Environmental stability of aluminum tris(8-hydroxyquinoline) (Alq3) and its implications in light emitting devices

The thermal stability of the aluminum tris(8-hydroxyquinoline) (Alq3) is currently discussed, in light of its vital role in failure mechanisms of molecular-based light emitting diodes (LEDs). This was investigated with the use of gas chromatography/mass spectroscopy (GC/MS), assisted by a specialized accessory that permits heating of powders or thin films of Alq3 under a controlled environment. We have shown that at elevated temperatures, Alq3 undergoes a ligand exchange reaction with water, which readily adsorbs on its surface. The increased sensitivity of GC/MS in detecting the liberated 8-hydroxyquinoline (8-Hq) indicates that Alq3 is extremely sensitive to the moisture above 90 °C. The surface of a freshly sublimed Alq3 powder or film becomes saturated with water in less than 2 minutes, under normal laboratory conditions. The implications of the underlying chemistry are discussed in relation to failure mechanisms observed in Alq3 based LEDs.