Mild oxygen plasma-treated nickel oxides for performance enhancement of hybrid perovskite light-emitting diodes

Nickel oxide (NiO_x), a representative transparent p-type semiconductor, has been a promising candidate for hole transport layer (HTL) in perovskite-based photovoltaic and light-emitting diode (LED) devices due to its high chemical stability and high transparency. However, the interface between the NiO_x and perovskite emission layers shows a relatively large electrical barrier for the holes to be transported, which degrades the interfacial electrical properties. To overcome these problems, we suggest a mild oxygen plasma treatment on the NiO_x surface to introduce Ni vacancies while retaining its advantages. By controllably forming the Ni vacancies, the hole concentrations could be controlled, which modulated the valence band edge level. This increases the work function of NiO_x from 4.979 to 5.364 eV, which facilitates the hole transport at the interface between NiO_x HTL and the perovskite emission layer. Ultimately, the overall process leads to improved electroluminescence intensity, reduced driving voltage reduction, and low charge trap density at the interface between the NiO_x HTL and the perovskite emission layers. These eventually improved the external quantum efficiency of the perovskite light-emitting diodes.