Highly stretchable graphene-nanocellulose composite nanopaper is fabricated for strain-sensor applications. Three-dimensional macroporous nanopaper from crumpled graphene and nanocellulose is embedded in elastomer matrix to achieve stretchability up to 100%. The stretchable graphene nanopaper is demonstrated for efficient human-motion detection applications.

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.

Stretchable and wearable WO3 electrochromic devices on silver nanowire (AgNW) elastic conductors are reported. The stretchable devices are mechanically robust and can be stretched, twisted, folded, and crumpled without performance failure. Fast coloration (1 s) and bleaching (4 s) time and good cyclic stability (81% retention after 100 cycles) were achieved at relaxed state. Proper functioning at stretched state (50% strain) was also demonstrated. The electrochromic devices were successfully implanted onto textile substrates for potential wearable applications. As most existing electrochromic devices are based on rigid technologies, the innovative devices in their soft form hold the promise for next-generation electronics such as stretchable, wearable, and implantable display applications.

The development of mechanically "robust" EL devices that can confront different demanding mechanical deformations, such as fl exing, folding, twisting, and stretching without incurring damage, is the primary requirement for fabricating selfdeformable EL devices. Reported attempts have demonstrated polymer light-emitting materials for intrinsically stretchable EL devices. [3][4][5][6][7]12 ] Different strategies have also been employed by engineering stretchable structures with assembled rigid inorganic light-emitting elements. [ 1,2,13,14 ] The substrates and electrodes of devices can be stretched while the light-emitting elements are kept intact during stretching. Here, a different method has been developed to fabricate an intrinsically stretchable inorganic EL device with both stretchable conductors and light-emitting layers. The elastic EL device could sustain its performance at stretching strains as large as 100% (close to the mechanical failure of the host elastomer). The simplicity of the device fabrication together with its excellent stretchability enabled the integration with actuators, which could drive the elastic EL devices into dynamic shapes. Dielectric elastomer actuators (DEAs) are emerging "smart materials" that can generate mechanical motions with applied electrical fi elds. DEAs have demonstrated extraordinary mechanical actuation performance with area strain reaching beyond 200% on prestrained elastomers; [15][16][17] this exceeds most actuators based on other working mechanisms, such as piezoelectric actuators (≈5%), [ 18 ] ionic gel actuators (≈40%), [ 19 ] and natural muscle (≈100%). [ 20 ] With their intrinsic stretchability, ease of minimization, high power density, and low-cost fabrication, DEAs have been applied in many applications such as wearable tactile display devices, [ 21,22 ] highspeed electromechanical transducers, [ 23,24 ] and smart artifi cial muscles [ 20,25 ] etc. In this report, DEAs are demonstrated to be ideal shape display components to integrate with stretchable EL devices. An unprecedented self-deformable EL device is fabricated by the innovative method in this work.A schematic drawing of the stretchable EL device is represented in Figure 1 a. The stretchable EL device was fabricated with a simple all-solution processable method. In brief, AgNW networks were fi rstly spray-coated onto the polydimethylsiloxane (PDMS) substrate, forming the bottom electrode. ZnS:Cu microparticles mixed with liquid PDMS were then spun onto the bottom electrode. ACEL devices have been developed for display or lighting applications for a few decades and have attracted persistent interest for their simple device architecture and low production cost. [26][27][28] ZnS:Cu is a widely available ACEL material with well-studied and understood emission behavior. [ 29,30 ] Its emission colors can be easily tuned by using different active dopants or adjusting the dopant concentrations. After crosslinking, the ZnS:Cu/PDMS composite layer harvests the excellent stretchability from the PDMS matrix with...

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...

Stretchable graphene thermistors with intrinsic high stretchability were fabricated through a lithographic filtration method. Three-dimensional crumpled graphene was used as the thermal detection channels, and silver nanowires were used as electrodes. Both the detection channel and electrodes were fully embedded in an elastomer matrix to achieve excellent stretchability. Detailed temperature sensing properties were characterized at different strains up to 50%. It is evident that the devices can maintain their functionalities even at high stretched states. The devices demonstrated strain-dependent thermal indices, and the sensitivity of the thermistors can be effectively tuned using strain. The unique tunable thermal index is advantageous over conventional rigid ceramic thermistors for diverse and adaptive applications in wearable electronics.

Textiles that are capable of harvesting biomechanical energy via triboelectric effects are of interest for self-powered wearable electronics. Fabrication of conformable and durable textiles with high triboelectric outputs remains challenging. Here we propose a washable skin-touch-actuated textile-based triboelectric nanogenerator for harvesting mechanical energy from both voluntary and involuntary body motions. Black phosphorus encapsulated with hydrophobic cellulose oleoyl ester nanoparticles serves as a synergetic electron-trapping coating, rendering a textile nanogenerator with long-term reliability and high triboelectricity regardless of various extreme deformations, severe washing, and extended environmental exposure. Considerably high output (~250–880 V, ~0.48–1.1 µA cm−2) can be attained upon touching by hand with a small force (~5 N) and low frequency (~4 Hz), which can power light-emitting diodes and a digital watch. This conformable all-textile-nanogenerator is incorporable onto cloths/skin to capture the low output of 60 V from subtle involuntary friction with skin, well suited for users’ motion or daily operations.