Phosphorescence of red Os(fptz)(2)(PPh2Me)(2) doped organic light-emitting devices with n and p hosts

Abstract

We have applied a stericly-hindered red phosphorescent dopant Os(fptz)(2)(PPh2Me)(2) [fptz=3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, PPh2Me=phosphine ligand] in p-type 4,4(')-N,N-'-dicarbazole-biphenyl or n-type bis(2-methyl-8-quinolinolato)(p-phenylphenolato) aluminum host and found that the latter produced higher luminance efficiency at lower doping concentration. We present a model to rationalize this phenomenon in which the n-type host impedes hole transport, which leads to narrower recombination zone near the hole transport layer/emission layer interface than the p-type host, hence, more effective recombination.