Preparation And Properties Of Black Silicon By RIE Mask Method And SIS Solar Cell

In recent years,silicon was applied in many fields due to its excellent performance.The crystalline silicon solar still took up the dominant position in the current photovoltaic market.The semiconductor-insulator-semiconductor?SIS?solar cell attracted lots of attention because of its simple structure,low cost,stable performance,simple manufacturation process and considerable conversion efficiency.In order to further improve the photon-electron conversion efficiency,many methods were put forward.It's a kind of simple and feasible method to reduce the silicon surface reflectance,so the concept of black silicon comes out.Broadly,the black silicon was a kind of material which can absorb light over 90%.In this thesis,we synthesised SiO₂ microspheres based on Stober method.Laser granulometer was used to analyze the effects of electrolyte and its concentration on SiO₂ microspheres particle size.Combined with the SiO₂ mechanism of Stober method to interpret the experimental results.The SiO₂ microspheres were spined on the silicon wafer by spin coating method.The single SiO₂ mask was successfully prepared by equilibrium between capillary force and centrifugal force.The results showed that the kinds of electrolyte and concentrations presented very important effects on SiO₂ microspheres particle size and uniformity.With the increase of electrolyte,SiO₂ microspheres particle size increased gradually,and uniformity gradually became poor.In order to form a single SiO₂ mask,it's very necessary to control the solution concentration and spin speed.Finally,the SiO₂ microspheres was in a hexagonal close-packed on the silicon wafers.After preparation of the SiO₂ mask,we used reactive ion etching?RIE?method to etch silicon wafer with sulfur hexafluoride?SF6?and oxygen?O₂?as reactive gas.Then we studied the effects of different etching power,etching gas flow ratio and etching time on black silicon morphology and its reflectance.Combined with mechanism of RIE,we explained the experimental results.Finally we obtained three kinds of morphologied.When etching power of 150 W,SF6:O₂ =18sccm:6sccm,etching time of 25 min,sample reflectance was 4.6% in the wavelength range of 400-1000 nm.The trapping-light ablilty of different structures we analyzed by FDTD simulation software and cone pillar had the best effect.The excellent effect of trapping-light came from its gradient refractive index.In order to get rid of damage by energetic ion,the sample was dipped NaOH solution.Then Al2O3 thin film was deposited by atomic layer deposition?ALD?and treated by thermal annealing.Results show that under the NaOH treatment time of 120 s,the reflectance of black silicon increased to 14.33% and small structures were removed.After deposited Al2O3 film,the reflectance of black silicon reduced to 7.12% and the minority carrier lifetime reached 29.34?s by rapid thermal annealing at 450?.It's shown that the damage layer is removed completely and Al2O3 thin film can passivate and reduce the reflectance of black silicon.For preparation of SIS solar cell,ITO thin film was deposited on the black silicon by magnetron sputtering.We studied the optical and electrical properties of ITO thin film under different temperature by ultraviolet visible light spectrophotometer,XRD,SEM and hall testing system.Finally,we successfully prepared SIS solar cell under different H₂O₂ pretreatment time and different substrate temperature.The energy band near the surface region of Si was bending because of the difference of work function between ITO and Si,and formed inversion layer finally.It would make up a quasi p-n junction in SIS solar cell and realize the photoelectric conversion.The results showed that the thickness of insulator is very important to SIS solar cell.The carrier transport needed through tunneling effect.Under H₂O₂ pretreatment of 15 min,and the substrate temperature of 50?,SIS solar cell possessed the best photoelectric conversion efficiency of 3.67%.