Black-Silicon on Micropillars with Minimal Surface Area Enlargement to Enhance the Performance of Silicon Solar Cells

Although black silicon is used widely as an antireflection coating in solar cells, the corresponding electrical properties are usually poor because the accompanied enlarged surface area can result in increased recombination. Moreover, the high aspect ratio of fragile nanostructured black silicon makes conformal passivation even more challenging. Micropillars are promising alternative candidates for efficiently collecting carriers because the diffusion distance for minority carriers to reach the p-n junction can be shortened; however, the pillar diameter is usually larger than the wavelength of light, inherently increasing the surface reflection. In this paper, we report an approach for decreasing the surface reflection of black silicon and micropillar structures: combining them together to create a dual-scale superstructure that improves the electrical and optical properties concurrently. The reflection of the micropillars decreased significantly as the surface was decorated with a thin black silicon layer, and the thickness of black silicon required for low reflection was reduced as the black silicon was positioned atop micropillars. Three-dimensional finite difference time domain simulations supported these results. Moreover, with such a thin decoration layer, the superstructure displayed improved power conversion efficiency after silicon nitride passivation, suggesting great potential for such superstructures when applied in solar cells.