Chemically Robust Ambipolar Organic Transistor Array Directly Patterned by Photolithography

n-Type Doping Effect of Anthracene-Based Cationic Dyes in Organic Electronics

n-Type doping for improving the electrical characteristics and air stability of n-type organic semiconductors (OSCs) is important for realizing advanced future electronics. Herein, we report a selection method for an effective n-type dopant with an optimized structure and thickness based on anthracene cationic dyes with high miscibility induced by a molecular structure similar to that of OSCs. Among the doped OSCs evaluated, rhodamine B (RhoB)-doped OSC exhibits the highest density, a smallest roughness of 2.69 nm, a phase deviation of 0.85° according to atomic force microscopy measurements, and the highest electron mobility (μ), showing its high miscibility. Surface doping of RhoB affords the lowest contact resistance of 2.01 × 105 Ω cm compared to bulk and contact doping, resulting in an effective doping structure. The RhoB-doped OSC retains 81.63% of the original μ value of 6.13 × 10-2 cm2 V-1 s-1 after 15 days, whereas pristine OSC shows a lower μ of 2.33 × 10-2 cm2 V-1 s-1 and maintains only 4.41% of the original value after 15 days. Our findings demonstrate that this methodology is effective for the selection of a high-performance n-type dopant for OSCs toward the development of high-performance and air-stable n-type organic electronics.

Tunable evaporation-induced surface morphologies on chitosan film for light management

The surface morphologies of polymer films have been used to improve the performance or enable new applications of films, such as controllable adhesion, shape morphing and light management. However, complicated and destructive methods were applied to produce surface morphologies on chitosan (CS) film. To overcome this challenge, we report an evaporation-induced self-assembly to form the tunable morphologies on the surface of short-chain chitosan film by varying the evaporation rates that influence the aggregation behavior of polymer chains between order and disorder. It enables the simple, tunable and scalable fabrication of surface morphologies on CS film (CS solution concentration: 2 wt%, drying from room temperature (RT) to 80 °C) that provides controllable haze (3-74 %) and high transmittance (>85 %) for the production of hazy and transparent window coatings. This simple approach to producing tunable surface morphologies could inspire the synthesis of multifunctional polymer films with different surface structures, whose applications can be extended to cell culture interfaces, flexible bioelectronic and optoelectronic devices.

Overcoming Downscaling Limitations in Organic Semiconductors: Strategies and Progress

Organic semiconductors have great potential to revolutionize electronics by enabling flexible and eco-friendly manufacturing of electronic devices on plastic film substrates. Recent research and development led to the creation of printed displays, radio-frequency identification tags, smart labels, and sensors based on organic electronics. Over the last 3 decades, significant progress has been made in realizing electronic devices with unprecedented features, such as wearable sensors, disposable electronics, and foldable displays, through the exploitation of desirable characteristics in organic electronics. Neverthless, the down-scalability of organic electronic devices remains a crucial consideration. To address this, efforts are extensively explored. It is of utmost importance to further develop these alternative patterning methods to overcome the downscaling challenge. This review comprehensively discusses the efforts and strategies aimed at overcoming the limitations of downscaling in organic semiconductors, with a particular focus on four main areas: 1) lithography-compatible organic semiconductors, 2) fine patterning of printing methods, 3) organic material deposition on pre-fabricated devices, and 4) vertical-channeled organic electronics. By discussing these areas, the full potential of organic semiconductors can be unlocked, and the field of flexible and sustainable electronics can be advanced.

Bionic Tactile-Gustatory Receptor for Object Identification Based on All-Polymer Electrochemical Transistor

Human sensory receptors enable the real world to be perceived effortlessly. Hence, massive efforts have been devoted to the development of bionic receptors capable of identifying objects. Unfortunately, most of the existing devices are limited to single sensory emulation and are established on solid-state electronic technologies, which are incompatible with the biological reactions occurring in electrolyte media. Here, an iontronic tactile-gustatory receptor using an all-polymer electrochemical transistor (AECT) is presented. The sensor is biocompatible with the operation voltage of 0.1 V, which is 1 to 2 orders lower than those of reported values. By this study, one receptor is able to accurately recognize various objects perceived by the human tactile and gustatory system without complex circuitry. Additionally, to promote its further application, flexible AECT arrays with channel length of 2 µm and density of 104 167 transistors cm^-2 (yield of 97%) are fabricated, 1 to 5 orders higher than those of related works. Finally, a flexible integrated network for electrocardiogram recording is successfully constructed. This study moves a step forward toward state-of-the-art bionic sensors.

