Low-Temperature Solution-Processed Soluble Polyimide Gate Dielectrics: From Molecular-Level Design to Electrically Stable and Flexible Organic Transistors

Aromatic soluble polyimides (PIs) have been widely used in organic field-effect transistors (OFETs) as gate dielectric layers due to their promising features such as outstanding chemical resistance, thermal stability, low-temperature processability, and mechanical flexibility. However, the molecular structures of soluble PIs on the electrical characteristics of OFETs are not yet fully understood. In this work, the material, dielectric, and electrical properties are evaluated to systematically investigate the chemical structure effect of aromatic dianhydride and diamine monomers on the device performance. Four soluble PIs based on 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 5-(2,5-Dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, in which the monomeric precursors contain different backbones, side groups, and linkages, were employed to compare the chemical structure impact. The dielectric properties, which significantly affect the charge transport and crystallinity of OSC thin films, clearly depended on the soluble PI types as well as the surface energy and the thermal stability. Furthermore, the electrical characteristic measurement and parameter extraction of OFETs based on TIPS-pentacene revealed that the 6FDA-based soluble PIs, which lead to high field-effect mobility, near-zero threshold electric field, and outstanding electrical stability under bias stress, are the most promising gate dielectric candidates. Finally, low-temperature solution-processed OFETs are successfully integrated with ultrathin flexible substrates, and they exhibit no significant electrical performance loss after mechanical flexibility tests. This work presents a step forward in the development of soluble PI gate dielectrics for flexible electronic devices with high device performance.

Design and Fabrication of Flexible Naked-Eye 3D Display Film Element Based on Microstructure

The naked-eye three-dimensional (3D) display technology without wearing equipment is an inevitable future development trend. In this paper, the design and fabrication of a flexible naked-eye 3D display film element based on a microstructure have been proposed to achieve a high-resolution 3D display effect. The film element consists of two sets of key microstructures, namely, a microimage array (MIA) and microlens array (MLA). By establishing the basic structural model, the matching relationship between the two groups of microstructures has been studied. Based on 3D graphics software, a 3D object information acquisition model has been proposed to achieve a high-resolution MIA from different viewpoints, recording without crosstalk. In addition, lithography technology has been used to realize the fabrications of the MLA and MIA. Based on nanoimprint technology, a complete integration technology on a flexible film substrate has been formed. Finally, a flexible 3D display film element has been fabricated, which has a light weight and can be curled.

Scalable Fabrication of Highly Flexible Porous Polymer-Based Capacitive Humidity Sensor Using Convergence Fiber Drawing

In this study, we fabricated a highly flexible fiber-based capacitive humidity sensor using a scalable convergence fiber drawing approach. The sensor’s sensing layer is made of porous polyetherimide (PEI) with its porosity produced in situ during fiber drawing, whereas its electrodes are made of copper wires. The porosity induces capillary condensation starting at a low relative humidity (RH) level (here, 70%), resulting in a significant increase in the response of the sensor at RH levels ranging from 70% to 80%. The proposed humidity sensor shows a good sensitivity of 0.39 pF/% RH in the range of 70%–80% RH, a maximum hysteresis of 9.08% RH at 70% RH, a small temperature dependence, and a good stability over a 48 h period. This work demonstrates the first fiber-based humidity sensor fabricated using convergence fiber drawing.

All-Solid-State Planar Sodium-Ion Microcapacitors with Multidirectional Fast Ion Diffusion Pathways

With the relentless development of smart and miniaturized electronics, the worldwide thirst for microscale electrochemical energy storage devices with form factors is launching a new era of competition. Herein, the first prototype planar sodium-ion microcapacitors (NIMCs) are constructed based on the interdigital microelectrodes of urchin-like sodium titanate as faradaic anode and nanoporous activated graphene as non-faradaic cathode along with high-voltage ionogel electrolyte on a single flexible substrate. By effectively coupling with battery-type anode and capacitor-type cathode, the resultant all-solid-state NIMCs working at 3.5 V exhibit a high volumetric energy density of 37.1 mWh cm-3 and an ultralow self-discharge rate of 44 h from V max to 0.6 V max, both of which surpass most reported hybrid micro-supercapacitors. Through tuning graphene layer covered on the top surface of interdigital microelectrodes, the NIMCs unveil remarkably enhanced power density, owing to the establishment of favorable multidirectional fast ion diffusion pathways that significantly reduce the charge transfer resistance. Meanwhile, the as-fabricated NIMCs present excellent mechanical flexibility without capacitance fade under repeated deformation, and electrochemical stability at a high temperature of 80 °C because of using nonflammable ionogel electrolyte and in-plane geometry. Therefore, these flexible planar NIMCs with multidirectional ion diffusion pathways hold tremendous potential for microelectronics.

