Issue 4, 2015

Probing the energy levels in hole-doped molecular semiconductors


Understanding the nature of polarons – the fundamental charge carriers in molecular semiconductors – is indispensable for rational material design that targets superior (opto-) electronic device functionality. The traditionally conceived picture of the corresponding energy levels invokes singly occupied molecular states within the energy gap of the semiconductor. Here, by employing a combined theoretical and multi-technique experimental approach, we show that this picture needs to be revised. Upon introducing an excess electron or hole into the material, the respective frontier molecular level is split by strong on-site Coulomb repulsion into an upper unoccupied and a lower occupied sub-level, only one of which is located within the semiconductor gap. By including also inter-site Coulomb interaction between molecular ions and circumjacent neutral molecules, we provide a complete picture for the electronic structure of molecular semiconductors in the presence of excess charges. With this understanding, a critical re-examination of previous results is called for, and future investigations of the properties and dynamics of polarons in weakly interacting molecular systems are put on sound footing.

Graphical abstract: Probing the energy levels in hole-doped molecular semiconductors

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Article information

Article type
23 Feb 2015
18 May 2015
First published
18 May 2015
This article is Open Access
Creative Commons BY license

Mater. Horiz., 2015,2, 427-433

Author version available

Probing the energy levels in hole-doped molecular semiconductors

S. Winkler, P. Amsalem, J. Frisch, M. Oehzelt, G. Heimel and N. Koch, Mater. Horiz., 2015, 2, 427 DOI: 10.1039/C5MH00023H

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