| In the context of the global energy crisis,photovoltaic solar cells are playing an increasingly important role in the global energy industry,especially the new energy industry.Silicon-based solar cells are the most widely used,and polycrystalline silicon cells have developed rapidly due to their simple preparation and low production costs.Sawing silicon brick into silicon wafer by diamond wire sawing technology is the first process of producing silicon-based solar cell substrate.The brittle removal of materials in the sawing process will leave microcracks on the surface and subsurface of silicon wafer.Microcracks will expand and interfere with each other under the action of stress,which will reduce the fracture strength of silicon wafer and lead to breakage,even produce macro-cracks to crack the silicon brick.In order to save costs and improve productivity,silicon wafers tend to be large-size and thin,which makes the problems of silicon wafer breakage and silicon brick cracking more prominent.Taking multi-crystalline silicon as the research object,this thesis explores the clamping stress distribution of silicon brick,the distribution and change law of stress in crystal during sawing,and the influence of hard particle impurities on real-time sawing stress distribution.The main work is as follows:(1)The three-dimensional finite element model of clamping silicon brick was established,the influence of the shape,number and distribution of cylinder joints on the clamping stress was studied,and the influence of resin plate structure on the distribution of clamping stress was analyzed.The results show that the clamping stress of silicon brick is reduced from 0.5 MPa to 0.15 MPa by using I-shaped cylinder joint,alloy connection plate with double rows connection slot,and the resin plate setting 30 mm diameter circular hole as well as setting 1 mm radius fillet at the edge of the hole,a decrease of 70%.(2)The sawing force model of diamond wire saw is established considering both plastic and brittle material removal methods.Based on the sawing force model,the finite element simulation of multi-wire sawing multi-crystalline silicon process was carried out,and the distribution and coupling characteristics of sawing stress and the influences of sawing parameters and silicon wafer size characteristics on the value and distribution of stress were studied.The results show that the mechanical stress is small and accounts for a small proportion of the thermal-mechanical coupling stress,but it will affect the distribution of the thermalmechanical coupling stress,and the thermal stress is dominant.The influence of clamping stress on coupling stress is not obvious.The increase of sawing speed and feed speed will lead to the increase of thermal-mechanical coupling stress.When the ratio of sawing speed to feed speed is constant,the greater the value,the greater the thermal-mechanical coupling stress.The increase of wafer size and thickness will increase the thermal-mechanical coupling stress,while the change of wafer thickness has little influence on the stress value.(3)The finite element model of multi-wire sawing multi-crystalline silicon containing hard particle inclusions is established.The influences of the types,size,location of hard particle inclusions,the coupling between adjacent inclusions and sawing parameters on thermalmechanical coupling stress and stress concentration factor are analyzed.The results show that the greater the thermal expansion coefficient of hard particle inclusions,the greater the stress concentration.The larger the size of hard particle inclusions,the greater the stress value.The inclusions distributed at the outlet and the center of the sawing kerf will produce greater thermal-mechanical coupling stress.The smaller the distance between adjacent inclusions,the greater the stress value.With the increase of sawing speed and feed speed,the thermalmechanical coupling stress caused by inclusions increases. |
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