Green and yellow pyridazine-based phosphorescent Iridium(III) complexes for high-efficiency and low-cost organic light-emitting diodes

Abstract

Despite efficient electroluminescence performance, the high fabrication cost due to the utilization of noble metals impedes the commercialization of phosphorescent organic light-emitting diodes (PHOLEDs) based on iridium(III) complexes. In this paper, we designed and synthesized a series of green and yellow phosphorescent iridium(III) complexes with 3-(2,4-difluorophenyl)-6-methylpyridazine as the cyclometalating ligand to fabricate high-performance and low-cost PHOLEDs. By the introduction of a pyridazine moiety to enhance the coordination bond between iridium(III) ion and cyclometalating ligands, these iridium(III) complexes were obtained in high yields and exhibit good thermal stabilities and volatilities, which are beneficial to reduce the device manufacturing cost. Besides, high photoluminescence quantum yields (PLQYs) and short phosphorescent lifetimes of these pyridazine-based iridium(III) complexes endow their PHOLEDs with excellent device performance, which can be promising for practical applications. Particularly, the green emitter (fpdz)2Irpic exhibited a high PLQY of 0.89 in solid doped thin-film; PHOLED based on (fpdz)2Irpic achieved an outstanding maximum external quantum efficiency (EQEmax) of 28.7% with ultralow efficiency roll-off of 2% at the high luminance of 1000 cd m−2, which was superior to the commercial green phosphor bis(phenylpyridineyl)iridium(acetylacetonate) [(ppy)2Ir(acac), EQEmax = 24.2%].