Green phosphorescent homoleptic iridium(III) complexes for highly efficient organic light-emitting diodes

Homoleptic Ir(III) complexes, Ir(ppyTMS)3 and Ir(mPppyTMS)3, based on 2-phenyl-5-(trimethylsilyl)pyridine (ppyTMS) and 2-(1,1′-biphenyl-3′-yl)-5-(trimethylsilyl)pyridine (mPppyTMS) as cyclometalated ligands, respectively, were synthesized for highly efficient green phosphorescent organic light-emitting diodes (OLEDs). The trimethylsilyl and phenyl groups introduced on the 2-phenylpyridine ligand suppressed the intermolecular interactions and the triplet-triplet annihilation process taking place via molecular aggregation, which otherwise decrease the OLED efficiency. The green phosphorescent OLEDs doped with Ir(ppyTMS)3 and Ir(mPppyTMS)3 as green emitters exhibited maximum electroluminescent wavelengths of 525 and 529 nm, respectively, at an optimized doping concentration of 5%. The Commission Internationale de L'Eclairage coordinates of these OLEDs were (0.35,0.62) and (0.37,0.61), respectively, at a luminance of 1000 cd m−2. The maximum external quantum efficiency and maximum power efficiency (PEmax) were 16.6%/66.1 lm W−1 for the Ir(ppyTMS)3 device and 18.1%/70.3 lm W−1 for the Ir(mPppyTMS)3 device, which were higher than those of Ir(ppy)3 without substituents on the 2-phenylpyridine ligand. Moreover, the PEmax value of the Ir(mPppyTMS)3 device is one of the highest values among the reported devices fabricated using homoleptic Ir(III) complexes for green phosphorescent OLEDs.