Poly(3-hexylthiophene)/polystyrene (P3HT/PS) blends based organic field-effect transistor ammonia gas sensor

Ammonia (NH3) gas sensors based on organic field-effect transistor (OFET) using poly(3-hexylthiophene) (P3HT) blended with polystyrene (PS) as a semiconductor layer were fabricated. An optimized composition of 1.6 wt% P3HT in PS matrix exhibited the best performance to various concentrations of NH3, which is comparable to that of pure P3HT (8 wt%). The results showed the percentage responses of saturation current were 52% and 16% under 50 ppm and 5 ppm NH3, respectively. Also, it showed that there was a remarkable shift in the field-effect mobility after exposed to NH3 gas. By analyzing the morphologies of blend films and the electrical characteristics of OFET sensors, it was found that the film of P3HT blended with PS has more interface to interact with NH3, resulting in more efficient detection to NH3 even in the range of low concentration. Besides, the PS matrix would prevent the gas from diffusing into the semiconductor/dielectric interface directly, which was beneficial to the selectivity of P3HT/PS blend OFET sensor. Moreover, the sensing property was related to the solvents and molecular weight of PS. In addition, the environmental stability of OFET sensors was measured after storing the sensors under ambient atmosphere for 40 days, and the device with the blend semiconducting layer exhibited the superior stability.