Self-Powered Colorful Dynamic Electrowetting Display Systems Based on Triboelectricity.

Electrowetting displays (EWDs) based on microfluidics are highly sought after in the fields of electronic devices, smart homes, and information communication. However, the power supply of the EWD systems for visually engaging multi-color displays remains a big challenge. Herein, self-powered colorful dynamic display systems are developed by integrating the triboelectric nanogenerator (TENG) with the EWD device. The TENG is designed with a nanotube-patterned surface and can generate open-circuit voltages ranging from 30 to 295 V by controlling the contact area. The wetting property of the micro-droplet exhibits a response to the applied voltage, enabling the triboelectricity-triggered electrowetting-on-dielectric. Driven by the voltage of 160 V, the monochromatic EWD exhibits bright color switching from magenta to transparent with a pixel aperture ratio of 78%, and the recovery process can be rapidly completed. Furthermore, the self-powered colorful dynamic EWD system can be achieved. By selectively applying the voltage to the pixels in the three monochromatic layers that constitute the colorful EWD, the wetting properties of the fluids can be controlled, allowing for colorful dynamic display. This work contributes to the advancement of color display technology for portable and wearable electronic ink displays, indoor and outdoor sports equipment, and information communication.

A phonic Braille recognition system based on a self-powered sensor with self-healing ability, temperature resistance, and stretchability.

Braille recognition is of great significance for the visually impaired and blind people to achieve convenient communication and learning. A self-powered Braille recognition sensing system with long-term survivability and phonic function could provide those people with greatly enhanced access to information and thus improve their living quality. Herein, we develop a skin-like self-powered Braille recognition sensor with self-healing, temperature-resistant and stretchable properties, which is further connected with the designed audio system to realize real-time conversion from mechanical stimulus to electrical signals and then to audio signals. The sensor is fabricated using dynamic interaction-based self-healing materials, which constitute an imine bond-based cross-linked polymer for the triboelectric layer and a hydrogen bond-based organohydrogel for the electrode layer. Moreover, the conductive organohydrogel-based electrode is provided with stretchable, anti-freezing, and non-drying properties. Consequently, minimized impact on the output performance of the sensor is found under mechanical impact, harsh environments and large deformation, enabling a long lifespan, high durability, and good stability. The self-powered sensor can be applied in a Braille recognition system, in which the Braille characters can be further decoded and read out. This work shows a reliable and flexible device with promising prospects in information technology.

Exciton Emissions in Bilayer WSe2 Tuned by the Ferroelectric Polymer.

In this work, a hybrid structure of multilayer transition-metal dichalcogenides (TMDs) and a ferroelectric polymer is designed to achieve passive control of optical properties in situ. The electrical polarization in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer can regulate the photoluminescence (PL) in bilayer WSe2. The total PL emission intensity is substantially suppressed or enhanced under large gate voltage in bilayer WSe2. This is because electrons transfer between the conduction band K valley and the conduction band Λ valley by the electrostatic field in the P(VDF-TrFE) polymer. This electron transfer further adjusts the proportion of direct and indirect excitons and, in turn, changes the overall optical radiation efficiency. We also illustrate that the engineered PL originates from the external electric-field-dependent transferred electron effect. The theoretical result matches the experimental data well. This work demonstrates a device platform in which passive regulation is achieved using 2D TMDs modulated by polarized ferroelectric materials.

Ambipolar Charge Storage in Type-I Core/Shell Semiconductor Quantum Dots toward Optoelectronic Transistor-Based Memories.

