Degradation induced decrease of the radiative quantum efficiency in organic light emitting diodes
The efficiency decrease during electrical operation of organic light emitting diodes is a crucial issue for both applied and fundamental research. In order to investigate degradation processes, we have performed an efficiency analysis for phosphorescent state of the art devices in the pristine state and after an accelerated aging process at high current density resulting in a luminance drop to less than 60% of the initial value. This loss in efficiency can be explained by a decrease of the radiative quantum efficiency of the light emitting guest/host system from 70% to 40% while other factors determining the efficiency are not affected.