Electroluminescence Properties of IrQ(ppy)2 Dual-Emitter Organometallic Compound in Organic Light-Emitting Devices

Abstract

This paper reports the influence of the charge carrier mobility on the electroluminescent properties of a dual-emitter organometallic compound dispersed in two conjugated organic small-molecule host materials and embedded in organic light-emitting devices (OLEDs). The electroluminescent processes in OLEDs are strongly influenced by the host–guest interaction. The charge carrier mobility in the host material plays an important role in the electroluminescent processes but also depends on the triplet–triplet interaction with the organometallic compound. The low charge carrier mobility in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host material reduces the electroluminescent processes, but they are slightly enhanced by the triplet–triplet exothermic charge transfer. The higher charge carrier mobility in the case of N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) host material influences the electroluminescent processes by the endothermic energy transfer at room temperature, which facilitates the triplet–triplet harvesting in the host–guest system. The excitation is transferred to the guest molecules by triplet–triplet interaction as a Dexter transfer, which occurs by endothermic transfer from the triplet exciton in the host to the triplet exciton in the guest.