Influence of the substrate temperature to the performance of tris (8-hydroxyquinoline) aluminum based organic light emitting diodes

We investigated the influence of substrate temperature as well as post-deposition annealing on the performance of tris (8-hydroxyquinoline) aluminum (Alq 3) based organic light emitting diodes (OLEDs). Devices with Alq 3 deposited at room temperature, deposited at 100 °C, and annealed at 100 °C were fabricated and characterized. It was found that the deposition at elevated substrate temperature improves both the maximum luminance and the stability of Alq 3 based OLEDs. Annealing at 100 °C resulted in inferior device performance. The differences in the performance of devices subjected to different temperature treatments were attributed to the changes in the film morphology, possible changes in the molecular packing, and different charge transport properties. Since the temperature used is below the glass transition temperature of Alq 3, no crystallization of the light emitting layer is expected.