Synthesis and Characterization of Highly Efficient Solution‐Processable Green Ir(III) Complexes with High Current Efficiency and Very Low Efficiency Roll‐Off

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Abstract
Three new highly efficient green‐emitting heteroleptic phosphorescent iridium(III) complexes are designed and synthesized for the fabrication of solution‐processable phosphorescent organic light‐emitting diodes (PHOLEDs). Their photophysical, thermal, and electroluminescent (EL) properties are systematically investigated. The Ir(III) complexes comprise an amide‐bridged trifluoromethyl (CF3)‐substituted phenylpyridine unit as the main ligand and picolinic acid (pic) and tetraphenylimidodiphosphinate (tpip) as ancillary ligands. In addition, the 2‐ethoxyethnol (EO2) solubilizing group is attached to the 4‐position of pic ancillary ligand via tandem reaction, which improved the absolute photoluminescence quantum yields (PLQYs) and EL performance. The high‐performance solution‐processable PHOLEDs based on the bis[5‐methyl‐8‐trifluoromethyl‐5H‐benzo(c)(1,5)naphthyridin‐6‐one](4‐(2‐ethoxyethoxy picolinate) iridium(III) (Ir1) complex exhibit a maximum external quantum efficiency (EQE) of 24.22% and a maximum current efficiency (CE) of 92.44 cd A−1, with the latter being among the best reported CEs achieved though solution processing. In contrast, PHOLEDs with the bis[5‐hexyl‐8‐trifluoromethyl‐5H‐benzo(c)(1,5)naphthyridin‐6‐one] (tetraphenylimidodiphosphinato)iridium (Ir3) complex show extremely low efficiency roll‐off, with an EQEmax of 19.40% and an EQE of 19.29% at 10 000 cd m−2.
Funding Information
  • National Research Foundation of Korea (2013M3C1A3065522, 2016M3A7B4909246)
  • Ministry of Science, ICT and Future Planning

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