Orientation-controlled charge transfer at CuPc/ F16 CuPc interfaces

Abstract

Molecular orientation-controlled charge transfer has been observed at the organic-organic heterojunction interfaces of copper-hexadecafluoro- phthalocyanine (F16 CuPc) or copper(II) phthalocyanine (CuPc) on both standing-up and lying-down CuPc or F16 CuPc thin films. In situ synchrotron-based photoemission spectroscopy reveals that the charge transfer at the standing F16 CuPc/CuPc or CuPc/ F16 CuPc interface is much larger than that at the lying F16 CuPc/CuPc or CuPc/ F16 CuPc interface. This can be explained by the orientation-dependent ionization potentials of well-ordered organic thin films, which place the highest-occupied molecular orbital of the standing CuPc film much closer to the lowest-unoccupied molecular orbital of the standing F16 CuPc film, facilitating stronger charge transfer as compared to that at the lying OOH interfaces. Our results suggest the possibility of manipulating interfacial electronic structures of organic heterojunctions by controlling the molecular orientation, in particular for applications in ambipolar organic field transistors and organic photovoltaics. © 2009 American Institute of Physics.