Fiber-based structures are highly desirable for wearable electronics that are expected to be light-weight, long-lasting, flexible, and conformable Many fibrous structures have been manufactured by well-established lost-effective textile processing technologies, normally at ambient conditions The advancement of nanotechnology has made it feasible to build electronic devices directly on the surface or inside of single fibers, which have typical thickness of several to tens microns However, imparting electronic functions to porous, highly deformable and three-dimensional fiber assemblies and maintaining them during wear represent great challenges from both views of fundamental understanding and practical implementation This article attempts to critically review the current state-of-arts with respect to materials, fabrication techniques, and structural design of devices as well as applications of the fiber-based wearable electronic products In addition, this review elaborates the performance requirements of the fiber-based wearable electronic products, especially regarding the correlation among materials, fiber/textile structures and electronic as well as mechanical functionalities of fiber-based electronic devices Finally, discussions will be presented regarding to limitations of current materials, fabrication techniques, devices concerning manufacturability and performance as well as scientific understanding that must be improved prior to their wide adoption

Fiber‐Based Wearable Electronics: A Review of Materials, Fabrication, Devices, and Applications

Flexible graphene fi ber (GF) stands for a new type of fi ber of practical importance, which integrates such unique properties as high strength, electrical and thermal conductivities of individual graphene sheets into the useful, macroscopic ensembles. GFs possess the common characteristics of fi bers like the mechanical fl exibility for textiles, while maintaining the uniqueness such as low cost, light weight, and ease of functionalization in comparison with conventional carbon fi bers. [ 1–3 ] Due to the extraordinary challenge to assemble two-dimensional (2D) microcosmic graphene sheets with irregular size and shape into macroscopic fi brillar confi guration, however, the success in fabrication of neat graphene fi bers only comes true recently. [ 1–4 ]

All‐Graphene Core‐Sheath Microfibers for All‐Solid‐State, Stretchable Fibriform Supercapacitors and Wearable Electronic Textiles

Developing lightweight, flexible, foldable and sustainable power sources with simple transport and storage remains a challenge and an urgent need for the advancement of next-generation wearable electronics. Here, we report a micro-cable power textile for simultaneously harvesting energy from ambient sunshine and mechanical movement. Solar cells fabricated from lightweight polymer fibres into micro cables are then woven via a shuttle-flying process with fibre-based triboelectric nanogenerators to create a smart fabric. A single layer of such fabric is 320 μm thick and can be integrated into various cloths, curtains, tents and so on. This hybrid power textile, fabricated with a size of 4 cm by 5 cm, was demonstrated to charge a 2 mF commercial capacitor up to 2 V in 1 min under ambient sunlight in the presence of mechanical excitation, such as human motion and wind blowing. The textile could continuously power an electronic watch, directly charge a cell phone and drive water splitting reactions. Energy harvesting from the environment by portable and flexible power sources can power a variety of devices sustainably. Chen et al. report a hybrid power textile with solar cells and triboelectric nanogenerators that can simultaneously harvest solar and mechanical energy.

Micro-cable structured textile for simultaneously harvesting solar and mechanical energy

many existing energy-harvesting and storage devices are stilltoo bulky and heavy for intended applications. For example,high-efficiency dye-sensitized solar cells (DSSCs) employfluorine-doped tin oxide (FTO) glass as the substrate ofworking electrode. However, the use of rigid FTO glass hasrestricted adaptability of DSSCs during transportation,installation, and application,

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Fiber Supercapacitors Made of Nanowire‐Fiber Hybrid Structures for Wearable/Flexible Energy Storage

