The research on the physical purification technology of polysilicon includes two topics: (1) the research on the purification technology of polysilicon by electron beam melting; (2) Study on purification technology of regional melting polysilicon.
The implementation scheme of the electric arc furnace electron beam melting method is as follows: firstly, repeatedly sintering polysilicon with a high vacuum electric arc furnace to make the purity of polysilicon reach above 5N; In the final stage of electron beam melting, oxygen-containing, hydrogen-containing and chlorine-containing gases are added to the protective gas, which react with impurity B to generate volatile substances, thus achieving the purpose of removing impurities; The preliminarily purified material is further purified to solar energy level or above in a zone melting single crystal furnace.
The key technology of electron beam melting in electric arc furnace lies in the directional solidification of molten polysilicon in vacuum, which makes the impurities on the surface volatilize. The main problem is how to transport the impurities in the melt to the surface of the melt and make it volatilize from the surface. When the melt volume is large, the impurities in it often cannot be transported to the surface in time. In order to solve this problem, shielding gas can be pumped out quickly, so that the impurity concentration in the gas phase is always low and the impurities in the melt can be volatilized as soon as possible; Another problem is that the polysilicon in direct contact with the crucible is not completely melted, which is not conducive to the transfer of impurities to the liquid and gas phases. Electromagnetic plasma method can solve this problem, so that the melt does not directly contact the crucible wall, thus increasing the surface area of the melt and evaporating the impurities in the melt as soon as possible. Because the saturated vapor pressure of element B (10-4Pa) is much lower than that of Si (10- 1Pa), impurity B cannot be removed by this method, and it is necessary to blow gas into the melt at the final stage of purification to improve the saturated vapor pressure of B. ..
The remarkable feature of zone melting method is that it does not use crucible to hold molten silicon, but relies on the surface tension and electromagnetic force of silicon to support locally melted silicon liquid under the action of high-frequency electromagnetic field. Therefore, zone melting method is also called suspension zone melting method. The principle of zone melting purification is to remove carbon, phosphorus and other impurities contained in polysilicon according to the different impurity concentrations in solid and liquid phases during the recrystallization of molten crystals. The biggest advantage of regional melting purification method is that the energy consumption is reduced by more than 60% compared with the traditional method. At present, the regional melting purification method is the most likely method to replace the traditional process to produce solar-grade polysilicon materials. REC company began to use zone melting purification method in its new factory in 2006.
The goal of this research direction is to develop and industrialize the physical solar-grade polysilicon purification technology with independent intellectual property rights, reduce environmental pollution and energy consumption during polysilicon purification, and reduce the cost of photovoltaic power generation.
In three years, he obtained 3-5 scientific research projects, applied for 2-3 national patents, published 3-5 research papers in national core journals, and trained 6 doctoral and master students.
Secondly, the research of silicon thin film solar cell materials.
The research contents of silicon thin film solar cell materials include: 1, the study of amorphous silicon thin film; 2. Study on polycrystalline silicon thin film materials.
At present, monocrystalline silicon and polycrystalline silicon are the most widely used solar cell materials, but the cost of crystalline silicon remains high due to the complexity of growth process and the waste of silicon materials. Therefore, thin-film silicon solar cells are considered to be the fundamental way to greatly reduce costs, the hot spot and mainstream direction of silicon solar cells in the future, and will occupy a dominant position in the solar cell market. The materials of silicon-based thin film solar cells mainly include amorphous silicon thin films and microcrystalline silicon thin films.
Study on 1 and amorphous silicon thin films
The light absorption coefficient of amorphous silicon thin film solar cells is large, and the required film thickness is much smaller than other materials. The manufacturing process is simple, the energy consumption is low, and large-area continuous production can be realized; Glass or stainless steel can be used as the substrate, which is easy to reduce the cost; It can be made into a laminated structure to improve efficiency. However, there are some main problems in amorphous silicon thin film solar cells, such as Staebler-Wronsk effect, low deposition rate and a large number of impurities in the film deposition process, which affect the quality of the film and the stability of the cell. In order to solve the above problems, the laboratory plans to explore the process of growing ZnO thin films on glass substrates by sputtering or PECVD, so as to obtain high-quality polycrystalline ZnO thin films with controllable grain size and excellent photoelectric properties, and study the changes of refractive index of ZnO thin films and the effects of element doping on conductivity, transmittance and antireflection. Further improve the PECVD production process of silicon thin film, optimize the parameters such as temperature (T), pressure (P), frequency (F), voltage (V) and chemical source (S), reduce the concentration of electron or hole traps, reduce electron-hole recombination centers and recombination probability, and further improve the battery conversion efficiency; Study the surface treatment technology and buffer layer design of ZnO thin film to reduce the photoinduced attenuation effect of the battery; Improve the preparation process to improve the stability of large-area amorphous silicon thin films.