Flexible Ultra-Wideband Terahertz Absorber Based on Vertically Aligned Carbon Nanotubes

Ultra-wideband absorbers have been extensively used in wireless communications, energy harvesting, and stealth applications. Herein, with the combination of experimental and theoretical analyses, we develop a flexible ultra-wideband terahertz absorber based on vertically aligned carbon nanotubes (VACNTs). Measured results show that the proposed absorber is able to work efficiently within the entire THz region (e.g., 0.1-3.0 THz), with an average power absorptance of >98% at normal incidence. The absorption performance remains at a similar level over a wide range of incident angle up to 60°. More importantly, our devices can function normally, even after being bent up to 90° or after 300 bending cycles. The total thickness of the device is about 360 μm, which is only 1/8 of the wavelength for the lowest evaluated frequency of 0.1 THz. The new insight into the VACNT materials paves the way for applications such as radar cross-section reduction, electromagnetic interference shielding, and flexible sensing because of the simplicity, flexibility, ultra-wideband operation, and large-scale fabrication of the device.

Heavy-Metal-Free Flexible Hybrid Polymer-Nanocrystal Photodetectors Sensitive to 1.5 μm Wavelength

Photodetection in the short-wave infrared (SWIR) wavelength window represents one of the core technologies allowing for many applications. Most current photodetectors suffer from high cost due to the epitaxial growth requirements and the ecological issue due to the use of highly toxic heavy-metal elements. Toward alternative SWIR photodetection strategies, in this work, high-performance heavy-metal-free flexible photodetectors sensitive to λ = 1.5 μm photons are presented based on the formation of a solution-processed hybrid composed of a conjugated diketopyrrolopyrrole-base polymer/PC₇₀BM bulk heterojunction organic host together with inorganic guest NaYF₄:15%Er³⁺ upconversion nanoparticles (UCNPs). Under the illumination of λ = 1.5 μm SWIR photons, optimized hybrid bulk-heterojunction (BHJ)/UCNP photodetectors exhibit a photoresponsivity of 0.73 and 0.44 mA/W, respectively, for devices built on rigid indium tin oxide (ITO)/glass and flexible ITO/polyethylene terephthalate substrates. These hybrid photodetectors are capable of performing SWIR photodetection with a fast operation speed, characterized by a short photocurrent rise time down to 80 μs, together with an excellent mechanical robustness for flexible applications. Exhibiting simultaneously multiple advantages including solution-processability, flexibility, and the absence of toxic heavy metal elements together with a fast operation speed and good photoresponsivity, these hybrid BHJ(DPPTT-T/PC₇₀BM)/UCNP photodetectors are promising candidates for next-generation low-cost and high-performance SWIR photodetectors.

Rectification Behavior on Polyelectrolyte-Modified Flexible ITO Electrode via Ionic Charge-Selective Electron Transfer

New types of diodes, such as molecular and ionic diodes, have drawn considerable attention because of their advantages from the viewpoint of potential applications such as the downscaling of electronic devices, ionic circuits, and biological systems. Researchers are motivated to develop a simple, scalable, and promising system that can overcome the existing limitations because this can enable their application in various devices. This study proposes a system that not only integrates the advantages of ionic and single-molecule diodes but also avoids their disadvantages, denoting the rectification behavior due to ionic charge-selective electron transfer between two redox species, i.e., Fe(CN)₆^3- and Ru(NH₃)₆³⁺, on the polyelectrolyte multilayer (PEM)-modified flexible indium tin oxide (ITO) electrodes. Flexible current rectification devices were easily prepared by sandwiching an electrolytic solution of ionic redox species using bare and PEM-modified plastic ITO electrodes. An ionic bilayer was initially formed via Coulombic interactions on a PEM-modified charge-selective ITO surface. The ionic bilayer was analogous to a conventional single-molecule diode's monolayer with consecutive molecular orbitals of two ionic redox species. Furthermore, the rectification ratio (RR) was increased from ∼6 to ∼10 using a conducting polymer to construct PEMs.

