Transient electroluminescence in organic alloy light emitting diodes

In this paper, we report on transient electroluminescence (EL) studies in (ITO/TPD/alloy/Alq(3)/Al) organic light emitting diodes. The alloy in the active layer is a co-evaporated mixture of TPD + Alq(3) in the ratio TPD:Alq(3) = 1:4. These results were compared with the transient EL response of a standard device (ITO/TPD/Alq(3)/Al). The EL response of the alloy device consists of two components - a fast component (10-20 mus) and a slow component (200-300 mus). It is shown that the slow component arises due to the leakage of electrons from the Alq(3) layer into the alloy layer and subsequent exciton formation in the alloy layer. The magnitude of the fast component depends on the pulse repetition rate and temperature. This is shown to be related to the presence of deep traps in the alloy layer. The presence of deep traps is also confirmed by current transients in the alloy device. (C) 2004 Elsevier B.V. All rights reserved.