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

Four new deep-blue-emitting iridium(III) NHC complexes containing sterically demanding ligands have been synthesised. The four complexes showed 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, ΦPL, in doped films of 80 and 89%. The two meridional isomers have been 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 produced the highest performing devices in this study, with these devices exhibiting deep-blue [λEL = 429 nm, CIE = (0.16, 0.08)] emission and a maximum external quantum efficiency (EQEmax) of 14.9%, which decreased to 11.7% at 100 cd m-2. The performance of the OLEDs is amongst the highest efficiencies and lowest efficiency roll-offs reported for phosphorescent deep-blue OLEDs with CIEy ≤ 0.08, as required for commercial displays.