Study of energy level alignment at weakly interacting small organic molecular thin film interfaces: The validity of classical model from inorganics

In this study, we discussed the validity of an inorganic semiconductor-based model on energy level alignment at weakly interacting substrate-organic film interfaces, in which the influence of Gaussian distributed density of states on injection barrier based on the thermal equilibrium condition after contacted with substrates was quantitatively investigated. A “Z”-like shape of the energy level alignment has been quantitatively obtained: a slope “S = 1” is clearly given, when the substrate work function is located approximately in between the threshold of ionization energy (IEth) and electron affinity (EAth); on the other hand, “S ∼ 0” is given while the substrate work function is lower than EAth or larger than IEth. Although different calculated results compared with experimental data can also be found, in which the calculated minimal injection barrier is ∼0.2 eV smaller than experimental data, this simplified practical method can be easily applied to calculate the device-related electrostatic potential inside dielectric films.