Plasma surface texturization for multicrystalline silicon solar cells

Textured front surfaces improve the efficiencies of solar cells due to reduced reflection and light trapping. Most methods of wet chemical surface texturing depend on crystal orientation. We have therefore developed a SF6/O-2 reactive ion etch process for the mask-less texturing of silicon independently from grain orientation. Following the black silicon method, we have optimised a surface texture with a typical lateral dimension in the order of 100 nm and with very good homogeneity. Since the texturing sensitively depends on the process parameters as well as on the condition of the reactor and the wafer surface, pre-conditioning is a crucial step. The weighted refection of an optimised process is less than 3 % without any additional antireflection coating. However, the texturing enlarges the surface drastically and shallow diffusions result in high sheet resistance. Multicrystalline silicon solar cells with black silicon texturing therefore outperform planar cells, but still suffer from bad short-wavelength response due to high surface recombination and internal resistance.