Sensitive and Selective NO₂ Sensing Based on Alkyl- and Alkylthio-Thiophene Polymer Conductance and Conductance Ratio Changes from Differential Chemical Doping

Abstract

NO-responsive polymer-based organic field-effect transistors (OFETs) are described, and room-temperature detection with high sensitivity entirely from the semiconductor was achieved. Two thiophene polymers, poly(bisdodecylquaterthiophene) and poly(bisdodecylthioquaterthiophene) (PQT12 and PQTS12, respectively), were used as active layers to detect a concentration at least as low as 1 ppm of NO. The proportional on-current change of OFETs using these polymers reached over 400% for PQTS12, which is among the highest sensitivities reported for a NO-responsive device based on an organic semiconducting film. From measurements of cyclic voltammetry and the electronic characteristics, we found that the introduction of sulfurs into the side chains induces traps in films of the PQTS12 and also decreases domain sizes, both of which could contribute to the higher sensitivity of PQTS12 to NO gas compared with PQT12. The ratio of responses of PQTS12 and PQT12 is higher for exposures to lower concentrations, making this parameter a means of distinguishing responses to low concentrations for extended times from exposures to high concentrations from shorter times. The responses to nonoxidizing vapors were much lower, indicating good selectivity to NO of two polymers. This work demonstrates the capability of increasing selectivity and calibration of OFET sensors by modulating redox and aggregation properties of polymer semiconductors.

A Study on the Impact of Poly(3-hexylthiophene) Chain Length and Other Applied Side-Chains on the NO2 Sensing Properties of Conducting Graft Copolymers

“…These methods include blending with other polymers, hybridization with inorganic materials (such as MOX, graphene oxide etc. ), chemical modification of the polymer chain, copolymerization, and grafting, among others [ 17 , 23 , 25 , 26 , 27 , 28 ].…”

A highly selective electron affinity facilitated H2S sensor: the marriage of tris(keto-hydrazone) and an organic field-effect transistor

“…In the case of a bilayer configuration, the preferred elements will have (i) appreciable chemical compatibility among layers, (ii) good porous structures to improve gas absorption and (iii) good stability under various ambient conditions. Some of the strategies employed to realize better-sensing performance using DPP-based OFET sensors include optimization of film thickness, 16,17,20,38 tuning the porous structures to improve the surface reactivity, 18,20,39,40 blending the polymers with materials (such as graphene oxide, 39 MoS 2 , 39 polystyrenes, 39 PBA 39 and MOF 22 ) and attaching functional groups (sulfur-based motif, 41 siloxane, 39 butoxycarboxyl, 39 tetraethyl glycol, 16 thymine 42 and naphthalene 20 ) to the side chain of polymers. However, major disadvantages include their poor stability under humidity and bias stress and the resultant failure to exhibit reproducible and reliable gas-sensing performance.…”

High Signal‐to‐Noise Chemical Sensors Based on Compensated Organic Transistor Circuits

“…shows a higher drain current than the PQTS12-based OFET under the same working voltages while the more dopable PQTS12-based OFET shows a higher normalized sensitivity for NO 2 detection. [30] Here, in order to achieve operationally stable OFETs regulated by compensatory light, we integrate PQT12 and PQTS12 transistors into one circuit, with the PQT12 transistor operating in the dark and the PQTS12 transistor, which is more phototunable, operating under compensatory light. After storing in air for 20 minutes, the light-regulated circuit shows limited change in current, usually <5%, which is a dramatic improvement compared to the PQTS12 transistor with a 40% increase in current from drift in the environment.…”

“…PQTS12 is somewhat more sensitive to moisture and oxygen. [30] The increase of mobility when PQTS12 transistor operated in the dark indicated that there were some gases in air that facilitated the carrier transport in the short term. In the long term, the OFETs would degrade with mobility decreasing anyway.…”

“…With gate voltage of −30 V, the sensitivity of parallel circuits can reach to about 550% after exposure to 5 ppm NO 2 for 20 min (as might be done for dosimetric monitoring) and that of series circuits can be as high as 1000% or more under the same conditions, which are outstanding sensitivities among polymer semiconductors interacting with NO 2 . [30][31][32][40][41][42][43] Even after exposure to 1 ppm NO 2 for just 2 min, the parallel and series circuits exhibited sensitivity of about 20% and 50%, respectively, which is also promising for detecting even lower concentrations of NO 2 . High sensitivities of semiconductor thin films to NO 2 were previously reported, however, their baselines during detecting have shown non-negligible shifts, which are likely to result in large and uncertain noise.…”