Flexible Organic Field-effect Transistors Research Articles

Electrophilic-Attack Doped Organic Field-Effect Transistors for Ultrasensitive and Selective Hydrogen Sulfide Detection.

Doping of organic semiconductors (OSCs) has been developed as an effective means of modulating the density and transfer efficiency of charge carriers; however, realization of effective doping to tailor the chemical sensing performance of OSC-based sensors still remains not explored extensively. In addition, the application of OSCs in chemical sensors is usually limited by the poor stability and low selectivity. Herein, flexible donor-acceptor copolymer-based organic field-effect transistor (OFET) chemical sensors are designed via an electrophilic attack doping strategy. The p-dopant trityl tetrakis(pentafluorophenyl) borate (TrTPFB) can be effectively doped into the host molecular N-alkyl-diketopyrrolo-pyrroledithienylthieno[3,2-b]thiophene (DPPDTT). It is simple to alter the doping efficiency and film thickness (ca. 5.5-17.7 nm) by adjusting the proportion and concentration of guest-host molecules, which endows facile carrier mobility and enhanced sensing sensitivity modulation toward reducing gases at room temperature. Particularly, 1.0 mol% TrTPFB-doped DPPDTT achieved the highest response to H2S gas, including ultralow detection concentration (0.5 ppb), excellent selectivity, high humidity stability, and long-term storage stability. This work can provide a new strategy for the potential applications of the organic electronic sensing devices.

Effect of Alkyl Side Chain Length on Electrical Performance of Ion-Gel-Gated OFETs Based on Difluorobenzothiadiazole-Based D-A Copolymers

The performance of organic field-effect transistors (OFETs) is highly dependent on the dielectric–semiconductor interface, especially in ion-gel-gated OFETs, where a significantly high carrier density is induced at the interface at a low gate voltage. This study investigates how altering the alkyl side chain length of donor–acceptor (D-A) copolymers impacts the electrical performance of ion-gel-gated OFETs. Two difluorobenzothiadiazole-based D-A copolymers, PffBT4T-2OD and PffBT4T-2DT, are compared, where the latter features longer alkyl side chains. Although PffBT4T-2DT shows a 2.4-fold enhancement of charge mobility in the SiO2-gated OFETs compared to its counterpart due to higher crystallinity in the film, PffBT4T-2OD outperforms PffBT4T-2DT in the ion-gel-gated OFETs, manifested by an extraordinarily high mobility of 17.7 cm2/V s. The smoother surface morphology, as well as stronger interfacial interaction between the ion-gel dielectric and PffBT4T-2OD, enhances interfacial charge accumulation, which leads to higher mobility. Furthermore, PffBT4T-2OD is blended with a polymeric elastomer SEBS to achieve ion-gel-gated flexible OFETs. The blend devices exhibit high mobility of 8.6 cm2/V s and high stretchability, retaining 45% of initial mobility under 100% tensile strain. This study demonstrates the importance of optimizing the chain structure of polymer semiconductors and the semiconductor–dielectric interface to develop low-voltage and high-performance flexible OFETs for wearable electronics applications.

Bioinspired Flexible and Low-Voltage Organic Synaptic Transistors for UV Light-Driven Vision Systems.

Neuromorphic vision systems, particularly those stimulated by ultraviolet (UV) light, hold great potential applications in portable electronics, wearable technology, biological analysis, military surveillance, etc. Organic artificial synaptic devices hold immense potential in this field due to their ease of processing, flexibility, and biocompatibility. In this work, we have fabricated a flexible organic field-effect transistor (OFET) that utilizes chitosan-silver nanoparticles (AgNPs) composite material as the active dielectric material. During UV light illumination, both silver nanoparticles and the pentacene layer generate a large number of charge carriers. The photogenerated carriers lead to a more significant hole accumulation at the pentacene interface, resulting in a current rise. In the absence of light, the trapped electron in the silver nanoparticles persists for a longer duration, preventing the instant recombination with holes. This extended retention of electrons leads to the observed synaptic performance of the transistor. The use of aluminum oxide (Al2O3) as one of the dielectric layers enables the device to operate effectively at low voltage (<1 V). The device mimics various crucial synaptic properties of the brain, including short-term potentiation and long-term potentiation (STP and LTP), paired-pulse facilitation (PPF), spike-duration dependent plasticity (SDDP), spike-number dependent plasticity (SNDP), and spike-rate dependent plasticity (SRDP), etc. This work introduces an approach to develop flexible organic synaptic transistors that operate efficiently at low voltages, paving the way toward high-performance, UV light-driven neuromorphic vision systems.

