Investigation On Fabrication And Properties Of Light Trapping Microstructure For Monocrystalline Silicon Solar Cells

At present, crystalline silicon solar cells are the dominator of PV market. In order to improve thecrystal silicon solar cell conversion efficiency, fabricating microstructures for trapping light toincrease the light absorption on silicon surface has been the research hotspot nowadays. This thesisfocuses on the light absorption of monocrystalline silicon and different light trapping microstructures,such as pyramids, porous silicon, multilayer porous silicon, porous-pyramids and multilayerporous-pyramids, have been fabricated and studied.During anisotropic etching of monocrystalline silicon, the relationship between the angle α of thepyramid and the reflectivity of etched surface was studied as well as the influence of the concentrationof NaOH and the etching time on the reflectivity of the textural silicon surface by fixing the etchingtemperature and the additive concentration. As a result, the textured silicon surface reflectivity in therange of400and1100nm is only10.54%when the silicon was etched40min in2.5%NaOHsolution. On the basis of experimental data，the simulate curve and the simulate equation of thereflectivity as a function of pyramid angle are obtained by Origin.A gradient-index multilayer porous silicon was obtained on silicon surface by electrochemicaletching in HF/C₂H₅OH solution with changed current. The pores’ diameter is about from20nm to30nm and the average reflectance of the antireflective structure in the range of400nm to1100nm was aslow as4.5%which can be well explained by the A.J.Fresnel’s formula. Corrosion pits which filledwith porous silicon was also gained on the silicon wafer when etched in HF/Fe（NO₃）₃solutions. Thediameter of the pore is in the range of0.1um to1um and an average reflectance of6%was obtainedover the range of400–1100nm.A porous-pyramid textured antireflective structure was obtained when the pyramid texturedsilicon wafer etched in HF/Fe （NO3）3solutions. The reflectivity of new antireflective structure in over400-1100nm was as low as10%, and especially, in the short wavelength the reflectivity reduced more.A new antireflective structure, porous-pyramids binary structure, was prepared first byelectrochemical second etching in HF/C₂H₅OH solution after texturization in NaOH solution. Thereflectance property of the surface was fantastical. For the porous-pyramids binary structured siliconsurface, an average reflectance of2.7%over a broad wavelength range （200–2000nm） could beobtained under an optimized condition, and the average reflectance of the binary structure in visiblerange（400-800nm） can even reach1.9%.