Organic Field-effect Transistors Sensors Research Articles

Engineering Steep Subthreshold Swings in High-Performance Organic Field-Effect Transistor Sensors.

Organic field-effect transistor (OFET)-based sensors have gained considerable attention for information perception and processing in developing artificial intelligent systems owing to their amplification function and multiterminal regulation. Over the last few decades, extensive research has been conducted on developing OFETs with steep subthreshold swings (SS) to achieve high-performance sensing. In this review, based on an analysis of the critical factors that are unfavorable for a steep SS in OFETs, the corresponding representative strategies for achieving steep SS are summarized, and the advantages and limitations of these strategies are comprehensively discussed. Furthermore, a bridge between SS and OFET sensor performance is established. Subsequently, the applications of OFETs with steep SS in sensor systems, including pressure sensors, photosensors, biochemical sensors, and electrophysiological signal sensors. Lastly, the challenges faced in developing OFET sensors with steep SS are discussed. This study provides insights into the design and application of high-performance OFET sensor systems.

Practical organic electronic noses using semi-permeable polymer membranes

Electronic noses (E-noses) mimic olfactory organs and quantify volatile organic compounds (VOCs), emulating the sense of smell, with applications in real-time monitoring of VOCs in food, healthcare, and law enforcement industries. Organic field-effect transistor (OFET) based sensors can be fabricated in large arrays by economical processes, however, lack the selectivity necessary to differentiate wide varieties of VOCs. Here, we explore the use of permeable polymer membranes with OFET sensors to improve their selectivity. Acylated poly(vinyl alcohol) (PVA) derivatives were synthesized, characterized, and evaluated in OFET vapor sensors as tunable membranes. Sensors with and without acylated PVA membranes were tested with VOC analytes. By monitoring drain current over time, we found that membranes dramatically changed responses to different analytes. We show that VOCs including methanol, ethanol, hexane, toluene, tetrahydrofuran, methyl ethyl ketone, and ethyl acetate can all be detected and differentiated with much greater selectivity than sensors without membranes. In particular, methanol and ethanol, which are difficult to differentiate in vapor sensors, showed significant quantitative differences in the initial slope (0.0403 s−1 vs 0.0192 s−1 respectively; 6 σ) and decay constants (5.5 s vs 15.9 s respectively; 26 σ) of their current vs time responses, allowing methanol and ethanol to be differentiated with 100 % confidence. This approach enables the economical fabrication of large varieties of unique organic vapor sensors by simply changing the membrane layer and results in an outstanding level of selectivity for OFET vapor sensors.

Influence of Volatile Organic Compound Adsorption on the Characteristics of Organic Field-Effect Transistors and Rules for Gas-Sensing Measurements.

Owing to the advantages of organic field-effect transistors (OFETs) in the versatility of organic synthesis, multiparameter measurement, and signal amplification, sensors based on OFETs have received increasing attention for detecting volatile organic compounds (VOCs). However, false device operation and gas-sensing measurements often occur to vitiate the advantages of OFETs and even output error gas-sensing signals. In this work, by experimentally and theoretically studying the effects of VOC adsorption on the operational characteristics of the OFET, the proper operations of OFETs in gas-sensing measurements were clarified. The multiparameter measurements of OFETs showed that the source-drain current was the optimized parameter for achieving high responsivity, and other OFET parameters could be used for fingerprint analysis. By operating OFETs in the near-threshold region, the amplification effect was switched to enhance the responsivity by orders of magnitude to VOCs, while in the overthreshold region, the OFETs had a low signal-to-noise ratio. Besides, a counteraction effect and an uncertainty effect were discovered, leading to error gas-sensing signals. A theoretical study was carried out to reveal the dependency of the gas-sensing properties of OFETs on VOC adsorption. A series of rules were proposed for guiding the measurements of OFET sensors by taking full advantage of transistors in gas-sensing applications.

Organic Charge‐Transfer Complex based Microstructure Interfaces for Solution‐Processable Organic Thin‐Film Transistors toward Multifunctional Sensing

AbstractThe development of organic field‐effect transistor (OFET) based sensors is in high demand for flexible electronics. Herein, a new and feasible procedure to grow donor‐acceptor complex microstructures sandwiched between the semiconducting and insulating layers is reported. To realize a well‐distributed, uniform‐sized structure through coating on the gold patterned substrate, the dopping ratio of the organic donor‐acceptor complex in the host polymer is optimized. This method leads to one‐step fabrication of high‐performance semiconductor thin‐films and a microstructured binary system attached to it via successful phase separation. The OFET sensors prepared by this technique demonstrate ideal hole‐transport properties and good pressure response. In addition, the thermal‐sensitivity is also revealed, which enables the device architectures to be multifunctional. This work opens a new avenue to manufacture functional microstructure and flexible OFET based pressure sensors.

