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 dyes have been investigated by using pectrophotometry and cyclic voltammetry respectively, while their photovoltaic performance was evaluated by a device fabrication study. The DSSCs based on IK-1 and IK-2 have demonstrated an efficiency of h = 0.37% (FF = 73%) and h = 0.79% (FF = 69%) under 100 mW / cm2 simulated AM 1.5 G solar irradiation, respectively.