Solution-Processed High Color-Purity Red PhOLEDs Based on Heteroleptic Bis-Cyclometalated Iridium Complexes

Solution-processing techniques offer a simpler fabrication process and enable the production of large-area optoelectronic devices, providing significant advantages over traditional vacuum deposition methods. This study focuses on developing high color-purity red solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) using five bis-cyclometalated iridium(III) complexes, previously developed by our group, as emissive dopants. These emitters have high photoluminescence quantum yields and use 1-phenylisoquinoline (piq) as the common cyclometalating (C∧N) ligand, combined with two complementary classes of monanionic ancillary (L∧X) ligands: N-substituted salicylaldimine (sal-R) and N-substituted 2-picolinamide (pic-R), where R denotes the N-substituent. The complexes were doped into a host matrix consisting of poly(vinyl carbazole) (PVK) for hole transport and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) for electron transport at varying concentrations. The optical and photophysical properties of PVK:PBD thin films doped with these Ir complexes were characterized. The doped thin films were used as emissive layers in solution-deposited PhOLED devices, all of which emitted red light. Notably, the device using the emitter with the highest quantum yield, which includes an N-propyl salicylaldimine L∧X ligand, displays red color coordinates (CIEx, CIEy) of (0.67, 0.33), matching the standard red color coordinates (CIEx, CIEy) of (0.67, 0.33) recommended by the National Television System Committee (NTSC) standard.