LAUSR

The thin-film structures of chemical sensors based on conventional organic field-effect transistors (OFETs) can limit the sensitivity of the devices toward chemical vapors, because charge carriers in OFETs are usually concentrated within a few molecular layers at the bottom of the organic semiconductor (OSC) film near the dielectric/semiconductor interface. Chemical vapor molecules have to diffuse through the OSC films before they can interact with charge carriers in the OFET conduction channel. It has been demonstrated that OFET ammonia sensors with porous OSC films can be fabricated by a simple vacuum freeze-drying template method. The resulted devices can have ammonia sensitivity not only much higher than the pristine OFETs with thin-film structure but also better than any previously reported OFET sensors, to the best of our knowledge. The porous OFETs show a relative sensitivity as high as 340% ppm−1 upon exposure to 10 parts per billion (ppb) NH3. In addition, the devices also exhibit decent selectivity and stability. This general and simple strategy can be applied to a wide range of OFET chemical sensors to improve the device sensitivity.