Graphene: Preparation, tailoring, and modification

Graphene is a 2D material with fruitful electrical properties, which can be efficiently prepared, tailored, and modified for a variety of applications, particularly in the field of optoelectronic devices thanks to its planar hexagonal lattice structure. To date, graphene has been prepared using a variety of bottom-up growth and top-down exfoliation techniques. To prepare high-quality graphene with high yield, a variety of physical exfoliation methods, such as mechanical exfoliation, anode bonding exfoliation, and metal-assisted exfoliation, have been developed. To adjust the properties of graphene, different tailoring processes have been emerged to precisely pattern graphene, such as gas etching and electron beam lithography. Due to the differences in reactivity and thermal stability of different regions, anisotropic tailoring of graphene can be achieved by using gases as the etchant. To meet practical requirements, further chemical functionalization at the edge and basal plane of graphene has been extensively utilized to modify its properties. The integration and application of graphene devices is facilitated by the combination of graphene preparation, tailoring, and modification. This review focuses on several important strategies for graphene preparation, tailoring, and modification that have recently been developed, providing a foundation for its potential applications.

Patterning an Erosion-Free Polymeric Semiconductor Channel for Reliable All-Photolithography Organic Electronics

Reliable patterning of organic semiconductors (OSCs) with high uniformity is essential to all-photolithography organic electronics. However, the majority of cross-linked OSCs experience performance fluctuations after photolithography because of the inherent vulnerability of low-ordered regions. Herein, we develop an anti-solution penetration photolithography process to achieve the reliable patterning of the OSC layer for all-photolithography integrated organic electronics. Using a thick and highly cross-linked semiconductor film and a low-solubility developer, an erosion-free semiconductor channel is obtained with a high mobility of up to 1.254 cm² V^-1 s^-1 and a uniform threshold voltage close to zero. Compared with existing all-photolithography organic circuits, the unit logic gate area consumption is lower by 1-3 orders of magnitude at 0.0069 mm², while the transistor density is higher by 1-2 orders of magnitude at 6780 Tr cm^-2. The miniaturized organic inverters maintain uncompromised voltage gains, and the 15-stage organic ring oscillators feature higher oscillation frequencies, making them promising for applications in wide-ranging integrated organic circuits.

Facile Fabrication of ZnO-ZnFe2O4 Hollow Nanostructure by a One-Needle Syringe Electrospinning Method for a High-Selective H2S Gas Sensor

Herein, a facile fabrication process of ZnO-ZnFe₂O₄ hollow nanofibers through one-needle syringe electrospinning and the following calcination process is presented. The various compositions of the ZnO-ZnFe₂O₄ nanofibers are simply created by controlling the metal precursor ratios of Zn and Fe. Moreover, the different diffusion rates of the metal oxides and metal precursors generate a hollow nanostructure during calcination. The hollow structure of the ZnO-ZnFe₂O₄ enables an enlarged surface area and increased gas sensing sites. In addition, the interface of ZnO and ZnFe₂O₄ forms a p-n junction to improve gas response and to lower operation temperature. The optimized ZnO-ZnFe₂O₄ has shown good H₂S gas sensing properties of 84.5 (S = R_a/R_g) at 10 ppm at 250 °C with excellent selectivity. This study shows the good potential of p-n junction ZnO-ZnFe₂O₄ on H₂S detection and affords a promising sensor design for a high-performance gas sensor.

