Study On Surface Modification Of Multi-crystalline Silicon Wafer Cut By Diamond Wire Saw For Acid Texturing

Multi-crystalline silicon(Mc-Si)solar cells,as one of the main products for solar photovoltaic applications,have a substrate of mc-Si wafers that can be obtained by processing by wire saw.Earlier,the processing method for silicon ingot cutting was mainly slurry wire saw(SWS).However,with the increase of silicon wafer size and higher requirements for sawing efficiency in industrial production,the shortcoming of low processing efficiency of SWS has become increasingly prominent.The development of diamond wire saw(DWS)technology has effectively solved these problems.However,the surface morphology of mc-Si wafers cut by DWS shows a large number of saw marks,and there is a thin layer of amorphous silicon on the surface.This morphological feature is not conducive to the etching and texturing by the acid solution.In order to solve the problem of incompatibility between diamond wire saw technology and conventional acid texturing process,the main research contents of this thesis are as follows:(1)This paper proposes to pretreat the diamond wire sawn mc-Si wafers surface with wet sandblasting before acid texturing in order to solve this problem.The effect of wet sandblasting pretreatment on the surface morphology of mc-Si wafers was analyzed,as well as the surface morphology and antireflection performance of mc-Si wafers after wet acid etching were studied.Observing the experimental results,it can be seen that wet sandblasting with appropriate process parameters can effectively remove the line marks and the crystal phase transition silicon layer on the surface of the sawed polycrystalline silicon wafer.The reflectivity of pretreated mc-Si wafers after acid texturing is significantly lower than that of the unpretreated ones,which can meet the production requirements of solar photovoltaic cells.(2)A new pretreatment process of turbine-type stirred slurry is proposed to modify the surface of mc-Si wafer cut by diamond wire saw to make it suitable for the subsequent conventional wet acid cashmere process.Through experiments to explore the appropriate process parameters and device structure,the surface structure consistency of mc-Si wafer can be effectively improved after being treated with t turbine-type stirred slurry.After acid texturing of pretreated mc-Si wafers,the reflectivity of the silicon wafers is greatly reduced compared with that before processing,which can meet the production requirements of solar photovoltaic cells.Furthermore,based on ANSYS Workbench and Fluent,numerical simulation of the surface pretreatment process of large-size silicon wafers in practical industrial applications was carried out,and the uniformity of the surface modification treatment was analyzed.(3)A novel fixed and free abrasive combined wire saw technology for machining mc-Si wafers are proposed.Diamond wire is used as the main processing tool,and free SiC abrasive particles are added into the lubricating coolant to lap the surface of mc-Si wafers.The results show that there are no significant saw marks and ductile smooth area on the surface of silicon wafer processed by the composite wire saw when the SiC abrasive mass fraction is appropriate.The surface roughness and fracture strength of silicon wafers in parallel and perpendicular the wire saw motion directions tend to be the same.The anisotropy of mechanical properties of silicon wafers in different directions is significantly reduced,which is conducive to reducing the wafers breakage rate.Compared with the diamond wire sawn wafers,the reflectivity of the mc-Si wafer cut by the composite wire sawing is greatly reduced after wet acid etching,which can meet the needs of solar cell preparation.