In thin-film silicon solar cells, a flexible optical design for light collection is developed that can lead to zero reflection loss and enhance the optical path length in the absorber layer. In this work, we demonstrate two-filling-factor asymmetric binary gratings on the top of the solar cells and metallic diffraction gratings as a back reflector. The potential of the structures in the solar cells is investigated by means of numerical simulations, i.e., the rigorous coupled wave analysis enhanced by the modal transmission line theory. The impact of the structure parameters of the gratings on reflectivity is investigated. The results show that a close to zero reflection can be achieved by the two-filling-factor asymmetric binary gratings, and the path length of the transmitted light can be increased within the absorber layer by the metallic diffraction gratings.