What are the advantages of silicon solar cells? This chapter mainly introduces the advantages of silicon solar cells.
The most basic component of solar photovoltaic power generation is solar cells, and the most used material for making solar cells is silicon. Crystalline silicon is currently the most mature and widely used solar cell material, accounting for more than 85% of the photovoltaic industry, 99% of integrated circuits are made of Si materials, and global Si semiconductor sales account for more than 90%. Sun Power in the United States has recently developed a new technology for manufacturing solar cells, with a photoelectric conversion efficiency of 20%, and the photoelectric conversion efficiency far exceeds the current industrialized monocrystalline silicon solar cells (photoelectric conversion efficiency of 15%) and polysilicon Solar cells (photoelectric conversion efficiency is 12%). However, it should be emphasized that this new technology still uses silicon as the solar cell material.
Silicon is the most ideal material for making solar cells, mainly because in addition to the abundant silicon-containing compounds on the earth, silicon solar cells have these advantages.
① It is easy to increase to extremely pure purity. At present, Si material can be purified to 12 “9”, which is the purest material on earth. This is a very important issue, because the higher the purity of the St material, the higher the power generation efficiency of the produced solar cell material.
②Since the silicon atoms in the silicon crystal only occupy 34% of the space in the crystal lattice (the lattice form is the same as that of diamond, as shown in Figure 1-1), most of the silicon crystal is empty. Because of this, electrons are easy to move in the crystal, and the dopant is easy to exist in the crystal, and it does not affect the lattice integrity of Si, which is conducive to the formation of shallow junctions.
Figure 1-1 Silicon crystal structure (same as diamond)
③There are four electrons outside the nucleus of metallic silicon. After being infiltrated by some foreign impurities, free electrons and holes are easily formed. Under the action of solar energy, it is easy to form P zone and N zone. Controllable doping of Si can reach a wide concentration range.The ionization energy of its main dopants, boron, phosphorus, and antimony, are all small, so that they can be fully ionized at room temperature.
④ It is easier to grow single crystals with large diameter and no dislocation. Now it has successfully produced Si single crystals with a diameter of 400mm, a length of 1100m and a weight of 438kg, and a single crystal with a diameter of 450mm and a weight of 442kg without dislocation. This single crystal is also the largest and most complete single crystal on earth. This not only increases the diameter of the wafer, but also greatly increases the number of chips produced, thereby significantly reducing the cost of single chip production.
⑤It is easy to prepare single crystal Si, polycrystalline Si and amorphous Si thin layer materials through deposition process.
⑥Easy to perform corrosion processing, including wet chemical corrosion or dry corrosion.
⑦The band gap size is “moderate”, under general practical conditions, it will not affect the performance of semiconductor devices due to intrinsic excitation.
⑧Si has quite good mechanical properties: silicon crystals with large diameters can be cut into thin wafers. It also has quite good processing stability, and the processed wafer is not easy to warp. When the heating rate is very fast and relatively high (heating from 25°C to 1000°C in 10s), there will be no greater stress and deformation, and it will not affect the basic properties of the material. Its hardness and yield strength are both high.
⑨Si is a stable material that has stable physical and chemical properties and can resist corrosion in humid air and acid and alkali atmospheres. It is also a non-toxic material (but some toxic substances are used in its processing).
⑩A variety of metals can be doped on Si materials to make low-resistance contact materials, thereby reducing the parasitic resistance of the manufactured devices.
⑪ Cut the Si material into thin slices, even if it is cut very thin, it will not cause major damage to the surface of the Si sheet, and it is easy to controllable passivation.
⑫ A high-quality SiO2 layer prepared on the surface of Si has a simple manufacturing process and low price. This SiO2 layer can reduce the reflectivity of incident light, improve the power generation efficiency of the solar cell, and increase the power output of the solar cell. The SiO2 layer is also a very ideal insulating layer, which is conveniently used for passivation and insulation on the surface of electrical appliances. SiO2 is a good (layer-to-layer) mask material. For impurity diffusion and ion implantation, SiO2 is another good barrier layer.
It is precisely because of the many excellent properties of Si materials that Si materials are used in large-scale solar photovoltaic power generation.