We designed and synthesized two new zinc porphyrin dyes for dye-sensitized solar cells (DSCs). Subtle molecular structural variation in the dyes significantly influenced the performance of the DSC devices. By utilizing these dyes in combination with a cobalt-based redox electrolyte using a photoanode made of mesoporous TiO2, we achieved a power conversion efficiency (PCE) of up to 12.0% under AM1.5G (100mWcm(-2)) simulated solar light. Moreover, we obtained a high PCE of 6.4% for solid-state dye-sensitized solar cells by using 2,2,7,7-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene as a hole-transporting material.