Study On Electrical Properties Of Cell And Black Silicon Produced By Diamond Wire Cut Polycrystalline Silicon

In recent years,the cost gap has greatly reduced between monocrystalline silicon and polycrystalline silicon cells because of diamond wire cutting technology.There are some technical bottleneck of texturing of diamond wire cutting polysilicon wafer such as texture difficulty,high reflectivity and low conversion efficiency,so diamond wire cutting polysilicon wafer cannot be applied in the industry on a large scale.At present,the industry uses black silicon technology to solve this problem,but the research on large scale black silicon technology and influencing factors of black silicon is not in-depth.In this paper,the diamond wire cutting polycrystalline silicon wafer as the research object,using two processes of reactive ion etching?RIE?of dry etching and silver catalytic chemical etching of black silicon,the large-scale production line as the test platform,the best process of preparing black silicon is studied from three aspects of RIE dry etching process,silver catalytic chemical etching process and the influence of electrical property degradation,and the influencing factors of process parameters and electrical properties and solutions are analyzed.The main research work and achievements are summarized as follows:?1?Reactive ion etching?RIE?dry method was used to prepare black silicon on diamond wire cut polysilicon.The influence of etching parameters on the surface morphology of polysilicon was analyzed.It is found that the surface of polycrystalline silicon wafer after RIE etching is covered with a white object which is not easy to volatilize,and the edge of the etched hole has a sharp structure.After cleaning in acid solution,it is found that with the prolongation of cleaning time,the edges of holes become smooth and the diameter increases gradually.After 300 seconds of cleaning,the holes are fairly even with a reflectivity of 11.5%.Then the holes become flat gradually with the cleaning time increasing.In the RIE etching process experiments,it is found that the surface morphology of polycrystalline silicon is uniform with the change of RIE etching power at different high and low frequencies,but the size of etched holes varies greatly.With the increase of high frequency power,low frequency power decreases,gas ionization increases,silicon etching speed increases,and etched hole diameter increases.When the high frequency power+low frequency power is 1500W+450W,the surface is etched more evenly with an average reflectivity of 12.5%,resulting in better etching morphology.In RIE etching reaction,it is found that with the increase of the flow ratio of SF₆/O₂,the nano-hole depth increases gradually and becomes uniform.When the flow ratio of SF₆/O₂ is 0.55,the nano-hole size is relatively uniform,and the nano-hole depth is greater than 100 nm,with an average reflectivity of 11.9%.When the flow ratio of SF₆/O₂increases again,the surface nano-hole becomes flat,the pore size increases because when the SF₆/O₂ flow ratio is small,the F ions in the vacuum chamber are less,the etching speed is slow,the oxygen is more,and the formation of non-volatile Si OF increases,which will inhibit the etching of silicon.When the SF₆/O₂ flow ratio is increased to 0.55,the F ions concentration increases,the etching speed is faster,and the surface of silicon shows uniform holes with deep etching.When the etching reaction occurs When the flow ratio of SF₆/O₂ gas is further increased,the F ion concentration is too high,the oxygen concentration is reduced,the inhibition is weakened,the etching speed of silicon is too fast,and the surface of silicon becomes flat,so the etching effect is poor.?2?Silver-catalyzed chemical etching?MCCE?was used to prepare black silicon by wet method.The influence of preparation parameters on the performance of black silicon was analyzed.Through the experimental study of Ag NO₃wet deposition process of MCCE,it is found that when Ag NO₃solution concentration and HF volume concentration are constant,and the reaction temperature is normal temperature,with the increase of deposition time,Ag particles gradually grow up,and Ag particles appear rapidly at the edge of corrosion pit;when the deposition time is 10 seconds,the Ag particles are more uniform on the surface of crystalline silicon,and then with the increase of deposition time,Ag particles are precipitated and the particle size is not uniform.When the reaction time and HF volume concentration are constant,it is found that with the increase of Ag NO₃solution concentration,the number of Ag particles on the surface