Large-Area Exfoliated Lead-Free Perovskite-Derivative Single-Crystalline Membrane for Flexible Low-Defect Photodetectors

Wide applications of personal consumer electronics have tended to cause a huge demand for smart and portable electronics, featuring mechanical flexibility, lightweight, and environmental friendliness. However, most of the recently reported flexible photodetectors based on microcrystalline and amorphous components commonly suffer from severe drawbacks, including plenty of grains, boundaries, and surface defects. Here, we present a new lead-free chiral perovskite-derivative light absorber of (aminoguanidinium)₃Bi₂I₉ (AG₃Bi₂I₉), which displays a narrow direct band gap of about 1.89 eV. High-quality bulk single crystals were successfully grown with dimensions up to 24 × 12 × 5 mm³. Emphatically, as-grown bulk single crystals are easy to be exfoliated for large-area ultrathin wafers with an exfoliated area up to 0.6 cm², showing promise for low-defect flexible optoelectronic applications. The remarkable surface smoothness and crystalline quality of single-crystalline thin layers were further confirmed by TEM, HRTEM, AFM, single-crystalline X-ray diffraction, and space-charge limited current (SCLC) measurements. As expected, the planar photodetectors based on flexible exfoliated wafers are first fabricated and exhibit notable photoelectric performance. This work represents an important step forward as it offers an effective strategy for the fabrication of high-quality large-area flexible exfoliated wafer devices.

Superomniphobic Silk Fibroin/Ag Nanowires Membrane for Flexible and Transparent Electronic Sensor

Superwetting surfaces that repel various liquids have been exciting for biomimetic research and have displayed versatile potential applications. Generally, superhydrophobic coatings can allow for droplet rolling off and antifouling, whereas it is a challenge to achieve superomniphobic surfaces with transparency, flexibility, and conductivity. Here, we adopt an effective and simple method to fabricate a superomniphobic, transparent, and flexible smart silk fibroin (SF) membrane by spray-coating long AgNWs dispersed in polydimethylsiloxane (PDMS), followed by treatment with vacuum drying. The resulting SF/AgNWs membranes are super-repellent to different liquids with low surface tension and water, and demonstrate high contact angles (CAs) more than 150° and low rolling-off angles (RAs) even less than 10°. Moreover, the obtained membranes display superior sensitivity under stretching and bending, as well as intact stability of high transparency, which can be considered as promising flexible sensing electronics to detect human motions under wet conditions.

Investigation on Low-temperature Annealing Process of Solution-processed TiO2 Electron Transport Layer for Flexible Perovskite Solar Cell

Flexible perovskite solar cells (PSCs) have received increasing attention in wearable and portable devices over the past ten years. The low-temperature process of electron transport layer plays a key role in fabricating flexible PSCs. In this paper, we improve the performance of flexible PSCs by controlling the thermodynamic procedure in the low-temperature annealing process of solution-processed TiO₂ layers and modulating the precursor concentration of (6,6)-phenyl c₆₁ butyric acid methyl ester (PC₆₁BM) deposited on fluorine-doped tin oxide (FTO)/TiO₂ substrate. The results show that slowing down evaporation rate of residual solvent and adopting PC₆₁BM of appropriate precursor concentration are confirmed to be effective methods to improve the performance of flexible PSCs. We also demonstrate carbon electrode-based flexible PSCs. Our work expands the feasibility of low temperature process for the development of flexible perovskite photodetectors and light-emitting diodes, as well as flexible PSCs.

