Figure 1: Spin and charge transport mechanisms across hybrid interfaces.

When an organic material is deposited on a metallic substrate, the large hybridization between molecules of the first organic layer and the substrate leads to the formation of a broad HIS at the interface Fermi energy. In contrast, for molecules in the second layer, that have a much weaker hybridization with the substrate, the HIS has a much more pronuced molecular character and is located at an energy far away from the Fermi level. Then the difference between the energy of the HIS and the Fermi energy defines the potential barrier ϕ that must be overcome to achieve charge injection (a). If the substrate is ferromagnetic, different mechanisms for spin-transport through the interface are possibile. In case of tunnelling transport, metallic spin filtering (b) is caused by the spin-split (sp) HIS stemming from the first organic layer that is located at the interface Fermi level. In contrast, resistive spin filtering (c) is due to tunnelling of electrons across the spin-dependent potential barrier (ϕ_↑ ≠ϕ_↓) due to the energy difference between the spin-split second layer HIS and the Fermi level. In case of spin-injection and not tunnelling transport, dynamic spin filtering (d) occurs when electrons are injected into the HIS of the molecules in the second layer. This HIS is not necessarly spin-split, but presents a spin-dependent lifetime.