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

Energy level alignment of rubrene adsorbed on Au(111) was studied by photoemission spectroscopy. After rubrene adsorption, the work function is reduced from 5.24eV for clean Au to 4.31eV, 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 0.4eV for a monolayer of rubrene to 0.9eV for a thick layer.Using organic molecules as components in nanoscale electronic and optoelectronic devices has attracted widespread attention. Rubrene characterized by an extended system of delocalized π electrons has been used in organic light emitting diodes and organic field effect transistors (OFETs). Rubrene increases the efficiency and stability of devices as a dopant. The very high charge carrier mobility of typically 15–20cm2/Vs measured for rubrene crystals has led to its integration into p-type OFETs. Fabrication of large-area patterned rubrene single crystal OFET arrays on solid and flexible substrates has been recently achieved