Conductivity Enhancement of Nickel Oxide by Copper Cation Codoping for Hybrid Organic-Inorganic Light-Emitting Diodes

We demonstrate a Cu(I) and Cu(II) codoped nickel(II) oxide (NiOx) hole injection layer (HIL) for solution-processed hybrid organic-inorganic light-emitting diodes (HyLEDs). Codoped NiOx films show no degradation on optical properties in the visible range (400–700 nm) but have enhanced electrical properties compared to those of conventional Cu(II)-only doped NiOx film. Codoped NiOx film shows an over four times increased vertical current in comparison with that of NiOx in conductive atomic force microscopy (c-AFM) configuration. Moreover, the hole injection ability of codoped NiOx is also improved, which has ionization energy of 5.45 eV, 0.14 eV higher than the value of NiOx film. These improvements are a consequence of surface chemical composition change in NiOx due to Cu cation codoping. More off-stoichiometric NiOx formed by codoping includes a large amount of Ni vacancies, which lead to better electrical properties. Density functional theory calculations also show that Cu doped NiO model structure with...