Simple novel cyclometallated iridium complexes for potential application in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are considered a real solution for harnessing the energy of the sun and converting it into electrical energy, exceeding the value of 11% efficiencies with the most performing Ru(II) sensitizers. The photosensitizer dye plays a key role in DSSCs, and iridium complexes are potentially good candidates for application in those kind of cells. Here we report the synthesis and characterization of three new simple cyclometallated Ir(III) complexes of the type: [Ir(C^N)2(4,4′- dicarboxybipyridine)][PF6] (C^N = variously substituted phenylpyridine cyclometallating ligand) and we try to understand if there is an influence of the nature of the cyclometallating ligand on the photovoltaic performance of the related dye-sensitized solar cells. The use of more conjugated π-delocalized cyclometallating ligands, that slightly shifts the UV bands to higher wavelengths, affords little better photovoltaic parameters. In addition we report the emission spectra and the emission quantum yields of all the phosphorescent Ir(III) complexes.