Porous-pyramids structured silicon surface with low reflectance over a broad band by electrochemical etching

Porous-pyramids structured silicon surface was prepared and its influence on the reflectance of the silicon surface was studied. The porous-pyramids structured surface was prepared by electrochemical etching in HF/C2H5OH solution after texturization in NaOH/IPA solution. The average reflectance of the surface in the range of 400-800 nm was as low as 1.9%. The optical photographs and SEM images of the surfaces prepared under optimized condition were investigated. The porous-pyramids structured surface has a gradient-index multilayer structure (i.e., the refraction index of the structure increase from the top to the bottom). A formula that describes the relationship between the reflectance and the index of refraction was used to explain the excellent broadband antireflection of the multilayer silicon surface. The technique of this paper may be valuable in the texturization process for high-efficiency silicon solar cells.

► Porous-pyramids structured silicon surface was fabricated and the PS was formed by using electrochemical etching firstly. ► Much lower reflectance of silicon wafer with this structure was obtained compared with that of single pyramid or porous silicon. ► An average reflectance of 2.7% has been achieved over a broad wavelength range (200-2000 nm) and from 400 to 800 nm. ► The antireflection mechanism of multilayer PS possessing gradient indices was discussed according to A.J. Fresnel formula about reflectance.