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

Abstract

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.