D-π-A organic dyes with carbazole as donor for dye-sensitized solar cells

Two donor-π-acceptor (D-π-A) organic dyes with carbazole as donor, phenylethynyl, thienylethynyl as π-spacers and cyanoacrylic acid as acceptor, have been synthesized and characterized. These dyes exhibit charge transfer character in the ground and excited states as supported by the UV-vis and fluorescence studies. They also show interesting electrochemical properties. DFT and TDDFT studies reveal that large intramolecular charge transfer takes place from the HOMO to LUMO, though the donor carbazole is twisted (∼51°) with respect to the π-conjugated spacer and acceptors with an idea of testing the dyes as sensitizers for DSSC. The DSSC devices were fabricated with these dyes by using redox electrolyte in a nonvolatile methoxypropionitrile solvent. The efficiency of the cells, short circuit current density, Jsc, and open circuit photovoltage, Voc, and fill factor, FF, has been obtained for the two molecules. Calculations based on DFT plane wave method reveal the strong binding of the dyes on the surface of TiO2 (1 0 1) surface. It is concluded that these dyes can play the role of sensitizers in DSSC.