Low voltage flexible high performance organic field-effect transistor and its application for ultraviolet light detectors

ABSTRACT A novel highly π-extended heteroarene Benzo[1,2-b:4,5-b’]di(naphtho[1,2-d]thiophene) (DBTBT) was used for organic field-effect transistors (OFETs). The mobilities of OFET were greatly improved from 0.34–0.58 cm2V−1s−1 to 1.02–1.75 cm2V−1s−1 by morphology tuning through 2 steps’ controlling substrate temperature. More importantly, the OFETs showed a good ambient stability in 30 days measurements. The flexible OFET arrays were prepared on polyethylene terephthalate substrate with octadecyl trichlorosilane modified polymethylsilsesquioxane/polyacrylonitrile gate dielectrics and demonstrated a 100% yield. Further, this flexible cell was used for ultraviolet light detection, which showed good ability of detecting low power light (such as λ = 254 nm, 7 μW/cm2).

Breaking Fundamental Limitation of Flow-Induced Anisotropic Growth for Large-Scale and Fast Printing of Organic Single-Crystal Films.

Advanced organic electronic technologies have put forward a pressing demand for cost-effective and high-throughput fabrication of organic single-crystal films (OSCFs). However, solution-printed OSCFs are typically plagued by the existence of abundant structural defects, which pose a formidable challenge to achieving large-scale and high-performance organic electronics. Here, it is elucidated that these structural defects are mainly originated from printing flow-induced anisotropic growth, an important factor that is overlooked for too long. In light of this, a surfactant-additive printing method is proposed to effectively overcome the anisotropic growth, enabling the deposition of uniform OSCFs over the wafer scale at a high speed of 1.2 mm s-1 at room temperature. The resulting OSCF exhibits appealing performance with a high average mobility up to 10.7 cm2 V-1 s-1, which is one of the highest values for flexible organic field-effect transistor arrays. Moreover, large-scale OSCF-based flexible logic circuits, which can be bent without degradation to a radius as small as 4.0 mm and over 1000 cycles are realized. The work provides profound insights into breaking the limitation of flow-induced anisotropic growth and opens new avenues for printing large-scale organic single-crystal electronics.

Novel Frequency Dependent OFET Attenuator Using ClInPc with Al2O3 Embedded Nanoparticles in Nylon 11 for Flexible Electronics

The Organic field-effect transistors (OFETs) have been largely investigated due to their low-cost manufacturing, flexibility, and lightweight, as well as their optical and electrical characteristics. That allow its application in sensors, amplifiers, attenuators signal filtering, and high-frequency response devices, like biosensing, wearable electronics, optoelectronics, telecommunications, and other potential applications. Throughout this investigation, a ClInPc flexible OFET with Al2O3 embedded particles in nylon 11, was manufactured and characterized to evaluate the optoelectronic and morphological properties. For the manufacturing, a high-vacuum thermal evaporation deposition technique was used, and UV-vis spectroscopy analysis and scanning electron microscopy were conducted to evaluate the optoelectronic and morphological properties. Also, a study regarding the electrical characteristics for different time-dependent wavefunction input signals, changing the input voltage and frequency, has been conducted. The latter was driven to determine the time-response characteristics, gains, phase shift and to determine whether the device function as an attenuator or an amplifier with the selected configuration. The device has been modelled to obtain the OFET operation parameters. A resulting capacitance of 567 pF was calculated. Uniform and continuous films where obtained, which guarantees an efficient charge transport. For all signals the output voltage is lower than that of the input voltage. Also, for the higher frequency the output voltage is decreased compared to lower frequencies. Gains decreasing variation of up to 0.05 indicate the operating application as an attenuator. Phase variation of up to 100 °, resulted while varying the input frequency. The model resulted on a gate capacitance value between 500 and 1180 pF, and gate-drain capacitance value between 50 and 500 pF. All of this could give evidence that state of the art ClInPc flexible OFET device with Al2O3 embedded nanoparticles in nylon 11 could be used toward current high-performance frequency-dependent flexible applications.