of polysilicon wafer increases gradually,and the particles increase continuously.Especially at the edge of the pit,Ag particles are easy to deposit.This is because the energy of surface state at the edge of polycrystalline silicon pit is lower than that inside the pit,or there is defect damage,which is more conducive to Ag particles Gather here and grow up.When the concentration of Ag NO₃solution is 0.01mol/L,the Ag particles deposited on the crystalline silicon are relatively uniform.With the increase of the concentration,the Ag particles will grow too fast due to too high Ag concentration,and gradually appear dendrite,and grow up with the increase of Ag NO₃solution concentration.Through the experimental study on the wet process of preparing black silicon from MCCE,it is found that when the volume concentration of H₂O₂and HF solution is constant and the reaction temperature is normal temperature,the morphology of silicon wafer gradually changes from nano pores to densely arranged small nano cones.With the increase of corrosion time,the nano cones become larger and larger,the nano holes become more and more variable,the hole diameter is gradually uniform,and the light trapping effect is getting better and better.When the corrosion time is 120 seconds,the average reflectivity is 5.47%,which indicates that the surface morphology is greatly affected by the change of corrosion time.The size of nano cone structure can be controlled by adjusting the corrosion time.When the concentration of HF solution and corrosion time are fixed,it is found that with the increase of H₂O₂concentration,the surface corrosion of polycrystalline silicon presents a cone shape and grows continuously.When the concentration of H₂O₂is 1%,the corrosion rate is faster,the corrosion depth increases,the length of the cone is relatively long,and the surface is disordered.When the concentration of H₂O₂is 1.5%,the corrosion of polysilicon surface is relatively uniform,and the boundary of each pit edge is not obvious.The reason is that when the concentration of H₂O₂increases,the formation rate of Si O₂on the silicon surface is accelerated,and the reaction between Si O₂and HF is severe,which leads to the increase of oxygen anion in the corrosion solution,and the speed of obtaining electrons from the self built electric field formed on the Ag surface increases.As a result,the corrosion rate increases,and the depth of the hole increases with the sinking of Ag nanoparticles.Through the experimental study on the process of cleaning and removing Ag and nano reconstruction of black silicon prepared by wet method of MCCE,it is found that the effect of alkaline cleaning is better than that of acid cleaning at room temperature;the effect of Ag removal is the best when the temperature is raised to 50?;the residual Ag greatly reduces the performance of the battery,and Ag particles will cause local leakage and composite center of the battery.It was found that the length of nano cone decreases with the extension of nanostructure remodeling time,and the distance between Nano cones increases with the extension of nanostructure remodeling time.When the nanostructure remodeling time is 90 seconds,the nano pores become regular and smooth,and form sub micron uniform pores of about 500 nm?600 nm,with an average reflectivity of 12.7%,and the suede size and uniformity are the best.?3?The black silicon battery was prepared and the performance degradation of the battery module was analyzed.It is found that the open circuit voltage V_oc,short circuit current I_sc and efficiency Eta of black silicon battery are improved compared with conventional acid velvet battery.The efficiency of RIE black silicon battery reaches 19.1%,which is 0.24%higher than that of MCCE black silicon battery.This is because RIE black silicon structure has better light trapping effect than MCCE black silicon structure.After light aging,it is found that the attenuation range of black silicon module is relatively large,and the efficiency enhancement of black silicon battery is not reflected at the end of module,and the attenuation of black silicon module is about 2.5%?3%.The thermal oxidation process after diffusion of black silicon wafers can effectively passivate and reduce the attenuation of black silicon cells.After infrared irradiation annealing and electric injection annealing,the decay rate of black silicon cells can be effectively reduced,and the electric injection annealing is better than the infrared irradiation annealing.The oxidation+annealing process has better passivation and attenuation reduction effect.There are 47 figures,24 tables and 122 references.