Intermolecular Coupling Related Electrical Transport Transition in Vanadyl-Phthalocyanine (VOPc) Molecular Bilayers

Abstract

We demonstrate the correlation between intermolecular coupling and electrical transport in VOPc molecular bilayers. The intermolecular electrical interaction is estimated by scanning tunneling spectroscopy. We find that the stronger coupling of LUMO–LUMO between VOPc molecular bilayers leads to thickness-independent LUMO positions and contact-dominating electron transport. On the other hand, intermolecular coupling of HOMO–HOMO is less; therefore, the measured HOMO positions are thickness-dependent, and transition from thermionic emission to Frenkel-Poole transport and to field emission can be observed with increasing thickness and applied bias. The findings show that the intermolecular coupling and electrical transport behavior can be revealed in situ at the same time, which is helpful in understanding the fundamental transport mechanism in organic semiconductors.