Free-standing Reduced Graphene Oxide/carbon Nanotube Paper for Flexible Sodium-ion Battery Applications

We propose a flexible, binder-free and free-standing carbonaceous paper fabricated via electrostatic spray deposition using reduced graphene oxide/carbon nanotube (rGO/CNT) as a promising electrode material for flexible sodium-ion batteries (NIBs). The as-prepared rGO/CNT paper exhibits a three-dimensional (3D) layered structure by employing rGO as conductive frameworks to provide sodium-storage active sites and CNT as spacer to increase rGO interlayer distance and benefit the diffusion kinetics of sodium ions. Consequently, the rGO/CNT paper delivers an enhanced sodium ion storage capacity of 166.8 mAh g^-1 at 50 mA g^-1, retaining an average capacity of 101.4 mAh g^-1 when current density sets back 100 mA g^-1 after cycling at various current rates. An average capacity of 50 mAh g^-1 at 200 mA g^-1 was stabilized when cycling up to 300 cycles. The well-maintained electrochemical performance of free-standing rGO/CNT paper is due to the well-established hybrid 3D nanostructures, which demonstrates our carbon based material fabricated by a facile approach can be applied as one of the high-performance and low-cost electrode materials for applications in flexible energy storage devices.

Dual Role of Amino-Functionalized Graphene Quantum Dots in NiOx Films for Efficient Inverted Flexible Perovskite Solar Cells

NiO_x has been widely used as an effective hole-transport material for inverted perovskite solar cells (PSCs), particularly flexible PSCs, owing to its low-temperature processing, low cost, and good electron-blocking ability. However, the band structure alignment between low-temperature-processed NiO_x and the perovskite layer is not satisfactory, resulting in reduced photovoltaic performance. Herein, we report a novel strategy to tune the NiO_x hole-transport layer for achieving high-performance flexible PSCs. Amino-functionalized graphene quantum dots (AGQDs) are employed in the NiO_x film as a dual-role additive. On the one hand, the added AGQDs can provide abundant N atoms at the modified NiO_x layer surface to enhance the crystallization of the perovskite film by a Lewis base-acid interaction. On the other hand, the AGQDs can optimize the band structure alignment between the NiO_x and perovskite layers, facilitating hole extraction at the NiO_x/perovskite interface. As a result, the inverted flexible PSCs exhibit a high efficiency of 18.10%, which is comparable to the values reported for the current state-of-the-art inverted flexible PSCs. In addition to good air stability, our best flexible devices have excellent mechanical stability, retaining 88% of their initial efficiency after continuously bending 1000 times. This new strategy highlights a promising way to enhance the performance of inverted flexible PSCs.

High-Performance Ag-Modified Bi0.5Sb1.5Te3 Films for the Flexible Thermoelectric Generator

Bi-Sb-Te-based semiconductors possess the best room-temperature thermoelectric performance, but are restricted for application in the wearable field because of their inherent brittleness, rigidity, and nonscalable manufacturing techniques. Therefore, how to obtain thermoelectric materials with excellent thermoelectric properties and flexibility through the batch production process is a serious challenge. Here, we report the fabrication of flexible p-type thermoelectric Ag-modified Bi_0.5Sb_1.5Te₃ films on flexible substrates using a facile approach. Their optimized power factors are ∼12.4 and ∼14.0 μW cm^-1 K^-2 at 300 and 420 K, respectively. These high-power factors mainly originate from the optimized carrier transport of the composite system, through which a high level of electrical conductivity is achieved, whereas a remarkably improved Seebeck coefficient is simultaneously obtained. Bending tests demonstrate the excellent flexibility and mechanical durability of the composite films, and their power factors decrease by only about 10% after bending for 650 cycles with a bending radius of 5 mm. A flexible thermoelectric module is designed and constructed using the optimized composite films and displays a power density of ∼1.4 mW cm^-2 at a relatively small ΔT of 60 K. This work demonstrates the potential of inorganic thermoelectric materials to be made on flexible/wearable substrates for energy harvesting and management devices.

