At present, there are two methods of industrialized black silicon velvet technology on the surface of Polycrystalline Solar Cells - wet velvet and dry velvet. (MCCE) technology utilizes the Ag / Ag + system energy in AgNO3 to be much lower than the valence band of silicon, so that Ag + obtains the valence band electrons of silicon, accelerates the reaction with silicon by the H2O2 / HF corrosion process, The system can corrosion in the silicon surface nano-grade suede. Drying black silicon (RIE) technology uses microwave to plasma SF6, O2, Cl2 three kinds of gas, in the electric field acceleration on the surface of the wafer bombardment, while the chemical reaction, in the silicon surface corrosion of nano-surface suede.
In increasing the efficiency of photoelectric conversion of solar cells, more and more people began to pay attention to polycrystalline ingots. This paper analyzes and contrasts the different aspects of polycrystalline ingot ingot furnace structure itself, optimization of ingot process and auxiliary materials, and puts forward the method to improve the efficiency of solar cells.
In 2012, China's photovoltaic industry due to the global economic recession, PV overcapacity, price decline, the United States "double reverse", the European "anti-dumping" and other factors into the winter, PV downstream business gross margin dropped significantly, most companies are facing serious losses. Domestic Polycrystalline Solar Cells production in the first half of 2013 compared with last year there is a significant decline in the first half of 2013 domestic Polycrystalline Solar Cells production of 28,000 tons, down 23.6%. Affected by the supply and demand and international trade and other factors, in 2012 the vast majority of China's Polycrystalline Solar Cells enterprises have been discontinued. Due to the downstream supply and demand situation has not been a substantial change, coupled with the main Polycrystalline Solar Cells production costs are still declining, Polycrystalline Solar Cells business in 2013 is still not optimistic about the operating situation, the Polycrystalline Solar Cells industry will remain low in the operation, industry consolidation is also expected to bottom industry Pick up is expected to go to 2014. Polystyrene bleak industry scene and did not cut people's satisfaction with the price of solar energy, it is because of the demand for solar energy market, people on the solar components of the power requirements are getting higher and higher, more began to focus on the efficiency of solar cells.
In order to improve the efficiency of solar cell photoelectric conversion, the PV industry has recently launched a highly efficient polycrystalline ingot technology. The use of ordinary battery chip production process, high efficiency Polycrystalline Solar Cells chip can achieve more than 17.3% conversion efficiency, and now up to about 18%. The key to efficient polycrystalline ingot technology is to reduce dislocations and other defects in the crystal. The industry estimates that at least ten more ways to produce efficient polycrystalline, such as the use of single crystal fragments or polycrystalline fragments as seed crystals, the use of special crucible or thermal field and so on.
The ingot furnace is a device that directly crystallizes the silicon material at high temperature and is crystallized by directional cooling to form a silicon ingot. After the silicon material is completely melted by heating, the heat released from the crystallization of the silicon material through the directional solidification block is radiated to the inner wall of the lower chamber so that a vertical temperature gradient is formed in the silicon material. This temperature gradient causes the silicon liquid in the crucible to solidify from the bottom and grow from the bottom of the melt to the top. After the silicon material is solidified, the ingot is annealed and cooled. The optimization of the structure plays an important role in the efficiency of the ingot ingot.
Polycrystalline silicon ingot furnace heater requirements: heating more than 1650 ℃; use of materials can not react with the silicon material; can be used in vacuum and inert gas for a long time. For the heater material, the current industry mainly use high-purity graphite as a heating material, the main use of a single power supply to the graphite heater heating.
The use of dual-power heater to bring the benefits: to improve the grain structure of the ingot silicon block; increase the size of the grain while reducing the grain boundary; to improve the crystal plane, you can flexibly control the shape of long crystal interface, To solve the late growth of silicon ingot too slow the problem