Efficient charge storage media play a pivotal role in transistor-based memories and thus are under intense research. In this work, the charge storage ability of type-I InP/ZnS core/shell quantum dots is well revealed through studying a pentacene-based organic transistor with the quantum dots (QDs) integrated. The quantum well-like energy band structure enables the QDs to directly confine either holes or electrons in the core, signifying a dielectric layer-free nonvolatile memory. Especially, the QDs in this device can be charged by electrons using light illumination as the exclusive method. The electron charging process is ascribed to the photoexcitation process in the InP-core and the hot holes induced. The QDs layer demonstrates an electron storage density of ≈5.0 × 1011  cm-2 and a hole storage density of ≈6.4 × 1011  cm-2 . Resultingly, the output device shows a fast response speed to gate voltage (10 µs), large memory window (42 V), good retention (>4.0 × 104 s), and reliable endurance. This work suggests that the core/shell quantum dot as a kind of charge storage medium is of great promise for optoelectronic memories.

Hyperbranched Poly(ester-enamine) from Spontaneous Amino-yne Click Reaction for Stabilization of Gold Nanoparticle Catalysts.

Hyperbranched polymers have garnered much attention due to attractive properties and wide applications, such as drug-controlled release, stimuli-responsive nano-objects, photosensitive materials and catalysts. Herein, two types of novel hyperbranched poly(ester-enamine) (hb-PEEa) were designed and synthesized via the spontaneous amino-yne click reaction of A2 monomer (1, 3-bis(4-piperidyl)-propane (A2a ) or piperazine (A2b )) and B3 monomer (trimethylolpropanetripropiolate). According to Flory's hypothesis, gelation is an intrinsic problem in an ideal A2 +B3 polymerization system. By controlling the polymerization conditions, such as monomer concentration, molar ratio and rate of addition, a non-ideal A2 +B3 polymerization system can be established to avoid gelation and to synthesize soluble hb-PEEa. Due to abundant unreacted alkynyl groups in periphery, the hb-PEEa can be further functionalized by different amino compounds or their derivates. The as-prepared amphiphilic PEG-hb-PEEa copolymer can readily self-assemble into micelles in water, which can be used as surfactant to stabilize Au nanoparticles (AuNPs) during reduction of NaBH4 in aqueous solution. As a demonstration, the as-prepared PEG-hb-PEEa-supported AuNPs demonstrate good dispersion in water, solvent stability and remarkable catalytic activity for reduction of nitrobenzene compounds.

Multifunctional Water Drop Energy Harvesting and Human Motion Sensor Based on Flexible Dual-Mode Nanogenerator Incorporated with Polymer Nanotubes.

In the world of increasing energy consumption, nanogenerators have shown great potential for energy harvesting and self-powered portable electronics. Herein, a flexible and dual-mode triboelectric nanogenerator (TENG) combining both vertical contact-separation and single electrical modes has been developed to convert environmental mechanical energy into electricity using highly encapsulated and multifunctional strategies. By introducing the polymer melt wetting technique, polymer nanotubes are fabricated on the surface of the TENG, which provides self-cleaning and hydrophobic features beneficial for water drop energy harvesting using the device. In such mechanical energy harvesting, the maximum output power of 0.025 mW and the open-circuit voltage of 41 V can be achieved. By designing the dimensions of the device, the dual-mode TENG is utilized as a self-powered sensor to detect human body motions such as phalanges' movement of fingers. The fabricated dual-mode TENG promotes the development of energy-harvesting and self-powered human motion sensors for artificial intelligent prosthetics, human kinematics, and human body recovery treatment.

Enhanced dielectric properties of colossal permittivity co-doped TiO2/polymer composite films.

Colossal permittivity (CP) materials have shown great technological potential for advanced microelectronics and high-energy-density storage applications. However, developing high performance CP materials has been met with limited success because of low breakdown electric field and large dielectric loss. Here, composite films have been developed based on surface hydroxylated ceramic fillers, (Er + Nb) co-doped TiO2 embedded in poly(vinylidene fluoride trifluoroethylene) matrix by a simple technique. We report on simultaneously observing a large dielectric constant up to 300, exceptional low dielectric loss down to 0.04 in the low frequency range, and an acceptable breakdown electric field of 813 kV cm-1 in the composites. Consequently, this work may pave the way for developing highly stable and superior dielectrics through a simple and scalable route to meet requirements of further miniaturization in microelectronic and energy-storage devices.

