Aging-induced Recombination Zone Shift in Mixed-Host Organic Light-emitting Devices

摘要

In this paper, we have demonstrated the time-dependent distribution of recombination-rate of a mixed-host (MH) organic light-emitting devices (OLEDs) by co-evaporating an ultra thin red-emitting doped layer (probe). With various probe position, the intensity ratio of red to green directly indicates the exciton distribution in MH layer. If the position of probe insertion is that of maximum recombination-rate, the driving voltage is also reduced which can be explained by the increase of the recombination current. From spectral and J-V analyses, the maximum recombination-rate position is 10 nm to the hole transporting layer when MH-OLED is not aged. After 48 hours of the DC aging test, the changes in the red to green intensity ratio of different devices are different. After 96 hours aging, this ratio does not change further among all devices, indicative of the achievement of steady state of recombination-rate distribution. The organic materials degrade more when it locates near the maximum of the recombination-rate.