Cathode Formed by Thermal Evaporation of Ba:Al Alloy and Estimations of Barrier Height in an Organic LED

It is demonstrated that barium and aluminum alloy synthesized by melting in a glass tube under low vacuum is applicable for organic laser emitting diodes (LEDs) as a thin film cathode. The alloy film obtained by the thermal evaporation of pre-synthesized alloy is used in a single-boat organic LED device with the structure: indium tin oxide (ITO)/4,4'-bisN−(1-naphthyl)-N−phenylaminobiphenyl(NPB)/tris-(8-hydroxyquinoline) aluminum(Alq₃)/barium:aluminum alloy. The experimental results show that devices with this alloy film cathode exhibit better current density-voltage-luminance characteristics than those with a conventional pure Al cathode, and more weight of barium in aluminum leads to better performance of the devices. Characteristics of current density versus voltage for the electron-only devices are fitted by the Richardson–Schottky emission model, indicating that the electron injection barrier has a decrease of about 0.3 eV by this alloy cathode.