On September 5, the 2019 China International Photovoltaic Technology Forum (CITPV) was held in Hangzhou. Yang Deren, academician of the Chinese Academy of Sciences and professor of Zhejiang University, said in his speech that ingot crystalline silicon is the main battery material for solar energy. After increasing the single crystal rate and reducing the cost of seed crystals, it will bring important breakthroughs to the industry.
Yang Deren pointed out that Czochralski single crystals have high efficiency and complete crystal lattice and good quality, but at the same time, due to high energy consumption, the corresponding cost is relatively high. Judging from the current technology status, the Czochralski single crystal mainly uses the repeated crystal pulling technology, which is to pull out the crystal after the growth is completed. "The water cooling jacket technology we use can shorten the growth time by increasing the cooling rate and greatly increase the growth time. The length of the crystal grows to reduce the cost. At present, it can achieve 3-4 meters and grow about 4-6. "
However, optical attenuation is a major challenge that Czochralski has not yet overcome. The core reason lies in the SiCI crucible used for crystal growth. "To fundamentally solve this problem requires reducing the oxygen content. The current research direction has two main points. One is to add a high-level silica or other coating to the existing SiCI crucible. To make it difficult for oxygen to enter the silicon ridge; the second is to make a high-purity silicon carbide SiCI crucible. "
The honeycomb silicon wafer is a new technology that is currently popular in the international market. Yang Deren introduced that by cutting monocrystalline silicon wafers into hexagons, the utilization rate of monocrystalline finished rods can be increased by 19%, the non-silicon cost of monocrystalline silicon wafers can be reduced by more than 10%, and can be compatible with various high-efficiency battery technologies such as PERC.
The ingot single crystal is a new technology after combining the advantages of straight pulling and casting, but Yang Deren said that in the actual production process, the ingot single crystal will still encounter some problems, "The first is the cost of adding new seed crystals. The second is the single crystal rate, the third is the high-density dislocation, and the fourth is the utilization rate of the materials. These problems are all problems that need to be overcome and solved in the process of putting into the industry. We propose a method for grain boundary engineering. "
For the problem of high-density misalignment, Yang Deren proposed a solution for grain boundary engineering. "Grain boundary engineering can suppress its dislocations. According to our experiment last year, when selecting the crystal plane of ∑13a, we can see that the entire grain boundary from the bottom to the top is very clear. The absolute value of the average efficiency of the silicon ingot preparation battery has increased. 0.59%, the efficiency difference between the casting single crystal in the central area and the Czochralski single crystal is 0.05%, reaching the level of Czochralski single crystal. "
"In the foreseeable future, silicon will be the main basic material of the photovoltaic industry. The oxygen concentration reduction and light attenuation suppression of Czochralski single crystals are expected to be better resolved. The single crystal rate, dislocation, and seed crystal problems of the cast single crystal technology remain To be broken. "
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