The working principle, working efficiency, manufacturing materials and general structure of solar photovoltaic cells

Solar cells can be divided into: 1. Silicon solar cells; 2. Batteries made of inorganic salts such as gallium arsenide III-V compounds, cadmium telluride, copper indium selenide, and other multiple compounds; 3. Large-scale preparation of functional polymer materials Yangon battery; 4, nanocrystalline solar photovoltaic cells.

Regardless of the type of materials used to make batteries, the general requirements for solar photovoltaic cells are: 1. The bandgap of semiconductor materials should not be too wide; 2 must have a high photoelectric conversion efficiency: 3. The material itself does not cause pollution to the environment; 4, the material is easy to industrial production and material properties and stability.

Based on the above considerations, silicon is the most ideal solar cell material. This is also the main reason why solar photovoltaic cells are dominated by silicon materials. However, with the continuous development of new materials and the development of related technologies, solar photovoltaic cells based on other villages are increasingly showing attractive prospects. This article briefly reviews the types of solar photovoltaic cells and their research status, and discusses the development and trends of solar photovoltaic cells.

Silicon-based solar cells 1 Single-crystal silicon solar photovoltaic cells In silicon-series solar cells, single crystal silicon solar cells have the highest conversion efficiency and the most mature technologies. High-performance single-crystal silicon cells are based on high-quality monocrystalline silicon materials and related heat-generating processing processes. Nowadays, the electrical ground technology of single-crystal silicon has been almost mature. In the production of batteries, surface texturing, passivation of emission regions, and zone doping techniques are generally used. The batteries developed mainly include planar monocrystalline silicon cells and etched trenches. Gate electrode monocrystalline silicon battery. Enhancing the conversion efficiency is mainly the monocrystalline silicon surface microstructure processing and zone doping process. In this respect, the Fleurieu Institute of Solar Energy Systems in Flanderhein, Germany has maintained a world-leading level. The Institute used photolithographic techniques to texture the surface of the cell to create inverted pyramid structures. And put a 13nm on the surface. A thick oxide passivation layer is combined with two antireflection coatings. The ratio of the width and height of the gate is increased by the improved plating process: the conversion efficiency of the battery obtained by the above is over 23%, which is a large value of up to 23.3%. The conversion efficiency of large-area (225cm2) single-crystalline solar cell prepared by Kyocera Co., Ltd. was 19.44%. The Beijing Solar Energy Research Institute also actively researched and developed high-efficiency crystalline silicon solar cells and developed a planar high-efficiency single crystal silicon cell (2cm X 2cm). ) The conversion efficiency reached 19.79%, and the conversion efficiency of the trench buried gate electrode crystalline silicon cell (5cm X 5cm) was 8.6%. The conversion efficiency of monocrystalline silicon solar cells is undoubtedly the highest. It still occupies a dominant position in large-scale applications and industrial production. However, due to the price of monocrystalline silicon materials and the corresponding cumbersome battery process, the cost of monocrystalline silicon is high. No less, it is very difficult to drastically reduce its cost. In order to save high quality materials and find substitutes for monocrystalline silicon cells, thin film solar cells have now been developed, among which polysilicon thin film solar cells and amorphous silicon thin film solar cells are typical representatives.

2 Polysilicon Thin Film Solar Photovoltaic Cells Conventional crystalline silicon solar cells are fabricated on high-quality silicon wafers with a thickness of 350 to 450 μm. These wafers are sawn from a pulled or cast silicon ingot. Therefore, more silicon material is actually consumed. In order to save materials, people began to deposit polysilicon films on inexpensive substrates since the mid-1970s, but due to the grain size of the grown silicon films, valuable solar cells could not be made. In order to obtain thin films of large size, people have not stopped researching and proposed many methods. At present, polysilicon thin-film batteries are prepared by chemical vapor deposition methods, including low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) processes. In addition, liquid phase epitaxy (LPPE) and sputter deposition methods can also be used to prepare polycrystalline silicon thin-film batteries. Chemical vapor deposition mainly uses SiH2Cl2, SiHCl3, SiCl4, or SiH4 as reaction gases, reacts under certain protective atmosphere to generate silicon atoms and deposits on heated substrates. Substrate materials generally use Si, SiO2, Si3N4, and the like. However, it has been found that it is difficult to form large grains on non-silicon substrates and easily form gaps between crystal grains. The solution to this problem is to use LPCVD to immerse a thin layer of amorphous silicon on the substrate, and then anneal this layer of amorphous silicon to get larger grains, and then on this layer of seed. Deposition of thick polysilicon films, therefore, recrystallization technology is undoubtedly a very important part of the current technology used mainly solid-phase crystallization and the middle zone remelting recrystallization. In addition to the recrystallization process, polysilicon thin-film batteries also employ almost all techniques for the production of monocrystalline silicon solar cells, which significantly improves the conversion efficiency of solar cells. The conversion efficiency of polysilicon cells fabricated on FZ Si substrates using the district hall recrystallization technology in Freiburg Institute of Solar Energy, Germany, was 19%. Japan Mitsubishi Corporation used this method to prepare batteries with an efficiency of 16.42%. The principle of the liquid phase epitaxy (LPE) method is to melt the silicon in the matrix and lower the temperature to precipitate the silicon film. US Astropower Corporation uses LPE to produce a battery efficiency of 12.2%. Chen Zheliang of the China Optoelectronics Development and Technology Center used the liquid phase epitaxy method to grow silicon grains on metallurgical grade silicon wafers, and designed a new type of solar cell similar to crystalline silicon thin film solar cells, called “silicon grains” solar energy. Battery, but reports about performance have not been seen. Polycrystalline silicon thin-film batteries use less silicon than single-crystal silicon, and have no efficiency degradation issues. They may be fabricated on inexpensive substrate materials. The cost is much lower than that of single-crystal silicon cells, and the efficiency is higher than that of amorphous silicon films. Batteries, therefore, polysilicon thin-film batteries will soon dominate the solar-electricity market.