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Novel cyanine dyes, in which a tetrahydroquinoline derivative is used as an electron donor and 1‐butyl‐5‐carboxy‐3, 3‐dimethyl‐indol‐1‐ium moiety is used as an electron acceptor and anchoring group, were designed and synthesized for application in dye‐sensitized solar cells. The photovoltaic performance of these solar cells depends markedly on the molecular structure of the dyes in terms of the n‐hexyl chains and the methoxyl unit. Retardation of charge recombination caused by the introduction of n‐hexyl chains resulted in an increase in electron lifetime. As a consequence, an improvement of open‐circuit photovoltage (V_oc) was achieved. Also, the electron injection efficiencies were improved by the introduction of methoxyl moiety, which led to a higher short‐circuit photocurrent density (J_sc). The highest average efficiency of the sensitized devices (η) was 5.6 % (J_sc=13.3 mA cm⁻², V_oc=606 mV, and …