Deep-blue phosphorescent organic light-emitting diode with external quantum efficiency over 30% using novel Ir complex

Abstract

We report a newly developed deep-blue phosphorescent iridium complex exhibiting a narrow emission spectrum. The use of this complex resulted in a deep-blue organic light-emitting diode (OLED) with an external quantum efficiency (EQE) exceeding 30%. Two iridium complexes with a 4 H -1,2,4-triazole ligand which has an adamantyl group at the 4-position were synthesized, with the resulting effects of the adamantyl group on photoluminescence (PL) behavior investigated. [Ir(Adm1) 3 ] having a 1-adamantyl group did not exhibit any emissions at room temperature, whereas [Ir(Adm2) 3 ] having a 2-adamantyl group exhibited a blue emission with a peak wavelength of 459 nm and a high PL quantum yield of 0.94. Structural transformations between the ground state and excited state were estimated by molecular orbital calculations, which suggests that [Ir(Adm1) 3 ] undergoes a considerably more extensive change than [Ir(Adm2) 3 ]. It is therefore probable that [Ir(Adm1) 3 ] ultimately experiences thermal deactivation owing to structural relaxation. Furthermore, an OLED was fabricated using [Ir(Adm2) 3 ] as a dopant. The associated electroluminescence spectrum had an emission peak at 457 nm and a relatively small shoulder peak at 485 nm, which are consistent with the PL spectrum. A narrowed emission spectrum with a full width at half maximum of 58 nm was obtained, leading to a deep-blue emission with high color purity (CIE, x = 0.15, y = 0.22). This device ultimately exhibited an extremely high EQE of 32% at 2 mA/cm 2 , which was likely attributable to an increase in outcoupling efficiency via molecular orientation.