Interfacial electronic properties of the heterojunctions C60/rubrene/Au and rubrene/C60/Au

Abstract

Using synchrotron-radiation photoemission, we have studied the electronic structures of rubrene:C60 heterojunctions on Au substrates. The photoelectron spectra show that the interfacial properties at the C60/rubrene/Au and rubrene/C60/Au interfaces are asymmetric and do not follow the commutation rule. In the C60/rubrene case, a gap state appearing in the initial deposition stage results from negative charges transferred from rubrene to C60, while in the inverse deposition process, no strong chemical reaction could be found. A significant shift of the vacuum level induced by alignment of the charge neutrality levels of the two materials was observed in both cases. Furthermore, the charge transfer strongly enhances the dipole potential of the C60/rubrene interface. The energy level diagrams show that the C60-on-rubrene process has a superior number of advantages in the photovoltaic applications.