A facile and convenient synthesis and photovoltaic characterization of novel thieno[2,3-b]indole dyes for dye-sensitized solar cells

•Novel dyes carrying the thieno[2,3-b]indole unit have been designed and synthesized, as promising sensitizers for solar cells.•Thieno[2,3-b]indole system was used for the first time as a donor part of dye-sensitizers for DSSC.•Major photophysical and electrochemical properties of thieno[2,3-b]indole dyes have been determined.•Photovoltaic performance of new sensitizers was evaluated by a device fabrication study.

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 CC 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 spectrophotometry 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 η = 0.37% (FF = 73%) and η = 0.79% (FF = 69%) under 100 mW cm−2 simulated AM 1.5 G solar irradiation, respectively.

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