Figure 1: Sketch of the energy level alignment at organic/electrode interfaces.
From: Organic semiconductor density of states controls the energy level alignment at electrode interfaces
(a) Schematic showing the Fermi-Dirac occupation function with Fermi level EF for the metallic side of the interface. The difference in binding energy (BE) between EF and the onsets of occupied and unoccupied density of states (DOS) on the organic semiconductor side are the charge injection barriers, Δh for holes and Δe for electrons, respectively. (b) Example of a possible initial situation for the iterative electrostatic model described in the text. The energy differences between the onsets of the DOS derived from the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) to the vacuum level (VL) define the ionization energy (IE) and the electron affinity (EA) of the organic semiconductor, respectively. The energy difference between EF and VL is the work function of the organic film (Wffilm). (c) Final energy level alignment after convergence of the iterative scheme discussed in the text. With increasing distance z from the electrode, the DOS increasingly shifts to higher BE by the local electron potential energy −eV(z), thus increasing Δh and decreasing Δe with respect to the initial situation.
