NO₂-Affinitive Conjugated Polymer for Selective Sub-Parts-Per-Billion NO₂ Detection in a Field-Effect Transistor Sensor

Abstract

Conjugated polymers (CPs) have provided versatile semiconducting implements for the development of soft electronic devices. When three CPs with the same conjugated framework but different side chains were adopted in the field-effect transistor (FET) sensor for NO2 detection, the response to NO2 showed an opposite tendency to the charge carrier mobility of each CP. Morphological and structural characterizations revealed that the flexible glycol side chain enhances NO2 affinity as well as prevents the formation of lamellar stacking of the CP chains, thereby providing routes for the facile diffusion of NO2. Additionally, theoretical calculations for CP–NO2 complex formation at the molecular level support the relatively low energy barrier for inter-chain transition of NO2 between the glycol-based conjugated frameworks, which implies the spontaneous internal diffusion of NO2 to the semiconductor–dielectric interface in the FET-based sensor. As a result, the CP with a NO2-affinitive morphology exhibited an exceptional sensitivity of 13.8%/ppb upon NO2 (100 ppb) exposure for 50 s and provided excellent selectivity to the FET-based sensor toward other environmentally abundant harmful gases, such as SO2, CO2, and NH3. In particular, the theoretic limit of detection reached down to 0.24 ppb, which is the lowest value ever reported for organic FET-based NO2 gas sensors.

Oxygen-bearing functionalities enhancing NO2, NH3, and acetone electronic response and response variation by polythiophenes in organic field-effect transistor sensors

“…PTOH, PTOH-co-P5MEEMT, PTOH-co-PT3C, and PTOH-co-PT4C reached a sensitivity of 3000%, 7200%, 2800%, and 2300%, respectively. PTOH homopolymer showed about the same sensitivity as had the PEG-P3HT copolymer discussed earlier and much higher than that of P3HT, while PTOH-co-P3MEEMT had sensitivity almost as high as the branched PEG copolymer reported earlier 33. Thus, a clear synergy between the OH and shorter PEG group was demonstrated.…”

“…PTOH homopolymer showed about the same sensitivity as had the PEG-P3HT copolymer discussed earlier and much higher than that of P3HT, while PTOH-co-P3MEEMT had sensitivity almost as high as the branched PEG copolymer reported earlier. 33 Thus, a clear synergy between the OH and shorter PEG group was demonstrated. Regarding NH 3 exposure (Fig.…”

“…This is consistent with the prior ''branched PEG'' study, where the larger PEG side chain resulted in the highest sensitivity. 19,20,33 470% regioregularity, PTOH-co-P5MEEMT had 15% polyether incorporation with 468% regioregularity, PTOH-co-PT3C had 26% crown incorporation with 466% regioregularity, and PTOH-co-PT4C had 29% crown incorporation with 474% regioregularity. Incorporation of additional oxygen bearing moieties suppresses the regioregularity compared to PTOH itself.…”

“…A recent paper by Kang et al 33 seems to be the first to analyze the use of an additional type of oxygenated group, polyether chains, in a conjugated polymer system for vapor sensing, reporting À1.5%/ppm sensitivity to ammonia and 8000%/ppm sensitivity to NO 2 from a branched polyethylene glycol (PEG) side chain on a high-mobility, weakly donating conjugated polymer backbone. They also indicated that alkyl side chains promoted carrier mobility while PEG side chains did not.…”

Organic-Transistor-Based NO2 Sensor Fabricated with Surface-Modified Faujasite-Type Zeolite as an Efficient Nanochannel for Gas Analytes

“…Air pollution has become an important social and environmental problem, and reactive gas sensors based on organic thin-film transistors (OTFTs), which can be used to detect nitrogen oxides and sulfur oxides, have consequently attracted special attention from researchers. − In particular, OTFTs are expected to offer excellent opportunities for fast and distributed measurements of outdoor air pollution because of not only the OTFTs’ functions with signal transducers and amplifiers but also their intrinsic advantages, which include multiparameter accessibility, low cost, low volumetric mass density, high flexibility, and ease of large-scale processing. − However, the sensitivity and sensing and recovery speeds, which are related to the performance and reliability of sensors, of current OTFT-based sensors are still insufficient for them to be used in practical applications. These shortcomings are closely associated with the operating principle of OTFTs, especially for the conduction channel formed at the interface between the organic semiconductor (OSC) and gate dielectric layers. − In the case of a bottom-gate OTFT configuration, an OSC film (usually tens of nanometers thick) itself may become a thick diffusion barrier that blocks the movement of gas analytes into the channel and thus suppresses the change of the channel resistance.…”