2. Study on microcrystalline silicon thin films.
The photo-induced instability of the efficiency of amorphous silicon thin film solar cells is determined by the metastable characteristics of the material microstructure, so the S-W effect is not easy to be completely eliminated. In recent years, polycrystalline (micro) silicon thin film batteries have appeared. Using polycrystalline silicon film instead of amorphous silicon film as the active layer of the battery has no obvious attenuation under long-term illumination. Growing polycrystalline silicon thin film on low-cost substrate and using thin crystalline silicon layer as the activation layer of the battery can not only maintain the high performance and stability of the crystalline silicon battery, but also avoid the S-W effect and effectively reduce the battery cost.
At present, the key problems of polysilicon battery are poor photoelectric properties of the material itself and low deposition rate. Therefore, the research focus of the laboratory in this area is mainly to improve the deposition rate of thin films and improve the sedimentary facies map data of high-speed and high-quality polysilicon thin films; The effects of deposition pressure and flow rate on the photoelectric properties of thin films and the relationship between microstructure, photoelectric properties and stability were studied. The film forming process was optimized, and the device quality and polysilicon thin films with stable photoelectric properties were obtained. How to prepare intrinsic layer with low defect density and microcrystalline silicon thin film with low amorphous silicon content at a relatively low process level is the key to further improve the conversion efficiency of microcrystalline silicon solar cells.
Research objectives: In the research of amorphous silicon and microcrystalline silicon thin film materials, broaden the light absorption area, improve the light absorption coefficient, improve the photoelectric conversion efficiency, optimize the film forming process, and prepare silicon-based solar cells with stable performance and low price.
In three years, he obtained 3-5 scientific research projects, applied for 2-3 national patents, published more than 8 research papers in national core journals, and trained 9 doctoral and master students.
Thirdly, research on non-silicon-based solar photovoltaic materials and technologies.
The research contents of non-silicon-based thin film solar cells include: 1, dye-sensitized nanocrystalline solar cells; 2. Organic-inorganic composite thin-film solar cells: 3. Study on 3.CIS thin-film solar cells.
1, dye-sensitized nanocrystalline solar cells
At present, there are two main problems surrounding dye-sensitized nanocrystalline solar cells, namely, the stability of liquid batteries and the improvement of photoelectric conversion efficiency of solid batteries. The laboratory plans to carry out research on dye sensitizers, solid electrolytes and new electrode materials. In the aspect of dye sensitizer, the new organic dyes are mainly explored to replace the commonly used Ru complex sensitizer, and the composite materials of TiO _ 2 and other inorganic semiconductor compounds are synthesized to realize the sensitization of inorganic composite materials. The energy band structure of TiO _ 2 is effectively changed by doping ion sites, and it is sensitized by doping with metals or nonmetals. In the study of solid electrolyte, lithium salt and Cui salt are filled into carbon nanotubes by using their unique conductivity and material storage function, which plays an important role in improving battery performance. The outer wall of filled carbon nanotubes is grafted with polymer to improve its compatibility with the matrix, and the grafted composite carbon nanotubes are further compounded with the matrix polymer to form a solid electrolyte layer. In the research of new electrode materials, functional dye-sensitized nano-TiO _ 2 porous membrane is used, and * * yoke polymer is used as hole transport medium to improve the compatibility between polymer and dye surface, enhance the interface charge injection and transport rate, introduce a dense barrier layer at the interface between conductive glass and porous TiO _ 2, reduce the probability of back electron transport, study the film-forming process of polymer, and improve its filling efficiency in dye-sensitized TiO _ 2 holes. In order to improve the conversion efficiency of the battery, titanium dioxide nanostructures such as nanotubes and core-shell nanoparticles were synthesized by hydrothermal method and electrochemical method. Explore non-titanium dioxide inorganic nano-electrode materials, such as zinc oxide, barium nitrate, zinc nitrate, etc.
