Ir(III) Phosphors Modified with Fluorine Atoms in Pyridine-1,2,4-triazolyl Ligands for Efficient OLEDs Possessing Low-Efficiency Roll-off

Five neutral heteroleptic Ir(III) complexes 1–5 using the same cyclometalated ligand and different pyridine-1,2,4-triazolyl derivatives as ancillary ligands with fluorine substituents attached, were rationally designed and prepared. Their photophysical, electrochemical, and thermal properties were studied, and theoretical calculations were performed to understand the emission behaviors as well. Introducing fluorine atoms has little effect on the photophysical and thermal properties, but the performances of the resulting devices can be fine-tuned. Among them, a heavy doping level device employing a phosphor with five fluorine atoms delivers superior device efficiencies with ηc = 32.6 cd A–1 and ηp = 27.6 lm W–1, respectively, which is higher than those of other counterparts. Importantly, such a device exhibits almost negligible roll-off in luminance efficiency. Despite nondoped devices achieving good EL performance, more fluorine atoms lead to a relatively higher efficiency roll-off. The results suggest th...