Energy level alignment and electronic properties at weakly-reactive interfaces for organic electronics

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The goal of this project is to acquire comprehensive knowledge about the fundamental electronic properties and equilibration mechanisms at heterojunctions comprising pi-conjugated organic molecules, which, despite the relevance for organic electronics, is still lacking. We propose to use direct and inverse photoemission to determine the electronic structure and the associated mechanisms of reaching electronic equilibrium at interfaces formed by organic molecules adsorbed on organic, alkali-halide, and oxide interlayer thin films supported by metal single-crystal substrates. Low energy electron diffraction and scanning tunneling microscopy will be employed to determine the structural properties of these systems. We will correlate quantitatively key properties of the pi-conjugated organic molecules (i.e., ionization energy, electron affinity, and orbital degeneracy) and those of the interlayers (i.e., work function, film thickness, and dielectric constant) with the resulting energy level alignment. The data will serve as benchmark for the development of a theoretical framework to explain the observed electronic structure, including Fermi-Dirac statistics, electrostatics, and interface-specific effects. We thus aim to unravel the fundamental mechanisms that establish electronic equilibrium upon formation of interfaces from weakly coupled entities and to provide a model that is able to accurately predict the energy level alignment for such systems.