Electronic structure and interactions of LiF doped tris (8-hydroxyquinoline) aluminum (Alq)

The electronic structure of co-evaporated LiF and tris (8-hydroxyquinoline) aluminum (Alq) films with different weight ratios have been investigated with ultraviolet and X-ray photoemission spectroscopy (UPS and XPS). The results indicate that pristine LiF has only a small n-doping effect. However, Alq films doped with freshly crushed LiF powder source show a much larger shift in the frontier orbital, suggesting that the doping is most probably induced by defects, as such effect disappears after several evaporations. The interactions of the LiF doped Alq with metal overlayers have also been investigated. Al causes significant n-doping of Alq, while Au does not, due to its inertness and p-doping nature.