Electrochromic Devices Based on 2D MoO3-x/PEDOT:PSS Composite Film with Boosted Ion Transport.

Electrochromic materials allow for optical modulation and have attracted much attention due to their bright future in applications such as smart windows and energy-saving displays. Two-dimensional (2D) molybdenum oxide nanoflakes with combined advantages of high active specific surface area and natural layered structure should be highly potential candidates for electrochromic devices. However, the efficient top-down preparation of 2D MoO3 nanoflakes is still a huge challenge and the sluggish ionic kinetics hinder its electrochromic performance. Herein, we demonstrated a feasible thiourea-assisted exfoliation procedure, which can not only increase the yield but also reduce the thickness of 2D MoO3-x nanoflakes down to a few nanometers. Furthermore, electrophoretic-deposited MoO3-x nanoflakes were combined with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-conjugated polymer to simultaneously enhance the ionic kinetics and electronic conductivity, with a diffusion coefficient of 3.09 × 10-10 cm2 s-1 and a charge transport resistance of 33.7 Ω. The prepared 2D MoO3-x/PEDOT:PSS composite films exhibit improved electrochromic performance, including fast switching speed (7 s for bleaching, 5 s for coloring), enhanced coloration efficiency (87.1 cm2 C-1), and large transmittance modulation (ΔT = 65%). This study shows outstanding potential for 2D MoO3-x nanoflakes in electrochromic applications and opens new avenues for optimizing the ion transport in inorganic-organic composites, which will be possibly inspired for other electrochemical devices.

Suppressing Carrier Recombination in BiVO4/PEDOT:PSS Heterojunction for High-Performance Photodetector.

The organic-inorganic hybrid heterojunction is introduced for the first time to break through the performance bottleneck of BiVO4-based photodetectors. Through a facile solution process, a p-n heterojunction is established at the BiVO4/PEDOT:PSS interface, and the built-in electric field is designed to separate photogenerated charge carriers. The hybrid heterojunction outputs a significantly increased photocurrent, which is 24 000 times larger than that of the bare BiVO4 thin film. The photodetector shows a satisfactory performance with a responsivity (R) and specific detectivity (D*) of 107.8 mA/W and 4.13 × 1010 Jones at 482 nm illumination. In addition to the fast response speed (100 ms), the device also exhibits an impressive long-term stability with a negligible attenuation in photocurrent after more than 700 cycles. This work provides a novel strategy to suppress carrier recombination of BiVO4, and the coupling of metal oxides and organic semiconductors opens up a new avenue for fabricating high-performance photodetectors.

Optoelectronic Synapses Based on MXene/Violet Phosphorus van der Waals Heterojunctions for Visual-Olfactory Crossmodal Perception.

The crossmodal interaction of different senses, which is an important basis for learning and memory in the human brain, is highly desired to be mimicked at the device level for developing neuromorphic crossmodal perception, but related researches are scarce. Here, we demonstrate an optoelectronic synapse for vision-olfactory crossmodal perception based on MXene/violet phosphorus (VP) van der Waals heterojunctions. Benefiting from the efficient separation and transport of photogenerated carriers facilitated by conductive MXene, the photoelectric responsivity of VP is dramatically enhanced by 7 orders of magnitude, reaching up to 7.7 A W-1. Excited by ultraviolet light, multiple synaptic functions, including excitatory postsynaptic currents, paired-pulse facilitation, short/long-term plasticity and "learning-experience" behavior, were demonstrated with a low power consumption. Furthermore, the proposed optoelectronic synapse exhibits distinct synaptic behaviors in different gas environments, enabling it to simulate the interaction of visual and olfactory information for crossmodal perception. This work demonstrates the great potential of VP in optoelectronics and provides a promising platform for applications such as virtual reality and neurorobotics.

From waste carbonated beverages to high performance electrochromic devices: a green and low-cost synthetic method for self-doped metal oxides.

