Ru-based sensitizers (N719, N3, black dye and etc.) have been developed continuously and have reached an efficiency of ~11.7% under A.M. 1.5 irradiation. However, these Ru-based sensitizers are not adequate to commercialization because of stability issue and need of thick TiO₂ film for high efficiency. Therefore, we researched 9 organic sensitizers (Fig. 1) changing functional groups (methoxy and carbazole group) and bonds between donor and π-bridge to know which functional groups can enhance the stability and perform high power conversion efficiency at thin TiO₂ film. The 9 sensitizers were basically composed of dithieno[3,2-b:2',3'-d]thiophene (DTT), having robust stability, as a π-conjugated bridge. As a result, TP2 having methoxy groups achieved the highest power conversion efficiency in dithieno[3,2-b:2',3'-d]thiophene (DTT) based sensitizers but stability of TP2 was the worst among the 9 sensitizers. On the other hands, although TP3 showed lower efficiency than that of TP2, TP3 achieved the highest stability against extreme environment. In particular, TP3 showed the strong stability against water because strong hydrophobicity of carbazole groups protected the anchoring groups of sensitizers from water. Finally, photovoltaic and electrochemical properties of 9 sensitizers were measured. Table 1. Shows the photovoltaic parameters of TP series under A.M. 1.5 illumination.