We have prepared polymer solar cells incorporating an active layer of poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT:PCBM) blended with platinum nanoparticles (Pt NPs). The short-circuit current density of the polymer solar cells improved after blending as little as 0.04 wt % of the Pt NPs into the P3HT:PCBM active layer. A polymer solar cell having the device structure indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/P3HT:PCBM:Pt NPs/Al exhibited a power conversion efficiency of 4.08% (under AM1.5G 100 mW cm(-2) illumination), which is a 55% improvement relative to that of the unblended device. This enhanced efficiency originated from the increased carrier mobility of the active layer when the Pt NPs were present.