Introduction to polycrystalline silicon basics and development

Overview of high purity silicon

Polysilicon is an electronic material with industrial silicon as raw material and purified by a series of physical and chemical reactions. It is the main raw material of silicon polishing sheet, solar cell and high purity silicon products. According to the different purity can be divided into electronic grade polysilicon and photovoltaic grade polysilicon.

Polysilicon appearance is gray metallic luster, melting point is about 1410℃, at room temperature is not active, more active melting state. Polysilicon has semiconductor properties and is an extremely important fine semiconductor material, but trace impurities can greatly affect its electrical conductivity.

According to the Silicon Branch of the Non-Ferrous Metal Industry Association, global polysilicon consumption was 543,000 tons in 2020. The consumption of polysilicon in the photovoltaic field is 513,000 tons, accounting for 94%. Therefore, the prosperity of photovoltaic industry is the main factor affecting the demand of polysilicon. As a whole, polysilicon is the downstream industry of industrial silicon, but also in the upstream of the photovoltaic and semiconductor industry chain.

Industrial polysilicon impurity content requirements are strict, the industry has the characteristics of high capital investment and high technical barriers. Because the purity of polysilicon will seriously affect the monocrystalline silicon drawing link, so the purity requirements are extremely strict, the minimum purity of polysilicon is 99.9999%, the highest is infinitely close to 100%. In addition, the national standards set clear requirements for impurity content, and the polysilicon is divided into I, II, III grade, among which boron, phosphorus, oxygen, carbon content is an important reference index.

It can be divided into P type and N type according to the impurity incorporation and conductive type. When the silicon doped with acceptor impurity elements, such as boron, aluminum, gallium, etc., the main conductive hole, P-type. When the silicon doped with donor impurity elements, such as phosphorus, arsenic, antimony, etc., the electronic conduction is dominant, N-type.

Polysilicon is located in the upstream of the PV industry chain

After 2015, as the world's major economies pay more and more attention to the development and utilization of clean energy, the second prosperity of photovoltaic industry also makes the global demand and production of polysilicon increase synchronously, and the new production capacity gradually gathered to China.

The photovoltaic industry mainly uses solar level polysilicon, and the photovoltaic industry chain is generally polysilicon - silicon wafer - cell wafer - module - photovoltaic installation.

Polysilicon is located in the upstream of the semiconductor industry chain

The semiconductor industry uses electronic-grade polysilicon, and the semiconductor industry chain is generally polysilicon - monocrystalline silicon wafer-silicon wafer-chip.

Compared with polycrystalline silicon, monocrystalline silicon is composed of grains with the same crystal orientation, so it has superior conductivity and conversion efficiency. Monocrystalline silicon rods can be cut and processed into monocrystalline silicon sheets and cells, and then become the key part of photovoltaic modules, which are used in the field of photovoltaic.

In addition, monocrystalline silicon wafers can be formed by repeated polishing, polishing, epitaxy, cleaning and other processes, which can be used as substrate materials for semiconductor electronic devices.

China dominates polysilicon production

In recent years, the global production of polysilicon increased year by year, and gradually gathered to our country. From 2017 to 2021, the annual global polysilicon production rose all the way from 432,000 tons to 631,000 tons, with the fastest growth of 21.11% in 2021. During the period, global polysilicon production gradually concentrated in China, and the proportion of polysilicon production in China increased from 56.02% in 2017 to 80.03% in 2021. Compared with the global polysilicon production capacity of the top 10 enterprises in 2010 and 2021, it can be found that the number of Chinese enterprises rose from 4 to 8, and the proportion of some American and South Korean enterprises in production capacity decreased significantly, falling out of the top 10 team.

With the development of the global PV industry, China's polysilicon production capacity continues to grow. From 2012 to 2021, China's polysilicon production capacity increased from 160,000 tons to 560,000 tons, China's polysilicon production increased from 84,000 tons to 487,000 tons, with a compound growth rate of 19%. China's global production accounted for 35% to 78%, while overseas polysilicon production showed a declining trend. In 2021, China's net polysilicon imports were 103,800 tons, and the apparent consumption was 590,800 tons, up 20% year on year.

The global installed demand for photovoltaics is growing rapidly

According to the purity requirements and different uses, polysilicon can be divided into solar level polysilicon and electronic grade polysilicon. Solar-level polysilicon is mainly used in the production and manufacturing of photovoltaic cells, while electronic-grade polysilicon is widely used in the integrated circuit industry as the raw material for the production of chips. The purity of solar level polysilicon is 6~8N, that is, the total impurity content is required to be less than 10-6, and the purity of polysilicon needs to reach more than 99.9999%. The purity requirement of electronic grade polysilicon is more strict, the minimum is 9N, and the highest is 12N at present. The production of e-grade polysilicon is difficult, and there are fewer enterprises mastering the production technology of e-grade polysilicon in China, which is still more dependent on imports. The current production of solar grade polysilicon is much larger than that of electron grade polysilicon, the former is about 14 times the latter.

As a renewable energy source, photovoltaic has been paid more attention worldwide, and the global photovoltaic installation continues to grow. In 2021, the world's newly installed PV capacity increased by 183GW, up by 38% year-on-year, and China's newly installed PV capacity increased by 11% year-on-year to 54.88GW. According to the China Photovoltaic Association, China will add 90-110GW of photovoltaic installed capacity in 2025, while the world will add 270-330GW of photovoltaic capacity. The continued growth in installation will drive the demand for polysilicon, which in turn will drive the demand for industrial silicon.