Dynamic electrical characteristics of organic light-emitting diodes

The charge carriers conduction mechanism of single-layer device ITO/Alq₃ (90 nm)/Al has been studied by impedance spectroscopy. According to the frequency-dependent response and its equivalent circuit model, the device can be interpreted in terms of the equivalent circuit model of a contact resistance R_S in series with a parallel combination of a capacitance C_P and a resistance R_P, and the values of R_P, C_P and R_S can be found from experimental data. Our experimental results confirmed that the charge carriers conduction mechanism of ITO/Alq₃(90 nm)/Al is trap-charge limited current with exponential distribution, and the dielectric relaxation time of the material decreases dramatically with increasing applied bias voltages.