Observation of Crystallization of Vapor-deposited TPD Films by AFM and FFM

Abstract

The morphological change of vapor-deposited TPD (N,N′-diphenyl-N,N′-bis-(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine) films, used as the hole transport layer of organic electroluminescent (EL) devices, on a glass plate was observed by atomic force microscopy (AFM) and friction force microscopy (FFM) in an ambient atmosphere. The TPD film was flat and amorphous as deposited, but was crystallized partially about a week later. By friction force loop measurement, we found that the bare glass surface was revealed between the crystals and between the amorphous film and the crystal due to mass transport for crystallization of TPD from the amorphous film.