1    What is polycrystalline silicon?

The production process of polycrystalline silicon is relatively simple and cost-effective, making it suitable for large-scale production. This gives polycrystalline silicon photovoltaic cells a price advantage in the market.

The production of polycrystalline silicon usually starts with metallurgical grade silicon (MG Si), which first needs to be purified to remove impurities from the silicon and produce high-purity silicon raw materials. The commonly used method is the Siemens process, which obtains high-purity polycrystalline silicon through chemical vapor deposition (CVD). 

Metallurgical grade silicon reacts with hydrogen chloride to produce trichlorosilane (HSiCl₃), which is then purified by distillation. Finally, trichlorosilane is reduced at high temperature to produce high-purity polycrystalline silicon.

Metallurgical grade silicon reacts with hydrogen chloride (HCl) to produce trichlorosilane (HSiCl₃) and other by-products. Si+3HCL→HSiCl₃+H₂

Based on the test results, polycrystalline silicon wafers are graded according to quality and performance to ensure that high-quality silicon wafers are used for efficient photovoltaic cell manufacturing.

2    What is monocrystalline silicon

Monocrystalline silicon is a high-purity silicon material composed of a single crystal structure. The atomic arrangement of single crystal silicon is orderly, the crystal structure is complete, and it has excellent electrical properties and mechanical strength. Monocrystalline silicon photovoltaic cells are currently one of the most efficient photovoltaic cells on the market, with high photoelectric conversion efficiency and suitable for various photovoltaic power generation systems. Can be used as the main material for manufacturing semiconductor devices such as integrated circuits (ICs), microprocessors, memories, sensors, etc. In addition, high-purity monocrystalline silicon wafers (wafers) are cut, doped, etched, and packaged to produce various electronic components and chips. Monocrystalline silicon is also used to manufacture optical lenses, infrared windows, laser devices, and more.

1. Raw material preparation: The raw material for monocrystalline silicon is high-purity silicon, usually using purified metallurgical grade silicon.

2. Production method:

Melt high-purity silicon in a crucible, insert a single crystal silicon seed crystal with the desired crystal orientation, then slowly rotate and pull the seed crystal to allow the silicon melt to crystallize on the seed crystal, gradually forming a single crystal silicon rod.

CZ method can produce large-diameter and high-purity monocrystalline silicon rods, but it is prone to introducing oxygen and other impurities.

Use high-frequency induction heating to melt a local area of the silicon rod without a crucible, and then move the melting zone on the silicon rod by moving the induction coil, gradually transforming polycrystalline silicon into monocrystalline silicon.

Single crystal silicon produced by FZ method has higher purity and lower impurity content, making it suitable for manufacturing high-performance semiconductor devices.

3. Cutting and processing

3    The difference between monocrystalline silicon and polycrystalline silicon

The main differences between monocrystalline silicon and polycrystalline silicon lie in their structure, properties, and applications. Monocrystalline silicon is composed of a single crystal structure, with ordered atomic arrangement and high photoelectric conversion efficiency (18% -24%). It has superior electrical properties and is suitable for high-performance photovoltaic cells and semiconductor devices, but the production cost is relatively high. Polycrystalline silicon is composed of multiple grains with grain boundaries, resulting in low photoelectric conversion efficiency (15% -20%) and poor electrical properties. It is mainly used for large-scale photovoltaic applications with low production costs. Monocrystalline silicon has a uniform appearance and good aesthetics, while polycrystalline silicon has an uneven appearance.