Investigation on the Effect of 8-Hydroxy-Quinolinato Lithium Between ITO and Hole Transport Layer

Abstract

We investigated the influence of 8-hydroxy-quinolinato lithium (Liq) as the anode buffer layer (ABL) on the performance of the organic light-emitting diodes (OLEDs) with indium tin oxide (ITO) as an anode, N,N′-bis-(1-naphyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) as a hole transport layer (HTL), tris-(8-hydroxy-quinolinato)aluminum (Alq3) as an emitter, Liq as an electron injection layer (EIL) and aluminum (Al) as a cathode. We used Liq with both the ABL and the EIL, respectively. While the ultrathin Liq layer as EIL between Al and Alq3 modified the electron injection properties, the same layer as ABL between ITO and NPB modified the hole injection properties. We considered that most of the holes move through the anode buffer layer by the tunneling effect. As a result, OLEDs using Liq as ABL showed enhanced luminance efficiency due to good balance between the injected holes and electrons. In this case, the thickness of Liq as ABL had influence on the current density, luminance and device stability. The investigation of various organic materials as ABL will be conducted.