Extremely stretchable self‐healing strain sensors based on conductive hydrogels are successfully fabricated. The strain sensor can achieve autonomic self‐heal electrically and mechanically under ambient conditions, and can sustain extreme elastic strain (1000%) with high gauge factor of 1.51. Furthermore, the strain sensors have good response, signal stability, and repeatability under various human motion detections.

The rational design and exploration of electrochromic devices will find a wide range of applications in smart windows for energy-efficient buildings, low-power displays, self-dimming rear mirrors for automobiles, electrochromic e-skins, and so on. Electrochromic devices generally consist of multilayer structures with transparent conductors, electrochromic films, ion conductors, and ion storage films. Synthetic strategies and new materials for electrochromic films and transparent conductors, comprehensive electrochemical kinetic analysis, and novel device design are areas of active study worldwide. These are believed to be the key factors that will help to significantly improve the electrochromic performance and extend their application areas. In this Account, we present our strategies to design and fabricate electrochromic devices with high performance and multifunctionality. We first describe the synthetic strategies, in which a porous tungsten oxide (WO3) film with nearly ideal optical modulation and fast switching was prepared by a pulsed electrochemical deposition method. Multiple strategies, such as sol-gel/inkjet printing methods, hydrothermal/inkjet printing methods, and a novel hybrid transparent conductor/electrochromic layer have been developed to prepare high-performance electrochromic films. We then summarize the recent advances in transparent conductors and ion conductor layers, which play critial roles in electrochromic devices. Benefiting from the developments of soft transparent conductive substrates, highly deformable electrochromic devices that are flexible, foldable, stretchable, and wearable have been achieved. These emerging devices have great potential in applications such as soft displays, electrochromic e-skins, deformable electrochromic films, and so on. We finally present a concept of multifunctional smart glass, which can change its color to dynamically adjust the daylight and solar heat input of the building or protect the users' privacy during the daytime. Energy can also be stored in the smart windows during the daytime simultaneously and be discharged for use in the evening. These results reveal that the electrochromic devices have potential applications in a wide range of areas. We hope that this Account will promote further efforts toward fundamental research on electrochromic materials and the development of new multifunctional electrochromic devices to meet the growing demands for next-generation electronic systems.

theoretical and practical aspects of supercapacitors in recent years. [4][5][6] Still, supercapacitors with more functionality and novel features are being sought to extend their application range. For example, fl exible, stretchable, and wearable supercapacitors have been developed to meet the requirements of portable and wearable electronics. [7][8][9][10] It would be highly attractive to integrate both an energy-storage and an electrochromism functionality into one device for multiple applications. Such device could be used not only for energy-storage smart windows, which can store energy by charging the window and adjusting the lighting and heating of the building, [ 11,12 ] but also for sensing variations in the level of stored energy and being able to respond to the variations in a noticeable and predictable manner. [13][14][15][16] As a key component of these smart devices, the transparent electrodes used not only need to be highly transparent but also highly conductive to simultaneously meet the needs of charging/discharging under high current density conditions and that of fast coloration switching speeds. However, the most commonly used transparent conducting electrodes are indium tin oxide (ITO)-coated glass, [ 11,16 ] fl uorine doped tin oxide (FTO)-coated glass, [ 13,15 ] poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate) (PEDOT:PSS), [ 12 ] and carbon nanotubes. [ 14 ] The sheet resistance of these transparent conducting electrodes is in the range of tens to hundreds of Ω per square, which could hinder the device charging/discharging process and may lead to the color changes lagging behind the changes in the stored energy, especially under high current densities. In addition, ITO and FTO as transparent electrodes are unsuitable for fl exible electronics applications because of their brittleness and high cost of the preparation procedure. [17][18][19] Therefore, it is very important to design an electrode with a low electrical resistance and a high optical transmittance for smart energystorage device applications.A variety of fl exible transparent electrodes have been investigated as low-cost ITO substitutes, including conducting polymers, [ 20 ] carbon nanotubes (CNTs), [ 21 ] graphene, [ 22 ] metal nanowires, [ 23,24 ] and metal grids. [25][26][27] Among these fl exible Silver grids are attractive for replacing indium tin oxide as fl exible transparent conductors. This work aims to improve the electrochemical stability of silverbased transparent conductors. A silver grid/PEDOT:PSS hybrid fi lm with high conductivity and excellent stability is successfully fabricated. Its functionality for fl exible electrochromic applications is demonstrated by coating one layer of WO 3 nanoparticles on the silver grid/PEDOT:PSS hybrid fi lm. This hybrid structure presents a large optical modulation of 81.9% at 633 nm, fast switching, and high coloration effi ciency (124.5 cm 2 C −1 ). More importantly, an excellent electrochemical cycling stability (sustaining 79.1% of their initial transmittance modulation a...

