Ambient effect on the electronic structures of tris-(8-hydroxyquinoline) aluminum films investigated by photoelectron spectroscopy

Thin films of tris-(8-hydroxyquinoline) aluminum (Alq3) were exposed to trace amounts of O2, CO2, H2O, or to ambient air. Evolution of electronic structures of Alq3 films with increasing gas exposure was measured using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy (XPS). The vacuum energy level, the highest occupied molecular orbital, and XPS core levels of the constituting elements in Alq3 shifted according to the kind of gas exposure. Chemical reaction between oxygen and the Alq3 films was observed upon oxygen exposure. Moreover, it was found that the dominant influence of ambient conditions on the electronic structures of the Alq3 films was from H2O.