Research On Fabrication Of Antireflection Hydrophobic Microstructure On Crystal Silicion Sureface By Chemical Assisted Picosecond Laser Controllable Processing Method

The preparation of surface texture with light trapping micro-structure is one of the important approaches to enhance the conversion efficiency of solar cells. At present, crystal silicon solar cells still occupy the majority of the photovoltaic industry market. The crystal silicon has two types including monocrystalline silicon and polycrystalline silicon. For single crystal silicon solar cells, the common method of texturing is to prepare random pyramids by alkaline anisotropic etching. For polycrystalline silicon solar cell, the common method is to prepare porous silicon texturing by acid solution corrosion. However, it is difficult to control the size and distribution of the textured microstructure fabricated by the two kinds of method, so the reflectance of the textured surfaces can hardly get further reduction with the typical values higher than 10%. Aiming to further reducing the surface reflectance of crystalline silicon solar cell, the thesis presents a chemical-assisted ultrafast picosecond laser processing technique. With this method the novel texture structures were fabricated, which both obtain the excellent properties of light-trapping, hydrophobicity and photoluminescence. The multiple functional properties of the fabricated surfaces are beneficial for enhancing the mechanical performance and service life of the devices, which has good prospect of application.The microstructure arrays were fabricated by using 1064 nm picosecond laser scanning on surface of monocrystalline silicon and polycrystalline silicon wafers, and then treated the surface by short-time chemical etching. With the hybrid controllable method using picosecond laser irradiation followed by chemical corrosion, two types novel Si-based anti-reflectance texture were obtained. For single-crystal silicon, by hot alkali anisotropic corrosion on hole arrays sample surface, the micro-nano hierarchical hole structure was achieved. There are finer nano- structures in the micro holes. For polycrystalline silicon, by acid solution isotropic corrosion on hole arrays sample surface, the porous silicon structure was obtained. There are intensive nano pores formed on micro hole units. The surface morphology of the two types textures were analyzed by SEM and laser confocal three-dimensional topography instrument. The reflectance of samples were measured using spectrophotometer. The mechanism of the laser process with the chemical assisted corrosion acting on the formation of the novel antireflection micro-textures was studied. Combining the measurement results of reflectance, the optimized etching time was determined. By FDTD simulation analysis, the influence of surface morphology acting on reducing reflectance was explained. The contact angle of the samples was measured, and the hydrophobic properties and advantages in application were also studied. The photoluminescence property was measured as well as the mechanism was analyzed.Combination of the literature investigation and the experimental results, there are four valuable research results were obtained in the study:1. Two novel types of micro/nano hierarchical structures, micro-nano hierarchical structure texture(monocrystalline silicon) and porous silicon texture(polysilicon), were fabricated by 1064 nm picosecond laser process combined with short-time chemical corrosion technique. Structural units are no longer randomly distributed, and the controllability of the process is promoted greatly by the technique.2. The light trapping properties of the two kinds of the micro/nano hierarchical textured surface structure are both better than traditional textures. The lowest average reflectance reached 5% in the range of 400~1050 nm. It was found that the finer nano-structure formed on the micro-structure played a positive role on the reduction of reflectance.3. Two kind of texture both have good hydrophobicity, and the porous silicon texture has reached the super hydrophobicity, which also shows the property of photoluminescence. Two PL band can be observed. Along with the red PL visible to the naked eye, a new violet PL band at 432 nm was detected.4. The technique presented in the study processed in open process environment without any background gas and mask. Compared with the traditional technique, the textured microstructure can be highly controllable, which can satisfy the different needs of the silicon surface texturization. Two national invention patents have passed the first trial, and now are in the stage of public summons.The study explores a novel fabrication technique of high performance silicon antireflection surface with good hydrophobic properties by chemical-assisted ultrafast picosecond laser irradiation, which can be applied in in solar cells and other semiconductor devices in a low-cost and controllable way.