Wearable, Stretchable, Transparent All-in-One Soft Sensor Formed from Supersonically Sprayed Silver Nanowires

The demand for wearable, stretchable soft electronics for human-machine interface applications continues to grow given the potential of these devices in humanoid robotics, prosthetics, and health-monitoring devices. We demonstrate fabrication of multifunctional sensors with simultaneous temperature-, pressure-, proximity-, and strain (or bending)-sensing capabilities, combined with heating and UV-protection features. These multifunctional sensors are flexible, light, and transparent and are thus body-attachable. Silver nanowires are supersonically sprayed on a large-scale transparent and flexible roll-to-roll substrate. The junctions between nanowires are physically fused by a strong impact resulting from supersonic spraying, which promotes adhesion and efficient deposition of the nanowire network. Accordingly, nanowires are strongly interconnected, facilitating efficient propagation of electric signals through the fused nanowire network, which allows simultaneous operation of such sensors while maintaining significant transparency. These multifunctional sensors are mechanically durable and retain long-term stability. A theoretical discussion is provided to explain the respective mechanisms of heating and proximity, pressure, and strain sensing.

Paper-Based ZnS:Cu Alternating Current Electroluminescent Devices for Current Humidity Sensors with High-Linearity and Flexibility

Humidity sensors are indispensable for various electronic systems and instrumentations. To develop a new humidity sensing mechanism is the key for the next generation of sensor technology. In this work, a novel flexible paper-based current humidity sensor is proposed. The developed alternating current electroluminescent devices (ACEL) consist of the electroless plating Ni on filter paper and silver nanowires (AgNWs) as the bottom and upper electrodes, and ZnS:Cu as the phosphor layer, respectively. The proposed humidity sensor is based on ACEL with the paper substrate and the ZnS:Cu phosphor layer as the humidity sensing element. The moisture effect on the optical properties of ACELs has been studied firstly. Then, the processing parameters of the paper-based ACELs such as electroless plated bottom electrode and spin-coated phosphor layer as a function of the humidity-sensitive characteristics are investigated. The sensing mechanism of the proposed sensor has been elucidated based on the Q ~ V analysis. The sensor exhibits an excellent linearity ( R 2 = 0.99965 ) within the humidity range from 20% to 90% relative humidity (RH) and shows excellent flexibility. We also demonstrate its potential application in postharvest preservation where the EL light is used for preservation and the humidity can be monitored simultaneously through the current.

Flexible, High-Power Density, Wearable Thermoelectric Nanogenerator and Self-Powered Temperature Sensor

We propose a flexible and wearable thermoelectric nanogenerator (FTEG) made from Bi₂Te₃, which allows high voltage and output power density. The proposed FTEG works as a thermopile with the end-to-end connection of 126 thermoelectric legs, and which is fabricated through magnetron sputtering Cu conductor on polyethylene terephthalate film. Bi, Te, Sb, and Se alloys are used to prepare thermoelectric materials by doping in a fixed proportion and zone melting, and nickel plating on the surface mitigates the deterioration of thermoelectric properties caused by the diffusion of Cu atoms or Cu⁺ ions. The thermoelectric figure of merit is stable and maintained above 0.7, up to 1.02. More flexibility is allowed by employing double sinusoidal serpentine connecting wires, and no significant property changes are observed even after being folded 200 times. When the temperature difference reaches 50 K, the output voltage of the FTEG will be no less than 520 mV, and the power density will reach 11.14 mW·cm^-2. By integration of a low-power, low-threshold voltage boost circuit on the back end of the FTEG, the electronic watch with a liquid crystal display screen can be easily powered to work properly. Furthermore, the FTEG is temperature-sensitive and, thus, can be used for temperature measurement with a resolution of 0.5 K. This work may have important prospects in flexible wearable physical sensors and individualized medical care.

Large-Area MXene Electrode Array for Flexible Electronics

MXenes, an emerging class of two-dimensional (2D) transition metal carbides and nitrides, have potential for application as high-performance, low-cost electrodes in organic field-effect transistors (OFETs) because of their water dispersibility, high conductivity, and work-function tunability. In this study, we successfully fabricated a large-scale, uniform Ti₃C₂T_x MXene electrode array on a flexible plastic substrate for application in high-performance OFETs. The work function of the Ti₃C₂T_x MXene electrodes was also effectively modulated via chemical doping with NH₃. The fabricated OFETs with Ti₃C₂T_x MXene electrodes exhibited excellent device performance, such as a maximum carrier mobility of ∼1 cm²·V^-1·s^-1 and an on-off current ratio of ∼10⁷ for both p-type and n-type OFETs, even though all the electrode and dielectric layers were fabricated on the plastic substrate by solution processing. Furthermore, MXene-electrode-based complementary logic circuits, such as NOT, NAND, and NOR, were fabricated via integration of p-type and n-type OFETs. The proposed approach is expected to expand the application range of MXenes to other OFET-based electronic devices, such as organic light-emitting displays and electronic skins.

