphorus-doped N-type amorphous silicon is first deposited on the substrate, and an undoped layer is deposited. The i layer is then deposited with a layer of boron-doped P-type amorphous silicon. Finally, an anti-reflection film is evaporated with an electron beam, and a silver electrode is vapor-deposited. This production process can use a series of deposition chambers to form a continuous process in production to achieve mass production. At the same time, amorphous silicon solar cells are very thin and can be made in a stack type or integrated circuit method. On a plane, a series of cells are fabricated at a time using a suitable masking process to obtain higher voltages. . Since ordinary crystalline silicon solar cells have a voltage of only about 0.5 volts, today's amorphous silicon tandem solar cells produced in Japan can reach 2.4 volts.


At present, the problem of amorphous silicon solar cells is that the photoelectric conversion efficiency is low, the international advanced level is about 10%, and it is not stable enough, and often there is a phenomenon that the conversion efficiency declines, so it has not yet been used in large quantities as a large-scale solar energy source. Weak light power, such as pocket calculators, electronic watches and copiers. After the problem of estimated efficiency degradation is overcome, amorphous silicon solar cells will promote the development of solar energy utilization because of its low cost, light weight, and ease of application. It can be combined with the roof of a house to constitute an independent power source for households.


In the strong sunlight, single-crystal solar panels can convert solar energy more than twice as much as amorphous ones, but unfortunately the price of single crystals is more than two or three times more expensive than that of amorphous ones, and in the case of cloudy days, The crystal type can collect almost as much solar energy as the crystal type.