Highly efficient orange-red electroluminescence of iridium complexes with good electron mobility

Abstract

Two iridium complexes with 1-(2,6-bis(trifluoromethyl)pyridin-4-yl)isoquinoline (tfmpiq) and 4-(2,6-bis(trifluoromethyl)pyridin-4-yl)quinazoline (tfmpqz) main ligands and a tetraphenylimidodiphosphinate (tpip) ancillary ligand were applied in organic light-emitting diodes (OLEDs). The introduction of quinazoline greatly influences the nature of the complex. The quantum yield and the electron mobility of Ir(tfmpqz)₂(tpip) are much higher than those of Ir(tfmpiq)₂(tpip) (Ir(tfmpiq)₂(tpip): Φ: 0.47, μ_e: 8.93–9.47 × 10⁻⁶ cm² V⁻¹ s⁻¹ under an electric field from 1040 (V cm⁻¹)^1/2 to 1300 (V cm⁻¹)^1/2; Ir(tfmpqz)₂(tpip): Φ: 0.98, μ_e: 6.44–7.20 × 10⁻⁶ cm² V⁻¹ s⁻¹ under an electric field from 1040 (V cm⁻¹)^1/2 to 1300 (V cm⁻¹)^1/2). In addition, the Ir(tfmpqz)₂(tpip)-based device also displayed better performance than that using Ir(tfmpiq)₂(tpip). Furthermore, with a europium complex, Eu(DBM)₃phen (DBM = dibenzoylmethide; phen = 1,10-phenanthroline) as a sensitizer, the device based on Ir(tfmpqz)₂(tpip) with a double emissive layer structure of ITO/MoO₃ (3 nm)/TAPC (50 nm)/Ir(tfmpqz)₂(tpip) (5 wt%):TcTa (10 nm)/Eu(DBM)₃phen (0.2 wt%):Ir(tfmpqz)₂(tpip) (5 wt%):26DCzPPy (10 nm)/TmPyPB (50 nm)/LiF (1 nm)/Al (100 nm) displayed the best performance with a maximum luminance of 129 466 cd m⁻², and a maximum current efficiency and a maximum power efficiency of 62.96 cd A⁻¹ and 53.43 lm W⁻¹, respectively, with low efficiency roll-off. The current efficiency still remains as high as 58.84 cd A⁻¹ at a brightness of 1000 cd m⁻² and 53.27 cd A⁻¹ at a brightness of 5000 cd m⁻². These results suggest that Ir(III) complexes with quinazoline units are potential orange-red phosphorescent materials for OLEDs.