Extended Solution Gate OFET‐Based Biosensor for Label‐Free Glial Fibrillary Acidic Protein Detection with Polyethylene Glycol‐Containing Bioreceptor Layer

A novel organic field effect transistor (OFET)‐based biosensor is described for label‐free glial fibrillary acidic protein detection. This study reports the first use of an extended solution gate structure where the sensing area and the organic semiconductor are separated, and a reference electrode is not needed. Different molecular weight polyethylene glycols (PEGs) are mixed into the bioreceptor layer to help extend the Debye screening length. The drain current change is significantly increased with the help of higher molecular weight PEGs, as they are known to reduce the dielectric constant. This study also investigates the sensing performance under different gate voltage (V _g). The sensitivity increases after the V _g is decreased from ?5 to ?2 V because the lower V _g is much closer to the OFET threshold voltage and the influence of attached negatively charged proteins becomes more apparent. Finally, the selectivity experiments toward different interferents are performed. The stability and selectivity are promising for clinical applications.     

Highly Sensitive Chemical‐Vapor Sensor Based on Thin‐Film Organic Field‐Effect Transistors with Benzothiadiazole‐Fused‐Tetrathiafulvalene

The synthesis of a new tetrathiafulvalene derivative with an electron‐withdrawing benzothiadiazole moiety and its use in thin‐film organic field‐effect transistors (OFETs) are reported. Compared to reported OFETs with other TTF derivatives, a high hole mobility up to 0.73 cm² V^?1 s^?1, low off‐current and high on/off ratio up to 10⁵ are demonstrated. In addition, the developed OFETs show fast responsiveness toward chemical vapors of DECP (diethyl chlorophosphate) or POCl₃ which are simulants of phosphate‐based nerve agents. In contrast to previously reported OFET‐based sensors, off‐current is used as the output signal, which increases quickly upon exposure to either DECP or POCl₃ vapors. High sensitivity is demonstrated toward DECP and POCl₃ vapors, with concentrations as low as 10 ppb being detected. These OFETs are also responsive to TNT vapor. The sensing mechanisms for the new type of OFET are discussed.     

Sensing of Alkylating Agents Using Organic Field‐Effect Transistors

Alkylating agents are simple and reactive molecules that are commonly used in many and diverse fields, such as organic synthesis, medicine, and agriculture. Some highly reactive alkylating species are also being used as blister chemical warfare agents. The detection and identification of alkylating agent is not a trivial issue because of their high reactivity and simple structure. Here, a novel polythiophene derivative that is capable of reacting with alkylating agents is reported, along with its application in direct electrical sensing of alkylators using an organic field‐effect transistor, OFET, device. Upon reacting with alkylators, the OFET containing the new polythiophene analogue as its channel becomes conductive, and the gate effect is lost; this is in marked contrast to the response of the OFET to “innocent” vapors, such as alcohols and acetone. By following the drain–source current under gate bias, one can easily follow the processes of absorption of the analyte to the polythiophene channel and their subsequent reaction.     

Bortezomib Dendrimer Prodrug‐Based Nanoparticle System

Bortezomib (BTZ) is mainly used to treat hematologic tumors, such as multiple myeloma and small cell lymphoma. However, its usefulness for solid tumor therapy is limited owing to its poor stability and toxicity in vivo. In the present study, an amphiphilic PEGylated dendrimer with dopamine molecule is synthesized from azide group–functionalized polyethylene glycol and alkyne group–functionalized dendrimer, which is produced from 1,1‐dimethylolpropionic acid and dopamine. The amphiphilic PEGylated dendrimer with dopamine molecule reacts with BTZ to construct a BTZ prodrug‐based nanoparticle through a ultrasonic emulsification method. The BTZ prodrug‐based nanoparticles have greater serum stability than BTZ alone and release the prototype drug in acidic environments. The BTZ prodrug‐based nanoparticle is more effective against subcutaneous tumors than BTZ itself. Furthermore, c(RGDyK) modification significantly improves the antitumor efficacy of the BTZ prodrug‐based nanoparticle with regard to subcutaneous and intracranial tumors. Moreover, the BTZ prodrug‐based nanoparticle significantly reduces the toxicity of BTZ in vivo. Therefore, the PEGylated BTZ dendrimer prodrug‐based nanoparticles have great potential for the treatment of solid tumors in vivo.     

