Temperature-independent electron tunneling injection in tris (8-hydroxyquinoline) aluminum thin film from high-work-function gold electrode

We fabricated electron-only tris (8-hydroxyquinoline) aluminum (Alq_3) single-layer devices with a device structure of glass substrate/MgAg anode (100 nm)/Alq_3 layer (100 nm)/metal cathode (100 nm), and systematically varied the work functions (WF) of the metal cathodes from WF = - 1.9 (Cs) to - 2.9 (Ca), - 3.8 (Mg), − 4.4 (Al), − 4.6 (Ag), and − 5.2 eV (Au) to investigate how electron injection barriers at the cathode/Alq_3 interfaces influence their current density–voltage (J–V) characteristics. We found that current densities at a certain driving voltage decrease and the temperature dependence of J–V characteristics of the devices gradually becomes weaker as the work functions of the metal cathodes are decreased. The device with the highest-work-function Au cathode exhibited virtually temperature-independent J–V characteristics, suggesting that a current flow mechanism of this device is mainly controlled by electron tunneling injection at the Au/Alq_3 interface