Band-offset engineering in organic/inorganic semiconductor hybrid structures

Control over the electronic structure of organic/inorganic semiconductor interfaces is required to realize hybrid structures with tailored opto-electronic properties. An approach towards this goal is demonstrated for a layered hybrid system composed of p-sexiphenyl (6P) and ZnO. The molecular orientation can be switched from "upright-standing" to "flat-lying" by tuning the molecule-substrate interactions through aggregation on different crystal faces. The morphology change has profound consequences on the offsets between the molecular frontier energy levels and the semiconductor band edges. The combination of ZnO surface dipole modification through molecule adsorption and the orientation-dependence of the ionization energy of molecular layers shift these offsets by 0.7 eV. The implications for optimizing hybrid structures with regard to exciton and charge transfer are discussed.