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

Abstract 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.