Bio-Inspired Pangolin Design for Self-Healable Flexible Perovskite Light-Emitting Diodes.

Despite tremendous developments in the luminescene performance of perovskite light-emitting diodes (PeLEDs), the brittle nature of perovskite crystals and their poor crystallinity on flexible substrates inevitably lead to inferior performance. Inspired by pangolins' combination of rigid scales and soft flesh, we propose a bionic structure design for self-healing flexible PeLEDs by employing a polymer-assisted crystal regulation method with a soft elastomer of diphenylmethane diisocyanate polyurethane (MDI-PU). The crystallinity and flexural strain resistance of such perovskite films on plastics with silver-nanowire-based flexible transparent electrodes are highly enhanced. The detrimental cracks induced during repeated deformation can be effectively self-healed under heat treatment via intramolecular/intermolecular hydrogen bonds with MDI-PU. Upon collective optimization of the perovskite films and device architecture, the blue-emitting flexible PeLEDs can achieve a record external quantum efficiency of 13.5% and high resistance to flexural strain, which retain 87.8 and 80.7% of their initial efficiency after repeated bending and twisting operations of 2000 cycles, respectively.

Research Progress of Intramolecular π-Stacked Small Molecules for Device Applications.

Organic semiconductors can be designed and constructed in π-stacked structures instead of the conventional π-conjugated structures. Through-space interaction (TSI) occurs in π-stacked optoelectronic materials. Thus, unlike electronic coupling along the conjugated chain, the functional groups can stack closely to facilitate spatial electron communication. Using π-stacked motifs, chemists and materials scientists can find new ways for constructing materials with aggregation-induced emission (AIE), thermally activated delayed fluorescence (TADF), circularly polarized luminescence (CPL), and room-temperature phosphorescence (RTP), as well as enhanced molecular conductance. Organic optoelectronic devices based on π-stacked molecules have exhibited very promising performance, with some of them exceeding π-conjugated analogues. Recently, reports on various organic π-stacked structures have grown rapidly, prompting this review. Representative molecular scaffolds and newly developed π-stacked systems could stimulate more attention on through-space charge transfer the well-known through-bond charge transfer. Finally, the opportunities and challenges for utilizing and improving particular materials are discussed. The previous achievements and upcoming prospects may provide new insights into the theory, materials, and devices in the field of organic semiconductors.

The Inhibition of SARS-CoV-2 3CL Mpro by Graphene and Its Derivatives from Molecular Dynamics Simulations.

At present, the most powerful new drugs for COVID-19 are antibody proteins. In addition, there are some star small molecule drugs. However, there are few studies on nanomaterials. Here, we study the intact graphene (IG), defective graphene (DG), and graphene oxide (GO) interacting with COVID-19 protein. We find that they show progressive inhibition of COVID-19 protein. By using molecular dynamics simulations, we study the interactions between SARS-CoV-2 3CL Mpro and graphene-related materials (GRMs): IG, DG, and GO. The results show that Mpro can be absorbed onto the surfaces of investigated materials. DG and GO interacted with Mpro more intensely, causing the decisive part of Mpro to become more flexible. Further analysis shows that compared to IG and GO, DG can inactivate Mpro and inhibit its expression effectively by destroying the active pocket of Mpro. Our work not only provides detailed and reliable theoretical guidance for the application of GRMs in treating with SARS-CoV-2 but also helps in developing new graphene-based anti-COVID-19 materials.

Bioinspired Hierarchical Nanofabric Electrode for Silicon Hydrovoltaic Device with Record Power Output.

