Sensors allow an electronic device to become a gateway between the digital and physical worlds, and sensor materials with unprecedented performance can create new applications and new avenues for user interaction. Graphene oxide can be exploited in humidity and temperature sensors with a number of convenient features such as flexibility, transparency and suitability for large-scale manufacturing. Here we show that the two-dimensional nature of graphene oxide and its superpermeability to water combine to enable humidity sensors with unprecedented response speed (∼30 ms response and recovery times). This opens the door to various applications, such as touchless user interfaces, which we demonstrate with a 'whistling' recognition analysis.

Electrochromic devices (ECDs) that display multicolor patterns have gradually attracted widespread attention. Considering the complexity in the integration of various electrochromic materials and multi-electrode configurations, the design of multicolor patterned ECDs based on simple approaches is still a big challenge. Herein, it is demonstrated vivid ECDs with broadened color hues via introducing carbon dots (CDs) into the ion electrolyte layer. Benefiting from the synergistic effect of electrodes and electrolytes, the resultant ECDs presented a rich color change. Significantly, the fabricated ECDs can still maintain a stable and reversible color change even in high temperature environments where operating temperatures are constantly changing from RT to 70°C. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of intelligent and portable electronics.

Electrochromic devices (ECDs) are the intelligent devices change color by applying electric potential, with the advantages of wide working temperature, high optical contrast, good reversible bistability, low driving voltage, and low energy consumption, which show great application potential in the field of dynamic smart windows, full-color electronic screens, anti-glare goggles, adaptive dual-stealth camouflage, and energy storage status visualization. Cathodically coloring material tungsten oxide and anodically coloring material nickel oxide are two widely studied inorganic electrochromic materials, and complementary electrochromic devices based on WO₃ and NiO films have high commercial values in the application of large scale smart windows. Improving the performance of the complementary ECDs such as optical modulation range, response rate, cycle life and weather fastness has attracted much attention. This review focuses on the structural composition of complementary electrochromic devices and summarizes the recent research progress of the electrochromic full devices based on WO₃ and NiO. Firstly, the electrochromic mechanism and decay mechanism of WO₃ and NiO films are clarified, the effects and latest research progress of four strategies for film performance optimization that include optimizing preparation conditions, element doping modification, designing nanostructure, and introducing composite materials are discussed in detail. Secondly, according to the composition and structure design of the device, the classification system of the complementary electrochromic full device is introduced, and the influence of selection for each component material and the device structure on device overall performance are summarized. Finally, the application of the electrochromic device prospects and development trends are forecasted.

Optical property, such as color, transmittance, reflectance and emissivity, of electrochromic materials can be changed reversibly under low applied voltages. Electrochromic materials have a wide range of regulatable spectrum, which can realize the broadband control from the visible to mid-far-infrared. Electrochromic materials show a wide application prospect in the fields of intelligent window, display, anti-glare rearview mirror, intelligent thermal control, and camouflage. At present, most of researches on inorganic electrochromic materials focus mainly on transmission characteristics, but less on reflection characteristics. This is mainly because most inorganic electrochromic materials have single color and are not as easy to design as organic electrochromic materials. In recent years, through special preparation and structural design, the research on reflective properties of inorganic electrochromic materials has gradually attracted researchers’ attention. Based on reflection characteristics of inorganic electrochromic materials, methods and principles of regulating the reflectance spectrum in the visible near infrared to mid-far-infrared bands are introduced, and the latest research progress is summarized. Within the visible band, reflectance spectrum control is mainly achieved by vanadium pentoxide (V₂O₅) and V₂O₅ doping, microstructure of one dimensional photonic crystal, Fabry Perot nanocavity structure and localized surface plasmon resonance (LSPR). Within the mid-to-far infrared band, electrochromic devices (ECDs) based on the molecular vibration absorption of tungsten oxide (WO₃) or other electrochromic materials and related theory are designed and fabricated to regulate reflectance spectra. Finally, the practical application of inorganic electrochromic materials in future is prospected.

In this study, we report on the development of a stretchable, transparent, and skin-attachable strain sensor integrated with a flexible electrochromic device as a human skin-inspired interactive color-changing system. The strain sensor consists of a spin-coated conductive nanocomposite film of poly(vinyl alcohol)/multi-walled carbon nanotube/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) on a polydimethylsiloxane substrate. The sensor exhibits excellent performance of high sensitivity, high durability, fast response, and high transparency. An electrochromic device (ECD) made of electrochemically synthesized polyaniline nanofibers and VO on an indium-tin-oxide-coated polyethylene terephthalate film experiences a change in color from yellow to dark blue on application of voltage. The strain sensor and ECD are integrated on skin via an Arduino circuit for an interactive color change with the variation of the applied strain, which enables a real-time visual display of body motion. This integrated system demonstrates high potential for use in interactive wearable devices, military applications, and smart robots.

