First-principles study of electronic structure and charge transport at PTCDA molecular layers on Ag(111) and Al(111) electrodes

Abstract

We performed first-principles transport calculations of the contact consisting of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecular layers and metal electrodes using the nonequilibrium Green's function method combined with the density functional theory. To analyze roles of organic/metal interfacial states for transport, we examined two kinds of electrodes: Ag(111) and Al(111). By quantitative evaluation of the coupling strength between PTCDA molecular orbitals and electrodes, we found the creation of the Shockley-type state at the interface of PTCDA and Ag(111). In contrast, the Al(111) surface formed a strong chemical bond with PTCDA. A clear Shockley-type state was not created, and an ohmic bias voltage ($V$) and electric current ($I$) behavior was found for contacts consisting of thin PTCDA layers and Al(111) electrodes. We also predicted that further stacking of PTCDA layers will make $I$-$V$ characteristics more Schottky-like for both Ag and Al electrodes, regardless the different microscopic mechanism.