Practical and Durable Flexible Strain Sensors Based on Conductive Carbon Black and Silicone Blends for Large Scale Motion Monitoring Applications

Presented is a flexible capacitive strain sensor, based on the low cost materials silicone (PDMS) and carbon black (CB), that was fabricated by casting and curing of successive silicone layers—a central PDMS dielectric layer bounded by PDMS/CB blend electrodes and packaged by exterior PDMS films. It was effectively characterized for large flexion-angle motion wearable applications, with strain sensing properties assessed over large strains (50%) and variations in temperature and humidity. Additionally, suitability for monitoring large tissue deformation was established by integration with an in vitro digestive model. The capacitive gauge factor was approximately constant at 0.86 over these conditions for the linear strain range (3 to 47%). Durability was established from consistent relative capacitance changes over 10,000 strain cycles, with varying strain frequency and elongation up to 50%. Wearability and high flexion angle human motion detection were demonstrated by integration with an elbow band, with clear detection of motion ranges up 90°. The device’s simple structure and fabrication method, low-cost materials and robust performance, offer promise for expanding the availability of wearable sensor systems.

Construction of Hierarchical NiCo2O4@Ni-MOF Hybrid Arrays on Carbon Cloth as Superior Battery-Type Electrodes for Flexible Solid-State Hybrid Supercapacitors

Metal-organic frameworks (MOFs) have been considered as a class of promising electrode materials for supercapacitors owing to their large surface area, rich porosity, and variable redox sites; however, direct application of pristine MOFs in energy storage has been largely hindered by their poor electrical conductivity and stability issues. In this work, we demonstrate a facile two-step approach to address the controlled growth of Ni-MOF arrays on the surface of NiCo₂O₄ nanowires by modulating the formation reaction of MOFs. By taking advantage of the intriguing merits from the NiCo₂O₄ core and Ni-MOF shell as well as their synergistic effects, the optimized NiCo₂O₄@Ni-MOF hybrid electrode exhibits boosted electrochemical performance, in terms of high specific capacity (208.8 mA h/g at 2 mA/cm²) and good rate capability. In addition, the assembled flexible solid-state HSC device based on the optimized NiCo₂O₄@Ni-MOF and activated carbon as the cathode and anode achieves a maximum energy density of 32.6 W h/kg at a power density of 348.9 W/kg without sacrificing its outstanding cycling performance (nearly 100% retention over 6000 cycles at 8 mA/cm²) and mechanical stability, outperforming most recently reported MOF-based HSC devices in an aqueous electrolyte. Our work demonstrates the possibility of exploiting novel MOF-based hybrid arrays as battery-type electrodes with enhanced electrochemical properties, which exhibits great potential in flexible energy storage devices.

Superbending (0-180°) and High-Voltage Operating Metal-Oxide-Based Flexible Supercapacitor

Among various energy storage devices, flexible supercapacitors having high mechanical stability with extreme bending and foldable features are highly attractive for a large number of emerging portable lightweight consumer devices. Here, we report the fabrication of such a superflexible supercapacitor by using novel octahedron-shaped NiCo₂O₄ nanoparticles as the electrode material for the first time. A new, low-cost hydrothermal method was used to synthesize 50-60 nm monodispersed perfect octahedron nanoparticles without any structural deformation. An all-solid-state symmetric flexible supercapacitor was fabricated by sandwiching the octahedron nanoparticles and [EMIM][BF₄] ionic liquid electrolyte between two sheets of newly developed superflexible current collector substrate. The calculated specific capacity and specific capacitance values are found to be 97.9 mAh g^-1 and 117.3 F g^-1, respectively, at 0.625 A g^-1 current density and 3.0 V applied potential. It also offered a high energy density value of 33.54 Wh kg^-1 and 10 000 measured cycling stability. The supercapacitor is so flexible that it can be bent or fold up to 180° without any mechanical deformation, and the measured capacitance and energy and power densities remain almost constant at any angle of twisting. For instance, calculated values of capacitances obtained by bending the cell at angles of 180, 150, 135, 90, and 45° are found to be 62, 63.3, 63.73, 64, and 66 F g^-1 respectively, in comparison to 67 F g^-1 for a nonbending or flat (0°) cell. A faster ion switching between electrode/electrolyte interface, [EMIM][BF₄] electrolyte, and octahedron shape of the nanoparticle electrode material is found to be responsible for the outstanding charge storage behavior.