Design and Fabrication of Ultrathin Nanoporous Donor-Acceptor Copolymer-Based Organic Field-Effect Transistors for Enhanced VOC Sensing Performance.

The development of organic field-effect transistor (OFET) chemical sensors with high sensing performance and good air stability has remained a persistent challenge, thereby hindering their practical application. Herein, an OFET sensor based on a donor-acceptor copolymer is shown to provide high responsivity, sensitivity, and selectivity toward polar volatile organic compounds, as well as good air stability. In detail, a polymer blend of N-alkyl-diketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene (DPP-DTT) and polystyrene is coated onto an FET substrate via shearing-assisted phase separation (SAPS) combined with selective solvent etching to fabricate the DPP-DTT-based OFET device having an ultrathin nanoporous structure suitable for gas sensing applications. This is achieved via optimization of the film morphology by varying the shear rate to adjust the dynamic balance between the shear and capillary forces to obtain an ultrathin thickness (∼8 nm) and nanopore size (80 nm) that are favorable for the efficient diffusion and interaction of analytes with the active layer. In particular, the sensor presents high responsivities toward methanol (∼70%), acetone (∼51.3%), ethanol (∼39%), and isopropyl alcohol (IPA) (∼29.8%), along with fast response and recovery times of ∼80 and 234 s, respectively. Moreover, the average sensitivity was determined to be 5.75%/ppm from the linear plot of the responsivity against the methanol concentration in the range of 1-100 ppm. Importantly, the device also exhibits excellent long-term (30-day) air and thermal storage stability, thereby demonstrating its high potential for practical applications.

Improved NO2 gas sensing performance of nanoporous conjugated polymer (CP) thin films by incorporating preformed CP nanowires

Conjugated polymer (CP)-based organic field-effect transistor (OFET) gas sensors can detect gas molecules at room temperature with high sensitivity and selectivity. However, their performance, particularly when detecting oxidizing gases, has fallen behind that of their metal oxide counterparts. Hence, improving their sensing performance as well as understanding the correlation between it and the structural and electrical properties of the sensing materials is necessary. Herein, we demonstrate that gas sensing performance of an OFET sensor based on nanoporous poly(3-hexylthiophene) (P3HT) films can be improved simply by incorporating preformed P3HT nanowires (NWs), which act as an efficient charge transport pathway. It detects nitrogen dioxide (NO2) molecules with high sensitivity due to the efficient charge transport pathway as well as ultrathin nanoporous structure of the P3HT films. Upon exposure to 10 ppm NO2 at room temperature, the OFET gas sensor based on the P3HT-NW embedded nanoporous P3HT film exhibits excellent responsivity (34%), fast response and recovery times (∼69 and ∼133 s, respectively), and a low limit of detection of under 0.1 ppm, which are comparable to those of conventional metal oxide-based gas sensors. Based on the correlation study between the morphology, charge transport ability, and sensing performance of the P3HT-NWs embedded nanoporous P3HT films, it is revealed that the efficient charge transport ability is an important factor for realizing high-performance CP-based OFET gas sensors, along with excellent morphological features such as thinness and high pore density.

High-Performance Nitric Oxide Gas Sensors Based on an Ultrathin Nanoporous Poly(3-hexylthiophene) Film.

Conjugated polymer (CP)-based organic field-effect transistors (OFETs) have been considered a potential sensor platform for detecting gas molecules because they can amplify sensing signals by controlling the gate voltage. However, these sensors exhibit significantly poorer oxidizing gas sensing performance than their inorganic counterparts. This paper presents a high-performance nitric oxide (NO) OFET sensor consisting of a poly(3-hexylthiophene) (P3HT) film with an ultrathin nanoporous structure. The ultrathin nonporous structure of the P3HT film was created via deposition through the shear-coating-assisted phase separation of polymer blends and selective solvent etching. The ultrathin nonporous structure of the P3HT film enhanced NO gas diffusion, adsorption, and desorption, resulting in the ultrathin nanoporous P3HT-film-based OFET gas sensor exhibiting significantly better sensing performance than pristine P3HT-film-based OFET sensors. Additionally, upon exposure to 10 ppm NO at room temperature, the nanoporous P3HT-film-based OFET gas sensor exhibited significantly better sensing performance (i.e., responsivity ≈ 42%, sensitivity ≈ 4.7% ppm-1, limit of detection ≈ 0.5 ppm, and response/recovery times ≈ 6.6/8.0 min) than the pristine P3HT-film-based OFET sensors.

