Single nanowire solar cells are a promising candidate as nanoelectronic power sources. Metallic cores were integrated in single nanowire solar cells, and the influence of the silver core on the absorption efficiency and the short circuit current was studied in this work. A Full-wave Vectorial Finite Element Method approach was used to rigorously solve Maxwell's equations in two dimensions. The photon absorption in solar cells was modulated delicately to achieve higher absorption efficiencies and short circuit currents, by tuning the core size and radius of nanowire solar cells. The light trapping stemmed mainly from the localized surface plasmons and also from Mie scattering and leaky mode resonances. The results showed that an enhancement of 16.6% in the photocurrent could be achieved by α-Si nanowire solar cells with the proper core size and filling-ratio compared to that without silver core.