Influence of Electric Field on Microstructures of Pentacene Thin‐Films in Field‐Effect Transistors

We report on electric‐field‐induced irreversible structural modifications in pentacene thin films after long‐term operation of organic field‐effect transistor (OFET) devices. Micro‐Raman spectroscopy allows for the analysis of the microstructural modifications of pentacene in the small active channel of OFET during device operation. The results suggest that the herringbone packing of pentacene molecules in a solid film is affected by an external electric field, particularly the source‐to‐drain field that parallels the a–b lattice plane. The analysis of vibrational frequency and Davydov splitting in the Raman spectra reveals a singular behavior suggesting a reduced separation distance between pentacene molecules after long‐term operations and, thus, large intermolecular interactions. These results provide evidence for improved OFET performance after long‐term operation, related to the microstructures of organic semiconductors. It is known that the application of large electric fields alters the semiconductor properties of the material owing to the generation of defects and the trapping of charges. However, we first suggest that large electric fields may alter the molecular geometry and further induce structural phase transitions in the pentacene films. These results provide a basis for understanding the improved electronic properties in test devices after long‐term operations, including enhanced field‐effect mobility, improved on/off current ratio, sharp sub‐threshold swing, and a slower decay rate in the output drain current. In addition, the effects of source‐to‐drain electric field, gate electric field, current and charge carriers, and thermal annealing on the pentacene films during OFET operations are discussed.     

Side Chain Optimization of Naphthalenediimide–Bithiophene‐Based Polymers to Enhance the Electron Mobility and the Performance in All‐Polymer Solar Cells

Tuning the side chains of conjugated polymers is a simple, yet effective strategy for modulating their structural and electrical properties, but their impact on n‐type conjugated polymers has not been studied extensively, particularly in the area of all‐polymer solar cells (all‐PSCs). Herein, the effects of side chain engineering of P(NDI2OD‐T2) polymer (also known as Polyera Activink N2200) are investigated, which is the most widely used n‐type polymer in all‐PSCs and organic field‐effect transistors (OFETs), on their structural and electronic properties. A series of naphthalenediimide‐bithiophene‐based copolymers (P(NDIR‐T2)) is synthesized, with different side chains (R) of 2‐hexyldecyl (2‐HD), 2‐octyldodecyl (2‐OD), and 2‐decyltetradecyl (2‐DT). The P(NDI2HD‐T2) exhibits more noticeable crystalline behaviors than P(NDI2OD‐T2) and P(NDI2DT‐T2), thereby facilitating superior 3D charge transport. For example, the P(NDI2HD‐T2) shows the highest OFET electron mobility (1.90 cm² V^?1 s^?1). Also, a series of all‐PSCs is produced using different electron donors of PTB7‐Th, PTB7, and PPDT2FBT. The P(NDI2HD‐T2) based all‐PSCs produce much higher power conversion efficiency (PCE) irrespective of the electron donors. In particular, the PTB7‐Th:P(NDI2HD‐T2) forms highly ordered, strong face‐on interchain stackings, and has better intermixed bulk‐heterojunction morphology, producing the highest PCE of 6.11% that has been obtained by P(NDIR‐T2) based all‐PSCs to date.     

Highly Sensitive and Selective Biosensors Based on Organic Transistors Functionalized with Cucurbit[6]uril Derivatives

Biosensors based on a field‐effect transistor platform allow continuous monitoring of biologically active species with high sensitivity due to the amplification capability of detected signals. To date, a large number of sensors for biogenic substances have used high‐cost enzyme immobilization methods. Here, highly sensitive organic field‐effect transistor (OFET)‐based sensors functionalized with synthetic receptors are reported that can selectively detect acetylcholine (ACh⁺), a critical ion related to the delivery of neural stimulation. A cucurbit[6]uril (CB[6]) derivative, perallyloxyCB[6] ((allyloxy)₁₂CB[6], AOCB[6]), which is soluble in methanol but insoluble in water, has been solution‐deposited as a selective sensing layer onto a water‐stable p‐channel semiconductor, 5,5′‐bis‐(7‐dodecyl‐9H‐fluoren‐2‐yl)‐2,2′‐bithiophene layer. The OFET‐based sensors exhibit a detection limit down to 1 × 10^–12 m of ACh⁺, which is six orders of magnitude lower than that of ion‐selective electrode‐based sensors. Moreover, these OFET‐based sensors show highly selective discrimination of ACh⁺ over choline (Ch⁺). The findings demonstrate a viable method for the fabrication of OFET‐based biosensors with high sensitivity and selectivity, and allow for practical applications of OFETs as high‐performance sensors for biogenic substances.     