Enhanced Nitric Oxide Sensing Performance of Conjugated Polymer Films through Incorporation of Graphitic Carbon Nitride.

Organic field-effect transistor (OFET) gas sensors based on conjugated polymer films have recently attracted considerable attention for use in environmental monitoring applications. However, the existing devices are limited by their poor sensing performance for gas analytes. This drawback is attributed to the low charge transport in and the limited charge-analyte interaction of the conjugated polymers. Herein, we demonstrate that the incorporation of graphitic carbon nitride (g-C₃N₄) into the conjugated polymer matrix can improve the sensing performance of OFET gas sensors. Moreover, the effect of graphitic carbon nitride (g-C₃N₄) on the gas sensing properties of OFET sensors based on poly(3-hexylthiophene) (P3HT), a conjugated polymer, was systematically investigated by changing the concentration of the g-C₃N₄ in the P3HT/g-C₃N₄ composite films. The obtained films were applied in OFET to detect NO gas at room temperature. In terms of the results, first, the P3HT/g-C₃N₄ composite films containing 10 wt.% g-C₃N₄ exhibited a maximum charge carrier mobility of ~1.1 × 10-1 cm2 V-1 S-1, which was approximately five times higher than that of pristine P3HT films. The fabricated P3HT/g-C₃N₄ composite film based OFET sensors presented significantly enhanced NO gas sensing characteristics compared to those of the bare P3HT sensor. In particular, the sensors based on the P3HT/g-C₃N₄ (90/10) composite films exhibited the best sensing performance relative to that of the bare P3HT sensor when exposed to 10 ppm NO gas: responsivity = 40.6 vs. 18.1%, response time = 129 vs. 142 s, and recovery time = 148 vs. 162 s. These results demonstrate the enormous promise of g-C₃N₄ as a gas sensing material that can be hybridized with conjugated polymers to efficiently detect gas analytes.

Highly-sensitive organic field effect transistor sensors for dual detection of humidity and NO2

Sensors based on organic field effect transistors have attracted extensive interests, but most sensors are applied to a single analyte detection. Herein, a facile strategy was proposed to optimize the growth of active layers by regulating the thickness of vanadyl-phthalocyanine (VOPc) films and carrying out the thermal annealing. Thanks to the improved film morphology and crystal properties, the carrier mobility of transistors reached 0.15 cm2V−1s−1, humidity and nitrogen dioxide (NO2) induced multi-parameter response of transistors could be considered as an efficient sensing approach. The sensitivity of threshold voltage reached 0.59 V/% RH ranging from 42%−82% RH. In addition, the gas sensing performance was systematically studied. Sensors based on 10 nm VOPc films achieved a 4710% response to 10 ppm NO2 gas, with a theoretical limit of detection down to 125.2 ppb, and the response current was improved by two orders of magnitude under the amplification effect of transistor. The obtained gas sensors also exhibited high repeatability after being stored at 90% ambient humidity. It was concluded that different charge carrier transfer mechanism in moisture and NO2 gas provided a simple idea for tunable applications of phthalocyanine-based transistors.

Facile Synthesis of Conductive Metal-Organic Frameworks Nanotubes for Ultrahigh-Performance Flexible NO Sensors.

Cu-benzenehexathiol (Cu-BHT) has attracted significant attention due to its record high electrical conductivity and crystal defects Cu2c . However, the nonporous structure and small specific surface area of Cu-BHT with two-dimensional kagome lattice invariably limit its practical application in sensing and catalysis. In this work, Cu-BHT nanotubes (Cu-BHT-NTs) are designed and prepared via a facile homogeneous reaction to solve these problems. Compared with the traditional nanorod-like structure, the Cu-BHT-NTs not only have a higher specific surface area but also possess a higher proportion of crystal defects (66.6%). The successfully configured DPPTT/Cu-BHT-NTs heterostructure organic field-effect transistor (OFET)-based sensor exhibits excellent sensitivity as high as 13610%, a minimum detection limits down to 5ppb, and exceptional selectivity to nitric oxide (NO) toxic gases. Theoretical analysis systematically shows that Cu2c sites in the Cu-BHT-NTs increase the number of electrons transferred from the heterostructure to NO molecules, confirming that the high sensitivity and selectivity result from the high binding between Cu-BHT-NTs and NO molecules. Furthermore, a fully flexible device based on the heterojunction OFET sensor is prepared to ensure the convenience of wearing and carrying gas sensors, opening up a new avenue for the next generation of wearable intelligent electronics.