Controlling Electrode Spacing by Polystyrene Microsphere Spacers for Highly Stable and Flexible Transparent Supercapacitors

Transparent polymer electrolytes such as poly(vinyl alcohol)-based H⁺, Li⁺, K⁺, and Na⁺ gels have been widely used as both an electrolyte and a separator for flexible transparent supercapacitors (FTSCs). However, these gels sandwiched between the electrodes in FTSCs are easily compressed under bending and compression due to their viscous flow behavior, resulting in the deformation of electrode spacing and the unstable capacitance performance. To resolve this issue, herein, we introduce monodispersed polystyrene (PS) microspheres into PVA-LiCl polymer gel electrolytes as spacers to precisely control the electrode spacing during the assembly of FTSCs using single-walled carbon nanotubes/indium tin oxide-polyethylene terephthalate (ITO-PET) or MnO₂/multiwalled carbon nanotubes/ITO-PET as transparent electrodes. The electrode spacing could be tuned by varying the diameter of PS microspheres, for example, 20, 40, and 80 μm. More importantly, the PS microsphere spacers protect the gel electrolyte from the squeeze when bending takes place, allowing the stable performance output by FTSCs under a bending state. After repeating bending tests, the capacitance remains 95.6%, indicating the high stability and flexibility of the devices with the assistance of PS microsphere spacers.

Substantially Improving Device Performance of All-Inorganic Perovskite-Based Phototransistors via Indium Tin Oxide Nanowire Incorporation

All-inorganic halide perovskites (IHPs) have attracted enormous attention due to their intrinsically high optical absorption coefficient and superior ambient stabilities. However, the photosensitivity of IHP-based photodetectors is still restricted by their poor conductivities. Here, a facile design of hybrid phototransistors based on the CsPbBr₃ thin film and indium tin oxide (ITO) nanowires (NWs) integrated into a InGaZnO channel in order to achieve both high photoresponsivity and fast response is reported. The metallic ITO NWs are employed as electron pumps and expressways to efficiently extract photocarriers from CsPbBr₃ and inject electrons into InGaZnO. The obtained device exhibits the outstanding responsivity of 4.9 × 10⁶ A W^-1 , which is about 100-fold better than the previous best results of CsPbBr₃ -based photodetectors, together with the fast response (0.45/0.55 s), long-term stability (200 h in ambient), and excellent mechanical flexibility. By operating the phototransistor in the depletion regime, an ultrahigh specific detectivity up to 7.6 × 10¹³ Jones is achieved. More importantly, the optimized spin-coating manufacturing process is highly beneficial for achieving uniform InGaZnO-ITO/perovskite hybrid films for high-performance flexible detector arrays. All these results can not only indicate the potential of these hybrid phototransistors but also provide a valuable insight into the design of hybrid material systems for high-performance photodetection.

Systematic Design of Polypyrrole/Carbon Fiber Electrodes for Efficient Flexible Fiber-Type Solid-State Supercapacitors

Fiber-type supercapacitors (FSC) have attracted much attention as efficient energy storage devices for soft electronics. This study proposes the synthesis of polypyrrole (PPy) on carbon fiber (CF) using electropolymerization as the energy storage electrode for FSC. Effects of the electrolyte, applied current, and time of electropolymerization for synthesizing PPy on CF are investigated. The configuration of the electrochemical system is also studied to better understand the electropolymerization of PPy. The highest specific capacitance (C_M) of 308.2 F/g are obtained for the PPy electrode prepared using 0.5 M pyrrole and 0.3 M NaClO₄ as the electrolyte at 40 mA for 20 min. The FSC assembled with PPy electrodes and the polyvinyl alcohol/H₃PO₄ gel electrolyte shows a C_M value of 30 F/g and the energy density of 5.87 Wh/kg at the power density of 60.0 W/kg. Excellent cycling stability with C_M retention of 70% and Coulombic efficiency higher than 98% in 3000 times charge/discharge process, and the good bending capability with C_M retention of 153% and 148%, respectively, under the bending angle of 180° and the bending times of 600 are achieved. This work gives deeper understanding of electropolymerization and provides recipes for fabricating an efficient PPy electrode for soft energy storage devices.

