New D–π–A organic dyes containing a tert-butyl-capped indolo[3,2,1-jk]carbazole donor with bithiophene unit as π-linker for dye-sensitized solar cells

Abstract

Two new D–π–A organic dyes containing a tert-butyl-capped indolo[3,2,1-jk]carbazole unit as a donor, bithiophene unit as a π-linker and cyanoacrylic acid as an acceptor (CL-10 and CL-11) have been designed and synthesized for dye-sensitized solar cells (DSSCs). By comparison, two dyes exhibit almost the same absorption and electrochemical properties, because the introduction of two hexyl groups at non-ortho β-positions of the 2,2′-bithiophene unit dose not destroy the planarity of the molecular skeleton of CL-11. However, the DSSC devices based on them show very different photovoltaic performances with power conversion efficiency (PCE) of 3.96% for CL-10 and 2.85% for CL-11, which can be attributed to the existence of the hexyl groups in CL-11 that lead to a big decrease of the dye adsorption onto TiO₂. The addition of chenodeoxylic acid (CDCA) as a coadsorbant can significantly improve the photovoltaic performances of the DSSCs with a big increase in the PCE for CL-10 (4.68%) and CL-11 (4.66%).