Two novel dyes IK-1,2 bearing the 8-alkyl-8H-thieno[2,3-b]indole unit as an electron-donating part of the push-pull system have been designed and prepared, as promising sensitizers for solar cells. The key steps of the synthesis involve the crotonic condensation of 1-alkylisatins with 2-acetylthiophene, followed by reduction of the C=C double bond and further cyclization through the Paal-Knorr reaction with the Lawesson reagent, thus leading to the formation of 2-(thien-2-yl) substituted thieno[2,3-b] indole derivatives. The optical and electrochemical properties of these dye's have been investigated by using spectrophotometry and cyclic voltammetry respectively, while their photovoltaic performance was evaluated by a device fabricatien study. The DSSCs based on IK-1 and IK-2 have demonstrated an efficiency of eta = 0.37% (FF = 73%) and eta = 0.7g% (FF = 69%) under 100 mW cm(-2) simulated AM 1.5G solar irradiation, respectively.