23 September 2016 Deep-blue phosphorescent organic light-emitting diode with external quantum efficiency over 30% using novel Ir complex
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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 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.
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Hideko Inoue, Hideko Inoue, Yui Yamada, Yui Yamada, Nobuharu Ohsawa, Nobuharu Ohsawa, Satoshi Seo, Satoshi Seo, Shunsuke Hosoumi, Shunsuke Hosoumi, Takeyoshi Watabe, Takeyoshi Watabe, Satomi Mitsumori, Satomi Mitsumori, Hiromitsu Kido, Hiromitsu Kido, } "Deep-blue phosphorescent organic light-emitting diode with external quantum efficiency over 30% using novel Ir complex", Proc. SPIE 9941, Organic Light Emitting Materials and Devices XX, 994127 (23 September 2016); doi: 10.1117/12.2237528; https://doi.org/10.1117/12.2237528
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