Worldwide survey of flexible ureteroscopy practice: a survey from European Association of Urology sections of young academic urologists and uro-technology groups

Introduction

To understand the current practice of flexible ureteroscopy (fURS), we conducted a worldwide survey among urologists with a special interest in endourology.

Material and methods

A 42-question survey was designed after an initial consultation with European Association of Urology young academic urologists (YAU) and uro-technology (ESUT) groups. This was distributed via the SurveyMonkey^® platform and an ESUT meeting to cover practice patterns and techniques in regard to ureteroscopy usage worldwide.

Results

A total of 114 completed responses were obtained. A safety guidewire was reportedly used by 84.5% of endourologists, an access sheath was always or almost always used by 71% and a reusable laser fibre was used by two-thirds of respondents. While a combination of dusting and fragmentation was used by 47% as a preferred mode of intra-renal stone treatment, some used dusting (43%) or fragmentation with basketing (10%).

Disposable scopes were only used by 40% and three quarters of them used it for challenging cases only. Antibiotic prophylaxis was limited to a single peri-operative dose by two-thirds (67%) of respondents. The procedural time was limited to between 1–2 hours by two-thirds (70%) of respondents and very rarely (7.4%) it exceeded 2 hours. The irrigation method varied between manual pump (46%), mechanical irrigation (22%) or gravity irrigation (27%).

Conclusions

Our survey shows a wide variation in the available endourological armamentarium and surgical practice amongst urologists. However, there seems to be a broad agreement in the use of peri-operative antibiotics, access sheath usage, method of stone treatment and the use of post-operative stent.

Recent Advances in Skin Chemical Sensors

This review summarizes the latest developments in the field of skin chemical sensors, in particular wearable ones. Five major applications are covered in the present work: (i) sweat analysis, (ii) skin hydration, (iii) skin wounds, (iv) perspiration of volatile organic compounds, and (v) general skin conditions. For each application, the detection of the most relevant analytes is described in terms of transduction principles and sensor performances. Special attention is paid to the biological fluid collection and storage and devices are also analyzed in terms of reusability and lifetime. This review highlights the existing gaps between current performances and those needed to promote effective commercialization of sensors; future developments are also proposed.

Self-Supporting, Flexible, Additive-Free, and Scalable Hard Carbon Paper Self-Interwoven by 1D Microbelts: Superb Room/Low-Temperature Sodium Storage and Working Mechanism

Hard carbon is regarded as a promising anode material for sodium-ion batteries (SIBs). However, it usually suffers from the issues of low initial Coulombic efficiency (ICE) and poor rate performance, severely hindering its practical application. Herein, a flexible, self-supporting, and scalable hard carbon paper (HCP) derived from scalable and renewable tissue is rationally designed and prepared as practical additive-free anode for room/low-temperature SIBs with high ICE. In ether electrolyte, such HCP achieves an ICE of up to 91.2% with superior high-rate capability, ultralong cycle life (e.g., 93% capacity retention over 1000 cycles at 200 mA g^-1 ) and outstanding low-temperature performance. Working mechanism analyses reveal that the plateau region is the rate-determining step for HCP with a lower electrochemical reaction kinetics, which can be significantly improved in ether electrolyte.

Heteroepitaxy of Co-Based Heusler Compound/Muscovite for Flexible Spintronics

Materials with high spin-polarization play an important role in the development of spintronics. Co-based Heusler compounds are a promising candidate for practical applications because of their high Curie temperature and tunable half-metallicity. However, it is a challenge to integrate Heusler compounds into thin film heterostructures because of the lack of control on crystallinity and chemical disorder, critical factors of novel behaviors. Here, muscovite is introduced as a growth substrate to fabricate epitaxial Co₂MnGa films with mechanical flexibility. The feature of heteroepitaxy is evidenced by the results of X-ray diffraction and transmission electron microscopy. Moreover, high chemical ordering with superior properties is delivered according to the observation of large Hall conductivity (680 Ω^-1 cm^-1) and highly saturated magnetic moment (∼3.93 μ_B/f.u.), matching well with bulk crystals. Furthermore, the excellence of magnetic and electrical properties is retained under the various mechanical bending conditions. Such a result suggests that the development of Co₂MnGa/muscovite heteroepitaxy provides not only a pathway to the thin film heterostructure based on high-quality Heusler compounds but also a new aspect of spintronic applications on flexible substrates.

