We propose an ultrathin solar cell architecture design which incorporates two periodic layers of metallic and dielectric gratings. Both layers couple the incident light to photonic and plasmonic modes, thus increasing absorption within the cell. The relative position between the two gratings is examined, and is shown to have significant impact on absorption. A lateral shift between the two layers introduces structural asymmetry, and enables coupling of the incident field to optically dark photonic modes. Furthermore, the lateral shift influences mode interactions. Current density enhancement is calculated under AM1.5G solar illumination, and is found to reach a value of 1.86. The structure proposed is optimized and compared to solar cells with a single layer of metallic or dielectric nanostructures.