Photoelectron Spectroscopic Study of C12A7:e^- and Alq₃ Interface: The Formation of a Low Electron-Injection Barrier

Abstract

12CaO·7Al2O3 electride (C12A7:e-) is a promising material for the cathode of organic light-emitting diodes (OLEDs), because it has a low work function (φWF = 2.4 eV), comparable to metal potassium, and good chemical/thermal stability in an ambient atmosphere. This study examines interfacial electronic structures between C12A7:e- and tris-8-hydroxyquinoline aluminum (Alq3) by ultraviolet photoelectron spectroscopy, finding that a low electron-injection barrier of 0.6 eV, which is approximately half of the value for the Al/LiF/Alq3 interface with the lowest injection barrier, is achieved when the interface is formed on the C12A7:e- film surface obtained by using vacuum annealing and subsequent He plasma treatment. This treatment yields little change in the surface chemical composition and retains a low φWF value (3.1 eV) of C12A7:e-. These results suggest that C12A7:e- has high potential as an efficient electron-injection electrode for OLEDs.