Flexible Transparent Electronics Research Articles

Hybrid additive-subtractive manufacturing of high-density copper-based flexible transparent circuits based on side-etch process

High-density flexible transparent circuits (FTCs) are widely used in 5G/6G flexible transparent antennas, wearable devices, flexible transparent electronics and other fields. However, the rapid iteration and upgrading of electronic circuits present significant challenges to the manufacturing of both high-density and high-precision circuits (especially copper-based circuits) at room temperature, in an efficient and flexible manner. Here, we employ the side-etching phenomenon, which is typically avoided, to propose a novel method for hybrid additive-subtractive fabricating high-density copper-based FTCs that combines electric field-driven (EFD) microjet printing and wet etching technology. Firstly, the customized photoresist mask was flexibly printed on the copper-clad flexible substrate by EFD microjet printing, and then the copper circuit with less than the mask resolution was obtained by the side etching process of the wet etching process. By optimizing process parameters and precisely controlling the speed of the side etching stage during the etching process, the manufacturing of high-precision copper-based FTCs with a minimum line width of 2.4 μm and a minimum pitch of 4 μm was achieved. The typical sample is manufactured with a resistivity of 4 × 10−6 Ω·cm, a sheet resistance of 3.58 Ω/sq at a transmittance of up to 87.65 % (including the substrate), and it exhibits excellent mechanical stability. The prepared high-density flexible transparent interdigital electrode has excellent sensitivity, and can detect the concentration change of dilute H2SO4 solution at a minimum of 1 nmol/L at a frequency of 100–10,000 Hz. This method provides a new solution for the fabrication of copper-based FTCs at room temperature with high efficiency and low cost, and shows a good prospect for industrial application.

Hypoeutectic Liquid Metal Printing of 2D Indium Gallium Oxide Transistors.

2D native surface oxides formed on low melting temperature metals such as indium and gallium offer unique opportunities for fabricating high-performance flexible electronics and optoelectronics based on a new class of liquid metal printing (LMP). An inherent property of these Cabrera-Mott 2D oxides is their suboxide nature (e.g., In2O3-x), which leads high mobility LMP semiconductors to exhibit high electron concentrations (ne >1019cm-3) limiting electrostatic control. Binary alloying of the molten precursor can produce doped, ternary metal oxides such as In-X-O with enhanced electronic performance and greater bias-stress stability, though this approach demands a deeper understanding of the native oxides of alloys. This work presents an approach for hypoeutectic rapid LMP of crystalline InGaOx (IGO) at ultralow process temperatures (180°C) beyond the state of the art to fabricate transistors with 10X steeper subthreshold slope and high mobility (≈18cm2Vs-1). Detailed characterization of IGO crystallinity, composition, and morphology, as well as measurements of its electronic density of states (DOS), show the impact of Ga-doping and reveal the limits of doping induced amorphization from hypoeutectic precursors. The ultralow process temperatures and compatibility with high-k Al2O3 dielectrics shown here indicate potential for 2D IGO to drive low-power flexible transparent electronics.

Robust ZTO-reinforced Ag nanowire hybrid transparent conductive thin films with absorption-enhanced electromagnetic interference shielding property

Technological advances have accelerated the pursuit of transparent conducting thin films (TCFs) with superior mechanical properties, durability, efficient optoelectrical performance and substrate compatibility as a pivotal focus in the realm of flexible transparent electronics. Against this background, this work investigates the fabrication of multilayer silver nanowire (AgNW) thin films reinforced by zinc tin oxide (ZTO) thin film encapsulation on polycarbonate substrates by a combination of sputtering and spin-coating techniques. An investigation of the influence of AgNW percolation networks on the optoelectrical properties of ZTO/AgNW/ZTO hybrid thin films was carried out. The impact of ZTO protective layers on the enhancement of electrical properties, adhesivity, flexibility and environmental stability of the multilayer TCF was elucidated. Additionally, to explore the compatibility of the fabricated TCF in integrated device and stealth applications, its electromagnetic interference shielding properties were investigated. The hybrid TCF showed 99.47% EMI shielding efficiency with an absorption-dominant EMI shielding effectiveness of 22.7 dB in the x-band region.

Highly Conductive PEDOT:PSS: Ag Nanowire-Based Nanofibers for Transparent Flexible Electronics.