Concentration recognition of gas sensor with organic field-effect transistor assisted by artificial intelligence

Many gas analytes have been detected with organic field-effect transistor (OFET) sensors. However, most of the analytes are detected with known concentrations and few OFET sensors have been used to quantify analytes. Here, we integrated the multiple independent parameters of OFETs with artificial neural network (ANN) to quantify toxic H2S. The precise concentration recognition was confirmed as the difference between real and predicted values was less than 5%. The H2S sensors also showed high responsivity over 6500% at 150 ppm, and quick response in ten seconds. Moreover, the multiple parameters provided the possibility to differentiate eight different analytes. Thus, the artificial intelligence combined with OFET sensors realized precise quantification and fingerprint recognition of gas analytes for real applications.

Sensitive sensors based on bilayer organic field-effect transistors for detecting lithium-ion battery electrolyte leakage

The leakage of flammable and explosive lithium-ion battery (LIB) electrolytes can be one of the early symptoms of battery malfunction and can even lead to spontaneous battery combustion or electric car explosion. Therefore, it is necessary to find a rapid and simple method to monitor any leakage of LIB electrolytes. However, LIB electrolytes are generally composed of volatile and redox neutral carbonate solvents. Trace amounts of electrolyte leakage are difficult to detect effectively and rapidly by existing compact sensors. Here, for the first time, we propose a strategy that cooperatively combines the sensitivity of organic field-effect transistors (OFETs) and the selectivity of biurea receptors to detect LIB electrolyte leakage. The fabricated sensors show much higher sensitivity than the pristine sensor without receptors, and the detection limit of the sensor toward diethyl carbonate was 1.4 ppm. Trace amounts of LIB electrolyte leakage could be detected effectively in seconds, with 200 nL electrolyte leakage leading to a 3% response. We also demonstrate the real-time detection of LIB electrolyte leakage by our OFET sensors. The excellent performance of the receptor-coated OFET sensor makes it a good candidate for LIB safety monitoring and provides a promising platform for the development of sensing technologies.

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

Thiophene copolymers (representative structures shown) gave enhanced, uncorrelated response to NO2, NH3, and acetone vapors. Linear discriminant analysis of responses of thirteen polymers correctly classified response groups as arising from individual vapors.

An organic transistor for the selective detection of tropane alkaloids utilizing a molecularly imprinted polymer.

This study proposes a chemical sensing approach for the selective detection of tropane alkaloid drugs based on an extended-gate-type organic field-effect transistor (OFET) functionalized with a molecularly imprinted polymer (MIP). From the viewpoint of pharmaceutical chemistry, the development of versatile chemical sensors to determine the enantiomeric purity of over-the-counter (OTC) tropane drugs is important because of their side effects and different pharmacological activities depending on their chirality. To this end, we newly designed an OFET sensor with an MIP (MIP-OFET) as the recognition element for tropane drugs based on a high complementarity among a template (i.e., (S)-hyoscyamine) and functional monomers such as N-isopropylacrylamide and 2,2-dimethyl-4-pentenoic acid. Indeed, the MIP optimized by density functional theory (DFT) has succeeded in the sensitive and selective detection of (S)-hyoscyamine (as low as 1 μM) by the combination of the OFET with highly selective recognition sites in the MIP. The MIP-OFET was further applied to determine the enantiomeric excess (ee) of commercially available (S)-hyoscyamine, and the linearity changes in the threshold voltages of the OFET corresponded to the % ee values of (S)-hyoscyamine. Overall, the validation with tropane alkaloids revealed the potential of the MIP combined with OFET as a chemical sensor chip for OTC drugs in real-world scenarios.

