A novel heteroleptic iridium complex with multifunctional ligands used for polymeric light-emitting diodes

A novel iridium complex using 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9H-carbazole containing both hole-transporting group and electron-transporting group as main ligand and 2-(5-p-tolyl-2H-1,2,4-triazol-3-yl)pyridine as ancillary ligand was synthesized and investigated in this paper. The iridium complex possesses high solubility, high thermal stability with 5% weight-reduction temperature (ΔT5%) of 390 °C and glass-transition temperature (Tg) of 218 °C. Polymeric light-emitting diodes (PLEDs) based on structure of ITO/PEDOT: PSS/PVK: PBD: iridium complex/TPBI/CsF/Al fabricated by solution-processed technology were measured. The PLED using the iridium complex as phosphorescent dopant at 4 wt.% doping concentration is optimal which shows the maximum luminance of 7746 cd·cm−2, maximum current efficiency of 14.0 cd A−1 and maximum external quantum efficiency of 5.8% with CIE coordinates of (0.48, 0.50). The EL emission originates from both monomers and exciplexes formed from the iridium complex and PVK.

► The main ligand contains a hole-transporting group, an electron-transporting group and a solubilizing group.
► The ancillary ligand is used for improving yield and stability.
► The iridium complex possesses good solubility, good thermal stability with ΔT5% of 390 °C and Tg of 218 °C.
► PLEDs using the iridium complex show the maximum luminance of 7746 cd cm−2 and maximum current efficiency of 14.0 cd A−1.