Photosynthesis is used by nature to convert light energy into chemical energy in some living systems. In such a process, a cascade of very efficient, short-range energy and electron transfer events between well-arranged, light-harvesting organic donor and acceptor pigments takes place within the photosynthetic reaction center, leading to the overall generation of chemical energy from sunlight with near quantum efficiency.1-8 During the past decade, a significant effort has been made by the scientific community toward the preparation of synthetic model compounds of natural photosynthetic systems able to convert light into other energy sources,9 probably fostered by the increasing concerns related to the utilization of fossils fuels for the production of electricity in terms of both availability and environmental issues. However, considering the structural complexity presented by the natural photosynthetic systems, much of the scientific effort has been devoted toward the preparation and study of structurally simpler systems, with the aim of reproducing some of the fundamental steps occurring in natural photosynthesis, one of the most important being the photoinduced charge separation (CS).10-12 Among the chromophores that have been used as molecular components in artificial photosynthetic systems, porphyrinoids, the ubiquitous molecular building blocks employed by nature in natural photosynthesis, have been the preferred and obvious choice, due to their intense optical absorption and rich redox chemistry.13-20 Within the large family of porphyrinoid systems, phthalocyanines (Pcs) enjoy a privileged position (Figure 1a). These chromophores, which have a two-dimensional 18-πelectron aromatic system isoelectronic with that of porphyrins (Pors), possess in fact unique physicochemical properties which render these macrocycles valuable building blocks in materials science.21-32 Pcs are thermally and chemically stable compounds which present an intense absorption in the red/near-infrared (IR) region of the solar spectrum with extinction coefficients (as high as 200 000 M-1 cm-1) and fluorescence quantum yields * To whom correspondence should be addressed. E-mail: tomas.torres@uam.es (T.T.); dirk.guldi@chemie.uni-erlangen.de (D.M.G.). † Universidad Autonoma de Madrid. ‡ Friedrich-Alexander-Universitat Erlangen-Nurnberg. § IMDEA-Nanociencia. Chem. Rev. 2010, 110, 6768–6816 6768

Covalent and noncovalent phthalocyanine-carbon nanostructure systems: synthesis, photoinduced electron transfer, and application to molecular photovoltaics.

In the past 20 years, dye-sensitized solar cells (DSSCs) have received more and more attentions from both academia and industry because of their advantages, such as high efficiency, low cost, environment-friendliness, low incident-light-angle dependence, flexibility, and so on. Through continuous development, it was reported that the efficiency (gAM1.5) of DSSC using fluorine-doped tin oxide (FTO) glass as the substrate of working electrode has exceeded 11 % (100 mW cm). However, the rigid FTO glass has restricted DSSCs’ adaptability during transportation, installation, and application. In order to strengthen DSSCs’ adaptability, the flexible cell has become a challenge. At present, researches on flexible DSSC were carried out mainly on polymer/ITO-composed conducting substrate. The gAM1.5 of the all-plastic, flat-shaped DSSC with PET/ITO as the working electrode’s substrate exceeded 2.3 % (100 mW cm). However, transparent conducting oxide (TCO) materials with both high transparency and high conductivity are difficult to obtain. Along with polymer substrate materials, there come many disadvantages, such as poor heat resistance and fatigue. Gang et al. reported a flexible DSSC assembled with a flexible stainless steel sheet as the substrate, in which its gAM1.5 reached 4.2 % (100 mW cm). However, they had to use Ptcoated PET/ITO as the counter electrode due to the opacity of the working electrodes. Our team once produced flexible DSSC working electrodes using heat-resistant conducting mesh to replace traditional TCO glasses, and assemble a flexible liquid DSSC without any TCO in both electrodes. This mesh-like working electrode is cheap, transparent, highly flexible, highly conductive, and possesses a temperature over 500 °C. In the rapid-developing electronic industry, especially in the fields of portable and high-integrated micro-electronic equipment, space provided for a cell is limited and unfavorable in terms of its shape, or even could be changing constantly. To further develop a photovoltaic device, which can meet theses requirements, weaveable wire-shaped flexible dye-sensitized solar cells (WSF-DSSCs) can be a good solution. In this Communication, we report a type of WSF-DSSC. The cell has a simple helical twisting structure formed by two fiber-like electrodes. Thanks to the twisting structure, many opaque conducting materials such as metal wires can be successfully applied. This flexible and very fine photovoltaic device also processes some interesting properties for photo sensors. Figure 1a shows an optical photo of a 5 cm long WSFDSSC. Figure 1b–d are the SEM photos of WSF-DSSC without the electrolyte. The working electrode is stainless steel fiber coated with a layer of dye-sensitized porous TiO2. The counter electrode could be conducting fiber, such as Pt wire, coated with a polymer protective layer (PPL). Because of the twisting structure of the two electrodes, the light can easily reach the working electrode. The cell’s apparent diameter was about 200lm. The entire cell was still a very fine wire with good flexibility. By changing the fibrous substrate, finer and more flexible cells could be further developed. Since the working electrode and counter electrode are twisted together symmetrically, it is predicted that the cell’s illumination state remains the same regardless of whether the incident light comes from any direction normalized to the twisting axis. Figure 2a shows the Isc (short-circuit curent) of a WSF-DSSC at different rotating degrees around or parallel to the twisting central axis, when the incident light’s intensity remains the same. The figure shows that the Isc rarely changed when the incident angles changed. The angle dependence of WSFDSSC’s IV output on incident light is extremely low, which brings convenience for the installation of a photovoltaic device module. It could also make a convenient photo-sensor for light intensity measurement. The electrode’s twisting process greatly influences the performance of WSF-DSSC. During the twisting process, high local pressure is easily produced between electrodes due to local stress concentration on certain parts. In these local parts, the carriers’ back-transfer rate increases, which results in the reduction of voltage and current. At different twisting states, the stress state between electrodes will also change accordingly. To relieve local stress, we have tried to coat PPL on the surface of the counter electrode. In Figure 2b, the IV curves of cells with different twisting states are summarized. Here, × represents a cell without PPL and the twisting screw-pitch is 3 mm. Others represent cells with a 30 lm-thick PVDF, but the twisting screw-pitches are different. The figure indicates the importance of PPL. With PPL, both open circuit voltage C O M M U N IC A TI O N

