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

The synthesis of seven iridium complexes [Ir(CˆN)2(NˆN)][PF6] (AS9-15) designed as dyes for p-type DSSC is described. These complexes comprise a 4-(pyrid-2-yl)benzoic acid as the cyclometalating/anchoring ligand with different diimine ligands acting as electron accepting ancillary ligands. DFT analysis together with photophysical investigations reveal how using different π-systems on the ancillary ligand it is possible to tune the absorption spectra of these complexes and to enhance the spatial separation between the HOMO and LUMO. Computational studies demonstrate an ideal HOMO to LUMO charge transfer directionality for the presented [Ir(CˆN)2(NˆN)]+ frameworks, promoting a favourable hole transfer into the NiO cathode valence band upon photoexcitation in p-type DSSC devices. Preliminary tests on NiO-based p-type DSSCs have been carried out confirming the potential use of complexes AS9-15 as a basis for continued development as DSSC chromophores.