Based on the WKB approximation of the tunneling model, we calculate the J–V characteristics of organic light-emitting devices (OLEDs) having buffer layers of different thickness. The results show how the insertion of a buffer layer with proper thickness lowers the OLED turn-on voltage. Further calculation suggests some parameters, such as the resistivity ratio and the position of the conduction band minimum of the buffer layer relative to the lowest unoccupied molecular orbital of the organic layer, are important in selecting a buffer material. A quantitative estimation of the optimal buffer layer thickness is also presented to serve as a guide to device design. The model is validated by comparison of its predictions to experimental results.

Arsenal for providing 1,3,5,7-tetrakis(chlorocarhonyl)cubane and 1,3,5,7-adamantanetetra-carboxylic acid chloride for the synthesis of compounds V, V1, and VII.

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A LiF-buffered silver cathode has been used in organic light-emitting devices (OLEDs) with structure indium–tin–oxide/N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine (50 nm)/Alq3 (100 nm)/cathode. The efficiency of electron injection from the cathode is strongly dependent on the thickness of the LiF buffer layer. While a LiF layer thinner than 1.0 nm leads to higher turn-on voltage and decreased electroluminescent (EL) efficiency, a LiF layer of 3.0 nm significantly enhances the electron injection and results in lower turn-on voltage and increased EL efficiency. A brightness of 16 000 cd/m2 and EL efficiency of 4.8 cd/A can be achieved with an Ag/LiF cathode. This dependence of electron injection on the LiF thickness is quite different from that reported for OLEDs with a Al/LiF cathode, but can be well understood using the tunneling model.