Novel approach for energy band diagram and barrier heights in metal/organic structures

We propose a new method for obtaining the Fermi-level aligned energy band diagram and the electron and hole barrier heights in metal/organic structure. It is obtained from the known metal work function, vacuum level shift at metal/organic interface, and orbital states of organic material. This theory has two assumptions: (i) metal work function can be deviated from the original one at metal/organic interface and (ii) the energetic disorders of transport sites in interfacial layer are broadened and the broadening is related to the change of the metal work function. Our theoretical results are verified by using a conventional drift–diffusion model. This new approach to electrical characteristic simulation is applied to Mg:Ag/Alq3/Mg:Ag, Mg:Ag/Alq3/Al, and Mg:Ag/Alq3/LiF/Al structures and then the current–voltage curves are consistent with experimental ones. From these results, we conclude that the above two assumptions are reasonable. Also we find that built-in potential and intrinsic carrier density are very important besides barrier heights in order to obtain more accurate current–voltage characteristics.