Reversible Gas Doping of Bulk alpha-Hexathiophene

The sensitivity of the electrical properties of alpha-hexathiophene single crystals to exposure to air, oxygen (O sub 2), helium (He) and nitrogen (N sub 2) is investigated by space charge limited current spectroscopy. Whereas no changes are seen in He and N sub 2 atmosphere, the acceptor concentration and trap density increase in air or oxygen. Nevertheless, stable equilibrium concentrations, much lower than in thin films, are reached after a few days of exposure and remain unchanged for many months. Therefore, the observed thin film device instabilities and their degradation have to be ascribed to grain boundary-enhanced or interface effects. The present results indicate that air-stable electronic devices can be prepared from oligothiophenes.