Engineering Zeolitic‐Imidazolate Framework (ZIF) Thin Film Devices for Selective Detection of Volatile Organic Compounds

Thin films of sodalite‐type zeolitic‐imidazolate frameworks (ZIFs, ZIF‐7, 8, 9, 67, 90, and ZIF‐65‐Zn) with different metal centers and functional moieties are fabricated on SiO₂ coated quartz crystal microbalance (QCM) substrates using automatic program controlled repeated direct growth method. The repeated direct growth procedure manipulated here shows great applicability for rapid growth of uniform ZIF thin films with controllable thickness. The fabricated ZIF/QCM devices are used to detect vapor phase volatile organic compounds including alcohol/water, BTEX compounds (benzene, toluene, ethylbenzene and xylene isomers), and hexane isomers. The ZIF/QCM devices exhibit selective detection behavior upon exposure to these chemical vapors. The effects of ZIF pore size, limited pore diameter, surface functionality, and structural flexibility on the sensing performances of ZIF/QCM devices are systematically investigated, which would be beneficial for the practical application of ZIF sensors based on array‐sensing technology. Furthermore, the selective adsorption behavior suggests that these ZIF materials have great potentials in the applications of biofuel recovery and the separation of benzene/cyclohexane, xylene, and hexane isomers.     

Air‐Stable n‐Type Organic Field‐Effect Transistors Based on Carbonyl‐Bridged Bithiazole Derivatives

An electronegative conjugated compound composed of a newly designed carbonyl‐bridged bithiazole unit and trifluoroacetyl terminal groups is synthesized as a candidate for air‐stable n‐type organic field‐effect transistor (OFET) materials. Cyclic voltammetry measurements reveal that carbonyl‐bridging contributes both to lowering the lowest unoccupied molecular orbital energy level and to stabilizing the anionic species. X‐ray crystallographic analysis of the compound shows a planar molecular geometry and a dense molecular packing, which is advantageous to electron transport. Through these appropriate electrochemical properties and structures for n‐type semiconductor materials, OFET devices based on this compound show electron mobilities as high as 0.06 cm² V^?1 s^?1 with on/off ratios of 10⁶ and threshold voltages of 20 V under vacuum conditions. Furthermore, these devices show the same order of electron mobility under ambient conditions.     

Digital‐Inverter Amine Sensing via Synergistic Responses by n and p Organic Semiconductors

Chemiresistors and sensitive organic field‐effect transistors (OFETs) have been substantially developed as cheap, scalable, and versatile sensing platforms. While new materials are expanding OFET sensing capabilities, the device architectures have changed little. Higher order logic circuits utilizing OFETs sensitive to amine vapors are presented. The circuits depend on the synergistic responses of paired p‐ and n‐channel organic semiconductors, including a rare analyte‐induced current increase by the n‐channel semiconductor. This is the first step towards ‘intelligent sensors’ that utilize analog signal changes in sensitive OFETs to produce direct digital readouts suitable for further logic operations.     

Detailed Characterization of Contact Resistance,Gate‐Bias‐Dependent Field‐Effect Mobility,and Short‐Channel Effects with Microscale Elastomeric Single‐Crystal Field‐Effect Transistors

The organic field‐effect transistor (OFET) has proven itself invaluable as both the fundamental element in organic circuits and the primary tool for the characterization of novel organic electronic materials. Crucial to the success of the OFET in each of these venues is a working understanding of the device physics that manifest themselves in the form of electrical characteristics. As commercial applications shift to smaller device dimensions and structure/property relationships become more refined, the understanding of these phenomena become increasingly critical. Here, we employ high‐performance, elastomeric, photolithographically patterned single‐crystal field‐effect transistors as tools for the characterization of short‐channel effects and bias‐dependent parasitic contact resistance and field‐effect mobility. Redundant characterization of devices at multiple channel lengths under a single crystal allow the morphology‐free analysis of these effects, which is carried out in the context of a device model previously reported. The data show remarkable consistency with our model, yielding fresh insight into each of these phenomena, as well as confirming the utility of our FET design.     

