For the commercialization of flexible dye sensitized solar cells (DSCs), to achieve high performance from a thin TiO₂ active layer (~1- μm) is indispensable because of mechanical stability and low cost fabrication. Molecular engineering of sensitizers plays a key role in the performance of thin film DSCs as the following strategies: (1) planarity for high extinction coefficients, (2) low aggregation to prevent the self-quenching of photo-excited excitons, and (3) strong intramolecular charge transfer (ICT) for efficient charge injection and broad absorption. Therefore, we developed the three types of dithieno[3,2-b;2′,3′-d]thiophene (DTT)-based organic sensitizers for high-performance thin photoactive TiO₂ films and investigate the different types of bonding between the triarylamine electron donor and the conjugated DTT π-bridge by the introduction of single (S-DAHTDTT), double (D-DAHTDTT), and triple bonds (T-DAHTDTT). As a result, with only 1.3-μm transparent and 2.5-μm TiO₂ scattering layers, the triple bond sensitizer (T-DAHTDTT) shows the highest power conversion efficiency (η = 8.4%; V_OC = 0.73 V, J_SC = 15.4 mA·cm⁻² and FF = 0.75) in an iodine electrolyte system under one solar illumination (AM 1.5, 1000 W·m⁻²), followed by the single bond sensitizer (S-DAHTDTT) (η = 7.6%) and the double bond sensitizer (D-DAHTDTT) (η = 6.4%). In this study, we suggests that the triple bond can increase the performance of DSC with a thin photoactive film by enhancing not only J_SC through improved ICT, but also V_OC through the evenly distributed sensitizer surface coverage. We analyzed these correlation mainly in terms of charge injection efficiency, level of photo-charge storage, and charge transport kinetics.