Metal oxides with reversible optical modulation capability are in the spotlight for smart windows and other emerging optoelectronic devices. Improving the electrochromic performance at a low cost is the only way to popularize their applications. Herein, we demonstrate a facile and versatile strategy to synthesize high-performance electrochromic metal oxides, in which waste carbonated beverages are used as the raw materials for the first time. It can not only reduce the production cost of electrochromic materials, but also alleviate the environmental pollution caused by such liquid waste. With an ingenious carbonization pre-step, both nanoscale pores and oxygen vacancies are created in an annealed tungsten oxide thin film. Multiscale structure optimization endows the self-doped WO3-x films with excellent electrochromic properties such as large transmittance modulation (81.2%), high coloration efficiency (98.7 cm2 C-1) and good cycling stability. DFT calculations show that oxygen vacancies reduce the Li+ ion insertion energy barrier, which is conducive to the interfacial reaction in coloring and bleaching processes. Moreover, this approach is universal to other oxides such as vanadium pentoxide, molybdenum oxide and nickel oxide. The waste-to-value concept paves the way for cost-effective electrochromic materials and sheds light on the multiscale optimization of superior metal oxides.

Temperature-Dependent Electrochromic Devices for Energy-Saving Dual-Mode Displays.

Electrochromic (EC) devices show promising prospects with the increasing demand for energy-efficient and sustainable technologies. Multifunctionality integration is an inevitable characteristic for EC devices to adapt to changing environments. Herein, a dual-mode temperature-dependent EC device is demonstrated for the first time. Combined with the transparent PVA/EG-ZnCl2 organohydrogel electrolyte, the devices exhibit good EC performances over a wide temperature range (-40 to 40 °C). The evolutions of ion/electron transport kinetics-related indicators with temperature are further explored and simulated to reveal the mechanism of the temperature dependence of EC devices. Significantly, the optimized tungsten oxide-based EC device shows high performances at the extremely low temperature of -40 °C with a large transmittance modulation (80.8% @660 nm) and outstanding optical memory effects (97.3% retention of the initial transmittance modulation after 32 h) without electrical energy consumption. Furthermore, with a perovskite quantum dot photoluminescence film serving as the backlight, the device can switch display modes between emissive and reflective to realize its functionality in bright or dark conditions. This work provides a broad application prospect for EC devices in diverse environments of light (bright/dark) and temperature (hot/cold).

A self-powered photoelectrochemical ultraviolet photodetector based on Ti3C2Tx/TiO2in situformed heterojunctions.

Transition metal carbides and nitrides (MXenes), as a large family of emerging two-dimensional materials, have demonstrated extraordinary performance in many fields such as electronics, optics and energy storage. However, their susceptibility to oxidation during preparation and storage in ambient air environment is undesirable for long-term and stable applications. Here, we have demonstrated that the spontaneous oxidation of Ti3C2Txcan be harnessed ingeniously to prepare Ti3C2Tx/TiO2in situformed heterojunctions. Furthermore, a self-powered ultraviolet photodetector was constructed based on the photoelectrochemical performance of Ti3C2Tx/TiO2heterojunctions. Since the highly conductive Ti3C2Txcan promote the separation and transfer of photogenerated carriers in TiO2, the prepared photodetector exhibits high responsivity (2.06 mA W-1), short rise and decay times (45 and 69 ms) and long-term stability. This work demonstrates the controllable synthesis of Ti3C2Tx/TiO2heterojunctions and provides a new promising potential of MXenes for photodetection applications.

Self-Powered Rewritable Electrochromic Display based on WO3-x Film with Mechanochemically Synthesized MoO3-y Nanosheets.

Electrochromic displays with bistable color states provide a promising means toward transparent human-machine interfaces. However, the need for external power and the weak optical modulation in the visible light region of most electrochromic devices hinder their practical applications in displays. Here we prepare the MoO3-y/WO3-x films based on MoO3-y nanosheets, which show a dark blue color that matches the response of the eye and meets visual comfort standards compared to pure WO3-x film. By introducing the highly transparent Al3+ ion hydrogel layer, a convenient electrochromic device driven by the internal chemical potential has been designed. The device based on the MoO3-y /WO3-x film exhibits a high optical modulation in the whole visible light range and can operate at self-powered mode with fast response speed and excellent cycle stability. Moreover, we develop an ionic writing board based on the MoO3-y/WO3-x film to surmount the fixed display information issue in conventional electrochromic displays. The ionic writing board exhibits excellent visual display quality and realizes arbitrary writing with a self-powered characteristic. This work provides a simple mechanochemical synthesis procedure of MoO3-y nanosheets and an ingenious design of self-powered electrochromic devices, which will enable the development of next-generation high-performance electrochromic displays.

