Inverted Top-emitting Organic Light-emitting Diodes Research Articles

P‐221: Enhancement of Electroluminescent Property of Inverted Top‐Emitting Organic Light Emitting Diodes with Transparent AgOx by O2 Plasma

AbstractWe demonstrate a transparent AgOx top anode by formed by O2 plasma treatment for inverted top‐emitting organic light emitting diodes (ITOLEDs). The turn‐on voltage decreased from 22 to 12 V, and the luminance increased from 175 to 630 cd/m2 by using this transparent AgOx anode. The AgOx lowered the injection barrier for holes, enhancing the electroluminescent properties of ITOLEDs.

Effective hole-injection layer for non-doped inverted top-emitting organic light-emitting devices

Non-doped inverted top-emitting organic light-emitting diode with high efficiency is demonstrated through employing an effective hole-injection layer composed of MoOx. One reason for high efficiency lies on the energy-level matching between MoOx and hole-transport, and another is due to the Ohmic contact formed between MoOx and Ag. Both of them lead to an improvement of the hole-injection capability from Ag top anode. Moreover, the symmetrical current of “hole-only” device with MoOx shows better hole-injection capability, which is independent of the deposition sequence. The optimized device with MoOx hole-injection layer exhibits maximum current efficiency of 3.7cd/A at a raised luminance level of 14,900cd/m2 and a maximum luminance of 47,000cd/m2 under 18V.

Effect of magnesium oxide buffer layer on performance of inverted top-emitting organic light-emitting diodes

The effect of magnesium oxide (MgO) buffer layer between cathode and emitting materials on performance of inverted top-emitting organic light-emitting diodes (ITOLEDs) was investigated. The operation voltage at the current density of 100mA∕cm2 decreased from 14.9to9.7V for ITOLEDs with 1nm thick MgO buffer layers. The maximum luminance value increased about 78% in ITOLEDs using MgO buffer layer, which is 1000cd∕m2 at the current density of 191mA∕cm2. Synchrotron radiation photoelectron spectroscopy results revealed that the atomic concentration of Al–O bond increased after deposition of MgO on Al, indicating the oxidation of Al surface. Secondary electron emission spectra showed that the work function increased about 0.8eV by inserting the insulating MgO buffer layer. Therefore, the enhancement of device performance results from the decrease of the energy barrier for electron injection based on the tunneling model.