Effect of thermal annealing on the lifetime of polymer light-emitting diodes

Thermal annealing of a polymer light-emitting diode (PLED) is shown to result in a remarkable improvement in the long-term stability of the device. The annealing for such a PLED has to be layer-specific in that the annealing should be carried out for the layer with the lowest glass transition temperature ${\mathrm{(T}}_g)$ to harvest the benefits of annealing. Annealing of this key layer, which is usually the emitting layer, can enhance the thermal stability of the device. The best half-life is obtained at an annealing temperature above the $T_g$ of emitting polymer. It is shown that the annealing of the emitting polymer layer results in a more than an order of magnitude increase in the half-life, in spite of a decrease in the efficiency of the device as the annealing temperature increases.