Fluorene-based organic dyes containing acetylene linkage for dye-sensitized solar cells

New organic dyes based on diphenylaminofluorene donors, cyanoacrylic acid acceptors and either ethynylbenzene or ethynylthiophene π-spacers have been synthesized and characterized as sensitizers for dye-sensitized solar cells. The dye with thiophene in the conjugation pathway exhibited longer wavelength absorption due to the significant lowering of the LUMO level when compared to the phenyl analog. However, the dye with the phenylacetylene linker displayed promising DSSC characteristics such as short circuit current, open circuit voltage and fill factor indicative of efficient charge generation and injection. The solvatochromic behavior of the dyes were examined in solvents of different polarity and found to exhibit negative solvatochromism of the fluorescence emission suggestive of a nonpolar solvent stabilized excited state with a significant structural reorganization. The TDDFT computations were used to explain the optical properties of the dyes.

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► Fluorene-based organic dyes featuring acetylene linkage are described.
► Thiophene containing dye exhibited red-shifted absorption.
► Photon-to-current conversion efficiency of 3.0% is realized for a ethynylbenzene-based dye.