Highly\nSensitive Flexible NH₃ Sensors Based on Printed Organic\nTransistors with Fluorinated Conjugated Polymers

Abstract

Understanding\nthe sensing mechanism in organic chemical sensors is essential for\nimproving the sensing performance such as detection limit, sensitivity,\nand other response/recovery time, selectivity, and reversibility for\nreal applications. Here, we report a highly sensitive printed ammonia\n(NH₃) gas sensor based on organic thin film transistors\n(OTFTs) with fluorinated difluorobenzothiadiazole-dithienosilole polymer\n(PDFDT). These sensors detected NH₃ down to 1 ppm with\nhigh sensitivity (up to 56%) using bar-coated ultrathin (<4 nm)\nPDFDT layers without using any receptor additives. The sensing mechanism\nwas confirmed by cyclic voltammetry, hydrogen/fluorine nuclear magnetic\nresonance, and UV/visible absorption spectroscopy. PDFDT-NH₃ interactions comprise hydrogen bonds and electrostatic interactions\nbetween the PDFDT polymer backbone and NH₃ gas molecules,\nthus lowering the highest occupied molecular orbital levels, leading\nto hole trapping in the OTFT sensors. Additionally, density functional\ntheory calculations show that gaseous NH₃ molecules are\ncaptured via cooperation of fluorine atoms and dithienosilole units\nin PDFDT. We verified that incorporation of functional groups that\ninteract with a specific gas molecule in a conjugated polymer is a\npromising strategy for producing high-performance printed OTFT gas\nsensors.