Direct electricity generation from water flow/evaporation, coined hydrovoltaic effect, has recently attracted intense interest as a facile approach to harvest green energy from ubiquitous capillary water flow or evaporation. However, the current hydrovoltaic device is inferior in output power efficiency compared to other renewable energy devices. Slow water evaporation rate and inefficient charge collection at device electrodes are two fundamental drawbacks limiting energy output efficiency. Here, we report a bioinspired hierarchical porous fabric electrode that enables high water evaporation rate, efficient charge collection, and rapid charge transport in nanostructured silicon-based hydrovoltaic devices. Such an electrode can efficiently collect charges generated in nanostructured silicon as well as induce a prompt water evaporation rate. At room temperature, the device can generate an open-circuit voltage (Voc) of 550 mV and a short-current density (Jsc) of 22 µA·cm-2. It can output a power density over 10 µW·cm-2, which is 3 orders of magnitude larger than all those reported for analogous hydrovoltaic devices. Our results could supply an effective strategy for the development of high-performance hydrovoltaic devices through optimizing electrode structures.

Single Vanadium Atoms Anchored on Graphitic Carbon Nitride as a High-Performance Catalyst for Non-oxidative Propane Dehydrogenation.

In comparison with oil-based cracking technologies, the on-purpose dehydrogenation of propane (PDH) is a more eco-friendly and profitable approach to produce propylene. By means of density functional theory calculations, the present work reveals that the single vanadium (V) atom anchored on graphitic carbon nitride (V1/g-C3N4) may serve as a promising single-atom catalyst for non-oxidative PDH with industrially practical activity, selectivity, and thermal stability. The high activity of V1/g-C3N4 for PDH is attributed to the low-coordinated 3d orbitals of single V atoms, while the propylene selectivity is originated from the inhibition of the di-σ binding mode of propylene on the single V atoms. This work provides a guideline to design and screen out promising single-atom catalysts for selective dehydrogenation of alkanes.

Rational Interface Engineering for Efficient Flexible Perovskite Light-Emitting Diodes.

Although perovskite light-emitting diodes (PeLEDs) are promising for next-generation displays and lighting, their efficiency is still considerably below that of conventional inorganic and organic counterparts. Significant efforts in various aspects of the electroluminescence process are required to achieve high-performance PeLEDs. Here, we present an improved flexible PeLED structure based on the rational interface engineering for energy-efficient photon generation and enhanced light outcoupling. The interface-stimulated crystallization and defect passivation of the perovskite emitter are synergistically realized by tuning the underlying interlayer, leading to the suppression of trap-mediated nonradiative recombination losses. Besides approaching highly emissive perovskite layers, the outcoupling of trapped light is also enhanced by combining the silver nanowires-based electrode with quasi-random nanopatterns on flexible plastic substrate. Upon the collective optimization of the device structure, a record external quantum efficiency of 24.5% is achieved for flexible PeLEDs based on green-emitting CsPbBr3 perovskite.

Carbon dots: advances in nanocarbon applications.

Carbon dots (C-Dots), defined by characteristic sizes of <10 nm, have become a rising star in carbon nanomaterials. C-Dots possess many unique physiochemical and photochemical properties which make them a promising platform for imaging, environmental, catalytic, biological and energy-related applications. To date, C-Dots have been investigated extensively, and their related applications have developed rapidly. However, quantitative understanding of the physiochemical properties of C-Dots still remains a difficult challenge because of their complex structures. Here, we will highlight the recent progress in the practical applications of C-Dots, with particular attention to the research in light-emitting devices, bioimaging and biodetection, catalysis, functional materials, and agriculture.

Dual-Band, High-Performance Phototransistors from Hybrid Perovskite and Organic Crystal Array for Secure Communication Applications.

High-performance phototransistors made from organic semiconductor single crystals (OSSCs) have attracted much attention due to the high responsivity and solution-processing capability of OSSCs. However, OSSC-based phototransistors capable of dual-band spectral response remain a difficult challenge to achieve because organic semiconductors usually possess only narrow single-band absorption. Here, we report the fabrication of high-performance, dual-band phototransistors from a hybrid structure of a 2,7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C8-BTBT) single-crystal array coated with CH3NH3PbI3 nanoparticles (NPs) synthesized by a simple, one-step solution method. In contrast to C8-BTBT and CH3NH3PbI3 NPs with respective absorption in the ultraviolet (UV) and visible (vis) region, their hybrid structure shows broad absorption covering the entire UV-vis range. The hybrid-based phototransistors exhibit an ultrahigh responsivity of >1.72 × 104 A/W in the 252-780 nm region, which represents the best performance for solution-processing, broadband photodetectors. Moreover, integrated phototransistor circuitries from the hybrid CH3NH3PbI3 NPs/C8-BTBT single-crystal array show applications for high-security communication.

