The effects of buffer layers, including LiF, LiCl, NaF, NaCl, NaI, KI, RbF, RbCl, CsF, CsCl, MgF(2), CaF(2), BaF(2), and BaCl(2) on electron injection and device performance in organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum, were investigated systematically. The insertion of the buffer layers at the organic/cathode interface not only reduced the operating voltage, but also enhanced the luminance and efficiency, which is attributed to the improvement of electron injection efficiency. It was found that the efficiency of the electron injection was closely related to the inherent properties of the buffer layer, such as its melting point (MP) and dielectric constant (epsilon), as well as with the buffer layer's interface with the metallic electrode through the effective work function (WF). Low MP, low epsilon and low WF values result in an effective improvement in the injection of the electrons, and thus to the device performance. The electroluminescent performance was further improved by the introduction of calcium between the buffer layer and the aluminum electrode. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.