Research On Copper-catalyzed Chemical Etching Of N-type Single Crystal Silicon For Texturing

Preparing low-cost and high-efficiency solar cells is the goal that the entire photovoltaic industry has been pursuing.The n-type monocrystalline silicon,which owns the advantages of light-induced attenuation and long lifetime of minority carriers,have attracted the attention of the industries and gradually becoming the preferential choice for high-efficiency solar cell technology in the future.High-efficiency surface trapping is an important method to improve solar cell efficiency,the traditional alkali etching process requires high temperature,long etching time,and the resulting upright pyramid structure which enables secondary reflections of light is not the ideal light-trapping structure.In addition,the upward spike of pyramid is not conducive the a-Si:H passivation in high-efficiency HIT solar cells,which has been reported to own great development potential in the future.Moreover,point contact among upright pyramid causes serious battery heating and affects the conversion efficiency of the solar cell.On the contrary,the copper catalytic chemical etching has the advantage of low cost and simple process,moreover,it forms a inverted pyramid structure which performance triple anti-reflection.Not only that,the inverted pyramid structure has no sharp peak,which makes it an excellent passivation substrate and attracted the attention of the industry.Exploring the mechanism of copper catalytic chemical etching and stably preparing inverted pyramid structure with low reflectivity is expected to promote the development of high-efficiency monocrystalline solar cells in the future.In this paper,diamond wire sawn n-type monocrystalline silicon is used as the substrate,the influence law of copper salt anions on the deposition and the etching behavior of copper nanoparticles is systematically studied by HF/Cu X/H₂O₂ etching system(Cu X,X:SO₄^2-,NO₃^-,Cl^-),reveals the formation mechanism of the inverted pyramid structure in the copper catalytic etching process,the stable preparation?large-area preparation and optimization of the inverted pyramid structure were carried out to improve the uniformity and reflectivity of the silicon wafer surface.The main research conclusions of this paper are as follows:(1)The morphology of nano-copper particles is affected by the combination of anion oxidation,complexation and the binding force between anion and cation in different copper salt system,and finally lead to different etching behaviors.Different from the weaker interaction in the SO₄^2-system,the stronger electrostatic attraction in the NO₃^-system helps to slow down the rapid deposition of copper particles(not to form a dense copper film);at the same time,compared to the strong complexation in the Cl^-system,which lead to the agglomeration of the deposited particles,the oxidation of NO₃^-are more beneficial to improve the dispersion and size uniformity of the deposited copper particles.The final uniformly dispersed copper particle system is more conducive to the progress of anisotropic silicon etching,and effectively forms an inverted pyramid structure with low reflectivity.(2)Through a systematic study of the influencing factors of the formation of the inverted pyramid by HF/Cu(NO₃)₂/H₂O₂etching system,regular and dense inverted pyramids were successfully prepared with mild reaction rate of 0.23?m/min,and the surface reflectivity can be reduced to 6.43%.Moreover,the theories of local etching and overall etching were put forward,and the formation principle of the inverted pyramid revealed,that is,in the balance of the deposition and dissolution of copper particles,both the local etching and the anisotropic etching of the silicon substrate lead to the formation of inverted pyramid structure.(3)Based on the above research foundation,several groups of inverted pyramid structures were stably prepared on two kinds of silicon wafer surface(derived from diamond wire sawing process with different wire diameter),with mild etching reaction and low reflectivity of 6.34%;Then,dense inverted pyramid arrays with low reflection was successfully fabricated on156×156 mm large-size silicon wafer.The reflectivity was as low as about 10%,and the mass loss accounted for about 4%of the total silicon wafer mass.Compared with traditional KOH etching,this method can not only prepared inverted pyramid structure with excellent reflection performance and good passivation,but also has the advantages of lower process temperature requirements,milder reaction,and fewer silicon consumption;finally,dodecane tetramethylammonium bromide(CTAB)was added as an additive to the HF/Cu(NO₃)₂/H₂O₂etching solution to optimize the inverted pyramid structure.CTAB molecules in HF/Cu(NO₃)₂/H₂O₂ solution can adsorb Cu²⁺near the silicon wafer surface,thus promoting the deposition of copper particles and making the etching reaction even.When 3mg CTAB is added to the 100m L etching solution,the size of the inverted pyramid structure is larger and the distribution is more uniform.The reflectivity can be further reduced from 10.8% to 4.6%...