Moving the recombination zone in two layer polymer LEDs using high voltage pulses

We have studied various two layer polymer light emitting diodes (LEDs) by applying 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/polymer heterojunction as a function of the applied voltage, and that the colour change depends on the charge injection, relative carrier mobilities and their field dependence. Preliminary simulation runs for these devices are also presented. Two current decay components (fast 100ns and slow 1ms) have been observed in the current response of a device after the application of microsecond pulses, which we attribute to the presence 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 peak brightnesses in LEDs in excess of 10 million Cd/m2 at current densities of 500A/cm2 under the application of 1MV/cm electric field.