However, many toxic substances and machines with strong electromagnetic radiation are used in the processing.
Preparation of photovoltaic polysilicon thin films by deposition method. Generally, high-purity silane or trichlorosilane is used as gas source, and chemical deposition, physical deposition and liquid phase epitaxy are adopted. The deposited films exist in amorphous, microcrystalline and polycrystalline forms. However, there is photodegradation in amorphous silicon thin film solar cells, so one aspect of this method is to prepare polycrystalline silicon thin films by changing deposition conditions or recrystallizing amorphous silicon. In the above methods, physical vapor deposition can not meet the requirements of solar cell materials because of the problems of "holes" and high hanging bond density. It is reported that Tokuyama Corporation of Japan has built a chemical vapor deposition photovoltaic polysilicon film experimental factory with an annual output of 200 tons. The main problems of these methods in industrial production are deposition rate and crystallization rate; Energy consumption is not lower than silane method.
(4) electrochemical deposition of amorphous silicon film or powder. This method was developed by Moscow Institute of Technology. The main steps are to obtain soluble silicon compounds through self-propagating high temperature synthesis, and then to obtain more than five kinds of amorphous silicon films or powders through membrane separation process and ultra-high frequency electrolysis technology. The idea of this technology comes from the ultra-high frequency electrolysis technology to extract uranium.
Three, research content, objectives, specific assessment indicators
1, technical scheme
The method for producing polysilicon from chlorine-free alkoxysilane includes five steps: synthesis of triethoxysilane; Purification of triethoxysilane: Triethoxysilane is disproportionated to produce silane; Silane purification; Preparation of polysilicon by pyrolysis of silane. The process flow adopted by this method is shown in figure 1.
Pure ethanol react with dry silicon powder with purity of 99% and particle size of 200 mesh to generate triethoxysilane. The main by-product is a small amount of tetraethoxysilane. The reaction was carried out at atmospheric pressure and 180℃ with a copper-based catalyst. Ethanol is recovered by distillation. Triethoxysilane is purified by removing tetraethoxysilane by adsorption or distillation.
The purified triethoxysilane was disproportionated by liquid catalyst at normal pressure and near normal temperature. The separated silane is purified by adsorption, and then enters a fluidized bed reactor at 800℃ for thermal decomposition. 150- 1500? M granular polysilicon.
Tetraethoxysilane and hydrogen, the main by-products produced in the reaction process, are recycled through the following reactions:
3si (oc2h5) 4+si+2h2 → 4sih (oc2h5) 3 (50 atm, 150℃)
In addition, TEOS can be processed into many valuable commodities, such as silica sol, silicone oil and resin.
2. Research content
(1) Determine the optimum process conditions of each process, including reaction temperature, pressure, flow rate, adsorbent, etc. ;
(2) Kinetics of synthesis of triethoxysilane, preparation of silane by disproportionation of triethoxysilane and preparation of polysilicon by pyrolysis of silane.
(3) The selection of catalysts for the synthesis of triethoxysilane and the disproportionation of triethoxysilane to silane, as well as the molecular design and preparation of new efficient catalysts.
(4) Study on the technology of preparing triethoxyhydrosilane from tetraethoxysilane.
(5) The simulation of the whole process, especially the simulation of fluid flow state, provides theoretical guidance for expanding the scale of production line.
3. Research objectives
(1) Determine the technological process and conditions for preparing polysilicon from chlorine-free siloxane.
(2) Determine the kinetic parameters such as reaction rate or adsorption rate of each process, and provide complete data for the design of production equipment.
(3) Complete the simulation of the whole process.
(4) Complete the laboratory equipment with an annual output of 500kg polysilicon.
4. Specific evaluation indicators
The conversion rate of (1) silicon powder reached 90%, the conversion rate of ethanol reached 90%, the selectivity of triethoxysilane to tetraethoxysilane reached 98%, and the conversion rate of the disproportionation reaction of triethoxysilane reached 90%.
(2) The average particle size of polysilicon powder is 800- 1000? m .
(3) The quality index of polysilicon reaches the national first-class standard.
Impurity resistivity or concentration
Volume purity donor (P, As, Sb) resistivity ≤ 300Ω? centimetre
Acceptor (b, Al) resistivity ≤ 3000Ω? centimetre
Carbon ≤ 100ppba
Total amount of bulk metal
(Fe, Cu, Ni, Cr, Zn) ≤ 500pptw
Total surface metal ≤ 1000pptw
Fourth, key technologies and innovations.
1, key technologies
Selection of catalyst and determination of technological conditions for disproportionation of (1) triethoxysilane.
(2) Determination of technological conditions and conversion rate of TEOS.
(3) Determination of silane pyrolysis process conditions.
(4) Control of impurity content on the surface of granular polysilicon.
2. Innovation and innovation
(1) silane is prepared by fluorine-free and chlorine-free process, and raw materials and intermediate products do not corrode equipment.
(2) The fluidized bed process is adopted for silane decomposition, which reduces energy consumption.
(3) The product is granular and suitable for continuous feeding and drawing of monocrystalline silicon.
(4) Adopt closed circulation to improve the utilization rate of raw materials.
(5) At the same time, the simulation system is established, which provides theoretical guidance for expanding production in the future.
Five, the existing basic conditions (preliminary research work, technical team, equipment, etc ... )
1, preliminary research work
(1) The method of synthesizing triethoxyhydrosilane from silicon powder and ethanol was studied. The phased results obtained include: the conversion rate of silicon powder is 95%, the conversion rate of alcohol is 90%, and the selectivity of triethoxysilane reaches 97%. The accompanying product is hydrogen. Distilling the prepared triethoxysilane to separate the incompletely reacted alcohol, and then purifying the triethoxysilane by chemical adsorption. This method has applied for national invention patent.
(2) Theoretical research and preliminary experimental exploration on the following steps prove that the process route is feasible.