Boosting Transport Kinetics of Ions and Electrons Simultaneously by Ti3C2Tx (MXene) Addition for Enhanced Electrochromic Performance.

Electrochromic technology plays a significant role in energy conservation, while its performance is greatly limited by the transport behavior of ions and electrons. Hence, an electrochromic system with overall excellent performances still need to be explored. Initially motivated by the high ionic and electronic conductivity of transition metal carbide or nitride (MXene), we design a feasible procedure to synthesize the MXene/WO3-x composite electrochromic film. The consequently boosted electrochromic performances prove that the addition of MXene is an effective strategy for simultaneously enhancing electrons and ions transport behavior in electrochromic layer. The MXene/WO3-x electrochromic device exhibits enhanced transmittance modulation and coloration efficiency (60.4%, 69.1 cm2 C-1), higher diffusion coefficient of Li+ and excellent cycling stability (200 cycles) over the pure WO3-x device. Meanwhile, numerical stimulation theoretically explores the mechanism and kinetics of the lithium ion diffusion, and proves the spatial and time distributions of higher Li+ concentration in MXene/WO3-x composite electrochromic layer. Both experiments and theoretical data reveal that the addition of MXene is effective to promote the transport kinetics of ions and electrons simultaneously and thus realizing a high-performance electrochromic device. This work opens new avenues for electrochromic materials design and deepens the study of kinetics mechanism of ion diffusion in electrochromic devices.

A highly transparent humidity sensor with fast response speed based on α-MoO3 thin films.

Metal oxide based humidity sensors are important indicators in environmental monitoring. However, most of them are non-transparent and have a long response time, which cannot meet the application of real-time humidity sensing in transparent electronics. Here, we report a metal oxide humidity sensor based on chemically synthesized molybdenum oxide (α-MoO3) thin films. By a green reaction in an ice water bath, the stable precursor containing nanocrystalline colloids was obtained. Molybdenum oxide films with controllable morphology were fabricated through one-step spin coating. The α-MoO3 based humidity sensor exhibits extremely high transparency (85%) in the visible region and has short response and recovery times (0.97 and 12.11 s). In addition, it also shows high sensitivity, good logarithmic linearity and selectivity in a wide relative humidity range of 11% to 95%. The mechanism of humidity sensing was further studied by complex impedance spectroscopy. This novel metal oxide humidity sensor combined with high transparency and fast response speed is expected to broaden the application ranges of humidity sensors.

Torus-Event-Based Fault Diagnosis for Stochastic Multirate Time-Varying Systems With Constrained Fault.

In this paper, the torus-event-based fault detection and isolation (FDI) problem is investigated for a class of time-varying multirate systems. An ellipsoidal constraint is first adopted to describe the fault in a more practical pattern, and a novel torus-event-triggering scheme is proposed to improve the unilateral triggering mechanism. The aim is to design the torus-event-based fault detection filter and fault isolation estimators such that both the prescribed variance constraint on the estimation error and the desired H∞ performance on the disturbance are guaranteed over the finite horizon. Especially, the residual evaluation function is employed to detect the fault, and the residual matching function is developed to isolate the fault. Furthermore, three optimization problems are provided to seek separately the minimal parameters on the H∞ performance level, the upper bound of the estimation error variance, and the triggering torus. Finally, two simulation examples are utilized to show the effectiveness of the FDI scheme proposed in this paper.

High-performance stretchable photodetector based on CH3NH3PbI3 microwires and graphene.

