SCL Seminar by Nenad Vukmirovic

The Scientific Computing Laboratory seminar will be held on Friday, 18 December 2015 at 14:00 in the library reading room of the Institute of Physics Belgrade. The talk entitled

"Organic Semiconductors as Playground for Interesting Physics"

will be given by Dr. Nenad Vukmirović (Scientific Computing Laboratory, Institute of Physics Belgrade).

Abstract of the talk:

Organic semiconductor materials are held together by weak van der Waals interactions in contrast to covalently bonded conventional inorganic semiconductors. This difference leads to richness of organic semiconductor physics where the effects of electron-phonon interaction, disorder and electron-hole interaction play a very prominent role. In this talk, I will review our results that provide deeper insight into the role of these effects.

We find that in small molecule based organic crystals electron-phonon interaction is not sufficiently strong to lead to formation of localised small polarons. On the other hand, in quantum dot arrays electron-phonon interaction localizes the carriers to single dots and charge carrier transport takes place by small polaron hopping between adjacent dots although the transport is not thermally activated. In amorphous conjugated polymers the effects of disorder lead to localisation of carriers and thermally activated electrical transport. Activation energy for conductivity is much smaller at high frequencies than for DC transport. At the interface between the material domains, in small molecule based organic crystals formation of interface trap states in the band gap of the material takes place, while such states do not exist in materials based on conjugated polymers. Finally, we find that in photoexcited organic semiconductors formation of bound excitons occurs on a several-hundred-femtosecond timescale, while their subsequent relaxation and equilibration takes at least several picoseconds.