Transparent, Flexible, Fatigue-Free, Optical-Read, and Nonvolatile Ferroelectric Memories

Perovskite oxide films are widely used in various commercial industries. However, they are usually prepared at high temperature and in oxygen ambience, detrimental to most transparent and flexible substrates and bottom conductive electrodes such as indium tin oxide (ITO). It remains challenging to integrate perovskite oxides into transparent and flexible electronics. Here, the 1.2 wt % Ag-doped ITO (Ag-ITO) grown on a mica substrate is employed as the bottom electrode, which can withstand high temperature and repeated bending, and then we achieve the transparent, flexible, fatigue-free, and optical-read ferroelectric nonvolatile memories based on the mica/Ag-ITO/Bi_3.25La_0.75Ti₃O₁₂/ITO structures. The as-prepared memories show ∼80% transmittance for visible lights and fatigue-free performance after more than 10⁸ writing/erasing cycles. These performances are stable after repeated bending down to 3 mm in a curvature radius. More importantly, the "1/0" state of the memory can be read out by the photovoltaic current rather than destructive polarization switching, an emergent functionality for many applications. This work substantially promotes the applications of perovskite oxide films in transparent and flexible electronics, including wearable devices.

Multifunctional All-Inorganic Flexible Capacitor for Energy Storage and Electrocaloric Refrigeration over a Broad Temperature Range Based on PLZT 9/65/35 Thick Films

Multifunctional capacitors can efficiently integrate multiple functionalities into a single material to further down-scale state-of-the-art integrated circuits, which are urgently needed in new electronic devices. Here, an all-inorganic flexible capacitor based on Pb_0.91La_0.09 (Zr_0.65Ti_0.35)_0.9775O₃ (PLZT 9/65/35) relaxor ferroelectric thick film (1 μm) was successfully fabricated on LaNiO₃/F-Mica substrate for application in electrostatic energy storage and electrocaloric refrigeration simultaneously. The flexible PLZT 9/65/35 thick film presents a desirable breakdown field of 1998 kV/cm, accompanied by a superior recoverable energy density (W_rec) of 40.2 J/cm³. Meanwhile, the thick film exhibits excellent stability of energy-storage performance, including a broad operating temperature (30-180 °C), reduplicative charge-discharge cycles (1 × 10⁷ cycles), and mechanical bending cycles (2000 times). Moreover, a large reversible adiabatic temperature change (ΔT) of 18.0 °C, accompanied by an excellent electrocaloric strength (ΔT/ΔE) of 22.4 K cm/V and refrigerant capacity (RC) of 11.2 J/cm³, is obtained at 80 °C in the flexible PLZT 9/65/35 thick film under the moderate applied electric field of 850 kV/cm. All of these results shed light on a flexible PLZT 9/65/35 thick film capacitor that opens up a route to practical applications in microenergy-storage systems and on-chip thermal refrigeration of advanced electronics.

Low-Voltage, High-Performance Flexible Organic Field-Effect Transistors Based on Ultrathin Single-Crystal Microribbons

Organic field-effect transistors (OFETs) have acquired increasing attention because of their wide range of potential applications in electronics; nevertheless, high operating voltage and low carrier mobility are considered as major bottlenecks in their commercialization. In this work, we demonstrate low-voltage, flexible OFETs based on ultrathin single-crystal microribbons. Flexible OFETs fabricated with 2,7-dioctylbenzothieno[3,2-b]benzothiophene (C8-BTBT) based solution-processed ultrathin single-crystal microribbon as the semiconductor layer and high-k polymer, polysiloxane-poly(vinyl alcohol) composite as an insulator layer manifest a significantly low operating voltage of -4 V, and several devices showed a high mobility of >30 cm² V^-1 s^-1. Besides, the carrier mobility of the fabricated devices exhibits a slight degradation in static bending condition, which can be retained by 83.3% compared with its original value under a bending radius of 9 mm. As compared to the bulk C8-BTBT single-crystal-based OFET, which showed a large crack only after 50 dynamic bending cycles, our ultrathin single-crystal-based counterpart demonstrates a much better dynamic force stability. Moreover, under a 20 mm bending radius, the mobility of the device decreased by only 11.7% even after 500 bending cycles and no further decrease was observed until 1000 bending cycles. Our findings reveal that ultrathin C8-BTBT single-crystal-based flexible OFETs are promising candidates for various high-performance flexible electronic devices.

