Head-to-Head Comparison of Monocrystalline Silicon and Polycrystalline Silicon Technologies

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Polaris Solar PV News: The difference between monocrystalline silicon and polycrystalline silicon is that when molten elemental silicon solidifies, silicon atoms arrange themselves in a diamond lattice to form numerous crystal nuclei; if these nuclei grow into grains with the same crystal plane orientation, monocrystalline silicon is formed. If these nuclei grow into grains with different crystal plane orientations, polycrystalline silicon is formed. The differences between polycrystalline silicon and monocrystalline silicon are mainly reflected in their physical properties. For example, in terms of mechanical properties and electrical properties, polycrystalline silicon is inferior to monocrystalline silicon. Polysilicon can be used as a raw material for pulling single-crystalline silicon. Monocrystalline silicon can be considered one of the purest substances in the world; typical semiconductor devices require a silicon purity of over six 9s. Large-scale integrated circuits have higher requirements; the purity of silicon must reach nine nines. Currently, it is already possible to produce single-crystalline silicon with a purity of twelve 9s. Monocrystalline silicon is an essential basic material in modern science and technology, such as electronic computers and automatic control systems. High-purity silicon is extracted from quartz. Taking single-crystal silicon as an example, the purification process involves the following steps: quartz sand → metallurgical-grade silicon → purification and refining → deposition of polycrystalline silicon ingots → single-crystal silicon → silicon wafer cutting. The purification of metallurgical-grade silicon is not difficult. Its production mainly involves the reduction of quartz sand with carbon in an electric arc furnace. The purity of silicon obtained in this way is around 98-99%, but silicon used in the semiconductor industry requires further high-level purification (electronic-grade polycrystalline silicon needs a purity of 11 nines, while solar cell-grade silicon only requires 6 nines). During the purification process, there is a key technology known as the \"trichlorosilane reduction method (Siemens method)\) that China has not yet mastered. Due to the lack of this technology, over 70% of the polysilicon produced in China is released into the atmosphere as chlorine gas, resulting not only in high production costs but also severe environmental pollution. Every year, our country extracts large amounts of industrial silicon from quartz rock, and exports it to countries such as Germany, the United States, and Japan at a price of $1 per kilogram. These countries then process the industrial silicon into high-purity crystalline silicon materials, which they sell to our country’s solar energy companies at a price of $46–80 per kilogram. After obtaining high-purity polycrystalline silicon, it must be melted into single-crystalline silicon in a crystal growth furnace, and then sliced for use in integrated circuit manufacturing and other applications. What is monocrystalline silicon? It can be used in the production and further processing of monocrystalline products at the diode level, rectifier device level, circuit level, and solar cell level. The resulting integrated circuits and semiconductor discrete devices are widely used in various fields and hold an important role in electronic equipment as well. With the rapid advancement of photovoltaic technology and micro-scale semiconductor inverter technology, solar cells made from silicon single crystals can directly convert solar energy into light energy, marking the beginning of a transition toward a green energy revolution. The 2008 Beijing Olympics will present the concept of a \"Green Olympics\" as an important theme to the world, and the use of monocrystalline silicon will play a very important role in this regard. At present, solar photovoltaic power plants abroad have reached a stage of theoretical maturity and are transitioning to practical application. The use of solar silicon single crystals will become widespread across the world, and the market demand for them is self-evident. The Hebei Ningjin Monocrystalline Silicon Industrial Park was established in response to this international trend, aiming to supply the world with high-performance monocrystalline silicon products in a wide range of specifications. Single-crystalline silicon products include φ3”----φ6” single-crystalline silicon round rods, wafers, and square rods and wafers, which are suitable for the production needs of various semiconductor and electronic products. The quality of these products is tested using the most advanced testing equipment available in the world, ensuring that it meets world-class standards. Methods for refining monocrystalline silicon: Silicon is the second most abundant chemical element on Earth. As a semiconductor material, it has been the subject of the most extensive research and boasts the most advanced technologies available. Its stable properties and non-toxicity make it the primary material used in the research, development, production, and application of solar cells. However, high-purity polysilicon is in severe shortage in China, with the vast majority having to be imported. High-purity silicon is extracted from quartz. Taking single-crystal silicon as an example, the purification process involves the following steps: quartz sand → metallurgical-grade silicon → purification and refining → deposition of polycrystalline silicon ingots → single-crystal silicon → silicon wafer cutting. The purification of metallurgical-grade silicon is not difficult. Its production mainly involves the reduction of quartz sand with carbon in an electric arc furnace. The purity of silicon obtained in this way is about 98-99%, but silicon used in the semiconductor industry requires further high-level purification. The impurity content in electronic-grade silicon is below about (10^-10)%. During the purification process, there is a key technology known as the \"trichlorosilane reduction method (Siemens method)\) that China has not yet mastered. Due to the lack of this technology, over 70% of the polysilicon produced in China is released into the atmosphere as chlorine gas, resulting not only in high production costs but also severe environmental pollution. In fact, our country extracts large amounts of industrial silicon from quartz every year, exporting it to countries such as Germany, the United States, and Japan at a price of $1 per kilogram. These countries then process the industrial silicon into high-purity crystalline silicon materials, which they sell