The influence of LiF thickness on the built-in potential of blue polymer light-emitting diodes with LiF/Al cathodes

We use electroabsorption to investigate the built-in potential of polymer light-emitting diodes with LiF/Al cathodes, as a function of the LiF thickness d. We find that the built-in potential increases with d, reaching a plateau at d less than or equal to 7 nm. The results, obtained on finished devices, imply a correspondent lowering of the cathode work function, which correlates with the device luminance and efficiency. Consequently, we demonstrate that the improvement in device performance, brought about by the thin LiF layers, is predominantly attributable to the reduction of the barrier height to electron injection. (C) 2001 Elsevier Science B.V. All rights reserved.