Effect of Al/LiF cathodes on emission efficiency of organic EL devices

It has been reported that operational voltages of organic electroluminescent devices are much lowered by interposing a very thin LiF layer between an Al cathode and an Al-hydroxyquinoline (light emitting material) layer. At the same time, emission efficiency is increased. From the analyses of emission and currents of the devices, we attributed the lowering of the operational voltage to the enhanced electron injection due to a lowered work function of the cathode. The increased electron injection rate leads to a shift of the light emitting zone to a region close to the organic/organic interface. This shift was concluded to be the reason for the improvement of emission efficiency owing to die favorable interference effect of light in the device. (C) 1998 Elsevier Science S.A. All rights reserved.