Efficient green photoluminescence and electroluminescence of iridium complexes with high electron mobility

Abstract

Aiming to balance the injection and transport of electrons and holes, nitrogen heterocycle and 1,3,4-oxadiazole derivatives were introduced in iridium(III) complexes to obtain organic light-emitting diodes (OLEDs) with high performances. Thus, two novel Ir(III) complexes (Ir(tfmphpm)₂(pop) and Ir(tfmppm)₂(pop)) with green emissions using 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine (tfmphpm) and 2-(2,6-bis(trifluoromethyl)pyridin-4-yl)pyrimidine (tfmppm) as cyclometalating ligands, and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol (pop) as an ancillary ligand were synthesized. Both emitters show high photoluminescence efficiencies up to 94% and good electron mobility. The devices using two emitters with the structure of ITO (indium-tin-oxide)/MoO₃ (molybdenum oxide, 5 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 30 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 5 nm)/Ir(III) complexes (6 wt%) : PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/Al (100 nm) display good electroluminescence performances with a maximum luminance of 48 981 cd m⁻², a maximum current efficiency of 92.79 cd A⁻¹ and a maximum external quantum efficiency up to 31.8%, respectively, and the efficiency roll-off ratio is low, suggesting that they have potential application in OLEDs.