Condensed Matter & Materials Physics


Electroabsorption of polymer Light-Emitting Diodes and Photovoltaic Cells

Light-Emitting Diodes, LEDs, are simple devices constituted by one or more thin films of a semiconductor sandwiched between different electrodes, which are used for injecting charge carriers in the active polymers.

Electroabsorption experiments measure the variation of the absorption response of the semiconducting materials, induced by the application of an electric field. For this reason they can probe both the intrinsic properties of the semiconductors (e.g. details of the energy structure), and also the electric fields present in the devices. These measurements thus constitute a powerful, non-invasive probe of electro-optical devices such as LEDs and photovoltaic cells. The beauty of the technique is that it is applicable to finished devices, under operating conditions. This project will focus on the study of advanced electrodes for high-efficiency LEDs, especially those emitting in the blue spectral region, that are to play a major role in the next generation of flat organic displays. It is expected that this work will involve close interaction with industrial partners. To find out more you can have a look at the following papers:

  1. T.M. Brown, I.S. Millard, D.J. Lacey, T. Butler, J.H. Burroughes, R.H. Friend and F. Cacialli. Electronic line-up in light-emitting diodes with alkali-halide/metal cathodes. J. Appl. Phys. 93, 6159-6172 (2003).
  2. T.M. Brown, R.H. Friend, I. Millard, D. Lacey, J.H. Burroughes and F. Cacialli. LiF/Al cathodes and the effect of LiF thickness on the device characteristics and built-in potential of polymer light-emitting diodes.
    Appl. Phys. Lett. 77, 3096-3098 (2000).
  3. T.M. Brown, J.S. Kim, R.H. Friend, F. Cacialli, R. Daik and W.J. Feast. Built-in field electroabsorption spectroscopy of polymer light-emitting diodes incorporating a doped poly(3,4-ethylene dioxythiophene) hole injection layer
    Appl. Phys. Lett. 75, 1679-1681 (1999).