Highly conductive, transparent, and easily available materials are needed in a wide range of devices, such as sensors, solar cells, and touch screens, as alternatives to expensive and unsustainable materials such as indium tin oxide. Herein, electrospinning was employed to develop fibers of PEDOT:PSS/silver nanowire (AgNW) composites on various substrates, including poly(caprolactone) (PCL), cotton fabric, and Kapton. The influence of AgNWs, as well as the applied voltage of electrospinning on the conductivity of fibers, was thoroughly investigated. The developed fibers showed a sheet resistance of 7 Ω/sq, a conductivity of 354 S/cm, and a transmittance value of 77%, providing excellent optoelectrical properties. Further, the effect of bending on the fibers' electrical properties was analyzed. The sheet resistance of fibers on the PCL substrate increased slightly from 7 to 8 Ω/sq, after 1000 bending cycles. Subsequently, as a proof of concept, the nanofibers were evaluated as electrode material in a triboelectric nanogenerator (TENG)-based energy harvester, and they were observed to enhance the performance of the TENG device (78.83 V and 7 μA output voltage and current, respectively), as compared to the same device using copper electrodes. These experiments highlight the untapped potential of conductive electrospun fibers for flexible and transparent electronics.

A Dual‐Mode Programing Nonvolatile Floating‐Gate Memory with Convertible Ohmic and Schottky Contacts

AbstractResearch on van der Waals heterostructures based on stacked two‐dimensional atomic thickness crystals has received considerable attention because of their unique characters and great potential applications in flexible transparent electronics and optoelectronics. In this study, a nonvolatile memory device with a few‐layer bipolar material WS2 as channel and charge‐trapping layers is designed with a floating‐gate structure in which charges (electrons and holes) can be stored in the charge‐trapping layer using a dual‐mode processing program by changing the metal–semiconductor contact type. The device exhibits different programming currents during programming, in particular, the device has a low programming current for programming voltages ˂20 V. Moreover, the heterostructure exhibits a remarkable long retention time (≈10,000 s), with no apparent degradation and a strong endurance, retaining its original performance even after 1,000 programming/erasing cycles. This study proposes a novel method for reducing power consumption while programming to facilitate artificial synapse applications.

Coaxial Electrohydrodynamic Printing of Microscale Core-Shell Conductive Features for Integrated Fabrication of Flexible Transparent Electronics.

Reliable insulation of microscale conductive features is required to fabricate functional multilayer circuits or flexible electronics for providing specific physical/chemical/electrical protection. However, the existing strategies commonly rely on manual assembling processes or multiple microfabrication processes, which is time-consuming and a great challenge for the fabrication of flexible transparent electronics with microscale features and ultrathin thickness. Here, we present a novel coaxial electrohydrodynamic (CEHD) printing strategy for the one-step fabrication of microscale flexible electronics with conductive materials at the core and insulating material at the outer layer. A finite element analysis (FEA) method is established to simulate the CEHD printing process. The extrusion sequence of the conductive and insulating materials during the CEHD printing process shows little effect on the morphology of the core-shell filaments, which can be achieved on different flexible substrates with a minimum conductive line width of 32 ± 3.2 μm, a total thickness of 53.6 ± 4.8 μm, and a conductivity of 0.23 × 107 S/m. The thin insulating layer can provide the inner conductive filament enough protection in 3D, which endows the resultant microscale core-shell electronics with good electrical stability when working in different chemical solvent solutions or under large deformation conditions. Moreover, the presented CEHD printing strategy offers a unique capability to sequentially fabricate an insulating layer, core-shell conductive pattern, and exposed electrodes by simply controlling the material extrusion sequence. The resultant large-area transparent electronics with two-layer core-shell patterns exhibit a high transmittance of 98% and excellent electrothermal performance. The CEHD-printed flexible microelectrode array is successfully used to record the electrical signals of beating mouse hearts. It can also be used to fabricate large-area flexible capacitive sensors to accurately measure the periodical pressure force. We envision that the present CEHD printing strategy can provide a promising tool to fabricate complex three-dimensional electronics with microscale resolution, high flexibility, and multiple functionalities.

Zinc Oxide-Encapsulated Copper Nanowires for Stable Transparent Conductors.