Small‐Molecule‐Based Organic Field‐Effect Transistor for Nonvolatile Memory and Artificial Synapse

With the incorporation of tailorable organic electronic materials as channel and storage materials, organic field‐effect transistor (OFET)‐based memory has become one of the most promising data storage technologies for hosting a variety of emerging memory applications, such as sensory memory, storage memory, and neuromorphic computing. Here, the recent state‐of‐the‐art progresses in the use of small molecules for OFET nonvolatile memory and artificial synapses are comprehensively reviewed, focusing on the characteristic features of small molecules in versatile functional roles (channel, storage, modifier, and dopant). Techniques for optimizing the storage capacity, speed, and reliability of nonvolatile memory devices are addressed in detail. Insight into the use of small molecules in artificial synapses constructed on OFET memory is also obtained in this emerging field. Finally, the strategies of molecular design for improving memory performance in view of small molecules as storage mediums are discussed systematically, and challenges are addressed to shed light on the future development of this vital research field.     

Synthesis and characterization of an ester-terminated organic semiconductor for ethanol vapor detection

An organic-field effect transistor (OFET) based on a newly synthesized organic molecule with an ester end group (ANOAT) was tested in a sensor for the detection of ethanol vapor. The linearly fused acene in ANOAT forms channel layers in the OFET and the ester end group of ANOAT interacts with ethanol vapor. The ethanol sensing ability of the ANOAT-based OFET derives not from changes in the crystalline structure of the organic semiconductor but from the interaction between ethanol vapor and the ester end group, which we demonstrated by using FT-IR analysis, computational modeling, X-ray scattering, and AFM analysis.     

Effect of Donor Molecular Structure and Gate Dielectric on Charge‐Transporting Characteristics for Isoindigo‐Based Donor–Acceptor Conjugated Polymers

This study investigates the effect of the molecular structure of three different donor units, naphthalene (Np), bithiophene (BT), and thiophene–vinylene–thiophene (TVT), in isoindigo (IIG)‐based donor –acceptor conjugated polymers (PIIG‐Np, PIIG‐BT and PIIG‐TVT) on the charge carrier mobility of organic field‐effect transistors (OFETs). The charge transport properties of three different IIG‐based polymers strongly depend on donor units. PIIG–BT OFETs showed 50 times higher hole mobility (0.63 cm² V^?1 s^?1) than PIIG–TVT and PIIG–Np ones of ≈ 0.01 cm² V^?1 s^?1 with CYTOP dielectric though the BT units have less planarity than the TVT and Np units. The reasons for the different mobility in IIG‐based polymers are studied by analyzing the energy structure by absorption spectra, calculating transport levels by density functional theory, investigating the in‐ and out‐of‐plane crystallinity of thin film by grazing‐incidence wide‐angle X‐ray scattering, and extracting key transport parameters via low‐temperature measurements. By combining theoretical, optical, electrical, and structural analyses, this study finds that the large difference in OFET mobility mainly originates from the transport disorders determined by the different microcrystal structure, rather than the intrinsic transport properties in isolated chains for different polymers.     

Influence of Bioreceptor Layer Structure on Myelin Basic Protein Detection using Organic Field Effect Transistor‐Based Biosensors

Organic field‐effect transistor (OFET)‐based biosensors with antibody receptors are widely considered for protein antigen detection. To the authors' knowledge, there are no comparative evaluations to date of different choices for the matrix polymer to which the antibodies are attached. Herein, multiple acrylic copolymers are studied as receptor layers with myelin basic protein and its corresponding antibody as an archetypal antibody–antigen pair. Stability against multiple washing steps and the capacity for immobilizing antibodies on polymers on device surfaces with the help of fluorescein isothiocyanate‐labeled antibodies are compared. Electronic detection and selectivity are also observed. The conclusions provide guidance on the selection of bioreceptor material for increasing sensitivity and process stability of OFET biosensors.     

