Molecular Orientation Dependent Energy Level Alignment at Organic−Organic Heterojunction Interfaces

Abstract

Molecular orientation dependent energy level alignments at organic−organic heterojunction (OOH) interfaces have been investigated with synchrotron based high-resolution photoemission spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) measurements. Model systems of the lying-down 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) films on both standing-up and lying-down copper hexadecafluorophthalocyanine (F16CuPc) and copper(II) phthalocyanine (CuPc) thin films have been used to illustrate the molecular orientation dependent interface properties. The formation of different interface dipoles at the heterojunction interfaces is strongly influenced by the orientation dependent ionization potentials of the underlying F16CuPc or CuPc thin films. This is attributed to the intrinsic surface dipoles induced in the standing-up F16CuPc (CuPc) film due to the polar intermolecular C−F (C−H) bonds formed at the interface. In situ NEXAFS measurements reveal that the room-temperature deposition of PT...