We report a new approach to enhance the power conversion efficiency(PCE)of polymer photovoltaic cells(e.g.,P3HT:PC 61 BM)using electrospun composite nanofibers.Highly conducting silver(Ag)/poly(vinyl pyrrolidone)electrospun nanofibers with different patterns of nonwoven-,aligned-,and crossed-patterns were successfully prepared using the coaxial electrospinning technique.The composition,crystalline orientation,and particle size of Ag were successfully manipulated by controlling the core/shell solution concentration.The smallest diameter of the composite nanofibers led to the highest orientation of the Ag nanoparticles and resulted in the largest conductivity comparable to that of ITO,due to the geometrical confinement.As the crossed-pattern nanofibers were employed into P3H:PC 61 BM photovoltaics,the PCE had an 18.7%enhancement because of the enhanced carrier mobility and surface plasmon resonance effects.The incorporating of a conjugated polymer,poly[2,7-(9,9-dihexyl-fluorene)-alt-4,7-(2,1,3-benzothiadiazole)],into the composite nanofibers could further generate the excitons for enhancing the PCE of the polymer photovoltaic cells.