Transparent polymer nanoheterostructure films for flexible low-power organic transistors with high mobility, decent photostability, and ultralong-term air stability

Organic field-effect transistors (OFETs) are promising candidates for flexible electronic devices, but their instability remains a huge challenge that should be solved for practical applications. It is very difficult to achieve high-performance energy-efficient OFETs with good photostability and ultralong-term air stability. Here, a novel type of transparent and stable polymer films comprising p-type nanofibrous semiconductor and insulating polystyrene is developed, forming the nanoscale cross-interconnected heterostructures. The nanoheterostructure films as channel layers enable flexible low-power OFETs to achieve highly improved mobilities up to 6.78 cm2 V−1 s−1 at a low-operating voltage of −0.5 V despite the small semiconductor content, and the substantial amount of inert insulators can effectively prevent external factors such as light, moisture, and oxygen from interfering with the semiconductor layer. As results, the flexible OFETs using these nanoheterostructure films show slight performance changes under different light illuminations even by three laser beams, and their unencapsulated devices retain excellent performance even after over 450 days of ultralong-term and high-humidity air exposure. These findings demonstrate that nanoscale heterostructure films of polymer semiconductors and insulators constitute a simple yet efficient strategy for improving the OFET stability, which holds great promise for developing high-performance durable and energy-saving devices in flexible and transparent electronics.

Fabrication of flexible organic field effect transistors with high carrier mobility via sheath gas-assisted direct writing Poly(3-hexylthiophene) solution

Fabrication of flexible organic field effect transistors with high carrier mobility via sheath gas-assisted direct writing Poly(3-hexylthiophene) solution

Integration of Ordered Mesoporous Carbon Spheres-Based Ion-Sensitive Electrodes With Flexible Organic Field-Effect Transistors for Multiplexed Ion Sensing

In the path towards the integration of flexible organic field-effect transistors (OFETs) into the construction of manufactured-on-demand ion-sensors, it is still challenging to obtain high stability and sensitivity as required by high detection accuracy, especially for a multi-sensing system. In this work, ordered mesoporous carbon (OMC) spheres with high surface area and super-hydrophobicity were synthesized and introduced as ion-to-electron transducer layer to improve the sensitivity and stability of Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion-sensitive electrodes (ISEs). High-performance low-voltage (< 3 V) operated ion-sensitive OFETs (ISOFETs) were further fabricated by on-chip low-temperature packaging of the developed ISEs and OFETs. A three-channel multiplexed flexible sensing tag with improved detection accuracy was demonstrated in a hand-held circuit readout system. This ISOFET sensor has great potential in multiplexed sensing systems and will significantly improve efficiency and accuracy in the field of biochemical analysis.

High-performance flexible organic field effect transistors with print-based nanowires

Polymer nanowire (NW) organic field-effect transistors (OFETs) integrated on highly aligned large-area flexible substrates are candidate structures for the development of high-performance flexible electronics. This work presents a universal technique, coaxial focused electrohydrodynamic jet (CFEJ) printing technology, to fabricate highly aligned 90-nm-diameter polymer arrays. This method allows for the preparation of uniformly shaped and precisely positioned nanowires directly on flexible substrates without transfer, thus ensuring their electrical properties. Using indacenodithiophene-co-benzothiadiazole (IDT-BT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8-BT) as example materials, 5 cm2 arrays were prepared with only minute size variations, which is extremely difficult to do using previously reported methods. According to 2D-GIXRD analysis, the molecules inside the nanowires mainly adopted face-on π-stacking crystallite arrangements. This is quite different from the mixed arrangement of thin films. Nanowire-based OFETs exhibited a high average hole mobility of 1.1 cm2 V−1 s−1 and good device uniformity, indicating the applicability of CFEJ printing as a potential batch manufacturing and integration process for high-performance, scalable polymer nanowire-based OFET circuits. This technique can be used to fabricate various polymer arrays, enabling the use of organic polymer semiconductors in large-area, high-performance electronic devices and providing a new path for the fabrication of flexible displays and wearable electronics in the future.

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.

Impact of Planar and Vertical Organic Field-Effect Transistors on Flexible Electronics.

