Suppression of efficiency roll-off in solution-processed OLEDs using pyrimidine-based iridium complexes modified with...

Three bis-cyclometalated iridium complexes Ir1-Ir3 were successfully synthesized through mild reaction conditions. All complexes exhibit emission peaks at 507-509 nm, with excellent photoluminescence quantum efficiencies (PLQY) ranging from 69% to 97%. Self-quenching is significantly reduced because the steric spacers lead to minimum bimolecular interactions. Accordingly, the electroluminescence device based on complex Ir3 exhibits a maximum luminous efficiency of 39.6 cd A^-1, a high EQE of 13.1% with an efficiency roll-off of 4.2% at 1000 cd m^-2, which is much smaller than that (10.8%) of the Ir1-based device. Moreover, its devices exhibit excellent stability even at elevated doping concentrations, suggesting a notable reduction in intermolecular interactions caused by the steric pinene spacer.