Single atom tungsten doped ultrathin α-Ni(OH)2 for enhanced electrocatalytic water oxidation.

Electrocatalytic water oxidation is a rate-determining step in the water splitting reaction. Here, we report one single atom W6+ doped Ni(OH)2 nanosheet sample (w-Ni(OH)2) with an outstanding oxygen evolution reaction (OER) performance that is, in a 1 M KOH medium, an overpotential of 237 mV is obtained reaching a current density of 10 mA/cm2. Moreover, at high current density of 80 mA/cm2, the overpotential value is 267 mV. The corresponding Tafel slope is measured to be 33 mV/dec. The d0 W6+ atom with a low spin-state has more outermost vacant orbitals, resulting in more water and OH- groups being adsorbed on the exposed W sites of the Ni(OH)2 nanosheet. Density functional theory (DFT) calculations confirm that the O radical and O-O coupling are both generated at the same site of W6+. This work demonstrates that W6+ doping can promote the electrocatalytic water oxidation activity of Ni(OH)2 with the highest performance.

High-Efficiency Perovskite Light-Emitting Diodes with Synergetic Outcoupling Enhancement.

Perovskite light-emitting diodes (PeLEDs) show great application potential in high-quality flat-panel displays and solid-state lighting due to their steadily improved efficiency, tunable colors, narrow emission peak, and easy solution-processing capability. However, because of high optical confinement and nonradiative charge recombination during electron-photon conversion, the highest reported efficiency of PeLEDs remains far behind that of their conventional counterparts, such as inorganic LEDs, organic LEDs, and quantum-dot LEDs. Here a facile route is demonstrated by adopting bioinspired moth-eye nanostructures at the front electrode/perovskite interface to enhance the outcoupling efficiency of waveguided light in PeLEDs. As a result, the maximum external quantum efficiency and current efficiency of the modified cesium lead bromide (CsPbBr3 ) green-emitting PeLEDs are improved to 20.3% and 61.9 cd A-1 , while retaining spectral and angular independence. Further reducing light loss in the substrate mode using a half-ball lens, efficiencies of 28.2% and 88.7 cd A-1 are achieved, which represent the highest values reported to date for PeLEDs. These results represent a substantial step toward achieving practical applications of PeLEDs.

Memory phototransistors based on exponential-association photoelectric conversion law.

Ultraweak light detectors have wide-ranging important applications such as astronomical observation, remote sensing, laser ranging, and night vision. Current commercial ultraweak light detectors are commonly based on a photomultiplier tube or an avalanche photodiode, and they are incompatible with microelectronic devices for digital imaging applications, because of their high operating voltage and bulky size. Herein, we develop a memory phototransistor for ultraweak light detection, by exploiting the charge-storage accumulative effect in CdS nanoribbon. The memory phototransistors break the power law of traditional photodetectors and follow a time-dependent exponential-association photoelectric conversion law. Significantly, the memory phototransistors exhibit ultrahigh responsivity of 3.8 × 109 A W-1 and detectivity of 7.7 × 1022 Jones. As a result, the memory phototransistors are able to detect ultraweak light of 6 nW cm-2 with an extremely high sensitivity of 4 × 107. The proposed memory phototransistors offer a design concept for ultraweak light sensing devices.

Approaching the Volcano Top: Iridium/Silicon Nanocomposites as Efficient Electrocatalysts for the Hydrogen Evolution Reaction.

