Thermal and Morphological Effects on the Hydrolytic Stability of Aluminum Tris(8-hydroxyquinoline) (Alq₃)

An investigation into the physical and chemical characteristics of aluminum tris(8-hydroxyquinoline) (Alq 3 ), a reliable electron-transporting and emitting material for low molecular weight based organic light-emitting diodes (OLEDs), was performed. In the presence of atmospheric moisture, the thermal stability of Alq 3 was studied by monitoring the evolution of its volatile byproduct, 8-hydroxyquinoline (8-Hq), using thermogravimetric analysis and gas chromatography/mass spectroscopy (GC/MS). Sample morphology was shown to be an important parameter in the stability of Alq 3 . Annealed (more crystalline) samples exhibited greater stability to hydrolysis than freshly sublimed films, at the expense of photoluminescence efficiency. The possible implications of these phenomena are discussed with respect to failure mechanisms of Alq 3 -based OLEDs.