Comparative studies of substituted ruthenium(II)–pyrazoyl–pyridine complexes with classical N3 photosensitizer: the influence of NCS dye ligands on the efficiency of solid-state nanocrystalline solar cells

New dyes of the type [Ru(II)(bdmpp)(dcbpy)X](PF6) (where bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine, dcbpy is 2,2′-bipyridine-4,4′-dicarboxylic acid and X=Cl− (RuCl) or NCS− (RuNCS)) have been tested with success as molecular antennas in titania nanocrystalline photoelectrochemical cells (DSSCs) and compared with the Grätzel’s N3 photosensitizer, in modules fabricated using a composite polymer solid-state electrolyte The solar cells made using the complex with the NCS ligand have a significantly better performance than those fabricated with the dye containing the Cl− ligand. The comparison of their action spectra has revealed that the RuNCS dye presents higher incident monochromatic photon-to-current conversion efficiency (IPCE) values. The RuNCS cells produced a short-circuit photocurrent as high as 4.3 mA cm−2 and an open-circuit photovoltage of 584 mV, which led to an overall energy conversion cell efficiency (η) as high as 1.64%, about three times higher than the corresponding efficiency obtained with RuCl dye. On the basis of the obtained results the energetic diagrams of the corresponding DSSCs were constructed. The observed differences are attributed to the contribution of the isothiocyanato group on the light absorption, on the redox properties and on the increase of the charge injection efficiency. A gain in photovoltaic performance of the NCS containing dyes is also proposed through a reduction of the dark current of the corresponding solid-state solar cells.