Cu nanowire (NW)-based transparent conductors are considered to be highly promising constituents of next-generation flexible transparent electronics. However, the fast oxidation of copper under ambient conditions hinders the use of Cu NWs. Herein, we demonstrate a low-cost and scalable approach for preparing a ZnO shell on the surface of Cu NWs under ambient conditions. The covered ZnO shells enhance the oxidative stability of Cu NWs. The optical and electrical properties of ZnO@Cu NWs remain similar to the original performance of the Cu NWs (for example, before encapsulating: 13.5 Ω/sq. at 84.3%, after encapsulating: 19.2 Ω/sq. at 86.7%), which indicates that encapsulation with a ZnO shell enables the preservation of the transparency and conductivity of Cu NW networks. More importantly, the ZnO@Cu NWs exhibit excellent stability in terms of long-term storage, hot/humid environments, and strong oxidizing atmosphere/solution.

Selective Surface Treatment Using Atmospheric Ar Plasma Jet for Aluminum‐doped Zinc Oxide Based Transparent and Flexible Electronics

AbstractTransparent and flexible electronics are emerging technologies with the potential to enable new applications. However, to ensure high‐performance transparent electronics, post‐processing such as thermal annealing and vacuum plasma treatment is necessary, which are difficult to apply to polymer‐based flexible substrates. This study analyzed the feasibility of applying selective Ar plasma jet treatment at atmospheric pressure to transparent flexible electronics. When atmospheric Ar plasma treatment is applied to transparent flexible aluminum‐doped zinc oxide (AZO), it showed a maximum 83.1% improvement in sheet resistance while maintaining a high transmittance performance, of over 70%. To verify the mechanism behind the surface treatment effect using atmospheric Ar plasma, comprehensive analyses are performed using atomic force microscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy, which confirmed that the effect is due to oxygen vacancy formation caused by ion bombardment and thermal diffusion. The application of atmospheric plasma treatment to a patterned transparent flexible AZO device resulted in a reduction in contact resistance, and it is confirmed that the performance improvement effects can be retained for >500 h by applying additional passivation.

A Highly Transparent Flexible Antenna Based on Liquid Metal Mesh Film

In this paper, a convenient process for the fabrication of flexible liquid metal mesh films (LMMF) is proposed first. Then, the light transmittance and square resistance characteristics of LMMF are studied theoretically and experimentally. The light transmittance of the LMMF can reach 85% when the line width and spacing are 50 μm and 1000 μm, respectively. Furthermore, as an example of LMMF, a coplanar waveguide loop antenna is designed and fabricated that contains an LMMF with a line width of 50 μm and a line spacing of 500 μm. The measured square resistance and transmittance for the LMMF are 0.0456 Ω/sq and 72%, respectively. The measured peak gain of the antenna is 3.38 dBi while the average efficiency is 61%. The antenna’s working frequency covers most of the S-band, C-band, and X-band, as well as multiple channels of fifth generation (5G) communication. Therefore, the antenna can be used in fields such as radar and mobile communication. Uniquely, the fabricated antenna performs well in terms of light transmission, conductivity, and flexibility. In particular, it remains stable in stretching and bending deformation. As a highly light-transmissive stretchable flexible antenna, the antenna is equipped with various functions such as concealability, conformability, and reconfigurability. This LMMF-based antenna has good prospects for applications in the fields of flexible electronics and transparent electronics.

(Invited, Digital Presentation) Quantum Dots Based Transparent Light Emitting Diodes

Colloidal quantum-dot light-emitting diodes (QLEDs) have attracted considerable attention in the optoelectronic industry due to their remarkable performance, which makes them promising candidates for displays and lightning technology with a particular emphasis on color purity, brightness, and emission tunability. For these reasons over last few years a very impressive progress has been obtained in this research area in terms of improvement of QLED external quantum efficiency, their brightness and lifetime. While the race to improve the parameters of key importance for the operation of the QLED continues and QLEDs will be probably commercially available soon, the other topics related with QLED devices are at much less advanced level. This includes for example development of flexible, transparent or printable QLED devices or preparation of QLED devices in air. In this paper we will present our results related with flexible and/or transparent QLED devices obtained from green Cd-based quantum dots. We will discuss optical and electrical properties of QLED devices when using as transparent, conductive electrodes PMA/Ag, MoOx/Au/MoOx or silver metal-mesh fabricated by Ultra Precise Deposition (UPD). We will also describe thin-film deposition methods such as spin-coating/sputtering or inkjet-printing as a new versatile approach towards fabrication of flexible transparent electronics.

