Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states

The electronic structure of tris(8-hydroxyquinoline) aluminum (Alq₃) has been studied in the pristine molecular solid state as well as upon interaction (doping) with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calculations at the density functional theory level. Upon doping, each electron transferred from an alkali metal atom is stored on one of the three ligands of the Alq₃ molecule, resulting in a new spectral feature (peak) in the valence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq₃ molecule.