Electroluminescence property of highly soluble Ir(III) complex utilized by various hole blocking layers in polymer light emitting diodes.

The tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] is a well known highly efficient green light-emitting phosphorescent guest dye dopant, but its relatively low solubility has been obstructing it to be used in polymer light-emitting diodes (PLEDs). According to our latest reports the solubility of Ir(ppy)3 complexes with the carbazole ligands, i.e., Ir(Czppy)3, was improved significantly in organic solvents, and was sufficient to be used in soluble process. This highly soluble Ir(Czppy)3 complex showed remarkably higher photoluminescence characteristics than conventional Ir(ppy)3, but it showed similar or comparably better electroluminescence (EL) characteristics, when the PLED was composed by widely used conventional hole blocking layer (HBL) and electron transport layer; 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline and tris(8-hydroxyquinoline)aluminum, respectively. In this report, we applied various HBLs to improve the EL characteristics of soluble Ir(III) complex based phosphorescent PLEDs. The PLEDs utilized by the wide band-gap 3-(4-biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole demonstrated highly improved the current and the external quantum efficiency of 17.61 cd/A and 6.42%, respectively.