Electrolysis of water to generate hydrogen is an important issue for the industrial production of green and sustainable energy. The best electrocatalyst currently available for the hydrogen evolution reaction (HER) is platinum. We herein show that iridium can be manipulated to achieve a record high HER activity surpassing platinum in every aspect: a lower overpotential at any given current density, a higher current density, and mass activity for all bias potentials applied and a catalyst cost reduction of 50% for the same hydrogen generation rate. The superior HER activity was achieved by a binary Ir/Si nanowire catalyst design in which (as density functional theory calculations show) two distinct strategies act in synergy: (i) decreasing the size of the iridium nanoparticles to ∼2.2 nm and (ii) dividing the H2-generation process to three steps occurring on two different catalysts: H adsorption on iridium, H diffusion to silicon, and H2 desorption from silicon.

In-plane anisotropic and ultra-low-loss polaritons in a natural van der Waals crystal.

Polaritons-hybrid light-matter excitations-enable nanoscale control of light. Particularly large polariton field confinement and long lifetimes can be found in graphene and materials consisting of two-dimensional layers bound by weak van der Waals forces1,2 (vdW materials). These polaritons can be tuned by electric fields3,4 or by material thickness5, leading to applications including nanolasers6, tunable infrared and terahertz detectors7, and molecular sensors8. Polaritons with anisotropic propagation along the surface of vdW materials have been predicted, caused by in-plane anisotropic structural and electronic properties9. In such materials, elliptic and hyperbolic in-plane polariton dispersion can be expected (for example, plasmon polaritons in black phosphorus9), the latter leading to an enhanced density of optical states and ray-like directional propagation along the surface. However, observation of anisotropic polariton propagation in natural materials has so far remained elusive. Here we report anisotropic polariton propagation along the surface of α-MoO3, a natural vdW material. By infrared nano-imaging and nano-spectroscopy of semiconducting α-MoO3 flakes and disks, we visualize and verify phonon polaritons with elliptic and hyperbolic in-plane dispersion, and with wavelengths (up to 60 times smaller than the corresponding photon wavelengths) comparable to those of graphene plasmon polaritons and boron nitride phonon polaritons3-5. From signal oscillations in real-space images we measure polariton amplitude lifetimes of 8 picoseconds, which is more than ten times larger than that of graphene plasmon polaritons at room temperature10. They are also a factor of about four larger than the best values so far reported for phonon polaritons in isotopically engineered boron nitride11 and for graphene plasmon polaritons at low temperatures12. In-plane anisotropic and ultra-low-loss polaritons in vdW materials could enable directional and strong light-matter interactions, nanoscale directional energy transfer and integrated flat optics in applications ranging from bio-sensing to quantum nanophotonics.

Triboelectric Nanogenerator Driven Self-Powered Photoelectrochemical Water Splitting Based on Hematite Photoanodes.

Hematite is one of the most promising photoanodes for photoelectrochemical (PEC) solar water splitting. However, due to the low conduction band position for water reduction, an external bias is necessarily required with the consumption of extra power. In this work, a titanium modified hematite (Ti-Fe2O3) photoanode-based self-powered PEC water splitting system in tandem with a rotatory disc-shaped triboelectric nanogenerator (RD-TENG) has been developed. It is a fantastic strategy to effectively drive the hematite-based PEC water splitting by using the environmental mechanical energy through a TENG. When the rotation speed is 65 rpm (water flowing rate ∼0.61 m/s), the peak current reaches to 0.12 mA under illumination contrast to that in the dark with almost zero. As for 80 rpm, the peak currents are 0.17 and 0.33 mA in the dark or under illumination, respectively, indicating the simultaneous occurrence of electrolysis and PEC water splitting. When higher than 120 rpm, the peak current in the dark is nearly equal to that under illumination, which can be attributed to the high enough peak voltage for direct electrolysis of water. Such a self-powered PEC water splitting system provides an alternative strategy that enables to convert both solar and mechanical energies into chemical energies.

