(1) Polysilicon thin film modules
In order to save materials and improve economy, people have been depositing polysilicon films on cheap substrates since the mid-1970s, but the grown silicon film grains are too small to make valuable solar cells. At present, the preparation of polycrystalline silicon thin film batteries mostly uses chemical vapor deposition methods, including low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD) and rapid thermal chemical vapor deposition (RTCVD) processes, in addition to liquid phase epitaxy (LPPE) And sputtering deposition method.
Chemical vapor deposition mainly uses SiH2Cl2, SiHCl3, SiCl4 or SiH4 as the reaction gas, reacts in a certain protective atmosphere to generate silicon atoms and deposits on a heated substrate. The substrate material generally selects Si, SiO2, Si3N4, and so on. However, studies have found that it is difficult to form larger crystal grains on non-silicon substrates, and it is easy to form voids between the crystal grains. The solution to this problem is to first deposit a thinner amorphous silicon layer on the substrate by LPCVD, and then anneal this amorphous silicon layer to obtain larger crystal grains, and then on this layer of seed crystals Depositing thick polysilicon films, therefore, recrystallization technology is undoubtedly a very important link.
The currently used technologies mainly include solid phase crystallization and mid-zone melt recrystallization. In addition to the recrystallization process used in polycrystalline silicon thin film batteries, almost all the techniques for preparing monocrystalline silicon solar cells are also used, so that the conversion efficiency of the solar cells prepared in this way is significantly improved. The principle of the liquid phase epitaxy (LPE) method is to deposit silicon film by melting silicon in the matrix and lowering the temperature. Because polycrystalline silicon thin-film batteries use far less silicon than monocrystalline silicon, and there is no problem of efficiency degradation, and can be prepared on cheap substrate materials, their cost is much lower than that of monocrystalline silicon cells, and the efficiency is higher than that of amorphous silicon thin-film cells. . Therefore, polycrystalline silicon thin film batteries will become the fastest growing product in thin film solar cell technology.
(2) Amorphous silicon thin film modules
Amorphous silicon solar cells are a new type of thin-film solar cells that appeared in 1976. They are completely different from monocrystalline silicon and polycrystalline silicon solar cells in terms of their production methods. They consume very little silicon material and consume less power. There are many methods for manufacturing amorphous silicon solar cells, the most common ones are the glow discharge method, reactive sputtering method, chemical vapor deposition method, electron beam evaporation method and thermal decomposition of silane method.
The glow discharge method is to vacuum a quartz container, fill it with hydrogen or argon diluted silane, and heat it with a radio frequency power supply to ionize the silane to form a plasma. The amorphous silicon film is deposited on the heated substrate. If silane is doped with an appropriate amount of phosphorous hydride or boron hydride, an N-type or P-type amorphous silicon film can be obtained. The substrate material is generally glass or stainless steel plate. This process of preparing amorphous silicon thin films mainly depends on strict control of air pressure, flow rate and radio frequency power, and also has strict requirements on the temperature of the substrate.
The structure of amorphous silicon solar cells is different. One of the better structures is called PiN cell. It first deposits a layer of phosphorus-doped N-type amorphous silicon on the substrate, and then deposits a layer of undoped i Then, a layer of boron-doped P-type amorphous silicon is deposited, and finally a layer of anti-reflection film is evaporated by electron beam, and the silver electrode is evaporated. For this kind of manufacturing process, a series of deposition chambers can be used to form a continuous process in production to realize mass production. At the same time, amorphous silicon solar cells are very thin and can be made into a laminated type, or manufactured by an integrated circuit method, using a suitable mask process on a plane to fabricate multiple cells in series at a time to obtain a higher voltage.
The voltage of a single ordinary crystalline silicon solar cell is only about 0.5V. Currently, the amorphous silicon tandem solar cell produced in Japan can reach 2.4V. The current problem of amorphous silicon solar cells is that the photoelectric conversion efficiency is lower than that of crystalline silicon solar cells, and it is not stable enough, and the conversion efficiency often declines. Therefore, it has not been widely used as large-scale solar power sources, and most of them are used for low-light power sources. , Such as pocket electronic calculators, electronic clocks and copiers. After the problem of efficiency decay is overcome, amorphous silicon solar cells will promote the development of solar energy utilization because of its low cost, light weight and more convenient application. It can be combined with the roof of the house to form an independent power source for households.