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, eta) 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 J(SC) of 19.46 mA/cm(2), V-OC 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.