The aim of the reported study is to enhance the photovoltaic performance of a dye-sensitized solar cells (DSSCs) using co-sensitization approach and investigate how the concentration of an organic co-sensitizer influence the overall efficiency of the fabricated DSSCs. The overall efficiency of the fabricated DSSC with co-sensitization approach using a ruthenium (II) based dye, N749, and an organic sensitizer, RK1, is 8.15%. The solar cells were evaluated using UV-Vis spectroscopy, electrochemical impedance spectroscopy (EIS), incident photon to electron conversion efficiency (IPCE), and current-voltage (I-V) characteristics. The concentration of the organic co-sensitizer has a strong effect on the performance of the DSSC. An optimized solar cell fabricated with a dye solution of 0.2 mM RK1 and 0.3 mM N749 yielded a J(sc )(mA/cm(2)) = 19.45, V-oc (mV) = 688, FF (%) = 61 and power conversion efficiency (PCE) of eta(%) = 8.15 under standard (AM1.5 G) 1 sun illumination (100 mW/cm(2)). The efficiency of co-sensitized DSSCs is far better than the efficiency of fabricated solar cells sensitized with individual dyes [N749 (eta = 4.94%) and RK1 (eta = 5.76%)]. The efficiency enhancement is due to the lower rate of recombination of electrons and holes, decreased I-/I-3(-) competitive absorption, and lower aggregation of the dyes resulting from the synergistic action in the co-sensitized photovoltaic cells.