We introduced sensitizing dyes into the bulk-heterojunction (BHJ) photovoltaic (PV) layer of polymer solar cells (PSCs). The sensitizing dyes doped were Bis(tetra butyl ammonium) cis-dithio cyanato bis(2,2`-bipyridine-4-carboxylicacid-4`-carboxylate) ruthenium (II) (N719 dye) and the BHJ PV layer used was made of poly (3-hexylthiophene) (P3HT) and phenyl C61-butyric acid methyl ester (PCBM). It was found that the N719 dyes increase the photovoltaic performance, i.e., increasing open-circuit voltage and short-circuit current density with improved fill factor. For the P3HT: PCBM PV cells doped with the N719 dyes (0.24wt %), an increase in power conversion efficiency of 4.0% was achieved, compared to that of the control cells (3.6%) without the N719 dyes.