Ultra-high temperature tolerant flexible transparent electrode with embedded silver nanowires bundle micromesh for electrical heater

To realize high performance flexible transparent electronics with extreme environmental adaptivity, Ag nanowires (Ag NWs) electrodes should simultaneously meet the requirements of high-temperature tolerance, chemical and mechanical robustness. Herein, a scalable Ag NWs bundle micro-meshes embedded in polyimide (Ag BMs/ePI) conducting film via a facile spray coating and transfer method is reported. Due to the synergistic effect of bundle micromesh and embedded architecture, the Ag BMs/ePI electrode exhibits high thermal stability (370 °C and 400 °C under ambient and nitrogen atmosphere conditions, respectively), low sheet resistance variation (<4%), good corrosion and deformation resistance. As an electrical heater, the Ag BMs/ePI can achieve ~204 °C with the fast thermal response time of ~8 s at 8 V, and exhibits good heating stability under bent condition. This work offers a promising platform for the emerging flexible transparent electronics to adapt extreme environments, especially for those devices which require high-temperature processing.

High Stability Flexible Deep-UV Detector Based on All-Oxide Heteroepitaxial Junction

Transparent flexible electronics constitute a significant research field. Flexible deep-ultraviolet (UV) detectors have received much attention due to their potential in the applications of healthcare, communications, astronomy, and environment monitoring. Recent studies have investigated a variety of flexible photodetectors but show that the transparent, flexible, chemical, and thermal stability performances of these detectors cannot meet the requirements for practical applications. In this study, we demonstrate transparent flexible deep-UV detectors based on the combination of high-quality epitaxial n-type β-Ga2O3 and p-type NiO films as a photodiode on a flexible muscovite substrate. The electrical current of this heterojunction is increased over a 1000 times for on/off ratio under 265 nm wavelength illumination with a reasonable response (<1 s). Moreover, these photodetectors also exhibit good thermal stability as well as excellent mechanical flexibility. Our results exhibit the superior performance of the oxide-based solar-blind deep-UV detectors for advanced flexible sensing and smart applications.

Structural Integrity Preserving and Residue-Free Transfer of Large-Area Wrinkled Graphene onto Polymeric Substrates

Wrinkled graphene offers many advantageous features resulting from modifying the structural and physical properties as well as the chemical reactivity of graphene. However, its inadequate transferability to other substrates has limited its usability. This paper reports a roll-based clean transfer approach that enables the damage-free and contamination-free transfer of large-area wrinkled graphene onto polymeric substrates without compromising the integrity of wrinkle structures. The method implements the simultaneous imidazole-assisted etching and doping of chemical vapor-deposited graphene to fabricate multilayer graphene on a thermoplastic polystyrene (PS) substrate coated with a water-soluble poly(4-styrenesulfonic acid) (PSS) sacrificial layer via a roll-based transfer process. The compliant PSS layer affords the conformal contact between the PS substrate and graphene during the wrinkle formation process, enabling the controllable fabrication of graphene wrinkle structures on a large area. The water-soluble properties of PSS simplify the typically difficult separation of wrinkled graphene from the PS substrate after its transfer onto a target substrate. This improves the transferability of wrinkled graphene, rendering the transfer process solvent-free and residue-free. This work demonstrates the feasibility of the formulated method by transferring centimeter-scale wrinkled graphene onto currently used transparent flexible substrates (i.e., polyethylene terephthalate and polydimethylsiloxane). The results indicate that the transferred wrinkled graphene possesses the desirable combination of superior stretchability, optical transmittance, sheet resistance, and electromechanical stability, rendering its suitable application to transparent flexible and stretchable electronics.

Novel Fabrication of Silver-Coated Copper Nanowires with Organic Compound Solution.

Copper nanowires and Cu-Ag nanowires have various potential applications, such as transparent conductive film, flexible electronics, and conductive filler. In this study, we developed a new green fabrication method for silver-coated copper nanowires using methylsulfonylmethane (DMSO2), which is an environmentally friendly chemical at the food-grade level, to replace toxic chemicals, including ammonia, in the silver coating process. Copper nanowires were synthesized under various reaction temperatures and concentrations of hydrazine (N2H4), ethylenediamine (EDA), sodium hydroxide (NaOH), and copper precursor. The reaction temperature higher than 70 °C caused the oxidation of copper products and evaporation of the sample solution. The optimal conditions to synthesize copper nanowires more than 18 µm in length and 25–45 nm in diameter were determined: 9 M of NaOH, 50 µL of EDA, 17 mM of CuCl2, 5.7 mM of N2H4, and 70 °C reaction temperature. Cu-Ag nanowires, which have about a 12 nm thick silver shell, were successfully fabricated at room temperature under 1 mM of silver nitrate (AgNO3) and 1 wt % of DMSO2. Synthesis conditions for copper and silver-coated copper nanowires have been optimized.

