"Galileo Galilei" Colloquium (February 18th 2005)
"The Intriguing Challenge of Organic Semiconductors
and Related Nanostructures"


Franco Cacialli
University College London

Department of Mathematics "L. Tonelli"
Via F. Buonarroti, 2
Aula Magna Faedo - at 15:30

The most interesting physical properties of organic semiconductors, and of conjugated polymers in particular, are determined by the formation of a partially delocalised π-electron system that can support neutral and charged excitations. Such materials therefore display important analogies to inorganic semiconductors. However, they are more disordered than the latter. They also feature “softer lattices” and stronger electron-phonon coupling, which together with significant electron-electron correlation effects contribute to sizeable exciton binding energies (greater than 0.2 eV). In spite of their reactivity and environmental instability, conjugated functional materials have been developed intensely from a technological perspective, up to the point that they can now be regarded as a class of semiconductors in their own right. In fact, they enable a whole variety of applications spanning from light-emitting (LEDs) and photovoltaic diodes, to field-effect transistors. Some of these applications, such as LEDs and displays, have already reached the market.

After a brief introduction to the properties of conjugated polymers, illustrated with some notable examples, I will discuss a “top-down” and a “bottom-up” approach to polymer nanostructures that are significant for further probing the underlying physics and for optimisation of these intriguing semiconductors and related devices.