Advanced Organic Transistor-Based Sensors Utilizing a Solvatochromic Medium with Twisted Intramolecular Charge-Transfer Behavior and Its Application to Ammonia Gas Detection

Here, we designed and developed an organic field-effect transistor (OFET)-based gas sensor by applying solvatochromic dye (Nile red, NR) with twisted intramolecular charge-transfer (TICT) behavior depending on the polarity of the surrounding molecules, as an auxiliary NR sensing medium (aNR-SM). As a polar molecule approaches, intra-charge transfers from the donor diethylamine group to the ketone group occur in the NR molecule, resulting in the twisting of the donor functional group and thereby increasing its dipole moment. Using this characteristic, NR was applied as an auxiliary sensing medium to the OFET for detecting ammonia (NH₃), a representative toxic gas. The Top-NR case, where the aNR-SM covers only the top of the organic semiconductor layer, showed the best gas sensing performance, and its response and recovery rates were improved by 46 and 94%, respectively, compared to the pristine case. More importantly, a sensitivity of 0.87 ± 0.045 ppm^-1 % was measured, having almost perfect linearity (0.999) over the range of measured NH₃ concentrations, which is the result of solving the saturation problem in the sensing characteristics of the OFET-based gas sensor. Our result not only improved the sensing performance of the OFET-based sensor but also made an important advance in that the reliability of the sensing performance was easily secured by applying solvatochromic and TICT behaviors of an auxiliary sensing medium.

A comprehensive nano-interpenetrating semiconducting photoresist toward all-photolithography organic electronics

Owing to high resolution, reliability, and industrial compatibility, all-photolithography is a promising strategy for industrial manufacture of organic electronics. However, it receives limited success due to the absence of a semiconducting photoresist with high patterning resolution, mobility, and performance stability against photolithography solution processes. Here, we develop a comprehensive semiconducting photoresist with nano-interpenetrating structure. After photolithography, nanostructured cross-linking networks interpenetrate with continuous phases of semiconducting polymers, enabling submicrometer patterning accuracy and compact molecular stacking with high thermodynamic stability. The mobility reaches the highest values of photocrosslinkable organic semiconductors and maintains almost 100% after soaking in developer and stripper for 1000 min. Owing to the comprehensive performance, all-photolithography is achieved, which fabricates organic inverters and high-density transistor arrays with densities up to 1.1 × 10⁵ units cm^-2 and 1 to 4 orders larger than conventional printing processes, opening up a new approach toward manufacturing highly integrated organic circuits and systems.

High-Performance Full-Photolithographic Top-Contact Conformable Organic Transistors for Soft Electronics

Organic thin-film transistors (OTFTs) are identified to be the most promising candidate for next-generation wearable and implantable electronics because of their unique advantages including their flexibility, low cost, long-term biocompatibility, and simple packaging. However, commercialization of organic transistors remains an enormous challenge due to their low mobility and lack of scalable strategy for high-precise soft devices. Here, a novel photolithography fabrication strategy is proposed, which is completely compatible with various commercial organic semiconductor materials, for the first demonstration of the fully photolithographic top-contact conformable OTFTs with the device density as high as 1523 transistors cm-2. Excellent electrical and mechanical properties with device yield as high as 100%, field-effect mobility up to 1-2 cm2 V-1 s-1, and outstanding conformability are shown. This work provides a new strategy that can fully maximize the advantages of organic materials and photolithography technology, showing a great prospect in the development of high-performance, high-precise organic devices toward the commercialized and industrialized soft electronic products.

Blurred Electrode for Low Contact Resistance in Coplanar Organic Transistors

Inefficient charge injection and transport across the electrode/semiconductor contact edge severely limits the device performance of coplanar organic thin-film transistors (OTFTs). To date, various approaches have been implemented to address the adverse contact problems of coplanar OTFTs. However, these approaches mainly focused on reducing the injection resistance and failed to effectively lower the access resistance. Here, we demonstrate a facile strategy by utilizing the blurring effect during the deposition of metal electrodes, to significantly reduce the access resistance. We find that the transition region formed by the blurring behavior can continuously tune the molecular packing and thin-film growth of organic semiconductors across the contact edge, as well as provide continuously distributed gap states for carrier tunnelling. Based on this versatile strategy, the fabricated dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) coplanar OTFT shows a high field-effect mobility of 6.08 cm² V^-1 s^-1 and a low contact resistance of 2.32 kΩ cm, comparable to the staggered OTFTs fabricated simultaneously. Our work addresses the crucial impediments for further reducing the contact resistance in coplanar OTFTs, which represents a significant step of contact injection engineering in organic devices.

