Crystalline silicon is divided into single crystal silicon and polycrystalline silicon. Monocrystalline silicon is expensive. Although the quality of polycrystalline silicon is not as good as monocrystalline silicon, its production cost is only 1/20 of that of monocrystalline silicon because it does not require time-consuming and energy-consuming single crystal pulling processes, and it can be maintained by the application of gettering and other technologies in the industry. Higher life expectancy of few births. Although the efficiency of polycrystalline silicon solar cells is 1% to 2% lower than that of monocrystalline silicon cells, the cost of polycrystalline silicon solar cells is lower. Therefore, the current share of polycrystalline silicon cells in the solar cell market has surpassed that of monocrystalline silicon cells.
With the energy shortage and the rapid deterioration of the environment, the solar cell industry is developing rapidly, and the global demand for polysilicon is growing rapidly. The main reason is the rapid popularity and expansion of the European-centered solar market, and the imbalance between supply and demand of polysilicon will intensify. Short-term fluctuations in the market may change, but the long-term demand for polysilicon for solar cells will be strong.
Polysilicon uses metallic silicon as its raw material. China is the world’s high-grade raw silicon ore storage country, accounting for one-third of the world’s proven reserves. Silicon ore is first smelted into metallic silicon and further purified into high-purity polysilicon. China is a major exporter of silicon metal, which in turn is a major importer of high-purity silicon in the world.
Most of the internationally produced solar-grade polycrystalline silicon is made by smelting, doping, blending and re-melting and casting monocrystalline silicon rods with slightly lower purity head and tail materials or bottom materials left over from pulling single crystals. With the advancement of technology in the semiconductor industry, the proportion of monocrystalline silicon’s head and tail material is getting smaller and smaller, and the constraints on the output of monocrystalline silicon have become more and more obvious, leading to higher and higher costs of polysilicon. The methods of producing polysilicon mainly include improved Siemens method and physical method. Although the purity of the improved Siemens method can reach 11N level, it is a pity to be used in solar cells, because experiments have shown that polysilicon materials with a purity of 7N or higher have no obvious contribution to improving the conversion efficiency of solar cells.
In terms of chemical law, polysilicon technology and market are still in the hands of a few manufacturers in the United States, Japan, and Germany.
The most important issue is technology and production process. The reliability, advancement, maturity of the thousand-ton process and equipment technology, as well as the mutual matching of the various subsystems, all have to be verified by production and operation.
At present, the most advanced countries in the world for polysilicon production technology are a few developed countries such as the United States, Germany, Japan, and Italy. The output of the above four countries accounts for more than 90% of the total output of polysilicon in the world. Chemical purification method. Due to the limitation of monocrystalline silicon output and the impact of the substantial price increase, in recent years, the use of physical purification technology to produce solar cell-grade polycrystalline silicon is entering the industrialization stage. The research of physical purification technology began in the 1980s. The basic idea is to increase the purity from the bottom up (Bottom Up), and the current main production method in the world-the improved German Siemens chemical method purity from top to bottom ( Top Down) has a completely different pattern. From an investment point of view, an improved Siemens polysilicon production line of about 1,000 tons is like a medium-sized modern petrochemical company. It has complex engineering design and high power consumption (a production line with an annual output of 1,000 tons of polysilicon requires an installed power supply capacity of 98,000 Kilowatts, the total annual electricity consumption is 250 million kilowatt-hours), and the total investment is huge. In comparison, the physical production investment and unit energy consumption are greatly reduced.