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

Abstract

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 (0 nm⩽d⩽11 nm). 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.

Photoelectron Spectroscopy of the Contact between the Cathode and the Active Layers in Plastic Solar Cells: The Role of LiF

“…8,19) The use of both LiF and PEDOT-PSS in this way has proven effective in photovoltaic cells 20) and polymer light emitting diodes. 21,22) In fact, the use of alkali halide sandwich layers to improve injection at the cathode electrode has been used successfully in a wide variety of organic electronic devices, e.g., refs. 21, 23-26. In this work the cathode side is studied, particularly the beneficial effect that the LiF layer has on the interface between the Al and the active organic layer.…”

Improved electron injection in polymer light-emitting diodes using anionic conjugated polyelectrolyte

“…When incorporated into polymer light-emitting diodes ͑PLEDs͒, the LiF layer improves the device performance by increasing the electron attenuation length, by suppressing the interfacial reactions of the metal electrode with emissive layer during the cathode evaporation, and/or by reducing the barrier height of the electron injection through formation of a low work function interfacial layer at the cathode. 10,[13][14][15] The recent research using cationic systems [16][17][18] implies that anionic conjugated polyelectrolytes might offer several interesting opportunities for use in polymer-based optoelectronic devices. In light-emitting electrochemical cells ͑LECs͒, the mobile ions enable redox doping and the formation of ohmic contacts.…”

Temperature-dependent built-in potential in organic semiconductor devices

“…2 virtually inaccessible. 4,8,9 For a device that is connected to external terminals, the condition J = 0 by definition applies at zero bias. However, since the charge density in the vicinity of the contact is much higher than the densities associated with space-charge limited conduction ͑SCLC͒, it is reasonable to take the onset of SCLC, which occurs when flatband is reached in the bulk of the device, as a first-order approximation for the flatband condition ͓Fig.…”