Rational Design of Efficient Organometallic Ir(III) Complexes for High-Performance, Flexible, Monochromatic, and White Light-Emitting Electrochemical Cells

Highly efficient light-emitting electrochemical cells (LECs) have attracted tremendous interest because of their simple structures and low-cost fabrication processing, showing great potential for full-color displays and solid-state lighting. In this work, we rationally designed and synthesized two red-emitting cationic Ir(III) complexes, [Ir(tBuPBI)₂(biq)]PF₆ (R1) and [Ir(tBuPBI)₂(qibi)]PF₆ (R2), in which a tert-butyl-functionalized 1,2-diphenyl-1H-benzo[d]imidazole (PBI) unit and conjugated 2,2'-biquinoline (biq) and 2-(1-phenyl-1H-benzo[d]imidazol-2-yl)quinolone (qibi) were employed as cyclometalated and ancillary ligands, respectively. The introduced tert-butyl group led to homogeneous and highly emissive thin films by increasing the solubility and suppressing the strong intermolecular interactions due to steric hindrance. Based on the abovementioned high-quality emissive layer, high-efficiency LECs were achieved. An efficient red-emitting LEC fabricated on a glass substrate achieved a current efficiency (η_C) of 7.18 cd/A and an external quantum efficiency (η_ext) of 9.32%. By doping both complexes into a blue-green-emitting cationic Ir(III) complex, high-performance white LECs were also successfully fabricated with Commission International de L'Eclairage (CIE) coordinates of (0.39,0.39), a η_C of 17.43 cd/A, and a η_ext of 8.92%. In addition, we also fabricated flexible red and white LECs with outstanding efficiencies and mechanical flexibilities. The η_C and η_ext values of a flexible white LEC could be as high as 13.50 cd/A and 6.86%, respectively. The efficiency of the flexible device remained at approximately 95% of the initial value after 500 bends with a radius of curvature of 5 mm, demonstrating the great potential of these complexes for full-color displays and flexible optoelectronics.

Scalable, Alternating Narrow Stripes of Polyvinyl Alcohol Support and Unmodified PEDOT:PSS with Maintained Conductivity Using a Single-Step Slot Die Coating Approach

Slot die coating has been established as an economical approach for deposition of parallel narrow stripes, a constituent pattern feature in many printed device applications. However, the minimum feature size that can be achieved using this approach is constrained by wetting and liquid bridge phenomena at the deposition region. We hypothesize that pattern resolution and process control can be improved by co-depositing a support fluid to stabilize the pattern. Electrically conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is slot die-coated in parallel stripes on flexible poly(ethylene terephthalate) substrate, without wettability-enhancing dopants or substrate pretreatment. A miscible liquid phase, polyvinyl alcohol, is used as the support material. Feature size performance and conductivity of PEDOT:PSS stripe regions are evaluated across a range of process conditions. Narrow PEDOT:PSS stripes produced using our technique range from 400 to 850 μm and exhibit conductivity approaching 1.5 S cm^-1. This electrical performance falls within the upper range expected prior to standard conductivity-enhancing post-treatments. Significantly, dewetting effects normally present with undoped PEDOT:PSS on the plastic substrate are fully mitigated with our deposition technique. These results indicate high ease of processing and good feature size performance, with few inherent drawbacks to the functional properties of the patterned films.

A Flexible Potassium-Ion Hybrid Capacitor with Superior Rate Performance and Long Cycling Life

Potassium-ion batteries are promising candidates for large-scale energy storage applications owing to their merits of abundant resources, low cost, and high working voltage. However, the unsatisfying rate performance and cycling stability caused by sluggish K⁺ diffusion kinetics and dramatic volume expansion hinder the development of potassium-ion batteries. In this study, we design a flexible potassium-ion hybrid capacitor (PIHC) by combining the K-Sn alloying mechanism on the Sn anode and the fast capacitive behavior on the AC cathode with high surface area and mesoporous structure. After optimization, the fabricated Sn||AC PIHC achieves both a high energy density of 120 W h kg^-1 and high power density of 2850 W kg^-1, much better than other similar hybrid devices. Moreover, a gel polymer electrolyte with a 3D porous structure and high ionic conductivity was employed to improve the structural stability of the Sn anode, which not only realizes good flexibility but also achieves long cycling stability with a capacity retention of nearly 100% for 2000 cycles at a high current density of 3.0 A g^-1.

