Organic light-emitting devices based on a highly robust osmium(II) complex

Abstract

An osmium(II) complex, Os(fptz)(2)(PPh2Me)(2) [fptz=3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, PPh2Me=methyl-diphenyl-phosphan], when doped in a 4,4(')-N,N-'-dicarbazolebiphenyl host as a phosphorescent red emitter in organic light-emitting devices, has the unusual property of resisting concentration quenching and sustaining its external quantum efficiency (EQE) (8%-9%) over a wide range of doping concentration (20%-40%). Single-crystal x-ray diffraction evidence is presented that the difference in doping behaviors can be linked to the octahedral configuration of Os(fptz)(2)(PPh2Me)(2), which could prevent the undesirable molecular aggregation from occurring at high concentration, thus delaying the onset of quenching. Accordingly, the high doping concentration of Os(fptz)(2)(PPh2Me)(2) leads to a significant suppression of luminescence quenching at high brightness/current and achieves a "flat" EQE versus brightness response owing to the increase in the emission sites in the emission layer. (c) 2006 American Institute of Physics.