Advances in next-generation soft electronic devices rely on the development of highly deformable, healable, and printable energy generators to power these electronics. Development of deformable or wearable energy generators that can simultaneously attain extreme stretchability with superior healability remains a daunting challenge. We address this issue by developing a highly conductive, extremely stretchable, and healable composite based on thermoplastic elastomer with liquid metal and silver flakes as the stretchable conductor for triboelectric nanogenerators. The elastomer is used both as the matrix for the conductor and as the triboelectric layer. The nanogenerator showed a stretchability of 2500% and it recovered its energy-harvesting performance after extreme mechanical damage, due to the supramolecular hydrogen bonding of the thermoplastic elastomer. The composite of the thermoplastic elastomer, liquid metal particles, and silver flakes exhibited an initial conductivity of 6250 S cm −1 and recovered 96.0% of its conductivity after healing.

Natural leaves, with elaborate architectures and functional components, harvest and convert solar energy into chemical fuels that can be converted into energy based on photosynthesis. The energy produced leads to work done that inspired many autonomous systems such as light-triggered motion. On the basis of this nature-inspired phenomenon, we report an unprecedented bilayer-structured actuator based on MXene (Ti3C2Tx)–cellulose composites (MXCC) and polycarbonate membrane, which mimic not only the sophisticated leaf structure but also the energy-harvesting and conversion capabilities. The bilayer actuator features multiresponsiveness, low-power actuation, fast actuation speed, large-shape deformation, programmable adaptability, robust stability, and low-cost facile fabrication, which are highly desirable for modern soft actuator systems. We believe that these adaptive soft systems are attractive in a wide range of revolutionary technologies such as soft robots, smart switch, information encryption, infrared dynamic display, camouflage, and temperature regulation, as well as human-machine interface such as haptics.

An extremely stretchable electroluminescent device is fabricated based on alternating-current electroluminescent (ACEL) materials and ionic conductors. The stretchable ACEL device possesses extremely high stretchability, and can be linearly stretched to 700% with the luminance being maintained at 70% of the initial value before stretching. The ACEL device can be repetitively stretched to 400% with stable emission behavior.

Stretchable conductors are vital and indispensable components in soft electronic systems. The development for stretchable conductors has been highly motivated with different approaches established to address the dilemma in the conductivity and stretchability trade-offs to some extent. Here, a new strategy to achieve superelastic conductors with high conductivity and stable electrical performance under stretching is reported. It is demonstrated that by electrically anchoring conductive fillers with eutectic gallium indium particles (EGaInPs), significant improvement in stretchability and durability can be achieved in stretchable conductors. Different from the strategy of modulating the chemical interactions between the conductive fillers and host polymers, the EGaInPs provide dynamic and robust electrical anchors between the conductive fillers. A superelastic conductor which can achieve a high stretchability with 1000% strain at initial conductivity of 8331 S cm and excellent cycling durability with about eight times resistance change (compared to the initial resistance at 0% strain before stretching) after reversibly stretching to 800% strain for 10 000 times is demonstrated. Applications of the superelastic conductor in an interactive soft touch device and a stretchable light-emitting system are also demonstrated, featuring its promising applications in soft robotics or soft and interactive human-machine interfaces.

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