Preparation Technology And Experimental Study Of Surface Texture Of Crystalline Silicon Solar Cell

Reducing the reflection loss of light through texture treatment is an important method to improve the photoelectric conversion efficiency of solar cells.According to the type of crystalline silicon,commonly used treatment is not the same.For monocrystalline silicon,the structure of pyramid suiting is obtained by using the principle of anisotropic corrosion,in which the grain arrangement is orderly and the crystal surface（100）corrods much faster than the crystal surface（111）in alkaline solution.For polysilicon,uniform microstructure cannot be obtained by anisotropic corrosion due to the irregular grain orientation.Generally,the mixture of HF/HNO₃ is used for isotropic corrosion to obtain a pitted textured structure.Acidic solution is more toxic and volatile,which is harmful to the environment and human health,while NaOH solution is stable and safer to use.Therefore,NaOH solution was used as corrosion solution in this paper.When the polysilicon is corroded by alkaline solution,the limitation of irregular grain orientation in the chemical etching process of polysilicon can be weakened by applying voltage on the silicon wafer,so that the material surface can be corroded along the longitudinal and transverse directions,so as to obtain uniform corrosion pit and reduce the suiting reflectance.However,the reflectivity of crystal silicon textured surface prepared by chemical or electrochemical corrosion alone is generally above 10%.In order to further reduce the reflectivity,this paper proposes a surface texturing process combining laser etching with electrochemical corrosion.The main research contents are as follows:（1）The mechanism of laser etching and electrochemical etching to make textured surface was studied,including the energy transfer mechanism of photon,electron,phonon and lattice during the interaction between laser and material,and the material removal mechanism of coulomb explosion and phase explosion was analyzed.In addition,the cause of anisotropic corrosion of silicon in alkaline solution was analyzed.（2）Prepared textured surface by laser.Orthogonal experiments were designed and carried out to prepare suede on the surface of monocrystalline silicon and polycrystalline silicon by picosecond pulse laser.The laser processing parameters were optimized by using the range analysis method,and the effects of scanning spacing,laser energy,pulse frequency,scanning speed,element number,defocusing amount on the reflectivity and microstructure of the wool were analyzed.After laser textured,the surface reflectance of crystalline silicon is greatly reduced,in the wavelength range of 400¹000nm,the average reflectance of monocrystalline silicon suiting machined by the optimized process parameters is 5.5%,and that of polycrystalline silicon is 3%（3）The experimental study of laser etch-electrochemical corrosion was carried out.Based on the optimized process parameters,the electrochemical corrosion experiments were carried out to study the influence of the corrosion voltage,solution concentration and corrosion time on the surface reflectance after laser textured.After the treatment of laser texturing,electrochemical corrosion can produce nanoscale folded structure on the inner wall of the micron-scale pore structure prepared by laser.The composite of this micro-nano secondary structure can further reduce the reflectance of crystalline silicon suede.It was found that after electrochemical corrosion,the average reflectivity of monocrystalline silicon textured surface was as low as 4.3%and that of polycrystalline silicon textured surface was as low as 2.4%within the wavelength range of 400¹000nm,It shows that the electrochemical etching method can further reduce the reflectance of textured surface.The research results in this paper lay a theoretical and experimental foundation for the preparation of lower reflectivity textured structures on the surface of crystalline silicon solar cells,and promoted the development and application of low reflectivity crystalline silicon surface texturing in the field of solar cells.