Stability of low voltage hygroscopic insulator P3HT transistors

Abstract

Solid-state and low voltage operating organic transistors are highly desirable for the development of sensors and biosensors. Hygroscopic insulator field effect transistors (HIFETs) are a class of solid-state organic transistors that utilise a hygroscopic insulator film to enable low voltage operation. HIFETs have been reported for various sensing applications. However, the impact of moisture on the long-term performance of HIFETs has not yet been assessed. Therefore, in this work we have studied the impact of moisture on the performance of HIFETs by monitoring them at ambient and high relative humidity conditions over a prolonged period (∼five months). We found that even though moisture is essential for the working of the HIFET, a high level of moisture degrades the HIFET at a faster rate. Optical, morphological, surface and chemical composition analysis reveal that the impact of moisture on the channel material is higher at higher humidity and that the performance degradation is consistent with accelerated oxidation of the poly(3-hexylthiophene) (P3HT) channel material. The sensing performance of HIFETs stored in high humidity is also lower as compared to HIFETs stored in ambient conditions. Our work is relevant for the community working on improving the stability of organic transistors over time.