The development of flexible and conformable devices, whose performance can be maintained while being continuously deformed, provides a significant step toward the realization of next-generation wearable and e-textile applications. Organic field-effect transistors (OFETs) are particularly interesting for flexible and lightweight products, because of their low-temperature solution processability, and the mechanical flexibility of organic materials that endows OFETs the natural compatibility with plastic and biodegradable substrates. Here, an in-depth review of two competing flexible OFET technologies, planar and vertical OFETs (POFETs and VOFETs, respectively) is provided. The electrical, mechanical, and physical properties of POFETs and VOFETs are critically discussed, with a focus on four pivotal applications (integrated logic circuits, light-emitting devices, memories, and sensors). It is pointed out that the flexible function of the relatively newer VOFET technology, along with its perspective on advancing the applicability of flexible POFETs, has not been reviewed so far, and the direct comparison regarding the performance of POFET- and VOFET-based flexible applications is most likely absent. With discussions spanning printed and wearable electronics, materials science, biotechnology, and environmental monitoring, this contribution is a clear stimulus to researchers working in these fields to engage toward the plentiful possibilities that POFETs and VOFETs offer to flexible electronics.

Flexible Electronics Based on Organic Semiconductors: from Patterned Assembly to Integrated Applications.

Organic flexible electronic devices are at the forefront of the electronics as they possess the potential to bring about a major lifestyle revolution owing to outstanding properties of organic semiconductors, including solution processability, lightweight and flexibility. For the integration of organic flexible electronics, the precise patterning and ordered assembly of organic semiconductors have attracted wide attention and gained rapid developments, which not only reduces the charge crosstalk between adjacent devices, but also enhances device uniformity and reproducibility. This review focuses on recent advances in the design, patterned assembly of organic semiconductors, and flexible electronic devices, especially for flexible organic field-effect transistors (FOFETs) and their multifunctional applications. First, typical organic semiconductor materials and material design methods are introduced. Based on these organic materials with not only superior mechanical properties but also high carrier mobility, patterned assembly strategies on flexible substrates, including one-step and two-step approaches are discussed. Advanced applications of flexible electronic devices based on organic semiconductor patterns are then highlighted. Finally, future challenges and possible directions in the field to motivate the development of the next generation of flexible electronics are proposed.

High-performance flexible pentacene transistor memory with PTCDI-C13 as N-type buffer layer

Flexible organic field-effect transistor nonvolatile memories (OFET-NVMs) with polymer electrets have aroused great attention for its important role in next-generation flexible data storage devices application. However, the OFET-NVMs to date still hardly reach the requirements for practical applications. In air environment, the positively charged defects formed in pentacene near the interface with polymer, result in unsatisfied high programming/erasing (P/E) voltages. Here, we propose an OFET memory structure, in which an n-type semiconductor N, N′-Bis(3-pentyl) perylene-3, 4, 9, 10-bis(dicarboximide) (PTCDI-C13) is inserted between pentacene and poly(4-vinyl phenol. Based on the electrostatic induction effect, electrons are induced on the surface of PTCDI-C13 due to the electrostatic field generated by the positive charges at the interface of pentacene/polymer, and compensate part of the positive charges at the interface, resulting in the reduction of the height of hole-barrier. The flexible memory device with PTCDI-C13 exhibits a memory window of larger than 7 V at P/E voltages (±20 V), fast switching speeds (0.5 ms), good P/E endurance (>400 cycles), large field-effect mobility (0.026 cm2 V−1 s−1), and long retention time (over 104 s).

Light-responsive self-strained organic semiconductor for large flexible OFET sensing array

With the wide application of organic semiconductors (OSCs), researchers are now grappling with a new challenge: design and synthesize OSCs materials with specific functions to satisfy the requirements of high-performance semiconductor devices. Strain engineering is an effective method to improve the semiconductor material’s carrier mobility, which is fundamentally originated from the rearrangement of the atomic packing model of materials under mechanic stress. Here, we design and synthesize a new OSC material named AZO-BTBT-8 based on high-mobility benzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTBT) as the semiconductor backbone. Octane is employed to increase molecular flexibility and solubility, and azobenzene at the other end of the BTBT backbone provides photoisomerization properties and structural balance. Notably, the AZO-BTBT-8 photoisomerization leads to lattice strain in thin-film devices, where exceptional device performance enhancement is realized. On this basis, a large-scale flexible organic field-effect transistor (OFET) device array is fabricated and realizes high-resolution UV imaging with reversible light response.

