Iridium (III) complexes with 5,5-dimethyl-3-(pyridin-2-yl)cyclohex-2-enone ligands as sensitizer for dye-sensitized solar cells

The three iridium complexes based on 5,5-dimethyl-3-(pyridine-2-yl)cyclohex-2-enone ligand and pyridine-2,4-dicarboxyl acid (5b) or 2,2′-bipyridine-4,4′-dicarboxyl acid (5c) as ancillary anchoring ligands were synthesized and characterized as potential photosensitizer for dye-sensitized solar cells (DSSC). Using of cyclohexenone derivates as ligands extended the absorption response of the iridium complex to low energy band near 550 nm and shifted the maximum emission peak to deep red (near the 680 nm). The theoretical molecular orbital calculations shows that the HOMO orbitals of all the complexes are contributed by the combination of orbitals on Ir atom (about 50%) and π orbitals located on 5,5-dimethyl-3-(pyridine-2-yl)cyclohex-2-enone. While auxiliary ligands with anchoring group exclusively contribute to electron density of the LUMO orbital, accounting for 96.33% in 5b and 95.51% in 5c. It is beneficial for electron injection in DSSC application. Applying them to DSSC, the IPCE response of the DSSCs covered a wide visible spectral range from 350 to 675 nm and the cells presented an open-circuit voltage of 645 mV, a power conversion efficiency of 1.03%.