Carrier Injection Characteristics of Organic Electroluminescent Devices

Abstract

The junction characteristics of metal/organic (M/Org) and organic/organic (Org/Org) interfaces, composing an organic electroluminescent (EL) device, M/Alq3/Diamine/ITO, were studied by measuring the displacement current characteristics of M/Org/Org/ SiO 2 /Si structures. The M/Alq3 junction was found to be both electron and hole injective, depending on the metal electrode. As for the Alq3/Diamine interface, it was found that two band offsets (Φ VB and Φ CB ) existed for respective valence and conduction bands. Φ VB was not very large, and holes in Diamine were able to pass through into the adjacent Alq3 layer by applying a forward-bias, but Φ CB was so large that the electrons in Alq3 were blocked. Based on the standpoint that characteristics of the organic thin-film devices are governed by those junctions, we discussed carrier-injection mechanism, and explain the efficient EL emission.