New cyclometalated iridium(III) dye chromophore complexes for n-type dye-sensitised solar cells

The synthesis of seven iridium complexes where aryl-1,2,3-triazole (Ar-tz) moieties act as cyclometalating ligands with 2,2’-bipyridyl-4,4’-dicarboxylic acid (dcb) as a N^N ancillary/anchoring ligand, is described. The new dye complexes [Ir(Ar-tz)2(dcb)][PF6] (AS1-7) were prepared in a two stage procedure with iridium-chloride dimer isolation. DFT analysis together with photophysical investigations reveal how using different substituents on the phenyl ring, or a different aryl system, lead to the tuning of the absorption and emission properties of these complexes. Computational studies therefore demonstrate an ideal HOMO-LUMO directionality for the [Ir(Ar-tz)2(dcb)]+ framework, promoting a favourable electron transfer into the TiO2 conduction band upon photoexcitation. Preliminary unoptimized tests on TiO2 DSSCs have been carried out which show similar photovoltaic performance to the [Ir(ppy)2(dcb)][PF6] (ppy = 2-phenylpyridine) benchmark.