More and more people are focusing on polycrystalline ingots in improving the photoelectric conversion efficiency of Polycrystalline Solar Cells. In this paper, the method of improving the efficiency of the solar cell is proposed by analyzing and comparing the structure of the ingot furnace, the optimization of the ingot process and the auxiliary materials.
2012, China's photovoltaic industry due to global economic recession, photovoltaic overcapacity, price decline, the United States "double counter", Europe "anti-dumping" and other factors into the winter period, photovoltaic downstream enterprise gross profit margin fell sharply, most enterprises face serious losses. In the first half of 2013, the domestic polysilicon production was significantly lower than last year, and the domestic polysilicon production in the first half of 2013 was 28,000 tons, down 23.6%. By the relationship between supply and demand and international trade and other factors, the 2012 most of China's polysilicon enterprises have been discontinued. As the downstream supply and demand situation does not have a substantial change, coupled with the main production costs of polysilicon enterprises are still declining, 2013 polysilicon business status is still not optimistic, the polysilicon industry will remain low operation, industry integration is expected to see the bottom of the industry is expected to rebound to 2014 years. Polysilicon's dismal industry landscape does not cut the level of satisfaction with the price of solar energy, which is due to oversupply of solar energy market, the power of the solar modules are increasingly demanding, more attention to solar cell efficiency.
In order to improve the photoelectric conversion efficiency of Polycrystalline Solar Cells, more efficient polycrystalline ingot technology has been introduced in photovoltaic industry recently. Using the common cell production process, high efficiency polysilicon chips can achieve more than 17.3% conversion efficiency, now up to about 18%. The key of high efficiency polycrystalline ingot technology is to reduce dislocation and other defects in crystals. The industry estimates that there are at least 10 ways to make efficient polycrystalline, such as using single crystal fragments or polycrystalline fragments as seed grains, using special crucibles or heat fields, and so on.
The ingot furnace is a device which directly melts the silicon material into a continuous silicon ingot through the directional cooling and condensing crystallization after high-temperature melting. When the silicon material is completely melted by heating, the heat emitted by the directional solidification block will be radiated to the inner wall of the lower furnace cavity, 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 is solidified, the silicon ingot is annealed and cooled. The optimization of structure plays an important role in improving the efficiency of ingot silicon ingot.
Polysilicon ingot Furnace Heater requirements: heating more than 1650 ℃, the use of materials can not react with the silicon material, can be used in the vacuum and inert gas medium and long term. For the material of the heater, the main use of high purity graphite as heating material, the main use of single power supply to the graphite heater heating.
Benefits of using dual power heaters: Improving the crystal structure of ingot silicon, increasing grain volume and decreasing grain boundary, improving crystallization plane, controlling the shape of long crystal interface flexibly, longer crystal speed, and solving the problem of slow speed in the late growth of silicon ingot.
At present, there are two methods for the industrialization of polycrystalline silicon wafer surface: wet-process velvet and dry-pulping. Wet black Silicon (MCCE) technology utilizes AgNO3 ag/ag+ system energy far lower than the silicon valence band, so that + get silicon valence band electrons, using the h2o2/hf corrosion process around Ag to accelerate and silicon reaction, so that the corrosion system can corrode on the wafer surface of the cashier meter-level velvet surface. Dry black Silicon (RIE) technology uses microwave to SF6, O2, Cl2 three kinds of gases, such as ionization, under the accelerated electric field to bombard the surface of the silicon wafer, at the same time, chemical reaction, on the surface of the wafer corrosion cashier meter-level velvet surface.