Temporal and Remote Tuning of Piezophotonic-Effect-Induced Luminescence and Color Gamut via Modulating Magnetic Field.

Light-emitting materials have been extensively investigated because of their widespread applications in solid-state lighting, displays, sensors, and bioimaging. In these applications, it is highly desirable to achieve tunable luminescence in terms of luminescent intensity and wavelength. Here, a convenient physical approach of temporal and remote tuning of light-emitting wavelength and color is demonstrated, which is greatly different from conventional methods. It is shown that by modulating the frequency of magnetic-field excitation at room temperature, luminescence from the flexible composites of ZnS:Al, Cu phosphors induced by the piezophotonic effect can be tuned in real time and in situ. The mechanistic investigation suggests that the observed tunable piezophotonic emission is ascribed to the tilting band structure of the ZnS phosphor induced by magnetostrictive strain under a high frequency of magnetic-field excitation. Furthermore, some proof-of concept devices, including red-green-blue full-color displays and tunable white-light sources are demonstrated simply by frequency modulation. A new understanding of the fundamentals of both luminescence and magnetic-optics coupling is thus provided, while offering opportunities in magnetic-optical sensing, piezophotonics, energy harvesting, novel light sources, and displays.

Energy Device Applications of Synthesized 1D Polymer Nanomaterials.

1D polymer nanomaterials as emerging materials, such as nanowires, nanotubes, and nanopillars, have attracted extensive attention in academia and industry. The distinctive, various, and tunable structures in the nanoscale of 1D polymer nanomaterials present nanointerfaces, high surface-to-volume ratio, and large surface area, which can improve the performance of energy devices. In this review, representative fabrication techniques of 1D polymer nanomaterials are summarized, including electrospinning, template-assisted, template-free, and inductively coupled plasma methods. The recent advancements of 1D polymer nanomaterials in energy device applications are demonstrated. Lastly, existing challenges and prospects of 1D polymer nanomaterials for energy device applications are presented.

Magnetic-Assisted Noncontact Triboelectric Nanogenerator Converting Mechanical Energy into Electricity and Light Emissions.

A magnetic-assisted noncontact triboelectric nanogenerator (TENG) is developed by combining a magnetic responsive layer with a TENG. The novel TENG device is applied to harvest mechanical energy which can be converted into electricity and light emissions. This work has potential for energy harvesting, magnetic sensors, self-powered electronics and optoelectronics applications.

Self-aligned, full solution process polymer field-effect transistor on flexible substrates.

Conventional techniques to form selective surface energy regions on rigid inorganic substrates are not suitable for polymer interfaces due to sensitive and soft limitation of intrinsic polymer properties. Therefore, there is a strong demand for finding a novel and compatible method for polymeric surface energy modification. Here, by employing the confined photo-catalytic oxidation method, we successfully demonstrate full polymer filed-effect transistors fabricated through four-step spin-coating process on a flexible polymer substrate. The approach shows negligible etching effect on polymeric film. Even more, the insulating property of polymeric dielectric is not affected by the method, which is vital for polymer electronics. Finally, the self-aligned full polymer field-effect transistors on the flexible polymeric substrate are fabricated, showing good electrical properties and mechanical flexibility under bending tests.

Surface Decoration on Polymeric Gate Dielectrics for Flexible Organic Field-Effect Transistors via Hydroxylation and Subsequent Monolayer Self-Assembly.

