Determination of the optimal thickness of inserted LiF in bilayer organic light-emitting devices

An analytical model to calculate the current-voltage characteristics and the electroluminescence (EL) efficiency of bilayer organic light-emitting devices (OLEDs), considering the influence of introducing a LiF insulating buffer layer at the metal/organic interface on the barrier height for electron injection, is presented. The optimal thickness of inserted LiF in bilayer organic light-emitting devices has been calculated and discussed. According to the J-V curves, the calculated optimal thickness of the LiF layer for OLEDs with a Ag/LiF cathode is about 3.1 nm; The calculated EL efficiency reaches the maximum at L-d = 3.1 mu; When the electron injection barrier achieves its minimum value, L-dopt approximate to 2.95 nm. These results indicate that: for devices with a LiF/Ag cathode, the optimal thickness of inserted LiF should be about 3.0 nm; a too thick or too thin LiF layer will increase the turn-on voltage of the OLED and decrease its performance. (c) 2007 Elsevier Ltd. All rights reserved.