Electrical and Luminescent Properties of OLEDs by Nickel Oxide Buffer Layer with Controlled Thickness

摘要

In this study, we have investigated the role of a metal oxide hole injection layer (HIL) between an Indium Tin Oxide (ITO) electrode and an organic hole transporting layer (HTL) in organic light emitting diodes (OLEDs). Nickel Oxide films were deposited at different deposition times of 0 to 60 seconds, thus leading to a thickness from 0 to 15 nm on ITO/glass substrates. To study the influence of NiO film thickness on the properties of OLEDs, the relationshipsbetween NiO/ITO morphology and surface properties have been studied by UV-visible spectroscopy measurements and AFM microscopy. The dependences of the I-V-L properties on the thickness of the NiO layers were examined. Comparing these with devices without an NiO buffer layer, turn-on voltage and luminance have been obviously improved by using the NiO buffer layer with a thickness smaller than 10 nm in OLEDs. Moreover, the efficiency of the device ITO/NiO (< 5 nm)/NPB/Alq_3/ LiF/Al has increased two times at the same operation voltage (8 V). Insertion of a thin NiO layer between the ITO and HTL enhances the hole injection, which can increase the device efficiency and decrease the turn-on voltage, while also decreasing the interface roughness.