Photonic-Plasmonic Nanostructures for Solar Energy Utilization and Emerging Biosensors

Issues related to global energy and environment as well as health crisis are currently some of the greatest challenges faced by humanity, which compel us to develop new pollution-free and sustainable energy sources, as well as next-generation biodiagnostic solutions. Optical functional nanostructures that manipulate and confine light on a nanometer scale have recently emerged as leading candidates for a wide range of applications in solar energy conversion and biosensing. In this review, recent research progress in the development of photonic and plasmonic nanostructures for various applications in solar energy conversion, such as photovoltaics, photothermal conversion, and photocatalysis, is highlighted. Furthermore, the combination of photonic and plasmonic nanostructures for developing high-efficiency solar energy conversion systems is explored and discussed. We also discuss recent applications of photonic-plasmonic-based biosensors in the rapid management of infectious diseases at point-of-care as well as terahertz biosensing and imaging for improving global health. Finally, we discuss the current challenges and future prospects associated with the existing solar energy conversion and biosensing systems.

Ambipolar Deep-Subthreshold Printed-Carbon-Nanotube Transistors for Ultralow-Voltage and Ultralow-Power Electronics

The development of ultralow-power and easy-to-fabricate electronics with potential for large-scale circuit integration (i.e., complementary or complementary-like) is an outstanding challenge for emerging off-the-grid applications, e.g., remote sensing, "place-and-forget", and the Internet of Things. Herein we address this challenge through the development of ambipolar transistors relying on solution-processed polymer-sorted semiconducting carbon nanotube networks (sc-SWCNTNs) operating in the deep-subthreshold regime. Application of self-assembled monolayers at the active channel interface enables the fine-tuning of sc-SWCNTN transistors toward well-balanced ambipolar deep-subthreshold characteristics. The significance of these features is assessed by exploring the applicability of such transistors to complementary-like integrated circuits, with respect to which the impact of the subthreshold slope and flatband voltage on voltage and power requirements is studied experimentally and theoretically. As demonstrated with inverter and NAND gates, the ambipolar deep-subthreshold sc-SWCNTN approach enables digital circuits with complementary-like operation and characteristics including wide noise margins and ultralow operational voltages (≤0.5 V), while exhibiting record-low power consumption (≤1 pW/μm). Among thin-film transistor technologies with minimal material complexity, our approach achieves the lowest energy and power dissipation figures reported to date, which are compatible with and highly attractive for emerging off-the-grid applications.

Photolithographic Patterning of Perovskite Thin Films for Multicolor Display Applications

Metal halide perovskites are emerging as attractive materials for light-emitting diode (LED) applications. The external quantum efficiency (EQE) has experienced a rapid progress and reached over 21%, comparable to the state of the art organic and quantum dot LEDs. For metal halide perovskites, their simple solution-processing preparation, facile band gap tunability, and narrow emission line width provide another attractive route to harness their superior optoelectronic properties for multicolor display applications. In this work, we demonstrate a high-resolution, large-scale photolithographic method to pattern multicolor perovskite films. This approach is based on a dry lift-off process which involves the use of parylene as an intermediary and the easy mechanical peeling-off of parylene films on various substrates. Using this approach, we successfully fabricated multicolor patterns with red and green perovskite pixels on a single substrate, which could be further applied in liquid crystal displays (LCDs) with blue backlight. Besides, a prototype green perovskite micro-LED display under current driving has been demonstrated.

Universal three-dimensional crosslinker for all-photopatterned electronics

All-solution processing of large-area organic electronics requires multiple steps of patterning and stacking of various device components. Here, we report the fabrication of highly integrated arrays of polymer thin-film transistors and logic gates entirely through a series of solution processes. The fabrication is done using a three-dimensional crosslinker in tetrahedral geometry containing four photocrosslinkable azide moieties, referred to as 4Bx. 4Bx can be mixed with a variety of solution-processable electronic materials (polymer semiconductors, polymer insulators, and metal nanoparticles) and generate crosslinked network under exposure to UV. Fully crosslinked network film can be formed even at an unprecedentedly small loading, which enables preserving the inherent electrical and structural characteristics of host material. Because the crosslinked electronic component layers are strongly resistant to chemical solvents, micropatterning the layers at high resolution as well as stacking the layers on top of each other by series of solution processing steps is possible.

