Influence of oxygen on the performance of organic field effect transistors

Full text: Functional stability of organic electronic devices such as organic field-effect transistors is still a great challenge for everyday use and a long way from being solved. The instability discussed here results from an oxygen defect, which is crucial for logic elements. In a logic circuit the OFETs are often held in the off-state, thus under depletion, where they change their properties and therewith the properties of the complete electronic circuit. In the present talk we report on the temporal behavior of oxygen based light- and field-induced defects in state of-the-art poly(3-hexylthiophene), P3HT field-effect transistors. Experimentally a substantial shift of the threshold voltage and an increase in the off-current by three orders of magnitude has been reported when illuminating top-gate P3HT based field-effect transistors with visible light under forward gate bias. Three time constants have been found at room temperature: two for the detrapping of electrons released from oxygen defects and one for the elimination of the oxygen defect itself. A set of rate equations will be shown to describe the behavior of the temporal development of the threshold voltage and the off-current of a P3HT transistor whilst the traps are optically filled as well as during the subsequent detrapping of electrons from the oxygen defects. In addition, the activation energies of the detrapping are determined. (author)