2. Organic-inorganic composite thin film solar cells
Organic-inorganic composite semiconductor materials developed in 1980s, through the combination of structure and function, not only have the advantages of design diversity, flexibility and machinability of organic materials, but also have the advantages of high carrier mobility and stability of inorganic materials, which often produce synergistic optimization effect. They are a new type of composite functional materials with semiconductor properties, containing two or more organic and inorganic components, and become one of the key materials for future energy development.
The organic-inorganic composite solar cell has a simple structure. Generally, organic and inorganic layers are made on transparent conductive glass by simple spin coating process or vacuum evaporation technology to make bulk heterojunction structure, and then aluminum electrodes are vacuum evaporated. The main function of organic layer is to realize broad spectrum and high efficiency light absorption, while the function of inorganic semiconductor material is to realize charge separation and improve transport performance. In this way, in principle, we can avoid the limitation of using narrow band-gap semiconductor materials to achieve broad spectrum absorption, but we can use wide band-gap semiconductor materials with optical, thermal and chemical stability. On the one hand, we can solve the common problems of light corrosion and photodegradation in narrow band-gap semiconductor materials, on the other hand, we can use low-cost and environment-friendly wide band-gap semiconductor materials, such as ZnO and TiO2, to reduce the environmental pollution caused by waste in the production process. However, organic semiconductors have low carrier mobility and poor stability, and organic-inorganic composite semiconductors have poor structural stability, which leads to poor battery performance and process repeatability.
The laboratory will focus on the structural evolution, control and stability of organic-inorganic composite semiconductor materials under the action of light, heat and other external fields, organic-inorganic composite semiconductor materials with high carrier mobility, the relationship between the structure of organic-inorganic composite semiconductor materials and long-range carrier transport performance, the ways to achieve high carrier mobility, the synthesis of various new organic small molecules, the screening of organic molecules with high quantum yield as light absorption layers, and the systematic study of various systems composed of organic semiconductor materials and inorganic semiconductor materials.
3. Study on 3.CIS thin film.
CIS thin film solar cell is a direct band gap compound semiconductor material composed of copper, indium, selenium and other metal elements. Its visible light absorption coefficient is the highest among all thin film battery materials (a-Si, CdTe, etc.). ), but the consumption of raw materials is much lower than that of traditional crystalline silicon solar cells, and the development prospect is broad. CIS solar cells have three outstanding characteristics: ① High conversion efficiency, and CIS is the most promising photovoltaic material for high-efficiency thin-film solar cells. (2) Low manufacturing cost: CuInSe2 is a direct band gap material, and its light absorption rate is as high as 105, so it is the most suitable film for solar cells, and the thickness of the cells can reach 2 ~ 3 microns, thus reducing the expensive material consumption. Its cost is 1/2 ~ 1/3 of crystalline silicon solar cells. ③ The battery performance is stable. The research and development of thin-film solar cells are being carried out by using the thin-film growth system in the laboratory. By changing the window material of CIS thin film solar cell, the conversion efficiency is further improved. At present, ZnO thin film is used as window material, which improves the conversion efficiency from 6.5% to 9.5%.
Research purposes: To improve the conversion efficiency of CIS thin-film solar cells, improve the preparation process, and lay the foundation for industrialization. Continue to improve the performance of each component of the fuel-sensitized solar cell and the photoelectric conversion efficiency of the cell. Research and development of thin-film solar cells based on organic-inorganic composite semiconductor materials can improve their structural stability and photoelectric conversion efficiency and reduce the production cost of materials.
In the past three years, he has obtained 2-3 scientific research projects, applied for 3 national patents, published more than 0 research papers 10 in national core journals, and trained 2 doctoral and master students 12.
The overall goal of establishing the provincial key laboratory of photovoltaic materials is to overcome the key technical problems in the development of photovoltaic materials and technologies, constantly create new achievements, develop new technologies, carry out engineering research, and provide mature and supporting technologies, processes, equipment and new products for industrialization; Implement open services, accept engineering technology research, design, test and complete sets of technical services entrusted by industries or departments, enterprises, scientific research institutions and other units, and provide consultation for the promotion of their achievements; Cultivate and gather high-level engineering and technical talents and management talents in related majors, and provide engineering and technical personnel training for industries and enterprises in this province; Carry out various forms of international and domestic scientific and technological cooperation and exchanges, develop relevant standards and industry information services, and promote technological development in industries and fields.