Screen-Printing of a Highly Conductive Graphene Ink for Flexible Printed Electronics

Conductive inks for the future printed electronics should have the following merits: high conductivity, flexibility, low cost, and compatibility with wide range of substrates. However, the state-of-the-art conductive inks based on metal nanoparticles are high in cost and poor in flexibility. Herein, we reported a highly conductive, low cost, and super flexible ink based on graphene nanoplatelets. The graphene ink has been screen-printed on plastic and paper substrates. Combined with postprinting treatments including thermal annealing and compression rolling, the printed graphene pattern shows a high conductivity of 8.81 × 10⁴ S m^-1 and good flexibility without significant conductivity loss after 1000 bending cycles. We further demonstrate that the printed highly conductive graphene patterns can act as current collectors for supercapacitors. The supercapacitor with the printed graphene pattern as the current collector and printed activated carbon as the active material shows a good rate capability of up to 200 mV s^-1. This work potentially provides a promising route toward the large-scale fabrication of low cost yet flexible printed electronic devices.

CuCo2S4 Nanosheets@N-Doped Carbon Nanofibers by Sulfurization at Room Temperature as Bifunctional Electrocatalysts in Flexible Quasi-Solid-State Zn-Air Batteries

The performance of quasi-solid-state flexible zinc-air batteries (ZABs) is critically dependent on the advancement of air electrodes with outstanding bifunctional electrocatalysis for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), together with the desired mechanical flexibility and robustness. The currently available synthesis processes for high-efficiency bifunctional bimetallic sulfide electrodes typically require high-temperature hydrothermal or chemical vapor deposition, which is undesirable in terms of the complexity in experimental procedure and the damage of flexibility in the resultant electrode. Herein, a scalable fabrication process is reported by combining electrospinning with in situ sulfurization at room temperature to successfully obtain CuCo2S4 nanosheets@N-doped carbon nanofiber (CuCo2S4 NSs@N-CNFs) films, which show remarkable bifunctional catalytic performance (Ej = 10 (OER) - E 1/2 (ORR) = 0.751 V) with excellent mechanical flexibility. Furthermore, the CuCo2S4 NSs@N-CNFs cathode delivers a high open-circuit potential of 1.46 V, an outstanding specific capacity of 896 mA h g-1, when assembled into a quasi-solid-state flexible ZAB together with Zn NSs@carbon nanotubes (CNTs) film (electrodeposited Zn nanosheets on CNTs film) as the anode. The ZAB also shows a good flexibility and capacity stability with 93.62% capacity retention (bending 1000 cycles from 0° to 180°), making it an excellent power source for portable and wearable electronic devices.

Dendrite-Free Zinc Deposition Induced by Multifunctional CNT Frameworks for Stable Flexible Zn-Ion Batteries

The current boom of safe and renewable energy storage systems is driving the recent renaissance of Zn-ion batteries. However, the notorious tip-induced dendrite growth on the Zn anode restricts their further application. Herein, the first demonstration of constructing a flexible 3D carbon nanotube (CNT) framework as a Zn plating/stripping scaffold is constituted to achieve a dendrite-free robust Zn anode. Compared with the pristine deposited Zn electrode, the as-fabricated Zn/CNT anode affords lower Zn nucleation overpotential and more homogeneously distributed electric field, thus being more favorable for highly reversible Zn plating/stripping with satisfactory Coulombic efficiency rather than the formation of Zn dendrites or other byproducts. As a consequence, a highly flexible symmetric cell based on the Zn/CNT anode presents appreciably low voltage hysteresis (27 mV) and superior cycling stability (200 h) with dendrite-free morphology at 2 mA cm^-2 , accompanied by a high depth of discharge (DOD) of 28%. Such distinct performance overmatches most of recently reported Zn-based anodes. Additionally, this efficient rechargeability of the Zn/CNT anode also enables a substantially stable Zn//MnO₂ battery with 88.7% capacity retention after 1000 cycles and remarkable mechanical flexibility.