Bulky Iridium NHC Complexes for Bright, Efficient Deep‐Blue OLEDs

Abstract Four new deep‐blue‐emitting iridium(III) NHC complexes containing sterically demanding ligands are synthesized. The four complexes show bright, deep‐blue emission, with emission maxima between 420 and 427 nm in both acetonitrile solution and 30 wt% doped films in TSPO1; the two meridional isomers showing photoluminescence quantum yields, Φ _PL , in doped films of 80% and 89%. The two meridional isomers are used to assess the impact of emitters containing bulky, sterically demanding ligands on the performance of organic light‐emitting diodes (OLEDs). OLEDs employing a stepped doping profile with mer ‐Ir(tfpi_tmBn) ₃ as the emitter produce the highest performing devices in this study, with these devices exhibiting deep‐blue [λ _EL = 429 nm, CIE = (0.16, 0.08)] emission and a maximum external quantum efficiency (EQE _max ) of 14.9%, which decreases to 11.7% at 100 cd m ⁻² . The performance of the OLEDs shows very good efficiencies and moderate efficiency roll‐offs in comparison to reported phosphorescent deep‐blue OLEDs with CIE _y ≤ 0.08, as required for commercial displays. The promising results suggest that the design strategy of adding steric bulk to blue emitting iridium complexes containing NHC ligands is a useful strategy for reducing intermolecular interactions between emitters in OLEDs.