Efficient metal-free sensitizers bearing circle chain embracing π-spacers for dye-sensitized solar cells

Abstract

The circle chain embracing D–π–A dyes have been demonstrated as a promising type of sensitizer for dye-sensitized solar cells (DSCs). To further develop this type of organic dye for DSCs and discover the heuristic points on energy level matching, we introduced various donor moieties (carbazole, indoline and dimethoxytriphenylamine) into a D–π–A system bearing a circle chain embracing a π-spacer and cyanoacrylic acid as an acceptor, resulting in three new organic dyes LJ-4, LJ-5 and LJ-6, respectively. Among these dyes, the energy levels of the molecular orbitals in carbazole dye LJ-4 match best with the conduction band of TiO₂ and the redox potential of the redox species. DSCs employing the sensitizer LJ-4 and the iodine redox electrolyte exhibit a high power conversion efficiency of 9.20%, measured under the 100 mW cm⁻², simulated AM1.5 sunlight. This work highlights the importance of energy level matching in the further molecular design of a circle chain embracing D–π–A dyes.