A simple photochemical reaction based on confined photocatalytic oxidation (CPO) treatment and hydrolysis was employed to efficiently convert C-H bonds into C-OH groups on polymeric material surfaces, followed by investigation of monolayer self-assembly decoration on polymeric dielectrics via chemical bonding for the organic field-effect transistors (OFETs) applications. This method is a low temperature process and has negligible etching effect on polymeric dielectric layers. Various types of self-assembled monolayers have been tested and successfully attached onto the hydroxylated polymeric dielectric surfaces through chemical bonding, ensuring the stability of decorated functional films during the subsequent device fabrication consisting of solution processing of the polymer active layer. With the surface decoration of functional groups, both n-type and p-type polymers exhibit enhanced carrier mobilities in the unipolar OFETs. In addition, enhanced and balanced mobilities are obtained in the ambipolar OFETs with the blend of polymer semiconductors. The anchored self-assembled monolayers on the dielectric surfaces dramatically preclude the solvent effect, thus enabling an improvement of carrier mobility up to 2 orders of magnitude. Our study opens a way of targeted modifications of polymeric surfaces and related applications in organic electronics.

Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends.

Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices.

The role of a nanoparticle monolayer on the flow of polymer melts in nanochannels.

Understanding and controlling the flow properties of polymer melts at the nanoscale is of great relevance in fundamental research and in a variety of applications. In the present study we have analysed experimentally the flow behaviour of polymers in nanochannels of varying roughness, produced by gold nanoparticle absorption. The experimental results show that nanochannel roughness has a significant influence on surface energy and on the flow behaviour of polymer melts. These results provide fundamental information on the preparation of one-dimensional polymer nanochannels applicable in both micro- and nano-injection technology.

Poly(3-hexylthiophene) nanotubes with tunable aspect ratios and charge transport properties.

Regioregular poly(3-hexylthiophene) (RR-P3HT) nanotubes (200 nm in diameter) with tunable aspect ratios from 25 to 300 were prepared using a polymer melt wetting technique. Aspect-ratio tunability was achieved by controlling the wetting behavior of RR-P3HT melts in a template. The crystallinity and chain orientation of RR-P3HT were studied by grazing incidence X-ray diffraction, wide-angle X-ray diffraction, and polarized photoluminescence spectroscopy. Results suggest that RR-P3HT chains in the lamellar structure prefer to be perpendicular to the axis of the RR-P3HT nanotubes, forming a face-on conformation in the RR-P3HT nanotubes that leads to increased carrier mobility of RR-P3HT. Field-effect transistors were fabricated based on a single RR-P3HT nanotube and showed a carrier mobility of 0.14 ± 0.02 cm(2)/V·s.

Energy-band engineering for tunable memory characteristics through controlled doping of reduced graphene oxide.

Tunable memory characteristics are used in multioperational mode circuits where memory cells with various functionalities are needed in one combined device. It is always a challenge to obtain control over threshold voltage for multimode operation. On this regard, we use a strategy of shifting the work function of reduced graphene oxide (rGO) in a controlled manner through doping gold chloride (AuCl3) and obtained a gradient increase of rGO work function. By inserting doped rGO as floating gate, a controlled threshold voltage (Vth) shift has been achieved in both p- and n-type low voltage flexible memory devices with large memory window (up to 4 times for p-type and 8 times for n-type memory devices) in comparison with pristine rGO floating gate memory devices. By proper energy band engineering, we demonstrated a flexible floating gate memory device with larger memory window and controlled threshold voltage shifts.

Solution processed molecular floating gate for flexible flash memories.

Solution processed fullerene (C60) molecular floating gate layer has been employed in low voltage nonvolatile memory device on flexible substrates. We systematically studied the charge trapping mechanism of the fullerene floating gate for both p-type pentacene and n-type copper hexadecafluorophthalocyanine (F16CuPc) semiconductor in a transistor based flash memory architecture. The devices based on pentacene as semiconductor exhibited both hole and electron trapping ability, whereas devices with F16CuPc trapped electrons alone due to abundant electron density. All the devices exhibited large memory window, long charge retention time, good endurance property and excellent flexibility. The obtained results have great potential for application in large area flexible electronic devices.