To enable the large-area manufacture of solution-processed organic electronics, direct photocrosslinking processes has emerged as a promising technology solution. Here, the authors report an efficient universal crosslinking agent for micropatterning of stacked multi-layered organic electronics.

Roles of interfaces in the ideality of organic field-effect transistors

Organic field-effect transistors (OFETs) are fundamental building blocks for flexible and large-area electronics due to their superior solution-processability, flexibility and stretchability. OFETs with high ideality are essential to their practical applications. In reality, however, many OFETs still suffer from non-ideal behaviors, such as gate-dependent mobility, which thus hinders the extraction of their intrinsic performance. It is much desired to gain a comprehensive understanding of the origins of these non-idealities. OFETs are primarily interface-related devices, and hence their performance and ideality are highly dependent on the interface properties between each device component. This review will focus on the recent progress in investigating the non-ideal behaviors of OFETs. In particular, the roles of interfaces, including the organic semiconductor (OSC)/dielectric interface, OSC/electrode interface and OSC/atmosphere interface, in determining the ideality of OFETs are summarized. Viable approaches through interface optimization to improve the device ideality are also reviewed. Finally, an overview of the outstanding challenges as well as the future development directions for the construction of ideal OFETs is given.

Design and properties of novel photothermal initiators for photoinduced thermal frontal polymerization

Three synthesized photothermal initiators (2959-HDHP, 184-HDHP, 1173-HDHP) exhibited better photoinduced thermal frontal polymerization effect than mixture system due to higher heat transfer efficiency from photopolymerization to thermal initiator.

UV-Cured Poly(Ethylene Glycol) Diacrylate/Carbon Nanostructure Thin Films. Preparation, Characterization, and Electrical Properties

Carbon nanoallotropes such as carbon nanotubes, graphene, and their derivatives have been combined with a plethora of polymers in the last years to develop new composite materials with interesting properties and applications. However, the area of photopolymer composites with carbon nanostructures has not been analogously explored. In the present article, we study the photopolymerization of poly(ethylene glycol)diacrylate (PEGDA) enriched with different carbon nanoallotropes like graphene, pristine and chemically modified carbon nanotubes (CNTs and fCNTs), and a hybrid of graphene and CNTs. The products were characterized by several microscopic and spectroscopic techniques and the electrical conductivity was studied as a function of the concentrations of carbon nanoallotropes. In general, stable thin films were produced with a concentration of carbon nanostructures up to 8.5%, although the addition of carbon nanostructures in PEGDA decreases the degree of photopolymerization, and PEDGA/carbon nanostructure composites showed electrical conductivity at a relatively low percentage.

Universal Route to Impart Orthogonality to Polymer Semiconductors for Sub-Micrometer Tandem Electronics

A universal method that enables utilization of conventional photolithography for processing a variety of polymer semiconductors is developed. The method relies on imparting chemical and physical orthogonality to a polymer film via formation of a semi-interpenetrating diphasic polymer network with a bridged polysilsesquioxane structure, which is termed an orthogonal polymer semiconductor gel. The synthesized gel films remain tolerant to various chemical and physical etching processes involved in photolithography, thereby facilitating fabrication of high-resolution patterns of polymer semiconductors. This method is utilized for fabricating tandem electronics, including pn-complementary inverter logic devices and pixelated polymer light-emitting diodes, which require deposition of multiple polymer semiconductors through solution processes. This novel and universal method is expected to significantly influence the development of advanced polymer electronics requiring sub-micrometer tandem structures.

Highly stacked 3D organic integrated circuits with via-hole-less multilevel metal interconnects

Multilevel metal interconnects are crucial for the development of large-scale organic integrated circuits. In particular, three-dimensional integrated circuits require a large number of vertical interconnects between layers. Here, we present a novel multilevel metal interconnect scheme that involves solvent-free patterning of insulator layers to form an interconnecting area that ensures a reliable electrical connection between two metals in different layers. Using a highly reliable interconnect method, the highest stacked organic transistors to date, a three-dimensional organic integrated circuits consisting of 5 transistors and 20 metal layers, is successfully fabricated in a solvent-free manner. All transistors exhibit outstanding device characteristics, including a high on/off current ratio of ~10⁷, no hysteresis behavior, and excellent device-to-device uniformity. We also demonstrate two vertically-stacked complementary inverter circuits that use transistors on 4 different floors. All circuits show superb inverter characteristics with a 100% output voltage swing and gain up to 35 V per V.