Precise Patterning of Laterally Stacked Organic Microbelt Heterojunction Arrays by Surface-Energy-Controlled Stepwise Crystallization for Ambipolar Organic Field-Effect Transistors.

Ambipolar organic field-effect transistors (OFETs) combining single-crystalline p- and n-type organic micro/nanocrystals have demonstrated superior performance to their amorphous or polycrystalline thin-film counterparts. However, large-area alignment and precise patterning of organic micro/nanocrystals for ambipolar OFETs remain challenges. Here, a surface-energy-controlled stepwise crystallization (SECSC) method is reported for large-scale, aligned, and precise patterning of single-crystalline laterally stacked p-n heterojunction microbelt (MB) arrays. In this method, the p- and n-type organic crystals are precipitated via a stepwise process: first, the lateral sides of prepatterned photoresist stripes provide high-surface-energy sites to guide the aligned growth of p-type organic crystals. Next, the formed p-type crystals serve as new high-surface-energy positions to induce the crystallization of n-type organic molecules at their sides, thus leading to the formation of laterally stacked p-n microbelts. Ambipolar OFETs based on the p-n heterojunction MB arrays exhibit balanced hole and electron mobilities of 0.32 and 0.43 cm2 V-1 s-1 , respectively, enabling the fabrication of complementary-like inverters with large voltage gains. This work paves the way toward rational design and construction of single-crystalline organic p-n heterojunction arrays for high-performance organic, integrated circuits.

Buried MoO x/Ag Electrode Enables High-Efficiency Organic/Silicon Heterojunction Solar Cells with a High Fill Factor.

Silicon (Si)/organic heterojunction solar cells based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n-type Si have attracted wide interests because they promise cost-effectiveness and high-efficiency. However, the limited conductivity of PEDOT:PSS leads to an inefficient hole transport efficiency for the heterojunction device. Therefore, a high dense top-contact metal grid electrode is required to assure the efficient charge collection efficiency. Unfortunately, the large metal grid coverage ratio electrode would lead to undesirable optical loss. Here, we develop a strategy to balance PEDOT:PSS conductivity and grid optical transmittance via a buried molybdenum oxide/silver grid electrode. In addition, the grid electrode coverage ratio is optimized to reduce its light shading effect. The buried electrode dramatically reduces the device series resistance, which leads to a higher fill factor (FF). With the optimized buried electrode, a record FF of 80% is achieved for flat Si/PEDOT:PSS heterojunction devices. With further enhancement adhesion between the PEDOT:PSS film and Si substrate by a chemical cross-linkable silance, a power conversion efficiency of 16.3% for organic/textured Si heterojunction devices is achieved. Our results provide a path to overcome the inferior organic semiconductor property to enhance the organic/Si heterojunction solar cell.

Integrating a Silicon Solar Cell with a Triboelectric Nanogenerator via a Mutual Electrode for Harvesting Energy from Sunlight and Raindrops.

Solar cells, as promising devices for converting light into electricity, have a dramatically reduced performance on rainy days. Here, an energy harvesting structure that integrates a solar cell and a triboelectric nanogenerator (TENG) device is built to realize power generation from both sunlight and raindrops. A heterojunction silicon (Si) solar cell is integrated with a TENG by a mutual electrode of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film. Regarding the solar cell, imprinted PEDOT:PSS is used to reduce light reflection, which leads to an enhanced short-circuit current density. A single-electrode-mode water-drop TENG on the solar cell is built by combining imprinted polydimethylsiloxane (PDMS) as a triboelectric material combined with a PEDOT:PSS layer as an electrode. The increasing contact area between the imprinted PDMS and water drops greatly improves the output of the TENG with a peak short-circuit current of ∼33.0 nA and a peak open-circuit voltage of ∼2.14 V, respectively. The hybrid energy harvesting system integrated electrode configuration can combine the advantages of high current level of a solar cell and high voltage of a TENG device, promising an efficient approach to collect energy from the environment in different weather conditions.