Stable and charge recombination minimized π-extended thioalkyl substituted tetrathiafulvalene dye-sensitized solar cells

Abstract

Two new metal-free organic sensitizers have been designed based on tetrathiafulvalene scaffolds by implementing a donor–π–acceptor (D–π–A) approach in which thioalkyl substituted tetrathiafulvalene acts as a donor, substituted anthracene as a π-spacer and cyanoacrylic acid acts as an acceptor as well as an anchoring group. Spectroscopic, electrochemical and DFT studies confirmed the molecular integrity of both sensitizers. The onset of absorption of both sensitizers extends up to 600 nm in solution and up to 700 nm on nanocrystalline TiO₂. DFT studies specified that the HOMO is delocalized over the anthracene as well as the dithiole units, and the LUMO is delocalized over the anchoring group in both sensitizers. The new sensitizers have shown an improved efficiency of 7.15% in dye-sensitized solar cells using an I⁻/I₃⁻ redox couple. The enhanced efficiency might be due to the thioalkyl group wrapping over the anthracene π-spacer to prevent the recombination of electrons in the TiO₂ conduction band. Recombination studies indicate the regeneration of the oxidized dye due to the redox couple.