Texturization of cast multicrystalline silicon for solar cells

Abstract

The texturization of cast multicrystalline silicon (mc-Si) for solar cells with alkaline or acidic solution has been investigated, and two theoretical models were built on the basis of surface morphologies. For alkaline etching, tilted pyramid structure could be formed on the surface. It is reported that when the tilted angle, which is the angle between (100)-plane and as-cut surface, is larger than the critical angle (20°), the reflectance rapidly increases with the deviation from ⟨100⟩ orientation. For acidic etching, spherical structure was generated. If the ratio, which is the ratio of depth (h) and radius (r) of the spherical structure, is less than the critical value (0.29), the second reflection cannot take place. Therefore, improving the ratio of i and r is one effective way to decrease the reflectance of cast mc-Si, which was proved by subsequent experiment. With the addition of sodium nitrite (NaNO2) or sodium phosphate tribasic (Na3PO4 · 12H2O) into the acid etchant, it was found that the reflectance decreased remarkably. Finally the formation mechanism of spherical pits in acid etched mc-Si was discussed.