The concept of smart windows that can change the properties of windows and doors in response to external stimuli has recently been introduced. Smart windows provide superior energy savings and control of indoor environments. This concept can advance sustainable architecture, and it will make it possible to connect with the fourth industry, which has developed recently. However, unlike the relevant hardware, is advancing rapidly, research on methods of adjusting smart windows is slow. Therefore, in this study, an analysis of energy use over time was conducted on electrochromic windows, one of the main types of smart windows. Through this analysis, the optimal properties of electrochromic smart windows were identified, and an operation schedule was created. In addition, energy saving rates were derived through a comparison with existing architectural windows.

The present study sets out to review the thermal and optical properties of electrochromic windows (ECWs) through an analysis of the improvement in the energy performance of a building resulting from their application. The performance analysis was based on the change in the room temperature according to the solar transmittance and the orientation of the ECWs, the energy consumptions of the building’s heating/cooling systems, and that of the building’s lighting according to the visible light transmittance (VLT). To achieve this, the Quick Energy Simulation Tool (eQUEST), a building energy interpretation program, was used. The solar heat gain coefficient (SHGC) of the ECWs was found to be significantly reduced. This had the effect of lowering the room temperature in summer, such that the effect on the summer cooling energy consumption was also remarkable. However, with a reduction in the VLT, the lighting energy consumption increased. The net result of the changes in the heating/cooling and lighting energy consumptions was a reduction of about 11,207 kWh/yr (8.89%). The ECWs were found to realize a greater reduction in a building’s energy consumption than was possible with windows glazed with low-E coated glass.

This work demonstrated a pressure-based biosensor integrated with a flexible pressure sensor and an electrochromic device for visual detection. Initially, a sandwich-type immunoreaction for target carcinoembryonic antigen (CEA, as a model analyte) was carried out using the capture antibody (cAb) and platinum nanoparticles-labeled detection antibody (PtNPs-dAb) in a reaction cell. The added hydrogen peroxide (HO) could be catalyzed by the PtNPs to generate oxygen (O). In a sealed chamber, the pressure increased with the overflowing O. Meanwhile, a skin-inspired flexible pressure sensor with excellent sensing performance was fabricated to monitor the pressure change in real time. Thus, the electrical signal of the pressure sensor could reveal the target concentration. Moreover, a voltage-regulated electrochromic device based on polyaniline (PANI) and tungsten oxide (WO) was integrated into the platform to provide a visualized readout. According to the electrical signal of the pressure sensor, the electrochromic device would change its color from green to blue, which also revealed the target concentration and could be observed by the naked eye. Under optimal conditions, the biosensor presented a high sensitivity for CEA in a detectable range of 0.2-50 ng/mL. The limit of detection (LOD) was 94 pg/mL. The selectivity, reproducibility, and accuracy were also satisfying. Furthermore, this immunoassay gives a path for developing visualized biosensors in point-of-care settings.

Electrochromic materials show reversible color-changeable characteristics, which are widely used in smart windows, displays, adjustable reflective mirrors, electronic paper, military camouflage and other fields. Compared with other kinds of display devices, electrochromic display devices have advantages of multi-colors, high contrast, no blind visual angles, and maintainable color after power off. As a typical cathodic colored electrochromic material, molybdenum oxide exhibits advantages of short response time and colored state closer to the sensitive wavelength band of the human eye to light, so that the electrochromic devices composed of molybdenum oxide is important in the research. This paper briefly introduces the definitions and applications of electrochromism, electrochromic materials and devices. In particular, electrochromic technology recently realized a demonstration application in smart phones, indicating the good prospects for the future development of electrochromic technology. We summarized mainly the research progress of the preparation of molybdenum oxide films, the modification of molybdenum oxide, and the molybdenum oxide based electrochromic devices. Finally, we presented current existing problems and solutions on molybdenum oxide based electrochromic films and devices with development prospects.

