Detailed experimental and theoretical analysis of the pulsed excitation of polymer light emitting diodes is presented. We find a set of universal transient features for a variety of device configurations ͑different polymers/cathodes͒ which can be reproduced using our phenomenological numerical model. We find that the temporal evolution of the electroluminescence in response to a step voltage pulse is characterized by: ͑i͒ a delay followed by; ͑ii͒ a fast initial rise at turn-on followed by; ͑iii͒ a slow rise ͑slower by at least one order of magnitude͒. The large mobility mismatch between holes and electrons in conjugated polymers allows us to separately time resolve the motion of holes and electrons. We suggest a method for extracting mobility values that takes into account the possible field-induced broadening of carrier fronts, and which is found to be compatible with mobilities determined from constant wave measurements. By using appropriate device configurations it is possible to determine the mobilities of both holes and electrons from a single device. Mobilities for holes and electrons are extracted for a poly͑p-phenylenevinylene͒ copolymer and poly͑di-octyl fluorene͒.

We present a theoretical and experimental study of electrical pulsed excitation in polymer light-emitting diodes ͑LEDs͒. 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.

Articles you may be interested inBright and efficient exciplex emission from light-emitting diodes based on hole-transporting amine derivatives and electron-transporting polyfluorenes

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