Pulsed excitation of low-mobility light-emitting diodes: Implication for organic lasers

We present a theoretical and experimental study of electrical pulsed excitation in polymer light-emitting diodes (LEDs). We find that the low mobility results in a relatively high charge density within an electrically pumped structure. The broad spectrum of the charge-induced absorption and its overlap with the ground-state absorption pose a significant barrier for achieving net gain and lasing. We suggest an approach that might circumvent this problem using suitable emitters and an appropriate driving scheme. We also suggest methods for ultrafast modulation of LEDs as well as direct determination of the space charge within the recombination zone.