Polycrystalline silicon thin-film solar cells
Crystalline silicon solar cells are usually manufactured on high-quality silicon wafers with a thickness of 350 to 450 μm, which are sawn from drawn or cast silicon ingots. do. Therefore, more silicon is actually consumed. In order to save materials, people have been depositing polysilicon films on cheap substrates since the mid-1970s. However, due to the grain size of the grown silicon film, valuable solar cells have not been produced. produced. In order to obtain thin films with large grain sizes, researchers have never stopped researching and have proposed numerous methods. Currently, polycrystalline silicon thin-film batteries are mainly produced using chemical vapor deposition methods, including high-speed chemical vapor deposition processes.low pressure (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD). Additionally, 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 gas and reacts in a certain protective atmosphere to generate silicon atoms and deposit them on a heated substrate. Substrate materials generally use Si, SiO2, Si3N4, etc.
However, research has shown that it is difficult to form larger grains on non-silicon substrates, and it is easy to form gaps between grains. The way to solve this problem is to first use LPCVD to deposit a thin layer of amorphous silicon on the substrate, and then anneal this layer of amorphous silicon to obtain crystal grains.larger stallins, then depositing the seed crystal on this layer by depositing thick polysilicon films. , therefore, recrystallization technology is undoubtedly a very important link. The currently used technologies mainly include solid phase crystallization method and intermediate zone melt recrystallization method. In addition to the recrystallization process, polycrystalline silicon thin film cells also adopt almost all monocrystalline silicon solar cell preparation technologies. The conversion efficiency of the solar cells thus produced is significantly improved. The Freiburg Solar Energy Research Institute in Germany uses district recrystallization technology to produce polycrystalline silicon cells on FZSi substrates with a conversion efficiency of 19%. The Japanese company Mitsubishi Corporation usesise this method to prepare cells with a yield of 16.42%. The principle of liquid phase epitaxy (LPE) method is to melt the silicon in the matrix and lower the temperature to precipitate the silicon film. The efficiency of the battery produced by Astropower Company in the United States from LPE reaches 12.2%.
Chen Zheliang of the China Optoelectronic Development Technology Center used liquid phase epitaxy to grow silicon grains on metallurgical-grade silicon wafers, and designed a new solar cell similar to thin-film solar cells made of crystalline silicon, claiming it to be “silicon”. particle solar cell, but there are no reports on its performance. Since polycrystalline silicon thin film cells use much less silicon than monocrystalline silicon, there is no degradation problemefficiency and they can be produced on cheap substrate materials, their cost is much lower than monocrystalline silicon cells and their efficiency is higher than that. of amorphous silicon thin film cells, therefore, polycrystalline silicon thin film cells will soon dominate the solar energy market.
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