Ultraflexible Corrugated Monocrystalline Silicon Solar Cells with High Efficiency (19%), Improved Thermal Performance, and Reliability Using Low-Cost Laser Patterning

Flexible solar cells have received growing attention recently because of their ever-increasing range of applications. Here, the development of ultraflexible, lightweight, and high efficiency (19%) monocrystalline silicon solar cells with excellent reliability, mechanical resilience, and thermal performance is demonstrated by applying a corrugation method combined with laser patterning. The flexing mechanism converts large-scale rigid photovoltaic cells with interdigitated back contacts (IBCs) into a flexible version with a preserved efficiency. The corrugation technique is based on the formation of patterned grooves in active silicon to achieve ultraflexibility. As a result, islands of silicon with different shapes are obtained which are interconnected through the IBCs. Multiple corrugation patterns such as linear, honeycomb, and octagonal designs are studied, each resulting in different flexing capabilities in terms of flexing directionality and minimum bending radius, in addition to providing an atypical appearance with an aesthetic appeal. The corrugation method is shown to improve thermal dissipation (14.6% lower temperature) and to relieve the thermal mismatch challenge compared to the rigid cells because of the finlike architecture. Finally, encapsulation using a transparent polymeric material enables a robust performance of the flexible cells when exposed to different environmental conditions such as acid rain, snow, and mechanical shocks.

Ultra-Sensitive Flexible Pressure Sensor Based on Microstructured Electrode

Flexible pressure sensors with a high sensitivity in the lower zone of a subtle-pressure regime has shown great potential in the fields of electronic skin, human–computer interaction, wearable devices, intelligent prosthesis, and medical health. Adding microstructures on the dielectric layer on a capacitive pressure sensor has become a common and effective approach to enhance the performance of flexible pressure sensors. Here, we propose a method to further dramatically increase the sensitivity by adding elastic pyramidal microstructures on one side of the electrode and using a thin layer of a dielectric in a capacitive sensor. The sensitivity of the proposed device has been improved from 3.1 to 70.6 kPa⁻¹ compared to capacitive sensors having pyramidal microstructures in the same dimension on the dielectric layer. Moreover, a detection limit of 1 Pa was achieved. The finite element analysis performed based on electromechanical sequential coupling simulation for hyperelastic materials indicates that the microstructures on electrode are critical to achieve high sensitivity. The influence of the duty ratio of the micro-pyramids on the sensitivity of the sensor is analyzed by both simulation and experiment. The durability and robustness of the device was also demonstrated by pressure testing for 2000 cycles.

Adhesive-Layer-Free and Double-Faced Nanotransfer Lithography for a Flexible Large-Area MetaSurface Hologram

Herein, we develop an adhesive-free double-faced nanotransfer lithography (ADNT) technique based on the surface deformation of flexible substrates under the conditions of temperature and pressure control and thus address the challenge of realizing the mass production of large-area nanodevices in the fields of optics, metasurfaces, and holograms. During ADNT, which is conducted on a flexible polymer substrate above its glass transition temperature in the absence of adhesive materials and chemical bonding agents, nanostructures from the polymer stamp are attached to the deformed polymer substrate. Various silicon masters are employed to prove our method applicable to arbitrary nanopatterns, and diverse Ag and Au nanostructures are deposited on polymer molds to demonstrate the wide scope of useable metals. Finally, ADNT is used to (i) produce a flexible large-area hologram on the defect-free poly(methyl methacrylate) (PMMA) film and (ii) fabricate a metasurface hologram and a color filter on the front and back surfaces of the PMMA film, respectively, to realize dual functionality. Thus, it is concluded that the use of ADNT can decrease the fabrication time and cost of high-density nanodevices and facilitate their commercialization.

