Electronegativity and charge-injection barrier at organic/metal interfaces

Despite a large scatter in experimental data, charge-injection barrier at organic/metal interfaces has been traditionally described as a function of metal work function. By studying the interface between Alq3 and various metals with photoelectron spectroscopy, we show that the charge-injection barrier can be better described as a linear function of the metal electronegativity. This is consistent with our theoretical analysis in terms of a simple model involving metal-induced gap states in organic layer. The interface parameter S is calculated to be 0.8, in good accordance with the experimental value of 0.81. The present work presents a method for predicting the injection barrier at organic/metal interfaces and should be useful for designing various organic-based electronic and optoelectronic devices.