Chromogenic materials are capable of optical change reversibly in response to physical stimuli (e.g., electric field, temperature, illumination, and atmosphere). Among them, electrochromic materials are expected to be widely used in smart windows, screen displays, multi-functional energy storage devices and other fields due to their characteristics such as large adjustment range, fast response rate, high coloring efficiency and good cycle stability. However, compared with semi-solid-state electrochromic devices that are difficult to package and organic electrochromic materials that are prone to denaturation and failure, inorganic all-solid-state electrochromic materials and devices have better comprehensive application. This paper focuses on the typical inorganic all-solid-state electrochromic materials and devices, presents a brief review on the current preparation methods of each structure layer of electrochromic devices and compares its advantages and disadvantages, introduces in detail the main alternative electrochromic materials and its key performance evaluation index, and explains the principle of several representative electrochromic devices, proposes to use transparent flexible electrodes with both high light transmittance, low surface resistance and excellent bending fold to replace the traditional rigid substrate in order to realize multi-field responsible device application development. Finally, the application prospect of inorganic all-solid-state electrochromic devices is prospected from the perspective of performance bottleneck, process difficulty and industrialization opportunity, which provides reference for the industrialization process of electrochromic devices.

We demonstrate a perovskite single-phototransistor visible-light spectrometer based on a deep-learning method. The size of the spectrometer is set to the scale of the phototransistor. A photoresponsivity matrix for the deep-learning system is learned from the characteristic parameters of the visible-light wavelength, gate voltage, and power densities of a commercial standard blackbody source. Unknown spectra are reconstructed using the corresponding photocurrent vectors. As a confirmatory experiment, a 532-nm laser and multipeak broadband spectrum are successfully reconstructed using our perovskite single-phototransistor spectrometer. The resolution is improved to 1 nm by increasing the number of sampling points from 80 to 400. In addition, a way to further improve the resolution is provided by increasing the number of sampling points, characteristic parameters, and training datasets. Furthermore, artificial intelligence technology may open pathways for on-chip visible-light spectroscopy.

Electrochromic materials are attractive for applications like smart windows and thermal management which can modulate transmittance from visible to near-infrared wavelengths. Lithium titanate has been proven to be a potential electrochromic cathode material, but its application prospects in the field of smart windows still lack data support. In this work, Li₄Ti₅O₁₂ thin films with high transmittance and good crystallinity were prepared by Sol-Gel spin coating. The electrochromic properties of the films were characterized by different methods. It is found that all Li₄Ti₅O₁₂ thin films are very sensitive to the test conditions, such as scanning rate, displaying excellent dual band modulation property. Also, the thickness has a significant effect on the initial state transmittance, modulation amplitude, response time, voltage window and cycle durability of the Li₄Ti₅O₁₂ thin films. The colored and bleached response time of the 450 nm Li₄Ti₅O₁₂ is 19.1 and 8.9 s, respectively, while the transmittance modulation is 45% in the visible light region (550 nm). The performance of the films have not been significantly degraded after 20000 s continuous cycle. It is worth mentioning that the transmittance modulation in the near infrared band (1000 nm) is as high as 80%, showing excellent energy saving potential. Finally, Glass/FTO/Li₄Ti₅O₁₂/LiNbO₃/NiO _x/ITO, an all-solid-state inorganic electrochromic device with good cycle performance from gray to blue was successfully assembled. Above data demonstrate that lithium titanate is a strong competitive material for the popularization of electrochromic smart window.

Electrochromic materials with ability of changing color in response to periodically adjusted bias are an important class of optoelectric functional materials. The controllable modulation of light absorption and transmission can make a great contribution in applications such as smart windows, electrochromic displays and antiglare rear-view mirrors. In recent years, electrochromic technology has developed rapidly. However, the research so far mainly focuses on the traditional rigid electrochromic devices (ECD), mostly based on transparent conductive glass such as indium tin oxide (ITO) glass. The rigid electrochromic devices have some noticeable problems such as large thickness, poor conformability, low mechanical strength, high cost, etc., which hinder their further development of electrochromic technology and their forward commercialization. With the upsurge of developing flexible devices that can be used in wearable devices and e-skin, flexible electrochromic devices (FECD) have attracted extensive attention due to their possibility of foldability, wearability and even embeddability, and have become a research hotspot in the electrochromic field. Starting from the materials for preparing FECD, this review systematically summarizes the recent progress and trend of flexible electrochromic devices based on inorganic, organic, inorganic/organic composite and other new materials. The review also focuses on the research progress of up to date stretchable electrochromic devices. At the same time, challenges in performance improvement and practical application of flexible electrochromic devices at the present stage as well as the corresponding measures taken in the literatures are discussed. Finally, the key to the preparation and performance improvement of flexible electrochromic devices is defined, and the future development trend is prospected.