Analysis of the turn-off dynamics in polymer light-emitting diodes

We present experimental techniques to analyze the electroluminescence (EL) of polymer light-emitting diodes following the removal of an applied voltag e pulse. We explain the fast modulation of the EL intensity at turn-off in terms of the sudden reduction of the Langevin recombination rate, and extra ct the time evolution the device's internal electric field at the recombina tion zone during the application of a voltage pulse. The results are compar ed to, and found to be consistent with, those of simple numerical modeling. The subsequent long-lived EL tail is analyzed to give the time evolution o f the carrier distributions at the recombination zone once the voltage puls e has been removed. (C) 2000 American Institute of Physics. [S0003-6951(00) 00109-1].