Study Of Light Trapping Structure And Milling Forming On The Photovoltaic Crystal Silicon Surface

Solar energy is a kind of clean and sustainable energy.Making full use of solar energy is an effective way to solve the energy crisis and to ensure the sustainable development of modern industry.Solar photovoltaic technology is an important technical means to convert solar energy into electrical energy.However,the low efficiency of photovoltaic conversion is the technical bottleneck of the technology.Photovoltaic crystal silicon solar cell makes use of the crystal structure of the surface of the silicon wafer to make the multiple light reflection,thereby reducing the reflection loss of light and improving the utilization rate of light energy.Therefore,the surface morphology of crystalline silicon is very important to the photoelectric conversion.In this paper,the pyramidal texture was used as the light trapping structure of the silicon crystal surface.Considering the influence of the forming process,the optimized structural parameters were calculated.Based on the analysis of the removal mechanism of silicon crystal materials,the simulation of the mechanical forming of pyramidal texture mechanics was analyzed.The experimental study of micro-milling process of pyramidal texture was carried out.The research work is valuable for the research of surface texturing technology of solar photovoltaic crystal silicon.The main work of this paper is as follows:(1)Based on ray tracing method,a calculation method of weighted optical reflectance on the surface of silicon crystal was proposed.The effect of structural parameters on the light trapping efficiency was calculated and analyzed.The optimized parameters of the pyramidal texture were proposed,and the best incident angle was obtained.The calculation method was verified by calculating the weighted reflectance of typical pyramidal texture with alkali corrosion.Each light transmission process was tracked and the weighted reflectance was calculated numerically.Pyramid base angle size,structural height,fillet radius as the main structural parameter,the effect of structural parameters of pyramidal texture on the weighted optical reflectance and the trapping effect was analyzed.The optimized parameters of the pyramidal texture and the best incident angle were proposed.The structural height has little effect on the optical reflectance,the light trapping efficiency increased as the base angle size increased,and decreased greater as the fillet radius increased.The light trapping efficiency of the structure can reach the best level of receiving the vertical incident light.(2)The finite element model of the micro milling process was established.2D simulation and 3D simulation of the process were carried out.The effects of process parameters on the cutting force and material removal mode were studied.2D simulation results showed that the brittle ductile transition thickness of monocrystalline silicon is about 120nm.The cutting force increased with the increase of feed rate.The spindle speed and the milling depth have little influence on the cutting force.3D simulation results showed that the monocrystalline silicon can be ductile removed under certain process parameters.(3)The fabrication process of the V-grooves and the pyramidal structure on the surface of the photovoltaic crystal silicon with cemented carbide micro-milling tool was studied.V-grooves and pyramidal structure with different depth were prepared by a micro-milling tool on a 5-Axis high speeds ultra-precision machining center.The quality of completed structures was measured and analysed.Research showed that the effects of different milling depth on the machining quality are very small.The collapse on the pyramidal structure and tool damage was serious.