Simple, Fast, and Scalable Reverse-Offset Printing of Micropatterned Copper Nanowire Electrodes with Sub-10 μm Resolution.

Copper nanowires (CuNWs) possess key characteristics for realizing flexible transparent electronics. High-quality CuNW micropatterns with high resolution and uniform thickness are required to realize integrated transparent electronic devices. However, patterning high-aspect-ratio CuNWs is challenging because of their long length, exceeding the target pattern dimension. This work reports a novel reverse-offset printing technology that enables the sub-10 μm high-resolution micropatterning of CuNW transparent conducting electrodes (TCEs). The CuNW ink for reverse-offset printing was formulated to control viscoelasticity, cohesive force, and adhesion by adjusting the ligands, solvents, surface energy modifiers, and leveling additives. An inexpensive commercial adhesive handroller achieved a simple, fast, and scalable micropatterning of CuNW TCEs. Easy production of high-quality CuNW micropatterns with various curvatures and shapes was possible, regardless of the printing direction. The reverse-offset-printed CuNW micropatterns exhibited a minimum of 7 μm line width and excellent pattern qualities such as fine line spacing, sharp edge definition, and outstanding pattern uniformity. In addition, they exhibited excellent sheet resistance, high optical transparency, outstanding mechanical durability, and long-term stability. Flexible light-emitting diode (LED) circuits, transparent heaters, and organic LEDs (OLEDs) can be fabricated using high-resolution reverse-offset-printed CuNW micropatterns for applications in flexible transparent electronic devices.

Metal-Free Transparent Three-Dimensional Flexible Electronics by Selective Molecular Bridges.

Flexible and transparent electronics is a new generation of device enabling modern interactive designs, which facilitates the recent development of low-cost, lightweight, and flexible materials. Although conventional indium tin oxide material still dominates the major market, its brittleness and steadily increasing price drive scientists to search for other alternatives. To meet the high demand, numerous metallic or organic conductive materials have been developed, but their poor adhesion toward supporting substrates and the subsequent circuit patterning approach remains problematic. In this study, a robust metal-free flexible conductive film fabrication strategy is introduced. The flexible polyethylene terephthalate (PET) film is utilized as the base, where a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conductive layer is tightly linked onto this supporting substrate. An interface activation process, i.e., oxygen plasma treatment, generates PET surface active spots to react with the subsequently introduced poly(vinyl alcohol) (PVA) molecule functional groups. This spatially selective PVA molecular bridge therefore acts as a dual-function intermediate layer through covalent bonding toward PET and hydrogen bonding toward PEDOT:PSS to conjugate two distinct materials. This PEDOT:PSS/PVA/PET film delivers superior physical properties, such as a high conductivity of 38.2 Ω/sq and great optical transmittance of 84.1%, which are well tunable under conductive polymer thickness controls. The film is also durable and can maintain original electrical properties even under serious bending for hundreds of cycles. Relying on these outstanding performances, arbitrary conductive circuits are built on this flexible substrate and can function as normal electronics when integrated with multiple electronic parts, e.g., light-emitting diodes (LEDs). Superior electrical signal outputs are achieved when complicated stereo structures including folding, splicing, interlacing, and braiding are incorporated, enabling the use of these films for flexible three-dimensional electronics assembling. Space identifying smart key and lock pair, origami rabbit-carrot touch response, pressure-stimulated jumping frog, and moving dinosaur recognition designs realize these PEDOT:PSS/PVA/PET film-based human-machine interactive devices. This flexible, transparent, and conductive film generation approach by molecular bridge creation should facilitate future development of flexible or foldable devices with complex circuits.

