Chemical and morphological stability of aluminum tris(8-hydroxyquinoline) (Alq3): effects in light-emitting devices

Aluminum tris(8-hydroxyquinoline) (Alq₃) is presently considered one of the most reliable electron transporting and emitting materials for molecular-based organic light-emitting diodes (OLEDs). This paper summarizes the investigations that our group, over the past three years, have conducted into the physical and chemical response of Alq₃ in the presence of small amounts of moisture. The characteristic evolution of 8-hydroxyquinoline (8-Hq), a volatile byproduct of the hydrolysis of Alq₃, was quantified using thermogravimetric and gas chromatography/mass spectroscopy (GC/MS) analysis as a function of sample morphology. Annealed (more crystalline) samples exhibited greater stability to hydrolysis than freshly sublimed films, at the expense of photoluminescence (PL) efficiency. These phenomena are discussed with respect to failure mechanisms observed in Alq₃-based OLEDs