Efficient green electroluminescence based on an iridium(iii) complex with different device structures

Abstract

A series of phosphorescent organic light-emitting diodes (OLEDs) with single or double light-emitting layer(s) were fabricated using a green iridium(III) complex Ir(BTBP)₂POP containing 2′,6'-bis(trifluoromethyl)-2,4′-bipyridine (BTBP) cyclometalated ligand and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol (POP) ancillary ligand. The single light-emitting layer devices with the structure of ITO/MoO₃ (5 nm)/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 30 nm)/mCP (N,N′-dicarbazolyl-3,5-benzene, 5 nm)/Ir(BTBP)₂POP:PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 8 wt%, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) achieved the highest luminance, current efficiency, power efficiency and external quantum efficiency (EQE) up to 47 599 cd m⁻², 86.5 cd A⁻¹, 52.2 lm W⁻¹ and 31.0%, respectively. Furthermore, the double EML device with the structure of ITO/MoO₃ (5 nm)/TAPC (30 nm)/mCP:Ir(BTBP)₂POP (8 wt%, 10 nm)/PPO21:Ir(BTBP)₂POP (8 wt%, 10 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al (100 nm) obtained a higher maximum luminance of 49 139 cd m⁻² and slightly lower maximum current efficiency, power efficiency and EQE of 75.8 cd A⁻¹, 51.7 lm W⁻¹ and 27.2%, respectively, with lower turn-on voltage. This research suggested that not only the doping concentration but also the thickness of the emissive and electron transport layers strongly affect the EL performances.