In-situ Construction Of Porous Layer On Silicon Surface And Gettering Efficiency Of B And P

Climate warming and increasingly depleted fossil energy have prompted humans to develop and utilize solar energy on a large scale.At present,silicon-based solar cells occupy most of the market share.The metallurgical method for preparing solar-grade silicon has the potential for large-scale application due to its low cost and environmental friendliness.Although this method has achieved many research results,it has not been applied in large-scale commercial applications due to the unsatisfactory removal of non-metallic impurities such as B and P.In order to promote the solution of the key problem of B and P removal,the paper innovatively proposes to construct a porous layer in situ on the silicon surface,and strengthen the absorption of impurities B and P through the porous layer.The thesis mainly takes industrial silicon as the research object,uses the hydrothermal metal ion assisted method to construct the porous layer in situ,and explores the influence of various factors in the etching process on the porous morphology and the absorption of B and P impurities.The enhanced absorption of B and P impurities in silicon.On this basis,the mechanism of the porous layer's absorption of non-metallic impurities B and P is analyzed to deepen the theoretical understanding of the porous layer's absorption of B and P.The main research contents and conclusions of the paper are as follows:?1?In-situ construction of porous layer on silicon surface.First,single crystal silicon was used as the object,and the influence of metal ion species in HF-Mex?NO3?y-HNO₃ on the morphology of the porous layer was compared,and the process parameters of the hydrothermal metal ion assisted method were initially determined;industrial silicon wafers were also used.And industrial silicon powder verified the feasibility of HF-Me_x?NO₃?_y-HNO₃ system etching to prepare porous layer.The experimental results show that in the HF-Fe?NO₃?₃-HNO₃ etching system of industrial silicon powder,with a solid-to-liquid ratio of 1:25,the pore distribution of the porous layer structure obtained is more uniform and dense.?2?The influence of various factors in the HF-Fe?NO3?3-HNO3 etching system on the absorption of B and P in industrial silicon.The experimental results show that HF concentration and etching temperature have a significant effect on the absorption of B impurities;Fe?NO₃?₃ concentration,etching time,and HNO₃ concentration have significant effects on the absorption of P impurities;the best experimental parameter obtained is HF 4.00 M,Fe?NO₃?₃ 0.03 M,HNO₃ 1.00 M,solid-to-liquid ratio 1:25,etching temperature 170?,etching time 5 h,under these conditions,the content of B and P in industrial silicon ranges from 29 ppmw to 59 ppmw The ppmw was reduced to 7 ppmw and 15 ppmw,and the removal rates reached 75.862%and 74.576%,respectively.After annealing at 950?for enhanced absorption and pickling,the removal rates of B and P were increased to 82.759%and 76.271%.?3?The mechanism of the porous layer's absorption of B and P.The relationship between the structure of the porous layer,the oxygen content in the porous layer and the absorption of B and P is analyzed.The results show that the porous layer contains amorphous SiO₂.The specific surface area,pore volume and porosity of the porous layer are positively correlated with the removal rate of P impurities.The content of amorphous SiO2 is positively correlated with the removal rate of B impurities;thermodynamic calculations show that because the binding ability of O to B and P is stronger than that of Si to B and P,the amorphous SiO₂ porous layer is formed due to a large number of defects The vacancies of B and P are adsorbed and transferred,so that B and P enter the amorphous SiO2 porous layer and react with HF to generate ions that are easily soluble in water.On this basis,it is proposed that the porous layer is effective for B and P.Model of impurity absorption mechanism.