The Study Of Antireflection Of Textured Surface Of Silicon By The Electrochemical Method

It is wasteful for sunlight to be reflected from the surface of the solar cell, so it is necessary to do something to decrease the surface reflectivity to the minimum. The effect of the porous-pyramids morphology on the reflectivity of surface as well as the Photovoltaic Conversion Quantum efficiency and the effect of oxidation of porous silicon on the Photovoltaic conversion Quantum efficiency for different wavelengths were studied.Pyramids were made by the alkali etching method, and as a subsequence, a layer of porous silicon was formed on the surface of the pyramids on the silicon using the electrochemical method. The effect of the porous silicon on the reflectivity of surface as well as the Photovoltaic conversion Quantum efficiency and the effect of oxidation on the Photovoltaic conversion Quantum efficiency for different wavelengths were studied. It was observed that the density of hydrofluoric acid (HF) does not make a difference on the reflectivity of the surface, and the electrochemical etching time can determine the minimum-reflectivity wavelength. The average reflectivity of the structure can be2%. To make a comparison, the reflectivity of the morphology of the porous silicon on polished silicon as well as on the initial silicon was studied, and it was found that the reflectivity of the former one was lower than the latter one, even though the reflectivity of the porous silicon on polished silicon is higher than that of the porous silicon. So it can be concluded that the antireflection result of the complex morphology is not simply the addition of the antireflection results of the elementary-morphologies; both of them had shown worse antireflection result than the porous-pyramids morphology.The effect of the density of HF and the electrochemical etching time on the refractive index had been studied using the ellipsometer method. It was found that the refractive index would increase as the density of HF increases and there was no evidence that it would change with the etching time. The uniformity of the thickness of porous silicon which was also measured by the ellipsometer is largely related to the uniformity of the electrode contact during the electrochemical etching.Because of the porous silicon, the Photovoltaic Conversion Quantum efficiency is decreased to almost0%for the wavelength between300nm-500nm, and is increased to95%by7%for the wavelength beyond500nm. Rapid oxidation can decrease the surface recombination so as to increase the Photovoltaic Conversion Quantum efficiency for the short wavelength, and it can be a guidance for increasing the efficiency of the silicon solar cells.