A stretchable photodetector was fabricated by releasing a prestrained 3 M very high bond (VHB) substrate coated with perovskite CH3NH3PbI3 microwires and graphene. The light harvesting CH3NH3PbI3 microwires were realized through a transformation from CH3NH3PbI3 bulk single crystals. Graphene served as an expressway for photoinduced carriers in the perovskite. Under a very low working voltage bias of 0.01 V and irradiance power of 13.5 mW cm-2 under 785 nm laser illumination, the responsivity could be as high as 2.2 mA W-1. When the device was stretched up to 30%, 50%, and 80% strain, the responsivity was maintained at 0.96, 0.60, and 0.21 mA W-1, respectively. It also showed a fast photoresponse (<0.12 s) after stretching to 10%, 30%, 50%, 80%, and even to 100%. The device performed well after 100 cycles of stretching to 50% strain.

Piezoelectric Property of a Tetragonal (Ba,Ca)(Zr,Ti)O3 Single Crystal and Its Fine-Domain Structure.

A tetragonal (Ba,Ca)(Zr,Ti)O3 (BCZT) single crystal was grown by a flux method, and the piezoelectric coefficient ( d33) was characterized. The piezoelectric response was proved to be associated with polarization extension, which was successfully used to explain the variation in d33*. From the intrinsic aspect, the compositional effect on Landau free-energy profiles was discussed, showing an "extender" nature of the as-grown crystal and the increasing tendency of structural instability toward the morphotropic phase boundary. From the extrinsic aspect, the evolution of domain structure under various external fields (electric and temperature) was studied, revealing that the fine-domain structure of the as-grown BCZT single crystal was stable to E-field and temperature. The results manifest possibilities of further improving the piezoelectric property of the BCZT single crystal, which requires optimization of the crystal growth technique in future work.

Fault prediction for nonlinear stochastic system with incipient faults based on particle filter and nonlinear regression.

This paper is concerned with the fault prediction for the nonlinear stochastic system with incipient faults. Based on the particle filter and the reasonable assumption about the incipient faults, the modified fault estimation algorithm is proposed, and the system state is estimated simultaneously. According to the modified fault estimation, an intuitive fault detection strategy is introduced. Once each of the incipient fault is detected, the parameters of which are identified by a nonlinear regression method. Then, based on the estimated parameters, the future fault signal can be predicted. Finally, the effectiveness of the proposed method is verified by the simulations of the Three-tank system.

An Origami Perovskite Photodetector with Spatial Recognition Ability.

Flexible photodetectors are attracting substantial attention because of their promising applications in bendable display and smart clothes which cannot be fulfilled by the existing rigid counterparts. In this work, we demonstrate a newly designed photodetector constructed on the common printing paper. Pencil trace was applied as the graphite electrode. With such a simple and convenient method, the as-prepared photodetector exhibited a satisfactory responsivity of 4.4 mA/W, on/off current ratio of 32, coupled with a high response speed of <10 ms. It also demonstrated excellent mechanical flexibility and durability. Most inspiringly, by an ingenious origami, we created the first perovskite photodetector with a 3D configuration. The cubic photodetector array displayed an excellent spatial recognition ability which could not be achieved in all the previously reported 2D photodetectors. Such a fusion of materials science and the art of origami provides a robust strategy for the design of low-cost flexible electronics, especially for the applications in 3D configurations.

Self-Powered Ultrabroadband Photodetector Monolithically Integrated on a PMN-PT Ferroelectric Single Crystal.

Photodetectors capable of detecting two or more bands simultaneously with a single system have attracted extensive attentions because of their critical applications in image sensing, communication, and so on. Here, we demonstrate a self-powered ultrabroadband photodetector monolithically integrated on a 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-28PT) single crystal. By combining the optothermal and pyroelectric effect, the multifunctional PMN-28PT single crystal can response to a wide wavelength range from UV to terahertz (THz). At room temperature, the photodetector could generate a pyroelectric current under the intermittent illumination of incident light in absence of external bias. A systematic study of the photoresponse was investigated. The pyroelectric current shows an almost linear relationship to illumination intensity. Benefiting from the excellent pyroelectric property of PMN-28PT single crystal and the optimized device architecture, the device exhibited a dramatic improvement in operation frequency up to 3 kHz without any obvious degradation in sensitivity. Such a self-powered photodetector with ultrabroadband response may open a window for the novel application of ferroelectric materials in optoelectronics.

