Frequency-dependent response in ITO/Alq3/Al organic light-emitting diodes

Frequency-dependent response of organic light-emitting diodes was studied in a device structure of ITO/Alq3 (60 nm)/Al. Frequency was varied from 40 Hz to 1 MHz and the bias voltage was varied from −5 to +13 V. We have interpreted the frequency-dependent response in terms of equivalent circuit model of parallel combination of resistance Rp and capacitance Cp. From the frequency-dependent response, we are able to obtain characteristic crossover frequency ω0 separating resistive and capacitive response. And we found that there is an effect of interfacial polarization in the frequency range well below the crossover frequency when the applied voltage is lower than turn-on voltage.