Fully Passive Flexible Wireless Neural Recorder for the Acquisition of Neuropotentials from a Rat Model

Wireless implantable neural interfaces can record high-resolution neuropotentials without constraining patient movement. Existing wireless systems often require intracranial wires to connect implanted electrodes to an external head stage or/and deploy an application-specific integrated circuit (ASIC), which is battery-powered or externally power-transferred, raising safety concerns such as infection, electronics failure, or heat-induced tissue damage. This work presents a biocompatible, flexible, implantable neural recorder capable of wireless acquisition of neuropotentials without wires, batteries, energy harvesting units, or active electronics. The recorder, fabricated on a thin polyimide substrate, features a small footprint of 9 mm × 8 mm × 0.3 mm and is composed of passive electronic components. The absence of active electronics on the device leads to near zero power consumption, inherently avoiding the catastrophic failure of active electronics. We performed both in vitro validation in a tissue-simulating phantom and in vivo validation in an epileptic rat. The fully passive wireless recorder was implanted under rat scalp to measure neuropotentials from its contact electrodes. The implanted wireless recorder demonstrated its capability to capture low voltage neuropotentials, including somatosensory evoked potentials (SSEPs), and interictal epileptiform discharges (IEDs). Wirelessly recorded SSEP and IED signals were directly compared to those from wired electrodes to demonstrate the efficacy of the wireless data. In addition, a convoluted neural network-based machine learning algorithm successfully achieved IED signal recognition accuracy as high as 100 and 91% in wired and wireless IED data, respectively. These results strongly support the fully passive wireless neural recorder's capability to measure neuropotentials as low as tens of microvolts. With further improvement, the recorder system presented in this work may find wide applications in future brain machine interface systems.

A Flexible and Boron-Doped Carbon Nanotube Film for High-Performance Li Storage

Boron-doped carbon nanotubes are a promising candidate for Li storage due to the unique electronic structure and high crystallinity brought by the boron dopants. However, the relatively low Li storage capacity has limited its application in the electrochemical energy storage field, which is mainly caused by the predominantly intact graphitic structure on their surface with limited access points for Li ion entering. Herein, we report a novel B-doped CNTs (py-B-CNTs) film, in which the CNTs possess intrinsically rough surface but flat internal graphitic structure. When used as a flexible anode material for LIBs, this py-B-CNTs film delivers significantly enhanced capacity than the conventional B-doped CNTs or the pristine CNTs films, with good rate capability and excellent cycling performance as well. Moreover, this flexible film also possesses excellent mechanical flexibility, making it capable of being used in a prototype flexible LIB with stable power output upon various bending states.

Substrate Diameter-Dependent Photovoltaic Performance of Flexible Fiber-Type Dye-Sensitized Solar Cells with TiO2 Nanoparticle/TiO2 Nanotube Array Photoanodes

Fiber-type dye-sensitized solar cells (FDSSCs) are attractive as an energy source of soft electronics due to low-costs, non-toxicity and especially, their indoor-weak-light workable features. The TiO₂ nanotube array (TNA) can grow on flexible Ti wires directly using anodization technique, which is convenient and can provide better contact between substrate/TiO₂. However, a systematic study of assembling efficient TNA on photoanode of FDSSC is limited. This study investigated the anodization voltage and time effects of growing TNA on Ti wires. TiO₂ nanoparticles (TNP) are fabricated on TNA using dip-coating technique to compensate for low dye adsorption of TNA. Dip-coating rate is varied to optimize TNP thicknesses to provide effective dye adsorption and charge-transfer routes. The highest photon-to-electricity conversion efficiency (η) of 3.31% was obtained for FDSSCs with TNA/TNP photoanode prepared using 60 V as the anodization voltage and 40 cm/min as the dip-coating rate. The influence of titanium wire diameter on η of FDSSCs was studied. The bending test was carried out on flexible FDSSC assembled using plastic tube. The photocurrent retention of 84% is achieved for flexible FDSSC bended for 10 times. This work firstly provides facile ways to assemble efficient photoanode with composite TiO₂ structures for FDSSC and opens new insights on studying titanium wire natures on FDSSC performance.