Affinity driven ion exchange EG-OFET sensor for high selectivity and low limit of detection of cesium in seawater

The detection and quantification of Cs+ in aquatic media are an environmental safety and public health matter, so far limited by the lack of rapid, low cost, low limit of detection and selective analytical tools. Herein we demonstrate the efficient fabrication of a novel electrolyte-gated organic field-effect transistor sensor for the Cs+ detection in seawater based on the combination of two ultra-thin layers namely poly(3-hexylthiophene) as semiconductor and a single lipids monolayer as dielectric. The latter is end-capped with a specific Cs+ probe based on a calix[4]arene benzocrown ether to ensure the selectivity. Interestingly, we clearly evidence that by controlling affinity driven guest/host ion exchange, one can lift the general problem of selectivity encountered in all FET-based ion sensors, reaching a nearly perfect selectivity even in highly complex analyte solutions containing competitive ions, such as phosphate buffered saline solution or seawater. Such ultra-thin transistor structure exhibits, a limit of detection at the sub-femtomolar level which corresponds to a 5 folds’ magnitude lower than Inductively Coupled Plasma Mass Spectroscopy, the most commonly used technic today. These results pave the way to a generalized monitoring of Cs+ in complexed analytes.

Nanostructure-assisted solvent vapor annealing of conjugated polymer thin films for enhanced performance in volatile organic compound sensing

Controlling both the charge transport properties and morphologies of conjugated polymer (CP) films is critical for the practical use of CP-based organic field-effect transistor (OFET) sensors in diverse applications. Herein, we report a facile processing strategy for improving the sensing performance of OFET-based volatile organic compound (VOC) sensors, which significantly enhances charge transport and increases the surface-to-volume ratio of conjugated polymer thin films using solvent vapor annealing (SVA) in the presence of pre-formed nanostructures (PNs) on the films. In this study, two different PN-embedded poly(3-hexylthiophene) (P3HT) films, viz. PN1-P3HT and PN2-P3HT, were obtained from a sonication-treated P3HT solution with nanocrystals (NCs) and nanorods (NRs) and UV-light-irradiated P3HT solution with NCs and nanowires (NWs), respectively. The effect of SVA on the morphologies and charge transport of the PN-embedded P3HT films was systematically studied by atomic force microscopy, polarized optical microscopy, X-ray diffraction analysis, and charge-carrier mobility measurements. Gas sensing measurements were performed by exposing the sensors to VOCs in a concentration range of 1–100 ppm. After SVA, longer, one-dimensional P3HT nanostructures were formed in the PN-embedded films, while some small nanostructures appeared in the pristine P3HT films. Consequently, the PN2-P3HT OFETs exhibited a significant enhancement (2-fold) in charge transport and an increase (1.7-fold) in the surface-to-volume ratio after the SVA. Furthermore, the OFET sensors exhibited excellent responsivities (20–70%) and rapid response/recovery times (110–160 s) in the detection of VOCs.

Preparation of conjugated polymer/reduced graphene oxide nanocomposites for high-performance volatile organic compound sensors

We have reported a facile approach to fabricate poly(3-hexylthiophene)/reduced graphene oxide (P3HT/rGO) composite films via the photoirradiation of the corresponding composite solutions. The films are applied to organic field-effect transistor (OFET) sensors for the high-performance detection of volatile organic compounds (VOCs). The photoirradiation of the composite solutions and the presence of rGO act synergistically to facilitate the molecular ordering of P3HT. Thus, the P3HT/rGO composite films containing 20 wt% rGO exhibit a maximized charge carrier mobility of ~0.18 cm2 V−1 s−1, which is 6-folds higher than that of pristine P3HT films. The interfacial interactions between rGO and P3HT are enhanced by the favorable π − π and electrostatic interactions following photoirradiation. The OFET sensors based on the P3HT/rGO composites consistently show enhanced sensitivity to polar VOCs (methanol, acetone, ethanol, and isopropyl alcohol) compared to those based on the pristine P3HT, photoirradiated bare P3HT, and pristine P3HT/rGO composites. In particular, the photoirradiated P3HT/rGO-based OFET sensors achieve significantly improved responsivity (~110.6%) to methanol vapors (10 ppm) under rapid on/off pulses of 60 s, compared to those based on pristine P3HT (~6.8%), photoirradiated bare P3HT (~20.8%), and pristine P3HT/rGO (~55.1%) composites. Finally, excellent response and recovery behaviors (e.g., ~15 s and ~42 s, respectively) are also observed.