Research progress in skin-like ultraflexible organic field-effect transistors

<p indent="0mm">Field-effect transistor is one of the most important basic components in modern microelectronic industry. Organic field-effect transistors (OFETs) possess the outstanding advantages in flexibility, light weight, solution processability and good biocompatibility. They have presented great application potential in the field of skin-like electronics, such as software robots, implant devices and imperceptible wearable devices. Skin-like ultraflexible OFETs can be imperceptibly conformable to the three-dimensional static/dynamic surfaces such as skin and prosthesis, maintain the stable electrical performance under deformation, and give the wearer the minimized burden and maximized comfort. Decreasing the thickness and Young’s modulus will effectively reduce the resilience of the device due to deformation, which is the main strategy to obtain the skin-like ultraflexible devices with three-dimensional conformability. In this paper, two types of skin-like flexible OFETs, including ultra-thin transistors and stretchable transistors, are summarized. The research process of the skin-like ultraflexible OFETs is discussed.

Low-voltage flexible organic transistors based on a water-soluble natural gate dielectric exhibiting high-performance and stability

The use of natural material components in organic devices increases nature friendliness and biodegradability. In this paper, water-soluble natural protein gelatin is explored as a gate dielectric for demonstration of high performance and low voltage (−3 V) operation in flexible organic field-effect transistors (OFETs). The fabricated p-channel devices showed excellent electrical characteristics of maximum field-effect mobility up to 3.0 cm2 V−1 s−1, high current on/off ratios, low subthreshold swing, and nearly zero threshold voltage due to the high-quality dielectric semiconductor interface achieved through optimized processes of fabricating flexible OFET devices. These devices exhibited very high operational stability as confirmed by various stability tests including bias-stress, repeatability, electromechanical stability, cyclic stability, and long-term ambient stability. For electromechanical stability, no significant changes in the performance were observed upon application of compressive and tensile strain due to bending. A very high environmental stability with almost unchanged electrical characteristics over 24 weeks was demonstrated. Further, circuit applicability was analyzed by switching characteristics from resistive load inverters. These results indicate gelatin as a promising biodegradable dielectric candidate for low voltage flexible OFETs.

A PVP-silica-titania hybrid film for low-voltage organic field-effect transistor

A PVP-silica-titania hybrid film with excellent dielectric properties was fabricated by the sol–gel method at low temperature (180 °C). The film has a high dielectric constant (k = 13), a low leakage current density (<20nA cm−2 at 2 V), and a smooth surface (Rq < 0.4 nm). The organic field-effect transistor (OFET), with the PVP-silica-titania hybrid film, had been fabricated and compared with the OFET, which was fabricated with SiO2 dielectric. The electrical performance of the device had obviously improved in the operating voltage (−1.5 V), threshold voltage (−0.35 V), and mobility (0.7 cm2 V−1 s−1). To investigate the suitability of the PVP-silica-titania hybrid film in flexible applications, a low-voltage flexible OFET was fabricated. The device had been tested in the bending state and exhibited good performance under the ambition conditions. The result demonstrated that the PVP-titania hybrid film is a promising candidate material for flexible organic electronics with low power consumption.

Solution processed low power organic field-effect transistor bio-chemical sensor of high transconductance efficiency

Developing organic field-effect transistor (OFET) biosensors for customizable detection of biomarkers for many diseases would provide a low-cost and convenient tool for both biological studies and clinical diagnosis. In this work, design principles of the OFET transducer for biosensors were derived to relate the signal-to-noise ratio (SNR) to the device-performance parameters. Steep subthreshold swing (SS), proper threshold voltage (Vth), good-enough bias-stress stability, and mechanical durability are shown to be the key prerequisites for realizing OFET bio-sensors of high transconductance efficiency (gm/ID) for large SNR. Combining a low trap-density channel and a high-k/low-k gate dielectric layer, low-temperature (<100 °C) solution-processed flexible OFETs can meet the performance requirements to maximize the gm/ID. An extended gate-structure OFET biosensor was further implemented for label-free detection of miR-21, achieving a detection limit below 10 pM with high selectivity at a low operation voltage (<1 V).

Fabrication of Flexible Organic Field Effect Transistors with High Carrier Mobility Via Sheath Gas-Assisted Direct Writing Poly(3-Hexylthiophene) Solution

Fabrication of Flexible Organic Field Effect Transistors with High Carrier Mobility Via Sheath Gas-Assisted Direct Writing Poly(3-Hexylthiophene) Solution