Crossover from space-charge-limited to recombination-limited transport in polymer light-emitting diodes - art. no. 125328

By performing admittance spectroscopy as a function of frequency on polymer light-emitting diodes, inductive and capacitive charge-relaxation processe s with different characteristic time scales are separated. The inductive co ntributions arise from the finite transit time of injected carriers, while the capacitive contributions stem from dielectric redistribution of charge density in the device. The crossover from inductive charge relaxation at lo w bias to capacitive charge relaxation at high bias marks the transition fr om space-charge-limited to recombination-limited current flow. This unexpec ted result shows that, while the individual carrier mobilities are strongly enhanced by the applied field, the recombination mobility remains unaffect ed.