Reversible gas doping of bulk alpha-hexathiophene

The sensitivity of the electrical properties of alpha-hexathiophene single crystals to exposure to air, oxygen, helium, and nitrogen is investigated b y space charge limited current spectroscopy. Whereas no changes are seen in helium and nitrogen atmosphere, the acceptor concentration and trap densit y increase in air or oxygen. Nevertheless, stable equilibrium concentration s, 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 dev ice instabilities and their degradation have to be ascribed to grain bounda ry-enhanced or interface effects. The present results indicate that air-sta ble electronic devices can be prepared from oligothiophenes. (C) 1999 Ameri can Institute of Physics. [S0003-6951(99)00337-X].