Abstract Surface plasmon resonance was observed to red shift in hexagonal nanohemisphere Ag array covered by double-walled carbon nanotubes. By altering the density of carbon nanotubes, the surface plasmon resonance can be tuned from 563 nm to 586 nm and the light scattering is enhanced in the spectral range from orange to red. This leads to improved performance of amorphous silicon solar cells deposited on top, which yields a short-circuit current density of 14.07 mA/cm2 and a power conversion efficiency of 6.55% under the illumination of AM 1.5G. This carbon nanotubes' density-dependent surface plasmon shift is attributed to the dielectric constant change around the periodic Ag nanostructure, which can be applied to other solar cell materials by fine-tuning the surface plasmon resonance to enhance the absorption at wavelength where the active layer is less absorptive.