Infrared light gated MoS2 field effect transistor.

Molybdenum disulfide (MoS2) as a promising 2D material has attracted extensive attentions due to its unique physical, optical and electrical properties. In this work, we demonstrate an infrared (IR) light gated MoS2 transistor through a device composed of MoS2 monolayer and a ferroelectric single crystal Pb(Mg(1/3)Nb(2/3))O3-PbTiO3 (PMN-PT). With a monolayer MoS2 onto the top surface of (111) PMN-PT crystal, the drain current of MoS2 channel can be modulated with infrared illumination and this modulation process is reversible. Thus, the transistor can work as a new kind of IR photodetector with a high IR responsivity of 114%/Wcm⁻². The IR response of MoS2 transistor is attributed to the polarization change of PMN-PT single crystal induced by the pyroelectric effect which results in a field effect. Our result promises the application of MoS2 2D material in infrared optoelectronic devices. Combining with the intrinsic photocurrent feature of MoS2 in the visible range, the MoS2 on ferroelectric single crystal may be sensitive to a broadband wavelength of light.

A high performance triboelectric nanogenerator for self-powered non-volatile ferroelectric transistor memory.

We demonstrate an integrated module of self-powered ferroelectric transistor memory based on the combination of a ferroelectric FET and a triboelectric nanogenerator (TENG). The novel TENG was made of a self-assembled polystyrene nanosphere array and a poly(vinylidene fluoride) porous film. Owing to this unique structure, it exhibits an outstanding performance with an output voltage as high as 220 V per cycle. Meanwhile, the arch-shaped TENG is shown to be able to pole a bulk ferroelectric 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) single crystal directly. Based on this effect, a bottom gate ferroelectric FET was fabricated using pentacene as the channel material and a PMN-PT single crystal as the gate insulator. Systematic tests illustrate that the ON/OFF current ratio of this transistor memory element is approximately 10(3). More importantly, we demonstrate the feasibility to switch the polarization state of this FET gate insulator, namely the stored information, by finger tapping the TENG with a designed circuit. These results may open up a novel application of TENGs in the field of self-powered memory systems.

Takagi-Sugeno model based analysis of EWMA RtR control of batch processes with stochastic metrology delay and mixed products.

In many batch-based industrial manufacturing processes, feedback run-to-run control is used to improve production quality. However, measurements may be expensive and cannot always be performed online. Thus, the measurement delay always exists. The metrology delay will affect the stability and performance of the process. Moreover, since quality measurements are performed offline, delay is not fixed but is stochastic in nature. In this paper, a modeling approach Takagi-Sugeno (T-S) model is presented to handle stochastic metrology delay in both single-product and mixed-product processes. Based on the Markov characteristics of the delay, the membership of the T-S model is derived. Performance indices such as the mean and the variance of the closed-loop output of the exponentially weighted moving average (EWMA) control algorithm can be derived. A steady-state error of the process output always exists, which leads the output deviating from the target. To remove the steady-state error, an algorithm called compensatory EWMA run-to-run (COM-EWMA-RtR) algorithm is proposed. The validity of the T-S model analysis and the efficiency of the proposed COM-EWMA-RtR algorithm are confirmed by simulation.

Hexagonal crown-capped zinc oxide micro rods: hydrothermal growth and formation mechanism.

Hexagonal crown-capped ZnO micro rods were successfully prepared by a facile low-temperature hydrothermal method. The as-prepared ZnO micro rods are 4.4-5.2 µm in length and 2.4-3.6 µm in diameter, possessing a single-crystal hexagonal structure. The morphology evolution and structure changes were tracked during hydrothermal growth by field-emission scanning electron microscopy and X-ray diffraction, respectively. A three-stage growth mechanism of the hexagonal crown-capped ZnO micro rods was proposed and further verified by a growth solution renewal experiment. The room-temperature photoluminescence (PL) spectrum of the hexagonal crowns exhibits a strong UV emission at about 382 nm. The temperature dependent PL results indicate that the UV emission originates from the radiative free-exciton recombination.