The effects of changing ligand structures of cobalt complexes as electrolytes on the performance of the dye-sensitized solar cell were investigated. In this paper, cobalt(II/III) tris(2,2′-bipyridine), cobalt(II/III) tris(4,4′-dimethyl-2,2′-bipyridine) and cobalt(II/III) tris(4,4´-dimethoxy-2,2′-bipyridine) complexes as electrolytes in conjugate with organic dye D149 were investigated to consider the correlation of the cobalt complexes structural on the efficiency of the dye-sensitized solar cell. The Voc values of the prepared cells are related to the redox potential of their complexes and the maximum Voc was observed with cobalt(II/III) tris(2,2′-bipyridine) electrolyte. The obtained results represented that the cobalt(II/III) tris(4,4´-dimethyl- 2,2′-bipyridine) electrolyte has the highest efficiency in the solar cell compared with other cobalt complexes. These observed results have been interpreted by a possible interaction between the dye and cobalt complexes, which is more pronounced in the cobalt(II/III) tris(4,4´-dimethoxy- 2,2′-bipyridine) cell. This interaction should be fine-tuning with the structure of dye and complex to increase the efficiency of the dye-sensitized solar cell. In addition, the results demonstrated that a thinner layer of the TiO2 film decrease both the effects of mass transport issues and the charge recombination, therefore, it has significant advantages for cobalt electrolyte.