Though large-scale integration of organic transistors into integrated circuits via 3D stacking is a promising approach, reliable methods of device fabrication are still needed. Here, the authors report a metal interconnect scheme for reliable fabrication of 3D integrated organic transistor circuits.

Design of a coumarinyl-picolinoyl hydrazide Schiff base for the fluorescence turn-on–off sequential sensing of Al3+ and nitroaromatics, and electronic device fabrication

Designing a small organic molecule for fluorescence sensing and electrical conductivity is a challenging task.

Organic Transistor-Based Chemical Sensors for Wearable Bioelectronics

Bioelectronics for healthcare that monitor the health information on users in real time have stepped into the limelight as crucial electronic devices for the future due to the increased demand for "point-of-care" testing, which is defined as medical diagnostic testing at the time and place of patient care. In contrast to traditional diagnostic testing, which is generally conducted at medical institutions with diagnostic instruments and requires a long time for specimen analysis, point-of-care testing can be accomplished personally at the bedside, and health information on users can be monitored in real time. Advances in materials science and device technology have enabled next-generation electronics, including flexible, stretchable, and biocompatible electronic devices, bringing the commercialization of personalized healthcare devices increasingly within reach, e.g., wearable bioelectronics attached to the body that monitor the health information on users in real time. Additionally, the monitoring of harmful factors in the environment surrounding the user, such as air pollutants, chemicals, and ultraviolet light, is also important for health maintenance because such factors can have short- and long-term detrimental effects on the human body. The precise detection of chemical species from both the human body and the surrounding environment is crucial for personal health care because of the abundant information that such factors can provide when determining a person's health condition. In this respect, sensor applications based on an organic-transistor platform have various advantages, including signal amplification, molecular design capability, low cost, and mechanical robustness (e.g., flexibility and stretchability). This Account covers recent progress in organic transistor-based chemical sensors that detect various chemical species in the human body or the surrounding environment, which will be the core elements of wearable electronic devices. There has been considerable effort to develop high-performance chemical sensors based on organic-transistor platforms through material design and device engineering. Various experimental approaches have been adopted to develop chemical sensors with high sensitivity, selectivity, and stability, including the synthesis of new materials, structural engineering, surface functionalization, and device engineering. In this Account, we first provide a brief introduction to the operating principles of transistor-based chemical sensors. Then we summarize the progress in the fabrication of transistor-based chemical sensors that detect chemical species from the human body (e.g., molecules in sweat, saliva, urine, tears, etc.). We then highlight examples of chemical sensors for detecting harmful chemicals in the environment surrounding the user (e.g., nitrogen oxides, sulfur dioxide, volatile organic compounds, liquid-phase organic solvents, and heavy metal ions). Finally, we conclude this Account with a perspective on the wearable bioelectronics, especially focusing on organic electronic materials and devices.

Highly Enantioselective Graphene-Based Chemical Sensors Prepared by Chiral Noncovalent Functionalization

As a basic characteristic of the natural environment and living matter, chirality has been used in various scientific and technological fields. Chiral discrimination is of particular interest owing to its importance in catalysis, organic synthesis, biomedicine, and pharmaceutics. However, it is still very challenging to effectively and selectively sense and separate different enantiomers. Here, enantio-differentiating chemosensor systems have been developed through spontaneous chiral functionalization of the surface of graphene field-effect transistors (GFETs). GFET sensors functionalized using noncovalent interactions between graphene and a newly synthesized chiral-functionalized pyrene material, Boc-l-Phe-Pyrene, exhibit highly enantioselective detection of natural acryclic monoterpenoid enantiomers, that is, ( R)-(+)- and ( S)-(-)-β-citronellol. On the basis of a computational study, the origin of enantio-differentiation is assigned to the discriminable charge transfer from ( R)-(+)- or ( S)-(-)-β-citronellol into graphene with a significant difference in binding strength depending on surface morphology. The chemosensor system developed herein has great potential to be applied in miniaturized and rapid enantioselective sensing with high sensitivity and selectivity.

