The spectrum of solar radiation is mainly centered on visible light, and its main distribution range is 0.3 ultraviolet to several microns of infrared. If converted into the energy of photon, it is 0.4~4eV. When the energy of the photon is less than the energy gap of the semiconductor, the photon is not absorbed by the semiconductor, and the semiconductor is transparent to the photon. When the energy of the photon is greater than the energy gap of the semiconductor, the energy equivalent to the energy gap of the semiconductor will be absorbed by the semiconductor to generate electron-hole pairs, while the rest of the energy is consumed in the form of heat. Therefore, the energy gap of solar cell materials must be carefully selected to efficiently generate electron-hole pairs. In general, ideal solar cell materials must have the following properties:
(1) The energy gap is 1.1~1.7 eV.
(2) Direct energy gap semiconductors.
(3) The composition of the material is non-toxic.
(4) The technology of thin film deposition can be used, and it can be manufactured in a large area.
(5) Good photoelectric conversion efficiency.
(6) It has long-term stability.
The energy gap of silicon is 1.12 eV. And silicon is an indirect energy gap semiconductor, it does not absorb light well, so silicon is not the most ideal material in this regard; but on the other hand, silicon is in the earth’s crust The second most abundant element, and silicon itself is non-toxic, its oxide is stable and not water-soluble. Therefore, the development of silicon in the semiconductor industry has a solid foundation, and currently solar cells still use silicon as the main material.
There are three types of silicon solar cells: monocrystalline silicon, polycrystalline silicon, and amorphous silicon. The appearance is shown in Figure 1, and most of the current market applications are monocrystalline silicon and polycrystalline silicon. The reasons are: ① the highest efficiency of single crystal; ② more Crystal technology tends to mature, the price is cheaper. The efficiency is close to that of single crystal silicon; ③ Amorphous has the lowest efficiency and can only be applied to low-end products, and the above two are easier to recut and process. The characteristics of various classes are compared in Table 1.
|Monocrystalline silicon||24||High conversion efficiency|
Long service life
|Higher production cost|
Long manufacturing time
|Polysilicon||18.6||Simple steps to make|
|Lower efficiency than monocrystalline silicon|
|Reduced output power after outdoor setup|
(1) Monocrystalline silicon solar cells.
Monocrystalline silicon cells are the most common. It is mostly used in power plants, charging systems, road lighting systems and traffic signs, etc. It generates a wide range of power and voltage, has high conversion efficiency, and has a long service life. The world’s major manufacturers, such as Germany’s Siemens, BP and Japan’s Sharp, are all The production of such monocrystalline silicon solar cells is the main one, and the market share is about 50%. The efficiency of monocrystalline silicon cells ranges from 11% to 24%. Of course, the higher the efficiency, the more expensive the price.
(2) Polycrystalline silicon solar cells.
The efficiency of polycrystalline silicon cells is lower than that of monocrystalline silicon, but because of its simpler fabrication steps and lower cost, which is 20% cheaper than monocrystalline silicon cells, some low-power power application systems use polycrystalline silicon solar cells.
(3) Amorphous silicon solar cells.
Amorphous silicon power is also the commercial solar cell with the lowest cost at present, and it does not require packaging, and the production is also the fastest. There are many types of products, which are widely used, and are mostly used in consumer electronic products, and new application products are constantly being developed.