Effect of auxiliary chromophores on the optical, electrochemical, and photovoltaic properties of carbazole-based dyes

Organic dyes containing 2-diphenylaminocarbazole donors and decorated with auxiliary chromophores at the diphenylamine moiety have been synthesized and characterized. The nature of the chromophores on diphenylamine unit alters the light-harvesting properties and HOMO/LUMO energies of the dyes. Butoxy substitution raises the HOMO and lowers the LUMO energies. But the incorporation of fluorenyl units fine-tunes the LUMO upwardly, which improves the thermodynamic driving force for electron injection into the conduction band of TiO2 and hikes the incident photon-to-current conversion efficiency. Consequently, a dye with fluorene in the donor unit and thiophene in the π-conjugation pathway is the most efficient (5.76%) and has the highest photocurrent density (14.60mAcm-2) in the series. Electrochemical impedance analysis of the devices showed the importance of fluorene units in suppressing electron recombination. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.