Enhancement of hole injection using iridium-oxide-coated indium tin oxide anodes in organic light-emitting diodes

Abstract

We report the enhancement of hole injection using an IrOx layer between indium tin oxide anodes and 4,4’-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The turn-on voltage of OLEDs decreased from 7V to 4V and the maximum luminescence value increased from 1200cd∕m2 to 1800cd∕m2 as the Ir layer changed to IrOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.6eV as the Ir layer transformed into IrOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.

Improvement of highly efficient organic light-emitting diodes using Mg-doped ZnO buffer layers

“…Another problem with the ITO anode is the diffusion of indium into the organic layer during device operation, which is correlated with the decay of a device's performance [5]. Therefore, a lot of work has also been devoted to the anode buffer layers (ABLs) between ITO and the organic material [6][7][8][9][10][11].…”

Enhancement of hole-injection and power efficiency of organic light emitting devices using an ultra-thin ZnO buffer layer

“…Recently, the insertion of metal-oxides with a high work function and the formation of a metal-doped indium tin oxide layer have been studied [7][8][9][10][11]. Among various metal-oxides, zinc oxide (ZnO) and metal-doped ZnO films are relatively low-cost and have some unique characteristics, such as high transparency in the visible light region and controllability of ntype and p-type semiconducting properties by impurity doping [12].…”

“…Therefore, a lot of work has also been devoted to the anode buffer layers (ABLs) between ITO and the organic material [6][7][8][9][10][11].…”

Reduced turn-on voltage and improved efficiency with free interfacial energy barrier in organic light-emitting diodes

“…Yang et al employed the ultrathin light emitting layer (EML) to increase the efficiency, but it allowed charge and exciton leakage outside the emissive region, resulting in a decrease in efficiency at high current densities [7]. Many other methods and techniques, including insertion of a thin metal oxide layer [8][9][10], emissive layers with mixed hosts [11,12], gradient p-and n-doping or nonlinear crossfading doping [13], bipolar host structure and interfacial doping in hole-and electroninjection layers (EIL) [14,15] have also been proposed to improve J-V characteristics with enhanced performance of the devices up to now. Using a bipolar host in the device has many advantages.…”