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 4H-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/cm², which was likely attributable to an increase in outcoupling efficiency via molecular orientation.

Date Published: 23 September 2016
PDF: 12 pages
Proc. SPIE 9941, Organic Light Emitting Materials and Devices XX, 994127 (23 September 2016); doi: 10.1117/12.2237528

Published in SPIE Proceedings Vol. 9941:
Organic Light Emitting Materials and Devices XX
Franky So; Chihaya Adachi; Jang-Joo Kim, Editor(s)