Plasmonic nanostructures have been regarded as a promising light trapping strat- egy towards boosting solar cell efficiency recently. However, the absorption enhancement stem- ming from surface plasmon excitations always suffers from an inherent limitation of narrow band- widths, which may hamper the complete utilization of the solar radiation in a broadband spec- trum for solar cells. In this paper, we theoretically show that by cascading metal gratings with different sizes atop the amorphous Silicon thin film solar cells (TFSCs), the enhanced light ab- sorption band of the ultrathin active layer is extended due to the excitation of multiple localized surface plasmon resonances (LSPRs). For one-dimensional (1D) cascaded grating structure, the metallic gratings with different widths act as discrete nanoantennas which independently and efficiently collect the incoming photons at the LSPR wavelengths, leads to an enhancement of 60% in photocurrent for the T M -polarized incident illumination. Furthermore, it appears that both the coupling of plasmonic/photonic modes and their inter-coupling effects contribute to the light trapping in the 2D cascaded grating structures, which leads to an enhancement of 66.5% in the photocurrent over the bare TFSCs.