Monocrystalline silicon solar cell is currently the fastest developed solar cell. Its structure and production process have been finalized, and its products have been widely used in space and on the ground. This solar cell uses high-purity monocrystalline silicon rods as raw materials. Since monocrystalline silicon solar cells are cut through cylindrical crystal fleece, they are not a complete square shape, which causes some waste of refined silicon materials, so the manufacturing process is more expensive. Therefore, most monocrystalline silicon has gaps in the four corners, which are easy to distinguish in appearance. In order to reduce production costs, solar cells used on the ground now use solar-grade monocrystalline silicon rods, and the material performance indicators have been relaxed. Some can also use the head and tail materials and waste monocrystalline silicon materials processed by semiconductor devices, and make them into monocrystalline silicon rods for solar cells after redrawing.
Monocrystalline silicon solar cells use high-purity monocrystalline silicon rods as raw materials, with a purity requirement of 99.999%. The monocrystalline silicon rods are cut into slices during production, and the thickness of the monocrystalline silicon rods is generally about 0.3mm. The silicon wafers are processed into raw silicon wafers to be processed after polishing, cleaning and other processes. To process solar cells, first doping and diffusion on silicon wafers, generally dopants are trace amounts of boron, phosphorus, brocade, etc. Diffusion is carried out in a high-temperature diffusion furnace made of quartz tubes, so that a PN junction is formed on the silicon wafer. Then using the screen printing method, the finely prepared silver paste is printed on the silicon wafer to make grid lines, after sintering, the back electrode is made at the same time, and the surface with the grid lines is coated with a light reflection reducing material, to prevent a large number of photons from being reflected off the smooth silicon surface. The monocrystalline silicon solar cell produced by the monocrystalline silicon solar cell is subject to random inspection and inspection, and the solar cell module with a certain output voltage and current can be formed by the method of series and parallel connection according to the required specifications. Finally, the frame and sealing material are used for packaging. According to the system design, solar cell components can be formed into various solar cell arrays of different sizes, also known as solar cell arrays. The characteristics of monocrystalline silicon solar cells are as follows:
(1) Abundant reserves of raw silicon. Due to the extremely low density of sunlight, large-area solar cells are practically needed. Therefore, the supply of raw materials is very important. In addition, the Si material itself has an extremely low impact on the environment.
(2) The density of Si is low and the material is light.
(3) Compared with polycrystalline silicon and amorphous silicon solar cells, its conversion efficiency is higher.
(4) The power generation characteristics are extremely stable, and the durability is about 20 years.
(5) In the main area of the solar spectrum, the light absorption coefficient is quite small (1000/cm). In order to enhance the solar spectrum absorption performance, a 100um thick silicon wafer is required.
The current research and development issues for monocrystalline silicon solar cells are toward reducing costs and improving efficiency. The conversion efficiency of monocrystalline silicon solar cells is 15% to 17%, and the conversion efficiency is about 12% to 15% after modularization. The conversion efficiency of a solar cell module is based on the lowest conversion efficiency of the solar cell in the module, rather than the average conversion efficiency of the solar cell.
The most important issue for the practical application of solar cells is to develop solar cells with a high cost performance. In fact, only a thin layer of a few micrometers on the surface of the semiconductor is involved in the photoelectric conversion of solar cells. At present, the most commonly used and most successful preparation technology is to use the vapor deposition method of thermal decomposition of SiH4 gas to deposit a single crystal silicon film on sapphire.
Among the silicon solar cells, monocrystalline silicon solar cells have the highest conversion efficiency and the most mature technology. High-performance monocrystalline silicon cells are based on high-quality monocrystalline silicon materials and related mature production and processing techniques. Now the monocrystalline silicon electrical technology is nearly mature. In the production of solar cells, technologies such as surface texturing, emission zone formation, and zone doping are generally used. The developed monocrystalline silicon cells mainly include planar monocrystalline silicon cells and grooved buried gate electrode monocrystalline silicon cells. The improvement of conversion efficiency is mainly through the use of single crystal silicon surface microstructure treatment and zone doping technology. In this regard, the German Fraunhofer Freiburg Solar Energy System Research Institute maintains the world’s leading level. The institute used photolithography to texture the surface of the battery into an inverted pyramid structure. On the surface, a 13nm thick oxide layer is combined with two anti-reflection coatings, and the ratio of the width to the height of the gate is increased through an improved electroplating process. The maximum conversion efficiency of the monocrystalline silicon cell prepared by the above process can reach 23.3%. The large-area (225cm2) monocrystalline silicon solar cell produced by Kyocera has a conversion efficiency of 19.44%. The Beijing Institute of Solar Energy, China is also actively conducting research and development of high-efficiency crystalline silicon solar cells. The conversion efficiency of planar high-efficiency monocrystalline silicon cells (2cm×2cm) has reached 19.79%, and the conversion efficiency of grooved buried gate electrode crystalline silicon cells (5cm×5cm) has reached 8.6%.