Two green iridium(iii) complexes containing the electron-transporting group of 4-phenyl-4H-1,2,4-triazole for highly efficient OLEDs

Abstract

Two new iridium(III) cyclometalated complexes (Ir-TN₃T and Ir-TN₄T) with 2′,6′-bis(trifluoromethyl)-2,3′-bipyridine (TN₃T) and 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine (TN₄T) as the cyclometalated ligands and 2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenol (dptp) as the ancillary ligand were developed. Both complexes are green phosphors with high photoluminescence quantum efficiency yields (λ_max = 540 nm, Φ = 71.2% for Ir-TN₃T and λ_max = 513 nm, Φ = 91.0% for Ir-TN₄T, respectively) in CH₂Cl₂ solution at room temperature. Organic light emitting diodes (OLEDs) with single-emitting-layer and double-emitting-layer structures exhibit good performances. Particularly, device D2 with a double-emitting-layer structure based on a Ir-TN₄T complex of 8 wt% doped concentration exhibits superior performances with a peak current efficiency of 94.29 cd A⁻¹ and a peak external quantum efficiency (EQE_max) of 31.43%, and the efficiency roll-off is mild. When the luminance reaches 10 000 cd m⁻², the EQE value can still be maintained at 30.26%. This study demonstrates that the Ir(III) complexes containing the ancillary ligand attached with the electron-transporting group of 4-phenyl-4H-1,2,4-triazole could facilitate charge trapping across the bulk of the device and they have promising applications in OLEDs.