Lifetime of organic thin-film transistors with organic passivation layers

We fabricated a high-performance pentacene organic thin-film transistor (OTFT) on plastic and passivated it with polyvinylalcohol and photosensitive acryl layers. The pentacene was grown on the thin-film transistor area using a self-organized process. The OTFT after the passivation exhibited the field-effect mobility of 0.80 cm2 V s, threshold voltage of -9.2 V, and on/off current ratio of 108. The field-effect mobility and threshold voltage change exponentially with time in air. The lifetime, defined as the time required to decrease the on current by one-half, was found to be ∼11 000 h in ambient air. The absolute value of threshold voltage of the unpassivated OTFT increases with time in air, but it decreases with time in the passivated OTFT. This indicates that the origins for the degradation in the performances of the two OTFTs are different. H2 O in unpassivated and O2 in passivated OTFT appear to be the major origin for the degradation.