Project title: Tight-binding approach to the electronic and optical properties of conjugated molecular materials

Supervisors: Professor Jenny Nelson, Dr Jarvist Frost and Dr Kim Jelfs

Project description:

Organic semiconductors (OSCs) have attracted interest due to their processing advantages and unique properties, such as flexibility. OSCs have applications in optoelectronic devices such as OLEDs, thin film transistors and organic photovoltaics (OPVs) [1]. The performance of such devices is determined by the electronic transport properties of OSCs, which are modified for different chemical structures [2]. Therefore, good models of the electronic properties and charge transport that take into account the physical and chemical properties of OSCs are needed.

Charge transport in molecular electronic systems is usually modelled either in a hopping picture, where charges are assumed to localise on individual molecules and move by a hopping process, or in a band picture where charges are assumed to delocalise over space as in conventional semiconductors [1]. There are few models that can account for partial delocalisation of charges across molecular sites and for the transport of charge in such intermediately coupled systems [3] [4].

The aim of the research is to develop a model that uses a tight binding method to determine the states of such systems and study charge transport. We tested the model with fullerene molecules (where electrical properties have been experimentally determined) to investigate the effect on mobility of disorder and polaron formation. We intend to apply it to other conjugated molecules, along with quantum chemical and DFT calculations, to investigate electronic properties where they are less well known. 

[1] H. Hoppe and N. S. Sariciftci, Journal of Materials Research, vol. 19, pp. 1924–1945, 2011.
[2] J. Nelson, J. Kwiatkowski, J. Kirkpatrick et al., Accounts of Chemical Research 42 (2009) 1768-1778.
[3] F. Gajdos, H. Oberhofer, M. Dupuis et al., Journal of Physical Chemistry Letters 4 (2013) 1012-1017.
[4] D. Cheung and A. Troisi, Journal of Physical Chemistry C 114 (2010) 20488.