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Wire‐Shaped Flexible Dye‐sensitized Solar Cells

Conductive meshes are used to replace transparent conducting oxides (TCOs), which are commonly used in electrodes of dye-sensitized solar cells (DSSCs). The TCO-less flexible working electrode could be sintered under 400–500°C. A preliminary result that open-circuit voltage (VOC)=650mV, short-circuit current density (ISC)=4.5mA∕cm2, and efficiency (ηAM1.5)=1.49% (100mW∕cm2) is obtained from the liquid-type DSSC. The incident light could be dispersed uniformly inside the electrode. Testing results of the double-counterelectrode cell indicate that the transmission of electrolyte is not the rate-determining step. The dense TiO2 layer is critical in improving the cell’s performances.

Conductive mesh based flexible dye-sensitized solar cells

We report the development of physics based models for resistive random-access memory (RRAM) devices. The models are based on a generalized memristive system framework and can explain the dynamic resistive switching phenomena observed in a broad range of devices. Furthermore, by constructing a simple subcircuit, we can incorporate the device models into standard circuit simulators such as SPICE. The SPICE models can accurately capture the dynamic effects of the RRAM devices such as the apparent threshold effect, the voltage dependence of the switching time, and multi-level effects under complex circuit conditions. The device and SPICE models can also be readily expanded to include additional effects related to internal state changes, and will be valuable to help in the design and simulation of memory and logic circuits based on resistive switching devices.

Device and SPICE modeling of RRAM devices

We have explored a type of all-solid fibrous flexible dye-sensitized solar cells without transparent conducting oxide based on a CuI electrolyte. The working electrode’s substrate is a metal wire. Cu wire counterelectrode is twisted with the dye-sensitized and CuI-coated working electrode. The cell’s apparent diameter is about 150μm. The cell’s current-voltage output depends little on the incident angle of light. A 4-cm-long fibrous cell’s open-circuit voltage and short-circuit current generate 304mV and 0.032mA, respectively. The interfacial interaction between the two electrodes has a significant influence on the inner charge transfer of the cell.

Fibrous flexible solid-type dye-sensitized solar cells without transparent conducting oxide

Direct, nonvolatile, and reversible control of nanomagnetism in solid-state ferromagnetic thin films is achieved by controlling the chemical composition of the film through field-driven ion redistribution. The electric field-driven de-intercalation/intercalation of lithium ions can result in ≈100% modulation of the magnetization and drives domain wall motion over ≈100 nm. High-speed and multilevel magnetic information storage is further demonstrated.

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Lin Chen

Papers

Wire‐Shaped Flexible Dye‐sensitized Solar Cells

Conductive mesh based flexible dye-sensitized solar cells

Device and SPICE modeling of RRAM devices

Fibrous flexible solid-type dye-sensitized solar cells without transparent conducting oxide

In Situ Nanoscale Electric Field Control of Magnetism by Nanoionics