Abstract
The hole transport in poly(p-phenylenevinylene) (PPV) was investigated before and after bipolar electrical stress by the time-of-flight (TOF) method. Bipolar structures similar to organic light emitting diodes (OLEDs) were realized, yet with much thicker layers than usually prevailing in OLEDs. During fatigue, the hole mobility is reduced, the field dependence of the mobility is increased, and the hole transport becomes more and more dispersive. These results go along with the fatigue behavior of thin film OLEDs that were investigated by charge extraction via linearly increasing voltage (CELIV). Even though theoretical simulations could show that both thick- and thin-film PPV-based OLED structures are dominated by holes, the presented results indicate that the existence of electrons leads to degradation during hole transport. A possible reason for an enlarged electron density in the otherwise hole dominated device is suggested.
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