Amorphous hydrogenated silicon (a-Si:H) solar cells need efficient light trapping structures to achieve high efficiency. To this end, aluminum doped zinc oxide (ZnO:Al) as a transparent front contact was periodically structured. Solar cells with grating periods between 390 and 980 nm were realized. The structures were characterized by Atomic Force Microscopy (AFM) and optical reflection. A simple formula for the wavelength where total internal reflection starts is deduced for each diffraction order. Solar cells with a periodic grating show a significant reduction in the overall reflectance which is comparable to cells with an optimized statistical texture.