to our country’s solar energy companies at a price of $46–80 per kilogram. It is not easy to produce polysilicon. In fact, the upstream raw material for polysilicon, quartz sand, is not scarce in China. Many overseas polysilicon companies purchase directly from China. However, Chinese companies have made no progress in silicon purification technology. In the 1990s, more than 40 small companies in China were researching polysilicon technology, but none of them was able to undertake large-scale polysilicon production. A polysilicon production line with a capacity of around 1,000 tons is akin to a medium-sized modern petrochemical company, requiring complex engineering design. There are two types of polysilicon production technologies: the silane method and the trichlorosilane reduction method. If significant breakthroughs are achieved in these two types of technologies, China’s production of photovoltaic cells will increase further. In the \"Research Report on China’s Photovoltaic Industry\" prepared by the Office for the Development of Renewable Energy in China in October 2004, domestic solar-grade polysilicon was described as follows: \"The development and production of solar-grade silicon materials specifically for photovoltaic use in China is non-existent.\" Silicon is the second most abundant chemical element on Earth. As a semiconductor material, it has been the subject of the most extensive research and boasts the most mature technologies. Its stable properties and non-toxicity make it the primary material used in the research, development, production, and application of solar cells. However, high-purity polysilicon is in severe shortage in China, with the vast majority having to be imported. High-purity silicon is extracted from quartz. Taking single-crystal silicon as an example, the purification process involves the following steps: quartz sand – metallurgical-grade silicon – purification and refining – deposition of polycrystalline silicon ingots – single-crystal silicon – slicing of silicon wafers. The purification of metallurgical-grade silicon is not difficult. Its production mainly involves the reduction of quartz sand with carbon in an electric arc furnace. The purity of silicon obtained in this way is about 98–99%, but silicon used in the semiconductor industry requires further high-level purification. The impurity content in electronic-grade silicon is below about 10%. During the purification process, there is a key technology known as the \"trichlorosilane reduction method (Siemens method)\) that China has not yet mastered. Due to the lack of this technology, over 70% of the polysilicon produced in China is released into the atmosphere as chlorine gas, resulting not only in high production costs but also severe environmental pollution. There is no time to wait when developing the polysilicon industry; for Chinese solar companies, resolving the issue of high-purity silicon is an urgent task. Polysilicon is not a resource-based product like oil; however, once a monopoly is established in terms of technology, domestic companies are at a loss as to what to do. If there continues to be a shortage of polysilicon material and its prices keep rising, China’s photovoltaic industry is at risk of collapse, as the prices of solar panels are fixed, leaving no room for increases in the cost of materials. Yan Dazhou, chief designer at the China Non-ferrous Metals Engineering Design and Research Institute, made it clear that unless domestic polycrystalline silicon production is transformed through independent intellectual property rights and the expansion or establishment of new polycrystalline silicon manufacturing facilities is accelerated, China’s polycrystalline silicon industry will remain subject to the constraints of the international market, which in turn will threaten China’s integrated circuit, semiconductor device, and photovoltaic industries. Currently, as countries increase their support for the photovoltaic industry, the shortage of polysilicon supply is likely to worsen. Moreover, the new production capacity of polysilicon manufacturers has already been reserved by some companies, which means it is urgent to accelerate the development of China’s polysilicon industry. Therefore, there is a call for the introduction of favorable policies to support domestic enterprises in researching new processes and technologies at costs comparable to those of foreign companies. Currently, polysilicon has assumed an increasingly important role in the development of the semiconductor industry and the new energy sector. In the past one or two years, the major polycrystalline silicon producers in the world have been actively seeking new processes, new equipment, and new technologies for the production of polycrystalline silicon products, particularly those used in solar cells. This area of research and development is highly active, with numerous new research findings and technological breakthroughs emerging. This also indicates that a new leap in the industrial production technology of polysilicon worldwide is about to occur. The next 3 to 5 years represent a golden period for the development of China’s polysilicon industry. We must seize this opportunity to establish our own polysilicon industry as soon as possible, in order to break the monopoly and blockades imposed by developed countries. The evolving demands pose an urgent and important challenge for China’s silicon materials industry, whether it comes to expanding the scale of polysilicon production in the country or to researching and developing new polysilicon production processes that can help save energy, improve production efficiency, reduce costs, and enhance profitability. China’s polysilicon materials are facing such an important turning point. Looking at the situation abroad, each company involved in polysilicon production is developing independently; it is not possible to introduce technologies jointly, and the core technologies held by polysilicon plants are all located abroad. Lin Biqing, deputy general manager of Ningbo Lili Electronics Co., Ltd., believes that relying on technology transfer or forming joint ventures with foreign companies is not very feasible; therefore, it is necessary to abandon such illusions and focus on independent research and development in polysilicon technology, working together to develop new technologies and processes for polysilicon production. The main technical routes for producing polysilicon internationally include the modified Siemens method, the silane method, the fluidized bed method, and the metallurgical method, among which the modified Siemens method accounts for over 80% of global production. As for the technical approach that should be adopted for developing