In silicon solar cells, the reduced thickness of the absorbing layer has demanded the use of light trapping structure. A light trapping structure felicitates the unabsorbed photons from the absorbing layer and further, folding these back to stimulate the light absorption. Here, we propose a design of 50 nm ultrathin silicon solar cell and investigate the influence of plasmonic effect on its performance. The transverse magnetic field analysis shows the existence of plasmonic effects such as surface plasmon, Fabry-perot mode and surface plasmon polaritons. The obtained cell efficiency for the transverse magnetic mode is twice (∼16%) as comparison to transverse electric mode (∼8 %). The proposed solar cell design based on dual grating showed optimal performance in a wide wavelength spectrum due to an efficient light trapping mechanism.