Toward High-Performance Vacuum-Deposited OLEDs: Sublimable Cationic Iridium(III) Complexes with Yellow and Orange Electroluminescence.

Great advances in the development of efficient luminescent materials are the driving force behind organic light-emitting diodes (OLEDs). Sublimable ionic transition-metal complexes (iTMCs) have emerged as a large family of new emissive dopants applied for vacuum-deposited OLEDs, while the achievement of excellent performance remains arduous. A series of novel sublimable cationic iridium(III) complexes have been designed and synthesized, containing an imidazole-type ancillary ligand and tetraphenylborate-type negative counter-ions with large steric hindrance and well-dispersed charges. The photophysical properties, electrochemical behaviors, and thermal stability are fully investigated and discussed, then demonstrated by theoretical calculations. Yellow- and orange-emitting OLEDs thereof are fabricated by vacuum evaporation deposition, realizing a high external quantum efficiency of up to 11 %, maximum brightness over 27.3×103  cd m-2 and low turn-on voltages below 2.4 V, among the best results of analogous phosphorescent OLEDs based on iTMCs. This work indicates the promising applications of sublimable iTMCs in state-of-the-art vacuum-deposited optoelectronic devices.