Four organic dyes (TD1, TD2, TD3 and TD4) were synthesized which contained triphenylamine (TPA) moieties as electron donors and cyanoacrylic acid moieties as electron acceptors, ethenyl thiophene or ethenyl bithiophene/ alkyl bithiophene as π-conjugated linker. The structures of the molecules were characterized by IR, NMR and MS. The effects of the length of the π-conjugated unit and the alkyl chain on the photo-physical, electrochemical and photovoltaic properties. The results indicated that both short-circuit photocurrent density and open-circuit photovoltage have been remarkably improved by the alkyl-substituent, by which high PCE was obtained. TD3 dye with hexyl-substituted bithiophene as π-conjugated unit, exhibited a satisfied efficiency of 6.78%, which reached ～88.7% of an N719-based DSSCs (7.64%) fabricated and measured under the same conditions.