Three-dimensional CuPc films decorated with well-ordered PVA parallel nanofiber arrays for low concentration detecting NO2 sensor

Abstract Well-ordered polyvinyl alcohol (PVA) parallel nanofiber arrays (PNAs) were fabricated by using electrospinning receiving board with clined gap. A three-dimensional (3D) copper phthalocyanine (CuPc) organic field effect transistor (OFET) sensor was obtained by evaporating CuPc on the PVA PNAs. This 3D structure is conducive to the multi angle adsorption and desorption of the target gas and active layers. The detection limit of the obtained sensors is lower, and the response and recovery time are also shorter. Compared with single CuPc films and CuPc films with disordered PVA nanofibers sensors, the minimum detection concentration is reduced by one third. The CuPc/PVA PNAs sensors have been successfully used in real-time monitoring of NO2 at 0.3 ppm. The response and recovery time of the CuPc/PVA PNAs sensors are both 0.02 min for 25 ppm NO2. The response and recovery time are 350 and 130 times faster than those of CuPc sensors with disordered PVA nanofibers, respectively. Humidity has little effect on the response of the sensor. This convenient and effective method to prepare high performance OFET sensors can be extended to other gas monitoring.

Selective Hg2+ sensor: rGO-blended PEDOT:PSS conducting polymer OFET

The detection of water pollutants employing organic field-effect transistor (OFET) sensor requires a stable performance in an aqueous media. It is an essential condition of any sensor to present reliable measurements. Some organic-conducting polymers deteriorate almost immediately in the presence of an aqueous medium. However, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has proven its stability in both air and aqueous mediums. Nevertheless, due to inadequate structural and chemical properties of the PEDOT:PSS, it persists major obstacles and inhibits its performance in practical applications. These shortcomings can be overcome with the combination of carbon nanomaterials. Therefore, the present study deals with the effect of inclusion of reduced graphene oxide (rGO) into PEDOT:PSS, and it resulted in the enhancement of structural, morphological, and electrical properties of the PEDOT:PSS/rGO nanocomposite. The organic field-effect transistor (OFET) was fabricated with PEDOT:PSS/rGO nanocomposite to detect heavy-metal ions. This makes a highly sensitive and selective sensor platform for detecting Hg2+ in the linear concentration range of 1–60 nM. The presented OFET sensor manifests high sensitivity and selectivity to Hg2+ with a low detection limit of 2.4 nM. The variety of metal ions tested, i.e., Hg2+, Cd2+, Pb2+, Cu2+, Zn2+, Na+, and Fe3+, to investigate the selectivity. The sensor exhibits stable performance in an aqueous medium for the detection of Hg2+ in the presence of DI water. Moreover, the OFET sensor responded within 2–3 s after incubation of Hg2+ ions’ solution.

Design and Synthesis of Air-Stable p-Channel-Conjugated Polymers for High Signal-to-Drift Nitrogen Dioxide and Ammonia Sensing.

The development of high-performance-conjugated polymer-based gas sensors involves detailed structural tailoring such that high sensitivities are achieved without compromising the stability of the fabricated devices. In this work, we systematically developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by modifying the polymer backbone to achieve and rationalize enhancements in gas sensitivities and electronic stability in air. NO2- and NH3-responsive polymer-based organic field-effect transistors (OFETs) are described with improved air stability compared to all-thiophene conjugated polymers. Five DPP-fluorene-based polymers were synthesized and compared to two control polymers and used as active layers to detect a concentration of NO2 at least as low as 0.5 ppm. The hypothesis that the less electron-donating fluorene main-chain subunit would lead to increased signal/drift compared to thiophene and carbazole subunits was tested. The sensitivities exhibited a bias voltage-dependent behavior. The proportional on-current change of OFETs using a dithienyl DPP-fluorene polymer reached ∼614% for an exposure to 20 ppm of NO2 for 5 min, testing at a bias voltage of -33 V, among the higher reported NO2 sensitivities for conjugated polymers. Electronic and morphological studies reveal that introduction of the fluorene unit in the DPP backbone decreases the ease of backbone oxidation and induces traps in the thin films. The combination of thin-film morphology and oxidation potentials governs the gas-absorbing properties of these materials. The ratio of responses on exposure to NO2 and NH3 compared to drifts while taking the device through repeated gate voltage sweeps is the highest for two polymers incorporating electron-donating linkers connecting the DPP and thiophene units in the backbone, in this category of organic semiconductors. The responses to NO2 were much larger than that to NH3, indicating increased susceptibility to oxidizing vs reducing gases, and that the capability of oxidizing gases to induce additional charge density has a more dramatic electronic effect than when reducing gases create traps. This work demonstrates the capability of achieving improved stability with the retention of high sensitivity in conjugated polymer-based OFET sensors by modulating redox and morphological properties of polymer semiconductors by structural control.