Octadecyl tri-methoxysilane (OTMS) functionalized Au/SiO2core/shell nanorods were incorporated into the active layers of two different polymer bulk heterojunction (BHJ) systems: a broad band gap polymer (poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCB60M)) and a low band gap polymer poly{2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl) pyrrolo[3,4-c]pyrrole-1,4-dione} (PBDTT-DPP):PC60BM. The extinction peaks of the Au nanorod scattering centers was tuned to match the band edge of the two polymers by controlling their aspect ratio. For the P3HT:PC60BM system with a band edge around 700 nm, the addition of the core/shell nanorods of an aspect ratio 1:2.5 (resonant frequency peak is at around λ=650nm), resulted in 8% improvement in short circuit current (Jsc); for the low band gap polymer system PBDTT-DPP: PC60BM with band edge around 850 nm, we tuned the resonant frequency to near-infrared region by increasing the aspect ratio to 1:4 (resonant frequency peak is at around λ=800nm), the addition of the core/shell nanorods resulted in 18% improvement in short circuit current (Jsc). The Jsc enhancement was consistent with external quantum efficiency (EQE) measurements and the EQE improvement factor matched the absorption resonance spectrum of Au/SiO2 nanorods in both systems. This work will instruct us on how to utilize and manipulate plasmon resonance of metallic nanoparticles to improve device efficiency in different polymer solar cell systems.