Effect of Donors on Photophysical, Electrochemical and Photovoltaic Properties of Benzimidazole-Branched Dyes

Abstract

A series of benzimidazole-branched organic dyes containing different donors such as carbazole or phenothiazine at C4 and C7 positions of benzimidazole, bithiophene linker and cyanoacrylic acid acceptor are reported. Incorporation of donors increased the molar extinction coefficient of the intramolecular charge transfer absorption peak and contributed to the enhanced photocurrent generation than the control dye without donors. The favourable properties of the new dyes are attributed to the suitable HOMO and LUMO energy levels which facilitated dye regeneration and electron injection from the excited state of the dyes into the conduction band of TiO 2 . The dye-sensitized solar cells fabricated using the dyes possessing phenothiazine-based donor yielded better efficiency than the dyes containing carbazole donor. It is attributed to the effective retardation of electron recombination resulting from the non-planar molecular geometry of the former. These results suggest that opportunities exist for the improvement of benzimidazole-based organic dyes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim