The Institute of Physics has developed a new process for industrialized crystalline silicon inverted pyramids

Thanks to the substantial reduction in the cost of crystalline silicon raw materials and the effect of scale, crystalline silicon solar cells are the products that dominate the photovoltaic industry at present, and will maintain this situation for a long time to come. The surface of silicon wafers is the first process for manufacturing crystalline silicon cells. Also known as “surface texturing”, it is a core part of battery manufacturing. A good suede structure can not only reduce the solar reflectance, increase the absorption of light, but also can improve the characteristics of surface passivation and electrode contact, and thus improve the collection efficiency of carriers. Therefore, the innovative research of the texturing process has been crystal The focus of silicon solar cells.

In the current manufacturing process, the general texturing process of single crystal or quasi-monocrystalline silicon wafer adopts lye pyramid etching method, a random pyramid structure is formed on the surface of silicon, and the solar light can be reflected twice, and the general reflectance is 10%. about. The inverted pyramid structure of the pit is a more ideal suede, because the sun will experience three reflections on the inverse pyramidal suede, absorb more than the pyramid suede once, the reflectivity can be reduced to about 5%, which increases Battery efficiency, therefore, the low-cost and industrialized inverted pyramid technology has become a research and development hotspot. In the past 20 years, researchers have tried many solutions, but today there is still no major progress and it has become a recognized international problem.

Researcher of the Clean Energy Laboratory of the Institute of Physics, Chinese Academy of Sciences Researcher Du Xiaolong After more than five years of research, he has finally made significant progress in the use of nano-metal particle catalyzed chemical etching on the crystalline silicon inverted pyramid pile. Liu Yiping, Mei Zengxia, Wang Yan, Yang Lixia, Liang Huili, Du Xiaolong, etc. skillfully used the anisotropic deposition properties of copper nanoparticles on the surface of single crystal silicon to achieve copper-catalyzed anisotropic etching in acid solutions. A dense uniform inverted pyramidal suede over a large area (Figure 1).

The prepared 156 x 156 mm2 industrial monocrystalline silicon inverted pyramidal pile sheet has characteristics such as large area uniformity and adjustable inverted pyramid size. The reflectance is about 5%, and its excellent light trapping performance has been verified (Figure 2). ). The new process uses inexpensive copper compounds and acid solutions as raw materials for copper catalysts and etching solutions, while its texturing temperature is only 50°C, which is 30°C lower than the temperature of conventional pyramidal texturing, and the etching time It also shortened from 30 minutes to about 10 minutes, which greatly reduced the energy consumption of the velvet, the cost of the etching solution, and the time cost. Due to its compatibility with existing production lines, this original inverted pyramid technology is expected to become a new type of universal texturing process that can be applied to large-scale manufacturing of various monocrystalline silicon solar cells. Related pyramid pyramiding technology has applied for two patents, one of which has been authorized and the other has entered the PCT international patent (US, Japan, Europe, India, etc.) stage.

The research on the mechanism of the inverted pyramid pyramiding without template method was published recently [Scientific Reports 5 (2015) 10843]. The team further developed the inverted-pyramid crystal silicon solar cell. The photoelectric conversion efficiency of the cell has been higher than that of a conventional pyramid cellulosic cell. The bottom of the inverted pyramid is smooth, which helps the silver electrode cover the suede evenly, and the contact resistance has decreased significantly. This shows the advantages of the inverted pyramidal suede in both the light absorption and the carrier collection. These efforts have laid a solid foundation for the development of a major industrial application of basic inverted pyramid wool weaving.

The team also achieved a number of achievements in the polysilicon/single-crystal silicon nanotufting. The metal silver granule catalytic chemical etching method was used to develop a large-area uniform multi-crystalline silicon wafer nano-tufting process in an acidic etching solution. The rate is as low as 2%, showing the typical black silicon morphology [Small 8 (2012) 1392]. At the same time, the first step is to develop a low-temperature ozone passivation process of silicon nanostructures, and in combination with a selective emitter process, selective nanometers are prepared. Emitter black silicon solar cells have achieved a significant increase in the efficiency of polycrystalline silicon silicon cells [RSC Advances 3 (2013) 15483; 4 (2014) 24458], and have obtained a more complete black silicon battery patented technology system. As the cutting process of the silicon wafer is gradually transitioning from the steel wire to the diamond wire, the surface of the silicon wafer obtained through the diamond wire cutting process is smooth, the pile point is reduced, and the traditional process cannot realize high-performance texturing on the polysilicon, and the metal-catalyzed chemical etching The process is not affected by the surface morphology of the silicon wafer and is therefore expected to become a new process for the sizing of the polysilicon battery industry.

The above work was done in collaboration with the team of Zhang Fengming, a member of the Nanjing Daycare Photovoltaic Company, Wang Wenjing, a research fellow of the Institute of Electrical Engineering of the Chinese Academy of Sciences, and Professor Kuznetsov Andrei of the University of Oslo, Norway. The above work was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.

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