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

Abstract

High work-function metal oxides are common for enhancing hole injection into organic semiconductors. However, the current understanding of the electrostatic mechanism needs to be more consistent with materials’ electronic properties. Here, we study the electrostatic profile of high work-function oxides by considering their dielectricity and energetic disorder. Using MoO3 as an example, we first show that the significant vacuum-level change at the electrode–oxide interface originates from electrode doping rather than the conventionally assumed interface dipole. Moreover, electrode doping is enough to explain the Fermi-level shift, so MoO3’s characteristic n-type property is not necessarily due to intrinsic donors. This conclusion also applies to the n-type oxides with reduced work functions, like WO3, V2O5, and p-type NiO. Finally, the dielectricity of the oxide, either n-type or p-type, reduces the surface p-doping of the further deposited organic layer. Increasing the oxide’s metallicity and energetic disorder facilitates the hole injection.

Hole-Injection-Barrier Effect on the Degradation of Blue Quantum-Dot Light-Emitting Diodes

“…That results in an effective work function no higher than E-2. 21,29 Moreover, the dielectric properties of these oxides reduce the electrode-induced p-type doping in HTL, 21 which makes it a less favored method in solution-processed QLEDs. Next, we discuss Δ 2 .…”

“…As widely known, the work function of the MoO 3 -modified electrode is significantly reduced by ambient exposure, which is hardly avoidable in the subsequent solution process. That results in an effective work function no higher than E-2. , Moreover, the dielectric properties of these oxides reduce the electrode-induced p-type doping in HTL, which makes it a less favored method in solution-processed QLEDs.…”

“…It is worth mentioning that electrodes modified by high-work-function dielectric materials were not selected because their different working principle could complicate the discussion. 21 The HTL materials chosen here are low-conductivity polymers. HTL-1, HTL-2, and HTL-3 have HOMO levels of −5.4, −5.6, and −5.8 eV, respectively.…”

“…E-1 and E-2 have a work function of 5.1 and 5.4 eV, respectively. It is worth mentioning that electrodes modified by high-work-function dielectric materials were not selected because their different working principle could complicate the discussion . The HTL materials chosen here are low-conductivity polymers.…”