Transient electroluminesence in alloy-based organic light-emitting diodes

Transient electroluminescence of an organic alloy-based light-emitting device (ITO/TPD/alloy/Alq/Al) was studied and the results compared with a standard device without the alloy layer. Under forward bias condition, the electroluminesence (EL) of the alloy device consisted of two components, a fast (10-20 mus) and a slow (200-300 mus) component. The slow component in the EL matched with a corresponding, matching current transient. These transients are identified with the leakage of electrons into the alloy region across the alloy/Alq interface and subsequent exciton formation in the alloy layer. A large overshoot in EL intensity was also observed in the turn-off transient of the standard and alloy devices. The variations in the EL overshoot and decay at different forward bias voltages, repetition rates and temperatures were used to understand the role of traps in the device structures. (C) 2004 Elsevier B.V. All rights reserved.