A High‐Capacitance Salt‐Free Dielectric for Self‐Healable,Printable, and Flexible Organic Field Effect Transistors and Chemical Sensor

Printable and flexible electronics attract sustained attention for their low cost, easy scale up, and potential application in wearable and implantable sensors. However, they are susceptible to scratching, rupture, or other damage from bending or stretching due to their “soft” nature compared to their rigid counterparts (Si‐based electronics), leading to loss of functionality. Self‐healing capability is highly desirable for these “soft” electronic devices. Here, a versatile self‐healing polymer blend dielectric is developed with no added salts and it is integrated into organic field transistors (OFETs) as a gate insulator material. This polymer blend exhibits an unusually high thin film capacitance (1400 nF cm^?2 at 120 nm thickness and 20–100 Hz). Furthermore, it shows pronounced electrical and mechanical self‐healing behavior, can serve as the gate dielectric for organic semiconductors, and can even induce healing of the conductivity of a layer coated above it together with the process of healing itself. Based on these attractive properties, we developed a self‐healable, low‐voltage operable, printed, and flexible OFET for the first time, showing promise for vapor sensing as well as conventional OFET applications.     

Effects of Fullerene Bisadduct Regioisomers on Photovoltaic Performance

Fullerene bisadducts have emerged as promising electron‐accepting materials because of their ability to increase the open‐circuit voltage (V_OC) of polymer solar cells (PSCs) due to their relatively high lowest unoccupied molecular orbital (LUMO) energy levels. It should be noted that the as‐prepared fullerene bisadducts are in fact a mixture of isomers. Here, the effects of fullerene bisadduct regioisomers on photovoltaic performance are examined. The trans‐2, trans‐3, trans‐4, and e isomers of dihydronaphthyl‐based [60]fullerene bisadduct (NCBA) are isolated and used as acceptors for P3HT‐based PSCs. The four NCBA isomers exhibit different absorption spectra, electrochemical properties, and electron mobilities, leading to varying PCE values of 5.8, 6.3, 5.6, and 5.5%, respectively, which are higher than that based on an NCBA mixture (5.3%), suggesting the necessity to use the individual fullerene bisadduct isomer for high‐performance PSCs.     

Novel Photoinduced Recovery of OFET Memories Based on Ambipolar Polymer Electret for Photorecorder Application

A new design concept for novel photoresponsive flash organic field‐effect transistor (OFET) memory is demonstrated by employing the carbazoledioxazine polymer (Poly CD) as an electret. Photoactive electrets that can absorb the light effectively rather than photoactive semiconductors are proposed by the “photoinduced recovery” mechanism in the literature; however, the correlation between the chemical structure and photoresponsive electrical performances is ambiguous. In this study, it is reported for the first time that the OFET memory with trapped charges can be optically recovered by a polymer electret and the working mechanism can be explained by the structural design. The highly planar Poly CD electret exhibits photoluminescence quenching in film states, resulting in the generation of sufficient excitons to eliminate trapped charges under light excitation. Additionally, the Poly CD electret with coplanar donor–acceptor moieties is suitable for both p‐channel and n‐channel semiconductors. For p‐type memory devices, a large memory window (82 V) and stable nonvolatile retention performance with high ON/OFF ratio could be obtained. The memories also display good switching reliability for voltage‐programming and light‐erasing cycles. This study provides useful information for the development of polymer‐based photoresponsive flash OFET memories and demonstrates the practical applications of photorecorder and photosensitive smart tag.     

Solution Processable Fluorenyl Hexa‐peri‐hexabenzocoronenes in Organic Field‐Effect Transistors and Solar Cells

The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field‐effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa‐peri‐hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from ¹H NMR and 2D wide‐angle X‐ray scattering (2D WAXS) experiments that the sterically demanding 9,9‐dioctylfluorene groups are preventing π–π intermolecular contact in the hexakis‐substituted FHBC 4 . For bis‐substituted FHBC compounds 5 and 6 , π–π intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field‐effect mobility of FHBC 6 , deposited by spin‐casting, reached 2.8 × 10^?3 cm² V^?1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC₆₁BM.