CNT-Intertwined Polymer Electrode toward the Practical Application of Wearable Devices

One of the greatest challenges for wearable electronics is the lack of virtually flexible electrodes with satisfactory electrochemical performance, and there is always a "softness vs effective capacity" dilemma. Herein, a polymer electrode is proposed. The carefully chosen and partially conjugated polyimide realizes the dual function of a flexible agent and an active agent. The softness of the electrode is rendered by the polymer, while the carbon nanotube ensures electron transfer (ET) within the polymer. A modified electrospinning method has been used in the preparation of a carbon nanotube (CNT)-intertwined polyimide (PI) film. The binder-free and current collector-free polymer electrode has as high as 80% active phase and releases near-theoretical capacity accompanied by very stable cycling up to 200 cycles. Owing to the dual role of the polymer component, the softness vs effective capacity dilemma has been well addressed. Aiming at the practical application, a fatigue test has been first conducted in a practical mode and the well-reserved electrochemical activity under extreme stress change as well as in plenty of electrolyte has been revealed. The work realizes that the flexible electrode well fulfills the requirement and sheds more light on the application of the polymer electrode materials.

Detection and analysis of stable and flexible genes towards a genome signature framework in cancer

Comparison and detection of stable cancer genes across cancer types is of interest. The gene expression data of 6 different cancer types (colon, breast, lung, ovarian, brain and renal) and a control group from The Cancer Genome Atlas (TCGA) database were used in this study. The comparison of gene expression data together with the calculation standard deviations of such data was completed using a statistical model for the detection of stable genes. Genes having similar expression (referred as flexible genes) pattern to the control group in four out of six cancer types are PATE, NEUROD4 and TRAFD1. Moreover, 13 genes showed low difference compared to the control group with low standard deviation across cancer types (referred as stable genes). Among them, genes GDF2, KCNT1 and RNF151 showed consistent low expression while ODF4, OR5I1, MYOG and OR2B11 showed consistent high expression. Thus, the detection and analysis of stable and flexible cancer genes help towards the design and development of a framework (outline) for specific genome signature (biomarker) in cancer.

Direct Inkjet Printing of Aqueous Inks to Flexible All-Solid-State Graphene Hybrid Micro-Supercapacitors

In this article, the inkjet printing technique is demonstrated for the stacking of reduced graphene oxide (RGO) and molybdenum trioxide (MoO₃) nanosheets for flexible all-solid-state micro-supercapacitors. The ammonium molybdate tetrahydrate/graphene oxide ((NH₄)₆Mo₇O₂₄·4H₂O/GO) aqueous inks are facilely printed on polymide (PI) film and transformed to RGO/MoO₃ hybrids via thermal treatments at air atmosphere. The compound inks are water-based, inkjet-printable, and nontoxic for inkjet printing to form two-dimensional crystal materials. The physical properties of aqueous inks are optimized within a printable range characterized by the Ohnesorge number of 1 < Z < 14. The inkjet-printed symmetric micro-supercapacitors (MSCs) with poly(vinyl alcohol) (PVA)-H₂SO₄ gel electrolyte possess a wide voltage window of 0-0.8 V, excellent flexibility, a high volumetric specific capacitance of 22.5 F cm^-3 at 0.044 A cm^-3, as well as good cyclic stability due to the synergistic effect of RGO and MoO₃. Furthermore, the inkjet-printed composite MSCs delivered a maximum energy density of 2 mWh cm^-3 and a power density of 0.018 W cm^-3, and the capacity retention rate of inkjet-printed MSCs is still retained 82% even after 10 000 charge-discharge cycles, indicating good electrochemical properties. Above all, the as-designed inkjet printing technique shows potential for flexible and wearable energy storage electronics.

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.