LiF/Al cathodes and the effect of LiF thickness on the device characteristics and built-in potential of polymer light-emitting diodes

We report the characteristics of a series of polymer light-emitting diodes, fabricated with LiF/Al cathodes and differing only by the thickness of the LiF interlayer $\text{(0\hspace{0.05em}}\mathrm{nm}\text{⩽d⩽11\hspace{0.05em}}\mathrm{nm}\mathrm{).}$ Electroabsorption studies of the internal electrostatic potential give direct evidence of a sizable reduction of the cathodic barrier height brought about by the LiF films. These results also correlate with photoemission experiments [S. E. Shaheen, G. E. Jabbour, M. M. Morrell, Y. Kawabe, B. Kippelen, N. Peyghambarian, M. F. Nabor, R. Schlaf, E. A. Mash, and N. R. Armstrong, J. Appl. Phys. 84, 2324 (1998)] and with the electroluminescence performance of the diodes.