Developing photosensitizers with high extinction coefficients, proper electronic structures, and steric properties is warranted for the dye-sensitized solar cells (DSCs) employing one-electron outer-sphere redox shuttles. DSCs incorporating Co(II/III)tris(1,10-phenanthroline)based redox electrolyte and three synthesized organic dyes as photosensitizers (M14, M18, and M19) are described. The hexapropyltruxene group on the dyes retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the [Co(III)-(phenanthroline) 3 ] 3+ ions, which enables attainment of high photovoltages approaching 0.9 V. The measurement of photocurrent transients shows that the mass transport limitation of the cobalt redox shuttle has been largely removed by using thin TiO 2 films. DSCs sensitized with M14 in combination with the cobalt redox shuttle yield a DSC with an overall power conversion efficiency (PCE) of 7.2% under 100 mW cm −2 AM1.5 G illumination. The influences of the dye structure on the performance of DSCs were also investigated.