Transient hole transport in poly(-p-phenylene vinylene) LEDs

The transient transport of holes in poly(-p-phenylene vinylene) (PPV) is studied experimentally by monitoring the response times of PPV based light-emitting diodes (LEDs). For thin LEDs, a dispersive hole current is observed. This is well described by continuous-time random walk theory. It appears that the dispersion in hole transit times is mainly due to structural disorder in the polymer layer. For thicker LEDs, a transition towards nondispersive hole transport is observed. In this regime, the response times correspond well with the hole mobility observed in stationary experiments. The experimental results are compared with theoretical estimates for the transition from dispersive to nondispersive transport.