the polysilicon industry in our country, experts believe that the current production capacity of around 100 tons per year is achieved through the modified Siemens process. This method not only provides a solid technical foundation but has also enabled the development of a group of experienced researchers and technicians. Therefore, when developing production technologies at a scale of thousands of tons, efforts should focus on areas such as energy conservation and the recycling of materials. Many experts suggest that efforts in technological development should focus both on meeting the urgent demand for polysilicon products from related industries by improving production technologies using the modified Siemens process at a scale of thousands of tons, thereby reducing energy consumption and product costs and enabling large-scale production as soon as possible. At the same time, it is necessary to intensify research on new technologies and processes; using solar-grade polysilicon production technology as a starting point, efforts should be made to develop new technologies and processes for producing low-cost solar-grade polysilicon, thus ensuring the sustainable development of polysilicon technology. They recommend that the Ministry of Science and Technology organize efforts to develop technologies for the industrialization of polysilicon as soon as possible, so as to foster close collaboration among industry, academia, and research institutions and create a competitive polysilicon industry in China. Coordination and cooperation are essential. Currently, two companies in the country have begun to explore polysilicon production. Zhongsi High-Tech in Luoyang, Henan, began producing 300 tons of polysilicon in November 2005. Some of the company’s products are supplied to an IC company, while others are supplied to Suntech Power in Wuxi. In August 2005, the Ministry of Science and Technology approved Henan Luoyang Zhongsi High-Tech Co., Ltd. to carry out the project \"Technical Research on 24-Rod Polysilicon Reduction Furnace Systems\" as part of the **\"863\" Program**, providing an initial funding amount of 3 million yuan. The project is expected to be completed in 2006; upon completion, it will yield polycrystalline silicon production technologies and processes with independent intellectual property rights, thereby laying a technical foundation for the establishment of thousand-ton-scale polycrystalline silicon production lines in China. Xinguang Silicon Industry was established in Leshan, Sichuan in 2001; it was China’s first polysilicon production line with a capacity of over 1,000 tons per year, designed to produce 1,260 tons of polysilicon annually, with a total investment of around 1.29 billion yuan. It is estimated that after the project goes into operation in 2006, its annual output value will be around 600 million yuan, with the capacity to produce 900 tons of electronic-grade polysilicon, 200 tons of zone-melted polysilicon, and 150 tons of polysilicon for solar cells per year. It will become clear in 2006 whether this crucial breakthrough can be achieved. Currently, Shanghai Solar Technology is establishing a “Solar Energy Engineering Technology Research Center”. The center will make technological breakthroughs in polysilicon over a period of 2 years. Once the technical barriers are overcome, raw material costs will drop sharply. Solar technology companies can also entrust other firms to produce polysilicon for them. **Jinyi Group will invest 1 billion yuan in Chongqing to build a production facility capable of producing 50,000 tons of silicon micropowder and 1,000 tons of polysilicon per year. Zhu Lihui, secretary-general of the Semiconductor Materials Branch of the China Electronic Materials Association, said that many places are now interested in launching polysilicon projects, and it is hoped that **coordination can be established to avoid repeating the history of building multiple crystalline silicon factories. The polysilicon industry not only has high technical barriers and significant risks, but also requires a professional team to ensure its proper operation; therefore, **relevant authorities should impose strict approvals and restrictions on polysilicon projects. Although there has been strong demand for polysilicon in the international market for some time, with a significant gap in the domestic market, it should be noted that China’s polysilicon industry has a weak foundation. Moreover, foreign countries impose technical restrictions on us. If there is widespread duplication of projects, it will be extremely detrimental to the development of this industry. Therefore, it is recommended that **and the relevant industry authorities strengthen oversight; new projects should be approached with caution. It would be better to choose 1–2 existing factories that meet the requirements and expand their capacity through renovations. A reasonable economic scale for such operations is 2,500 tons. The current efforts to develop industrial-scale polysilicon technology should be led by **, with enterprises playing a key role, through independent innovation and collaborative research, in order to establish demonstration facilities for polysilicon technology and industry in China at a high level as soon as possible. When selecting industrialization technology demonstration projects, full consideration should be given to the environment and conditions for their implementation. Priority should be given to locations with sufficient and low-cost electricity supply, relatively abundant water sources, easy transportation of hydrogen and chlorine, and the ability to utilize by-products locally; areas with high population densities or those used for tourism should be avoided as much as possible. At present, there is a large supply-demand gap in the international market, but prices cannot be guaranteed not to fall in the future. Moreover, it is also very difficult for polysilicon plants to ensure production safety; they may be able to avoid accidents for five years, but there is no guarantee that such accidents will not occur over ten or twenty years. Therefore, in the development of the polysilicon industry, a strategy of multi-party financing should be adopted, with participation from various provinces, upstream and downstream industries, as well as private enterprises, all working together to build the industry and share risks. The diversified investment model adopted by foreign polysilicon manufacturers can serve as a reference; by partnering with enterprises along the supply chain through shareholding, such investments help to expand production scale, reduce costs, and establish a complete semiconductor industry chain for independent research and development and supply.