Texturization of silicon wafers for solar cells by anisotropic etching with sodium silicate solutions

Abstract

The efficiency of silicon solar cells greatly depends on the texturization of silicon wafers used in their fabrication. Texturization reduces the reflectance of the silicon surface which improves the light trapping ability of the solar cells. In this study, aqueous Na2SiO3 solutions were used as etchants in the texturization of monocrystalline silicon wafers. The main objective was to evaluate the performance of the etchant based on the silicon surface reflectance. The surface morphology and etching rate were also investigated. Results showed that Na2SiO3 solutions reduced the surface reflectance of the wafers better than other alkaline etchants. This was brought about by the formation of uniformly distributed pyramidal structures on the surface of the wafer after texturization. The effects of process parameters such as Na2SiO3 concentration, solution temperature and etching time on the reflectance were evaluated and optimized by applying ANOVA and Response Surface Method (RSM). The optimum process condition was found to be 6.2 wt% Na2SiO3, 80°C and 5 min at which the reflectance of the silicon wafer was reduced to 9.27%. Furthermore, the addition of small amounts of IPA (up to 0.03 wt%) to the Na2SiO3 solution reduced the reflectance of the wafer (9.13%) and slightly improved its wettability.