Printing Semiconductor-Insulator Polymer Bilayers for High-Performance Coplanar Field-Effect Transistors

Source-semiconductor-drain coplanar transistors with an organic semiconductor layer located within the same plane of source/drain electrodes are attractive for next-generation electronics, because they could be used to reduce material consumption, minimize parasitic leakage current, avoid cross-talk among different devices, and simplify the fabrication process of circuits. Here, a one-step, drop-casting-like printing method to realize a coplanar transistor using a model semiconductor/insulator [poly(3-hexylthiophene) (P3HT)/polystyrene (PS)] blend is developed. By manipulating the solution dewetting dynamics on the metal electrode and SiO₂ dielectric, the solution within the channel region is selectively confined, and thus make the top surface of source/drain electrodes completely free of polymers. Subsequently, during solvent evaporation, vertical phase separation between P3HT and PS leads to a semiconductor-insulator bilayer structure, contributing to an improved transistor performance. Moreover, this coplanar transistor with semiconductor-insulator bilayer structure is an ideal system for injecting charges into the insulator via gate-stress, and the thus-formed PS electret layer acts as a "nonuniform floating gate" to tune the threshold voltage and effective mobility of the transistors. Effective field-effect mobility higher than 1 cm² V^-1 s^-1 with an on/off ratio > 10⁷ is realized, and the performances are comparable to those of commercial amorphous silicon transistors. This coplanar transistor simplifies the fabrication process of corresponding circuits.

Experimental and computational investigations of the photosensitive Schottky barrier diode property of an azobenzene based small organic molecule

An azobenzene based small organic molecule has been designed to study photosensitive Schottky barrier diode property.

Toward Environmentally Robust Organic Electronics: Approaches and Applications

Recent interest in flexible electronics has led to a paradigm shift in consumer electronics, and the emergent development of stretchable and wearable electronics is opening a new spectrum of ubiquitous applications for electronics. Organic electronic materials, such as π-conjugated small molecules and polymers, are highly suitable for use in low-cost wearable electronic devices, and their charge-carrier mobilities have now exceeded that of amorphous silicon. However, their commercialization is minimal, mainly because of weaknesses in terms of operational stability, long-term stability under ambient conditions, and chemical stability related to fabrication processes. Recently, however, many attempts have been made to overcome such instabilities of organic electronic materials. Here, an overview is provided of the strategies developed for environmentally robust organic electronics to overcome the detrimental effects of various critical factors such as oxygen, water, chemicals, heat, and light. Additionally, molecular design approaches to π-conjugated small molecules and polymers that are highly stable under ambient and harsh conditions are explored; such materials will circumvent the need for encapsulation and provide a greater degree of freedom using simple solution-based device-fabrication techniques. Applications that are made possible through these strategies are highlighted.

High-Performance Furan-Containing Conjugated Polymer for Environmentally Benign Solution Processing

Developing semiconducting polymers that exhibit both strong charge transport capability via highly ordered structures and good processability in environmentally benign solvents remains a challenge. Given that furan-based materials have better solubility in various solvents than analogous thiophene-based materials, we have synthesized and characterized furanyl-diketopyrrolopyrrole polymer (PFDPPTT-Si) together with its thienyl-diketopyrrolopyrrole-based analogue (PTDPPTT-Si) to understand subtle changes induced by the use of furan instead of thiophene units. PTDPPTT-Si films processed in common chlorinated solvent exhibit a higher hole mobility (3.57 cm² V^-1 s^-1) than PFDPPTT-Si films (2.40 cm² V^-1 s^-1) under the same conditions; this greater hole mobility is a result of tightly aggregated π-stacking structures in PTDPPTT-Si. By contrast, because of its enhanced solubility, PFDPPTT-Si using chlorine-free solution processing results in a device with higher mobility (as high as 1.87 cm² V^-1 s^-1) compared to that of the corresponding device fabricated using PTDPPTT-Si. This mobility of 1.87 cm² V^-1 s^-1 represents the highest performances among furan-containing polymers reported to the best of our knowledge for nonchlorinated solvents. Our study demonstrates an important step toward environmentally compatible electronics, and we expect the results of our study to reinvigorate the furan-containing semiconductors field.