CARRIER INJECTION CHARACTERISTICS OF ORGANIC ELECTROLUMINESCENT DEVICES

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/ SiO2/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 off sets (PHI(VB) and PHI(CB)) existed for respective valence and conduction bands. PHI(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 PHI(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.