Crystalline silicon solar cells are divided into monocrystalline silicon solar cells and polycrystalline silicon solar cells.
(1) Monocrystalline silicon solar cells
This is the solar cell with the highest conversion efficiency and the most mature technology among solar cells. This is because the monocrystalline silicon material and its related processing technology are mature and stable, the monocrystalline silicon structure is uniform, the content of impurities and defects is small, and the conversion efficiency of the battery is high. In order to produce low contact resistance, the surface area of the battery requires heavy doping, and high impurity concentration will enhance the recombination rate of minority carriers in this area, making the minority carrier life of this layer extremely low, so it is called the “dead layer” . And this area is the strongest light absorption area. Violet light and blue light are mainly absorbed here. Usually, the thickness of the N+ layer of the solar cell is reduced to 0.1~0.2μm, that is, the “shallow junction” technology is used, and the surface phosphorous The concentration is controlled below the limit value of solid solubility. The solar cell made in this way can overcome the influence of the “dead layer” and improve the blue-violet light response and conversion efficiency of the battery. This kind of battery is called a “purple battery.” In addition, a concentration gradient of the same impurity is established between the battery substrate and the bottom electrode to prepare a P-P+ or N-N+ high-low junction to form a back electric field, which can improve the effective collection of carriers and improve the long-wave response of the solar cell. Improve short-circuit current and open-circuit voltage, this kind of battery is called “back field battery”. In the 1980s, the Green team developed the “slotted battery” with the above technologies. The battery uses laser groove technology to carry out secondary heavy doping. Compared with the printing method, this method increases the battery efficiency by 10% to 15%. Later, surface passivation technology was developed, from thin oxide layer (<10nm) of PESC battery to PERC, thick oxide layer (about 110nm) of PERL battery, thermal oxidation surface passivation technology can reduce the surface state density to 1010/cm2 Below, the surface recombination velocity drops below 100cm/s. The use of various technologies has increased the conversion efficiency of monocrystalline silicon cells to 24.7%. According to experts’ predictions, the limit efficiency of monocrystalline silicon cells is 29%. In order to reduce the cost of the battery, while improving the conversion efficiency, people are currently exploring ways to reduce the thickness of the battery, that is, to achieve thin slices.
(2) Polycrystalline silicon solar cells
Generally, polysilicon materials specially produced for solar cells are used. The most widely used polysilicon manufacturing method is the casting method, also known as the casting method. Polycrystalline silicon solar cells generally use low-grade semiconductor polycrystalline silicon, and most of the polycrystalline silicon wafers used are cut from controlled or cast crystalline silicon ingots. Polycrystalline silicon ingots are made by melting and casting inferior silicon, waste single crystals and metallurgical grade silicon powder in the semiconductor industry as raw materials. At present, with the explosive development of solar cell output, the above-mentioned raw materials can no longer meet the needs of the solar cell industry, and a production industry specifically targeting polysilicon solar cells is now being formed.
In order to reduce the loss during the cutting of silicon wafers, the polycrystalline silicon wafers required for solar cells are prepared directly from molten silicon. The batteries prepared by this method are generally referred to as cells with silicon. There are two ways to prepare silicon with silicon: one is called EFG “Fixed Edge Feeding Method”, in industrial applications, a polysilicon tube with eight sides is long, and each side is cut into silicon wafers; the other is called “phosphorus “Crystalization method”, Evergreen Solar uses this method. The method uses thin carbon rods to confine the molten silicon and pull it out of the molten pool. The silicon liquid confined in the two thin rods is cooled and solidified to form strip silicon. Compared with monocrystalline silicon solar cells, polycrystalline silicon solar cells have lower cost, and the conversion efficiency is relatively close to that of monocrystalline silicon solar cells. Therefore, in recent years, the development of polycrystalline silicon high-efficiency cells has been rapid. Among them, the most representative cell is Geogia Tech. Battery, UNSW battery, Kyocera battery, etc. Among the solar cells produced in recent years, polycrystalline silicon solar cells accounted for 52% more than monocrystalline silicon solar cells, and they are one of the main products of solar cells. However, compared with the existing energy prices, because the cost of power generation is still too high, crystalline silicon solar cells cannot be widely commercialized.
We know the types of crystalline silicon solar cells through the above articles, so we will introduce the types of thin film solar cells in the next article, so stay tuned.