Solution-processed red iridium complexes based on carbazole-phenylquinoline main ligand: Synthesis, properties and their applications in phosphorescent organic light-emitting diodes

New carbazole-phenylquinoline (CVz-PhQ) based iridium complexes were designed and synthesized for their application in red phosphorescence organic light-emitting diodes (PhOLEDs) and their photophysical, electrochemical and electroluminescence (EL) properties were investigated. The PhOLEDs were fabricated using bis[9-(2-(2-methoxyethoxy)ethyl)-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C2′]iridium 2-pyrazinecarboxylic acid (EO-CVz-PhQ)2Ir(prz) and bis[9-(2-(2-methoxyethoxy)ethyl)-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C2′]iridium 5-methyl-2-pyrazinecarboxylic acid (EO-CVz-PhQ)2Ir(mprz) as the emitter and PVK, co-doped with OXD-7 as the electron transport material and TPD as the hole transport material, as the polymer host. The red emissive PhOLEDs, based on the ITO/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/4,4′,4″-tris(carbazole-9-yl)triphenylamine (TCTA)/poly(N-vinylcarbazole) (PVK):N,N′-diphenyl-N,N′-(bis(3-methylphenyl)-[1,1-biphenyl]-4,4′-diamine (TPD):1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7):Ir complex/cathode configuration, exhibited a maximum external quantum efficiency of 3.68% and a maximum luminance efficiency of 6.69 cd/A. Furthermore, by introducing a TCTA interlayer, the PhOLEDs showed only a slight efficiency roll off of 5.4% from a low current density (1.81 mA/cm2) to a high current density (44.59 mA/cm2).