Thickness-dependent energy level alignment of rubrene adsorbed on Au(111)

Abstract

Energy level alignment of rubrene adsorbed on Au(111) was studied by photoemission spectroscopy. After rubrene adsorption, the work function is reduced from 5.24 eV for clean Au to 4.31 eV, suggesting the invalidity of vacuum level alignment and the presence of a strong interfacial dipole. The frontier molecular orbital energies of rubrene are modified by electrode surface polarization in the submonolayer regime. As a consequence, the hole injection barrier is thickness dependent and varies from about 0.4 eV for a monolayer of rubrene to 0.9 eV for a thick layer. © 2007 American Institute of Physics.