Charge equilibration and potential steps in organic semiconductor multilayers

Substantial potential steps ∼0.5 eV are frequently observed in organic multilayers of donor and acceptor molecules. Often such potential steps depend on the order in which the individual layers are deposited, or on which substrate they are deposited. In this paper we outline a model for these potential steps, based upon integer charge transfer between donors and acceptors, charge equilibration across the multilayer, and simple electrostatics. Each donor, acceptor, or substrate material is characterized by a pinning level, and the potential profile can be deduced from the sequential order of the layers, and the differences between their pinning levels. For particular orderings we predict that intrinsic potential differences lead to electric fields across individual layers, which may falsely be interpreted as band bending.

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► A model is presented for the potential steps in organic donor-acceptor multilayers.
► Based upon integer charge transfer, charge equilibration, and electrostatics.
► It explains the dependence of potential steps on the layer sequence.
► And the appearance of intrinsic electric fields across the layers.
► Potential steps are obtained from the Fermi energy pinning levels of all materials.