Internal photoemission spectroscopy measurement of Alq3/cathode interface by three layered electron only device

We have investigated the Schottky barrier height for electrons at aluminum tris (8-hydroxyquinoline) (Alq3)/cathode interfaces by internal photoemission (IPE) measurement. A three layered device consisting of ITO/TiO2/intermediate layer (IL)/Alq3/cathode structure was used to fabricate the “electron-only device” and to reduce the equivalent thickness of TiO2 and IL stack. The measured barrier heights were 0.86, 1.05, 1.3 and 1.55 eV for MgAg, Al, Ag and Au electrodes, and it gradually decreased with external voltage and it was explained as Schottky effect. Barrier height showed linear relationship with work-function and electronegativity of cathode materials. The slope parameter of 0.6 with electronegativity was attributed to the interfacial charge transfer through the metal-induced gap states at the cathode/Alq3 interface.