Electronic structures of Ba-on- Alq₃ interfaces and device characteristics of organic light-emitting diodes based on these interfaces

The device performance of organic light-emitting diodes was significantly improved by inserting a Ba coverage (Θ_Ba) of 1 nm between tris(8-quinolinolato)aluminum (III) (Alq₃) and the cathode. This improvement was attributed to the lowering of the electron-injecting barrier height that was induced by the formation of a new gap state from an interfacial chemical reaction, as well as band bending due to Fermi level pinning. However, the device with Θ_Ba above 1 nm showed poor device performance. The spectroscopic results indicated that the Alq3 molecules started to decompose by the reaction between Ba and the phenoxide moiety of the molecule.