The Fabrication And Application Study For Texturization On Diamond-wire-sawing Multi-Crystalline Silion Wafers

Reducing costs and improving the photoelectric conversion efficiency have always been the goals pursued by the development of Si-based solar cells.Given this,diamond-wire-sawing(DWS)technique has fully replaced slurry-wire-sawing(SWS)technique due to abundant advantages,such as low kerf loss,higher productivity,less environmental contamination and lesser breakage of wire.For multi-crystalline silicon(mc-Si)wafers,the surface is so smooth that the defect density required by the standard isotropic acidic texturing process cannot reach the ideal value.In addition,the top of DWS mc-Si wafers contains a thin layer of amorphous silicon after cutting.The presence of this amorphous silicon layer can hinder the etching of silicon wafers by acids.Thus,it is difficult to obtain an ideal surface light trapping structure after standard acidic texturing process for DWS mc-Si.Ag-assisted catalytic acid etching can be used to prepare an ideal texturization structure,but the high cost of silver and the discharge of silver-containing wastewater hinder the industrial application of this technology.People expect to find a low-cost base metal catalyst or metal-free catalyst to replace silver.In this thesis,the texturization preparation of DWS mc-Si was systematically studied,and two different texturing methods were proposed:acid texturization assisted by copper acetate and acid texturization assisted by alcohol organic additives.The main innovative results are as follows:(1)Copper acetate assisted acid catalyzed chemical etching to prepare DWS mc-Si texturization.The effect of various experimental parameters on the optical properties of the prepared texturization was systematically studied.The optimal reaction temperature and reaction time are 25?,5 min,respectively.The optimal solution composition:hydrofluoric acid:5 mol/L,hydrogen peroxide content:4 mol/L,copper acetate:0.02 mol/L.The etching mechanism was discussed.Under the optimal etching conditions,the minority carrier lifetime of the silicon wafer is 1.41 ?s,and the average reflectivity in the wavelength range of 300?1100 nm is 15.1%.When this method was applied to fabricate the 156 mm ×156 mm DWS mc-Si solar cells and the conversion efficiency of 19.401%has been obtained.(2)The effect of the acidic etching solution formed by polyethylene glycol and polyvinyl alcohol alone as additives,together with polyethylene glycol and polyvinyl alcohol as additives on DWS mc-Si wafers was studied.Among them,the light antireflection effect obtained by using polyethylene glycol alone as an additive is better.The reasons for the difference in light trapping effect between standard acid texturing and polyethylene glycol additive acid texturing were analyzed.We obtained the optimal solution ratio:the volume ratio of HF:HNO3:H2O is 1:3.75:2,and the optimal reaction temperature and time are 20? and 120 s,respectively.Under the optimal etching conditions,the minority life of the silicon wafer is 1.55 ?s,and the average reflectivity in the wavelength range of 300?1100 nm is 16.9%,which is much lower than the reflectivity of the silicon wafer after standard acid texturing.The surface of the silicon wafer etched under the best reaction conditions was modified with alkali.The average reflectivity of the modified silicon wafer in the wavelength range of 300?1100 nm is 22.6%.When this method was applied to fabricate the 156 mm ×156 mm DWS mc-Si solar cells and the conversion efficiency of 19.394%has been obtained.