New cyanoacetanilides based dyes as effective co-sensitizers for DSSCs sensitized with ruthenium (II) complex (HD-2)

The synthesis of six novel 2-cyanoacetanilide-derived metal-free organic dyes, named SA11-16, containing 4-dimethylaminophenyl, 4-anisyl or 2,4,5-trimethoxyphenyl as electron donating moieties, and carboxyl (–COOH) or nitro (–NO2) groups as anchoring moieties was reported along with their optical properties, theoretical geometrical studies and spectroscopic characterization. From the UV–Vis absorption spectra, co-sensitizers SA11-14 carrying –NO2 as an anchoring moiety are found to be more red-shifted than other co-sensitizers having –COOH as an anchoring group, this may be due to the strong electron withdrawing nature of –NO2 acceptor unit. Further, the co-sensitization technique was applied by combining the newly prepared organic dyes with a previously published HD-2 ruthenium-based complex for dye-sensitized solar cells (DSSCs) and the corresponding effect on the photovoltaic performance was studied. All the metal-free dyes exhibited improved photoconversion efficiencies (PCE, η) in the co-sensitized DSSCs compared to the one fabricated with HD-2 alone. Among the fabricated devices, SA12 as a co-sensitizer obtained the best photovoltaic performance with JSC of 19.46 mA/cm2, VOC of 0.69 V and the overall PCE of 8.69%. Finally, the calculated electron lifetimes obtained from electrochemical impedance spectroscopy (EIS) measurements coincided well with the photovoltaic measurements.