Temporal and thermal properties of optically induced instabilities in P3HT field-effect transistors

In this contribution we report on temporal and thermal properties of an optically induced instability in poly(3-hexylthiophene) (P3HT) based organic field-effect transistors (OFET) fabricated on a flexible polyethylene terephthalate (PET) substrate. By illuminating depleted p-type top-gate P3HT field-effect transistors with visible light a substantial shift of the threshold-voltage of up to +20 V and an increase in the off-current by three orders of magnitude has been observed. Both phenomena, the threshold-voltage shift and the increase of the off-current, require the presence of oxygen and are persistent for days at room temperature. The effect is explained by the formation of a charge-transfer-complex (CTC) of P3HT and oxygen known from literature to act as an electron trap. Here, we discuss the temporal and thermal stability of the detrapping of photo-generated charge carriers from such traps and the loss of trapping sites by diffusion of oxygen out of the P3HT layer. It is demonstrated that the thermally activated detrapping of electrons from the oxygen induced CTC states is much faster than the removal of the oxygen induced traps.