Tris(5-phenyl-1H-1,2,4-triazolyl)iridium(III) Complex and Its Use in Blue Phosphorescent Organic Light-Emitting Diodes to Provide an External Quantum Efficiency of up to 27.8%

Although studies have investigated various N-heterocyclic-based Ir(III)-cyclometalates that exhibit high efficiency and electrochemical stability, blue-phosphorescent Ir(III) complexes with further improved efficiency and blue-emission purity are needed for use as emitters in organic light-emitting diodes (OLEDs). Therefore, the preparation and comprehensive characterization of a phenyl-1,2,4-triazole-based facial-homoleptic iridium(III) complex, TzIr (fac-tris(1-(2,6-diisopropylphenyl)-3-methyl-5-phenyl-1H-1,2,4 triazolyl)iridium(III)) is herein described. The complex shows a definite blue-emission band (λ_em = 456 nm) in the solution and film states at ambient temperature. Moreover, this complex exhibits considerably high phosphorescent quantum efficiency (80%) and thermal stability (T_d5 = 362 °C). Multilayer phosphorescent OLEDs using TzIr as the emitter and 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP)/ 9-(3′-(9H-carbazol-9-yl)-5-cyano-[1,1′-biphenyl]-3-yl)-9H-carbazole-3-carbonitrile (CNmCBPCN) as the mixed host are fabricated. The devices exhibit outstanding performance, with a high external quantum efficiency (27.8%), current efficiency (38.7 cd A⁻¹), and CIEy (y coordinate value of the Commission Internationale de l'Eclairage color space) less than 0.18. The results of this study indicate that this novel 1,2,4-triazole-based dopant, TzIr, is a promising candidate for developing highly efficient blue-phosphorescent emitters for use in OLEDs.