In June 2015, the three ministries and commissions of the National Energy Administration, the Ministry of Industry and Information Technology and the Certification and Accreditation Administration jointly issued the “Opinions on Promoting the Application and Industrial Upgrade of Photovoltaic Technology Products†(Guoneng Xinneng [2015] No. 194). It is clear that the country will pass the “leadership. "The plan" supports the application of advanced photovoltaic technology products such as highly efficient batteries; On November 17, 2015, the Ministry of Industry and Information Technology released the "Guidelines for the Development of Common Key Technologies for Industries (2015)", and "High-efficiency Battery Production Technology" was identified as one of the priority development industrial technologies. What is "efficient battery production technology"? How do these technologies improve the photoelectric conversion efficiency? Which companies have mastered these technologies? What are the current status and prospects of industrialization of these technologies? Solar cell conversion efficiency The conversion efficiency of a solar cell is the ratio of the output electrical power of the cell to the incident optical power. Although sunlight contains a wide continuous spectral range, no matter which kind of solar cell, it can only absorb certain wavelengths of sunlight, so the solar cell can not convert all the sunlight that hits the surface of the cell into current. The maximum conversion efficiency of a battery cannot reach 100%. In fact, because of the extra loss, the efficiency of solar cells is very low. Only by understanding and minimizing the losses can we develop solar cells with high enough efficiency. For a monocrystalline silicon-silicon solar cell, the theoretical maximum conversion efficiency is 28%. At present, the efficiency of single-crystal silicon solar cells manufactured under the best conditions in the laboratory can reach 25%, and the efficiency of monocrystalline silicon solar cells mass-produced in the industry has reached over 19%, while the production efficiency of polycrystalline silicon solar cells is About 18%. Influence Factors of Photoelectric Conversion Efficiency of Crystalline Silicon Solar Cells For a crystalline silicon solar cell, only light with a wavelength of less than 1.1 μm can generate electron-hole pairs for the crystalline silicon material, and the rest of the solar light can not be utilized by the battery and is directly converted into heat. In addition, the recombination of electron-hole pairs, light reflection on the surface of silicon, etc. all affect the conversion efficiency of the battery. Overall, the factors that influence the conversion efficiency of crystalline silicon solar cells can be summarized into two broad categories: optical losses and electrical losses. (1) Optical loss, including non-absorption loss of the material (ie, spectral response characteristics of the silicon material), light reflection loss on the silicon surface, and shading loss of the front gate line electrode. (2) Electrical losses, including the composite loss of photogenerated carriers (electron-hole pairs) on the semiconductor surface and in the body, and the ohmic loss of semiconductors in contact with metal electrodes. The ohmic contact loss in optical loss and electrical loss is very easy to understand, but what is the composite loss of photo-generated carriers? The combination of photogenerated carriers is mainly due to the introduction of a large number of recombination centers on the front surface of the cell due to the high concentration of the diffusion layer. In addition, the back surface of the cell when the diffusion length of minority carriers is equal to or exceeds the thickness of the silicon wafer. The effect of the composite speed on the characteristics of solar cells is also obvious. Method for improving photoelectric conversion efficiency of crystalline silicon solar cells To reduce the various losses to improve ideas, improve the conversion efficiency of crystalline silicon solar cells are mainly the following methods: 1. Make a light trap structure. The light reflection loss on the silicon surface accounts for a significant proportion of the loss ratio. In order to reduce the light reflection loss, chemical etching method is usually used to produce a textured structure on the surface of the battery, which can reduce the reflectivity of the battery surface to less than 10%. The current advanced texturing technology is reactive plasma etching (RIE). In addition, an inverted pyramid trap structure can also be fabricated by means of photolithography. Although this method can reduce the optical reflectance more effectively, the cost is higher than that of chemical etching, and therefore it is not suitable for large-scale use in production. 2, the production of anti-reflection film. A layer of a film with a certain refractive index is formed on the surface of the crystalline silicon, so that the levels of reflection generated by the incident light interfere or even completely cancel each other out. The anti-reflective film can not only reduce the light reflection loss, but also increase the current density of the battery and protect the battery and improve the stability of the battery. Currently, single-layer or double-layer anti-reflection films are generally fabricated on crystalline silicon solar cells using materials such as TiO2, SiO2, SnO2, ZnS, and MgF2. 3, the production of passivation layer. By making the passivation layer, the complex behavior of carriers in some high recombination areas (such as the surface of the battery, the contact surface of the battery surface with the metal electrode) can be prevented, thereby improving the conversion efficiency of the battery. Thermal oxygen passivation, atomic hydrogen passivation, or the use of phosphorus, boron, or aluminum for diffusion passivation on the surface of the battery is generally used. Thermal oxygen passivation is the formation of silicon oxide film on the front and back of the battery, which can effectively prevent the recombination of carriers at the surface. Atomic hydrogen deactivation is due to the large number of dangling bonds on the surface of silicon. These dangling bonds are current-carrying. The effective recombination center of the child, while atomic hydrogen can neutralize dangling bonds, thus weakening the recombination. 4, increase the back field. The back field can be fabricated on a crystalline silicon cell by a process of sintering with a sintered aluminum vapor, a concentrated boron, or a concentrated phosphorus diffusion process. For example, in a P-type material battery, a P+ thick doping layer is added on the back surface to form a P+/P structure, and a built-in electric field from the P area to the P+ is generated at the P+/P interface, which can not only establish a The built-in electric field with the same polarity as the photovoltaic voltage improves the open circuit voltage of the battery, increases the diffusion length of the photo-generated carriers, increases the short-circuit current of the battery, reduces the recombination rate of the back surface of the battery, and improves the conversion efficiency of the battery. 5, improve the substrate material. Using high-purity silicon materials can reduce photo-carrier recombination caused by defects in the crystal structure. For example, the use of n-type silicon materials with long carrier lifetimes, low boron-oxygen reaction after the formation of junctions, good electrical conductivity, and low saturation current makes high-efficiency cells. Current high-efficiency crystalline silicon cell production technology Based on the above processes for improving the conversion efficiency of crystalline silicon solar cells, the currently widely used highly efficient crystalline silicon solar cell technologies in the industry include: PERC battery technology, N-type battery technology, IBC battery technology, MWT battery technology, HIT battery Technology and so on. "High-efficiency battery production technology" Main technical content: Development of high-efficiency battery production technology with battery efficiency above 22%, including key back-field passivation (PERC) batteries, metal perforated winding (MWT) batteries, N-type batteries, and heterojunctions Battery (HIT), back-contact battery (IBC) battery, laminated battery, double-sided battery, etc., and achieve industrial production. Fire Elevator,Fireman Elevator,Fireproof Elevator,Fire Service Elevator Homefriend&FUJI Elevator Co.,Ltd , https://www.jfujilift.com
Loss of conversion efficiency of crystalline silicon solar cells 
Inverted pyramid trap structure