Electrode Doping and Dielectric Effect in Hole Injection into Organic Semiconductors through High Work-Function Oxides

High work-function metal oxides are common for enhancinghole injectioninto organic semiconductors. However, the current understanding ofthe electrostatic mechanism needs to be more consistent with materials'electronic properties. Here, we study the electrostatic profile ofhigh work-function oxides by considering their dielectricity and energeticdisorder. Using MoO3 as an example, we first show thatthe significant vacuum-level change at the electrode-oxideinterface originates from electrode doping rather than the conventionallyassumed interface dipole. Moreover, electrode doping is enough toexplain the Fermi-level shift, so MoO3's characteristicn-type property is not necessarily due to intrinsic donors. This conclusionalso applies to the n-type oxides with reduced work functions, likeWO(3), V2O5, and p-type NiO. Finally,the dielectricity of the oxide, either n-type or p-type, reduces thesurface p-doping of the further deposited organic layer. Increasingthe oxide's metallicity and energetic disorder facilitatesthe hole injection.

Automated summary

High work-function metal oxides are commonly used to enhance hole injection into organic semiconductors. However, the current understanding of the electrostatic mechanism needs to be more consistent with the electronic properties of materials. This study investigates the electrostatic profile of high work-function oxides by considering their dielectricity and energetic disorder. It is found that the significant vacuum-level change at the electrode-oxide interface in MoO3 is mainly due to electrode doping, rather than the conventionally assumed interface dipole. Moreover, electrode doping is sufficient to explain the Fermi-level shift, indicating that the n-type property of MoO3 is not necessarily due to intrinsic donors. This conclusion also applies to other n-type oxides with reduced work functions, such as WO(3), V2O5, and p-type NiO. Additionally, the dielectricity of the oxide reduces the surface p-doping of the deposited organic layer, and increasing the oxide's metallicity and energetic disorder facilitates hole injection.