Efficient Organic Light-emitting Diode Using Lithium Tetra-(8-hydroxy-quinolinato) Boron as the Electron Injection Layer

High performance organic light-emitting diodes (OLEDs) with lithium tetra-(8-hydroxy-quinolinato) boron (LiBq4), instead of LiF, as the electron injection layer, and aluminum as the cathode were fabricated. In the fabrication of the devices, N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) was used as the hole transfer layer, and tri-(8-hydroxyquino-line) aluminum (Alq3) as the emitting and electron transfer layer. By using LiBq4 as the electron injection layer, the devices performance with regard to luminance, current efficiency, and turn-on voltage was superior to that of the device using LiF as the electron injection layer. The experimental results could be explained by the improved electron injection and charge balance.