Frequency-triggered circuit transition in organic light-emitting diodes probed by impedance spectroscopy

We demonstrate frequency-triggered internal circuit transition in high-performance organic light-emitting diodes. Blue fluorescent light-emitting devices are fabricated based on a stable and efficient host-dopant material system. Broad-band impedance spectroscopy reveals that these diodes systematically undergo two abrupt spectral transitions at two bands of small-signal frequencies. Nyquist plots recorded over a wide range of conditions are fitted to an equivalent circuit model, decoupling the key interface and bulk parameters. The sharp conductance increases identified from this procedure are conceptually linked to the trap deactivation at specific cut-off frequencies, suggesting new opportunities for alternating-current applications of organic light-emitting diodes.