Electronic coupling of optical excitations in organic/inorganic semiconductor hybrid structures

The epitaxial growth of small conjugated molecules on ZnO-based surfaces is studied. A weak substrate interaction allows for the preparation of organic layers with well-defined morphology and electronically intact interfaces without the need for extra passivation. Nonradiative energy transfer from inorganic quantum wells to various molecules is identified by optical spectroscopy. The strength of the dipole-dipole mediated coupling between Wannier and Frenkel excitons is as large as 2 meV. In hybrid structures with type-II energy level alignment, charge separation occurs at the organic/inorganic interface as well. These findings render organic/ZnO hybrid structures interesting for light-emitting as well as photovoltaic applications benefiting from favorable properties of both material classes.