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Mark Harrison


Sexithiophene (6T) - Optical spectroscopy of charged excitations

The Charged Excitations In Thin-Films Of Alpha-Sexithiophene Within Semitransparent Field-Effect Devices - Investigation By Optical Spectroscopy Of Field-Induced Charge and By Photoimpedance Spectroscopy

M. G. Harrison, R. H. Friend, F. Garnier and A. Yassar.

Synthetic Metals 67:1-3 (1994) p215-221 .

alkyl-substituted oligothiophenes, model thiophene oligomers, crystal-structure, oligothienyls, polythiophene, sexithienyl, orientation, transistor, polarons films, sexithiophene, field-effect devices, spectroscopy

We report measurements of optical absorption, photoimpedance and photovoltaic excitation spectra associated with field-induced (positive) charges present in semi-transparent metal-insulator- semiconductor (MIS) diodes, in which sexithiophene forms the semiconductor layer. We detect the presence of at least three types of charged excitations present under different conditions of bias voltage and device preparation. We assign them to radical cations, intramolecular dications and intermolecular pi-dimers. We discuss implications for the use of sexithiophene in thin-film transistors.

A Study Of the Charged Excitations In Thin-Films Of Alpha- Sexithiophene By Voltage-Modulation Spectroscopy and Photoimpedance Measurements

M. G. Harrison, R. H. Friend, F. Garnier and A. Yassar.

Molecular Crystals and Liquid Crystals Science and Technology Section a-Molecular Crystals and Liquid Crystals 252: (1994) p165-174 .

insulator-semiconductor structures, oligothiophene cation radicals, field-induced charge, thiophene oligomers, poly(2,5-dimethoxy-p- phenylene vinylene), optical spectroscopy, model, polythiophene, transistors, bipolarons sexthiophene, oligothiophene, photoimpedance, polaron, bipolaron

We report on the spectra of charged excitations present in solid- state thin films of alpha-sexithiophene. We use Voltage-Modulation Spectroscopy to charge the oligomer chains electrically by the field effect in Metal-Insulator-Semiconductor (MIS) devices in which alpha- sexithiophene is the active semiconductor layer. This technique allows us to probe the charged excitations in a solid state thin film device environment, whilst avoiding the steric and coulombic perturbations due to counter-ions present in chemically doped solutions. We observe the existence of two distinct charged excitations in addition to the radical cation. Photoimpedance spectra and some preliminary low temperature spectra provide further insight into these charged excitations.

If you cannot find any of these papers, drop me a line for a reprint...


Ed.: G. Wegner and K. Müllen, V.C.H. Verlag

Chapter 10: Optical Applications

M. G. Harrison and R. H. Friend


"Optical Device Applications" in "HANDBOOK OF POLYTHIOPHENES"

Ed.: D. Fichou, Wiley–V.C.H. Verlag - in press)

M. A. Granström, M. G. Harrison and R. H. Friend.


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Mark Harrison,       Marburg, May 3, 1998