Organic dyes containing fluoreneamine donor and carbazole π-linker for dye-sensitized solar cells

•Organic dyes containing fluoreneamine donor and carbazole linker are reported.•The optical and photovoltaic properties are tuneable by fluorene substitution in donor.•A dye with difluorenylamine donor exhibited high power conversion efficiency (6.4%).•Difluorenylamine donor is beneficial to retard electron recombination.

A series of new organic dyes containing fluoreneamine-based donor and carbazole π-spacer are reported. These dyes displayed longer wavelength charge transfer absorption when compared to that of the corresponding phenylamine analogs. Fluoreneamine-based donors shifted the lowest unoccupied molecular orbital upwardly which is beneficial for the injection of electrons from the excited dye into the conduction band of TiO2 and lowered the oxidation potential of the dyes. The electronic perturbations caused by the fluorene unit have been confirmed by the density functional theoretical calculations. A device fabricated using a dye featuring difluorenylaminocarbazole donor and thiophene in the π-spacer exhibited promising power conversion efficiency (6.4%). The interfacial electron transfer kinetics has been elucidated by electrochemical impedance spectroscopy which showed the beneficial role of difluorenylamine unit in suppressing the electron recombination.

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