Transparent, P‐channel CuISn Thin‐film Transistor with Field Effect Mobility of 45 cm2 V–1 s–1 and Excellent Bias Stability

AbstractThe p‐type semiconducting materials are essential building blocks for high performance complementary metal‐oxide semiconductor (CMOS) thin‐film transistor (TFT) circuits. Here, the development of the transparent and high performance of p‐channel copper‐iodide‐tin (CuISn) TFTs is reported. Sn alloy in CuI exhibits remarkable changes in structural and physical properties, which are studied by scanning electron microscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy, and Hall effect measurements. It is confirmed that 25% Sn‐alloyed CuI has p‐type conductivity with carrier concentration of 2.1 × 1017 cm–3 and Hall mobility of 63.8 cm2 V–1 s–1. The TFT made with 25% CuISn exhibits the high field‐effect mobility (μFE) of 45.5 cm2 V–1 s–1, which is 10‐fold higher than that of the pristine CuI TFT. The CuISn TFT on polyimide substrate exhibits the μFE of 42.5 cm2 V–1 s–1 and ON/OFF current ratio of ≈107. In addition, the CuISn TFT shows excellent stability with the threshold voltage shift of 0.6 V under negative gate bias stress. In addition, the hetrojunction with Li doped ZnO, CuISn/LZO p‐n junction exhibit excellent rectifying characteristics with the diode ideality factor of 1.3 and forward to reverse current ratio of ≈107, which is three order higher than that of CuI/LZO diode. Therefore, the p‐channel CuISn TFTs can be widely used to open up cost‐effective transparent CMOS TFT circuits, displays, and flexible electronics.

Arithmetic and Logic Circuits Based on ITO-Stabilized ZnO TFT for Transparent Electronics

In this paper, general logic cell and module designs in basic digital signal processing (DSP), for transparent, flexible chips and wearable electronics are presented. Modified Circuits from ratioed logic and pass transistor logic styles are modified and proposed, based on n-type-only indium tin oxide (ITO) stabilized ZnO thin-film transistors (TFTs) process. Elaborations on logic circuits with purely n-type TFT transistors were carried out to extend the logic swing of circuit outputs and accelerate the signal propagation in complex logic functions with simplified pull-up/pull-down or passive networks. To implement logic complexes on multiple OR-of-ANDs functions with better performance, tailored active controlled ratioed logic style is adopted with faster speed and smaller area by simplifying the transistor networks properly. All the circuits were fabricated on transparent glass plate. The featured 2-input/3-input XOR gate, 4-1 MUX and D flip flop (DFF) can operate with maximum featured delays of 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6~\mu \text{s}$ </tex-math></inline-formula> at 5 V power supply, with comparatively over 50% less delays and areas than other state-of-art works. The featured 4-bit adder performs maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16.41~\mu \text{s}$ </tex-math></inline-formula> delay at 5 V in measurement. A 4-bit multiplier is also presented based on the adder and DFF. These proposed TFT circuits exhibited smaller area with relatively moderate-high performance in comparison, which were promising building blocks for transparent flexible DSP electronics with low-speed requirements.

A Multidimensional Topotactic Host Composite Anode Toward Transparent Flexible Potassium-Ion Microcapacitors.

Transparent flexible supercapacitors (TFSCs) are a tantalizing power supplier for future transparent flexible electronics. However, their energy density is far behind a practical level while maintaining high transparency. We report here a transparent flexible potassium-ion microcapacitor, and its high energy density (15.5 μWh cm-2) roots in the battery-supercapacitor hybrid storage mechanism and much enlarged working voltage (3 V), outperforming the state-of-the-art TFSC, which is generally based on an aqueous electrolyte and an asymmetric pseudocapacitive mechanism. From an electrode material perspective, a multidimensional topotactic host composite anode is designed in which the component not only performs energy storage by synchronous and reversible uptake of potassium ions and electrons into its host structure, but also mutually compensates individual weakness in functional and structural aspects, efficiently constructing a three-dimensional potassium-ion diffusion and electron transport system. This conceptual exhibition provides design principles at material and device levels for high-performance TFSCs.

Flexible Transparent Electric-Double-Layer Junctionless Thin Film Transistors with Low Operating Voltage

Flexible transparent junctionless thin film transistors gated by microporous SiO2 dielectric with electric-double-layer (EDL) effect are fabricated onto PET substrates at room temperature. These devices exhibit high-performance n-type transistor characteristics operating in enhancement mode with low operating voltage of 1.5 V due to the huge gate specific capacitance (0.44 μF cm−2 at 40 Hz) related to EDL formation. The electron field-effect mobility of 28.4 cm2 V−1 s−1, current on/off ratio and the subthreshold swing are found to be 5 × 106 and 0.1 V decade−1, respectively. These achievements demonstrate that flexible transparent junctionless thin-film transistors are promising for the next-generation low-power flexible transparent electronics applications.