Electron traps in organic light-emitting diodes

This work presents the effects of electron traps in organic light-emitting diodes using a model which includes charge injection, transport, and recombination. For electron-only devices, the electron current is reduced by the traps for several orders of magnitude at fixed voltage, and the traps strongly increase the transient time. For bipolar devices, due to negative trapped charges, traps enhance the hole current and the total current, opposite to the electron-only devices. The traps also make the recombination region close to the cathode. There is a voltage-dependent critical trap density beyond which the quantum efficiency decreases and transient time rises dramatically. The quantum efficiency is doubled if the hole traps are added to balance the electron and hole injections. Finally, the trap effect can be used in a bilayer light-emitting diode to make the emission color-tunable. (C) 2005 American Institute of Physics.