Transient I-V-Characteristics of OLEDs with Deep Traps

Abstract

Measured current-voltage-characteristics of OLEDs show a large hysteresis for different sweep directions. To clarified this peculiarity we have carried out 2D simulations of transient current-voltage characteristics with a systematic variation of the relevant parameters to investigate this characteristics. It turns out that the transient behaviour can be explained by deep traps. Due to the high energy gap of organic materials deep traps can lie far from the bands. Further, the thermal velocity of the carriers is extremely low and consequently the time constant for trap recharging is very high. Therefore, a high delay time is necessary to measure the reverse steady-state current and to prevent the hysteresis effects.