Moving the recombination zone in two layer polymer LEDs using high voltagepulses

We have studied various two layer polymer light emitting diodes (LEDs) by a pplying a wide range of voltage pulses (100ns - 1 micosecond, 10-100V). We find that it is possible to move the recombination zone about the polymer/p olymer heterojunction as a function of the applied voltage, and that the co lour change depends on the charge injection, relative carrier mobilities an d their field dependence. Preliminary simulation runs or these devices are also presented. Two current decay components (fast similar to 100ns and slo w similar to 1ms) have been observed in the current:response of a device af ter the application of microsecond pulses, which we attribute to the presen ce of mobile and immobile carriers. IVL and efficiency data presented show that LEDs perform better in pulsed than in d.c. operation. We also report p eak brightnesses in LEDs in excess of 10 million Cd/m(2) at current densiti es of 500A/cm(2) under the application of 1MV/cm electric field.