Highly Efficient and Stable Green Phosphorescent Light-Emitting Diodes Based on Solution-Processable Ir(III) Complexes with Electron-Transporting Ancillary Ligands

Two green heteroleptic Ir(III) complexes are reported, namely, bis[5-(2-ethylhexyl)-8-trifluoromethyl-5H-benzo[c][1,5]-naphthyridin-6-one](2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenolate)iridium (III) (Ir(CF3BNO)(2)-pop) and bis[5-(2-ethylhexyl)-5H-benzo[c][1,5]naphthyridin-6-one](2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenolate)iridium (III) (Ir(BNO)(2)-pop) for solution-processed phosphorescent organic light-emitting diodes (PHOLEDs). Both the Ir(III) complexes exhibit high external quantum efficiency (EQE) and intense green emission upon using poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) as a hole injection layer (HIL); Ir(CF3BNO)(2)-pop based PHOLEDs perform better with an EQE of 23% and a current efficiency of 82 cd A(-1) than Ir(BNO)(2)-pop based PHOLEDs. In addition, to improve device operational lifetime, a crosslinkable HIL material, 9,9'-(cyclohexane-1,1-diylbis(4,1-phenylene))bis(N-phenyl-N-(4-(((4-vinylbenzyl)oxy)methyl)phenyl)-9H-carbazol-3-amine) (CPCzDPAX-1) is designed and synthesized. Device operational lifetimes of Ir(CF3BNO)(2)-pop and Ir(BNO)(2)-pop PHOLEDs incorporating the CPCzDPAX-1 HIL show 14-fold and 6-fold improvement, compared to the corresponding devices incorporating the PEDOT:PSS HIL. To the best of the authors' knowledge, this is the best device lifetime performance by using the combination of new Ir(III) complexes and HIL materials for solution-processed green PHOLEDs.