Light induced effects on the morphology and optical properties of tris-(8-hydroxyquinoline) aluminium (Alq3) small molecular thin film

The organic light emitting devices (OLEDs) material tris-(8-hydroxyquinoline) aluminum (Alq3) is synthesized and deposited in thin film form by thermal evaporation on silicon and glass substrates. Thin films are studied for environmental related degradation. The light induced effects on Alq3 films exposed to white light in air and vacuum are characterized by atomic force microscopy (AFM) for surface morphology and phases present. The photoluminescence (PL) and spectroscopic ellipsometry (SE) techniques have been used to study optical properties. The AFM images, both topography and phase contrast, indicate a second phase with enhanced crystallinity for the vacuum exposed samples. This observation is supported by PL experiments. The phase with increased lifetime and hence enhanced crystallinity has also been found for vacuum exposed films by time correlated single photon counting (TCSPC) measurements.