Achieving high response of poly (3-hexylthiophene-2,5-diyl) molecules to gaseous ammonia using anodic aluminum oxide nanoporous substrate operated under 1 V

Abstract

ppb level sensing of gaseous ammonia is of utmost importance in several sectors including health and industrial zones. Among various ammonia gas sensors based on different transducing principles (optical, electrical, electrochemical), conductometric sensors are highly promising due to simplicity in device fabrication and measurements but suffer from relatively low sensitivity and limit of detection. In this work, we have fabricated highly efficient conductometric ammonia gas sensors with custom-made interdigitated electrodes by laser-patterning 200 nm thick silver layer on anodic aluminum oxide (AAO) and on glass substrates for comparison. Poly (3-hexylthiophene-2,5-diyl) molecules (P3HT molecules) is used as the indicator molecules in the proposed ammonia gas sensor. The proposed sensor fabricated on AAO substrate exhibits an extraordinarily high response (ratio of difference in currents in presence and absence of gas molecules to the current in absence of gas molecules) of 0.56 at 100 ppb ammonia environment under 0.5 V, which is the highest response hitherto achieved in ammonia gas sensor based on P3HT molecules. The results suggest that a simple custom-made laser patterned silver electrode could replace the electrode designed by photolithographic or rigorous nano-engineering methods to achieve highly efficient devices. Interestingly, the unique application of AAO through-hole membrane as a substrate allows gas molecules to enter through the bottom of the substrate to interact with the indicator molecules on top, suggesting complete accessibility of the top substrate for the fabrication of devices without hindering the gas sensing phenomenon.