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We report synthesis of a new poly(4-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2-yl)-7-(4,4-bis(2-ethylhexyl)-6-(selenophene-2-yl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (PDFDSe) polymer based on planar 4,7-bis(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (DFD) moieties and selenophene linkages. The planar backboned PDFDSe polymer exhibits highest occupied molecular orbital and lowest unoccupied molecular orbital levels of −5.13 and −3.56 eV, respectively, and generates well-packed highly crystalline states in films with exclusive edge-on orientations. PDFDSe thin film was incorporated as a channel material in top-gate bottom-contact organic thin-film transistor with a solid-state electrolyte gate insulator (SEGI) composed of poly(vinylidene difluoride-trifluoroethylene)/poly(vinylidene fluoride-co-hexafluroropropylene)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, which exhibited a remarkably high hole mobility up to μ = 20.3 cm2V–1s–1corresponding to effective hole mobility exceeding 5 cm2V–1s–1and a very low threshold voltage of −1 V. These device characteristics are associated with the high carrier density in the semiconducting channel region, induced by the high capacitance of the SEGI layer. The excellent carrier mobility from the PDFDSe/SEGI device demonstrates a great potential of semiconducting polymer thin-film transistors as electronic components in future electronic applications.

Understanding the sensing mechanism in organic chemical sensors is essential for improving the sensing performance such as detection limit, sensitivity, and other response/recovery time, selectivity, and reversibility for real applications. Here, we report a highly sensitive printed ammonia (NH3) gas sensor based on organic thin film transistors (OTFTs) with fluorinated difluorobenzothiadiazole-dithienosilole polymer (PDFDT). These sensors detected NH3down to 1 ppm with high sensitivity (up to 56%) using bar-coated ultrathin (<4 nm) PDFDT layers without using any receptor additives. The sensing mechanism was confirmed by cyclic voltammetry, hydrogen/fluorine nuclear magnetic resonance, and UV/visible absorption spectroscopy. PDFDT-NH3interactions comprise hydrogen bonds and electrostatic interactions between the PDFDT polymer backbone and NH3gas molecules, thus lowering the highest occupied molecular orbital levels, leading to hole trapping in the OTFT sensors. Additionally, density functional theory calculations show that gaseous NH3molecules are captured via cooperation of fluorine atoms and dithienosilole units in PDFDT. We verified that incorporation of functional groups that interact with a specific gas molecule in a conjugated polymer is a promising strategy for producing high-performance printed OTFT gas sensors.