What is the production process of silicon ingots for Polycrystalline Solar Cells?

Polycrystalline silicon solar cells are the most widely used type of photovoltaic technology at present. Its core material is polycrystalline silicon, and the production process of polycrystalline silicon is an important link in the entire battery manufacturing chain. The following will introduce the production process of polycrystalline silicon ingots in detail, including key steps such as raw material selection, melting, cooling and crystal formation.

1. Selection of raw materials
The first step in producing polycrystalline silicon ingots is to select high-purity silicon raw materials. Usually, industrial silicon (Si) is purified to remove impurities to achieve a purity of 99.9999% (six nines). In order to obtain such high purity, advanced purification technologies such as chemical vapor deposition (CVD) are usually required. The selection of high-purity silicon raw materials is the basis for ensuring the performance of subsequent polycrystalline silicon cells, because impurities will affect the photoelectric conversion efficiency and service life of the cell.

2. Melting process
After obtaining high-purity silicon raw materials, the next step is melting. Melting is usually carried out in a high-temperature furnace with a temperature of up to 1400°C. This process requires high energy consumption, so choosing an efficient electric furnace is key. During the melting process, the crystal structure of silicon is broken and it becomes liquid silicon. The melting process must ensure uniform temperature to prevent bubbles or other defects.

3. Cooling and solidification
The melted liquid silicon needs to be gradually cooled so that it can recrystallize to form polycrystalline silicon. The speed and temperature of cooling are critical because they affect the crystal structure and quality of the final silicon ingot. During the cooling process, the liquid silicon will begin to solidify to form a preliminary polycrystalline silicon ingot. This stage is usually carried out in a special cooling device to ensure uniform cooling.

4. Crystal formation
During the cooling process, silicon atoms will rearrange to form multiple crystals instead of a single crystal structure. The formation process of polycrystalline silicon ingots involves crystal seeding and growth. During the cooling process, small crystal particles will first form in some areas, and these particles will continue to grow as the temperature decreases, eventually forming a complete polycrystalline silicon ingot. Reasonable cooling rate and time can optimize the size and distribution of crystals, thereby improving the performance of polycrystalline silicon.

5. Cutting and processing of silicon ingots
After the polycrystalline silicon ingot cools to room temperature, it needs to be cut into thin slices for use in the manufacture of solar cells. This process usually uses a high-precision wire cutting machine to ensure that the thickness of the cut silicon wafer is between 180-200 microns. Careful operation is required during the cutting process to avoid material waste and damage to the sheet.

6. Quality Inspection
In the production process of silicon ingots, quality control is crucial. Each production link will be strictly tested to ensure that the purity, crystal structure and physical properties of the silicon ingots meet the standards. Usually, spectral analysis, microscopic observation and other methods are used to conduct a comprehensive inspection of the silicon ingot to ensure that it can show good performance in subsequent battery manufacturing.