Flexible Energy Conversion Research Articles

Initiating crystal growth kinetics of α-HC(NH2)2PbI3 for flexible solar cells with long-term stability

Flexible and stable energy conversion devices are core components for next generation flexible electronics. Perovskite solar cells using formamidinium lead iodide (FAPbI3) exhibit superior power conversion efficiency (PCE), but the strenuous process of n-i-p configuration and the instability of α-FAPbI3 become inevitable obstacles for practical application in flexible electronics. Here, we for the first time report the particular crystal growth process of α-FAPbI3 grain with a controlled size for the development of flexible perovskite solar cells. Through morphology, element and thermostability measurements, the crystalline size and film homogeneity are found to mainly depending on decent thermal energy and doping density of methylammonium bromine. Additionally, stable “pseudocubic” lattice with larger crystalline size is established owing to the varied tolerance factor. We demonstrated that the flexible solar cells exhibiting an average PCE of 12.41±0.52% (the optimal 13.03%), which slightly decreased to 10.98±1.00% (the optimal 12.0%) over one month at 35% humidity without encapsulation, based on the modified α-FAPbI3 for most efficient devices. This work favors the understanding of the crystal growth kinetics of α-FAPbI3 for flexible substrate, and paves the way for potential application of flexible electronics.

Newborn 2D materials for flexible energy conversion and storage

Newborn two-dimensional materials (NB2DMs) beyond graphene such as transition metal dichalcogenides (TMDs) exhibit excellent optoelectronic and mechanical properties as well as high theoretical specific capacity, which make them become the promising building blocks of flexible energy devices related to energy conversion and storage. Compared to graphene with zero band gap or traditional friable materials such as Si, these NB2DMs are more suitable to construct flexible devices as active layers of optoelectronic devices or as active materials for batteries. The present review focuses on the recent advances in bendable energy devices based on NB2DMs, including batteries, supercapacitors (SCs), solar cells, photodetectors and nanogenerators (NGs). The NB2DMs pave a new way to construct next-generation flexible energy devices with improved performance and we believe that those devices will be seen in our daily life and change our lifestyle in the immediate future.

Blue Phosphorene/MS2 (M = Nb, Ta) Heterostructures As Promising Flexible Anodes for Lithium-Ion Batteries

The idea of forming van der Waals (vdW) heterostructures by integrating various two-dimensional materials breaks the limitation of the restricted properties of single material systems. In this work, the electronic structure modulation, stability, entire stress response and the Li adsorption properties of heterostructures by combining blue phosphorene (BlueP) and MS2 (M = Nb, Ta) together were systematically investigated using first-principles calculations based on vdW corrected density functional theory. We revealed that BlueP/MS2 vdW heterostructures possess good structural stability with negative formation energy, enhanced electrical conductivity, improved mechanical flexibility (ultimate strain >17%) and high-capacity (528.257 mAhg(-1) for BlueP/NbS2). The results suggest that BlueP/NbS2 and BlueP/TaS2 heterostructures are ideal candidates used as promising flexible electrode for high recycling rate and portable lithium-ion batteries, which satisfy the requirement of next-generation flexible energy storage and conversion devices.

Ultrasonic-electrodeposition of PtPd alloy nanoparticles on ionic liquid-functionalized graphene paper: towards a flexible and versatile nanohybrid electrode.

Here we fabricate a new type of flexible and versatile nanohybrid paper electrode by ultrasonic-electrodeposition of PtPd alloy nanoparticles on freestanding ionic liquid (IL)-functionalized graphene paper, and explore its multifunctional applications in electrochemical catalysis and sensing systems. The graphene-based paper materials demonstrate intrinsic flexibility, exceptional mechanical strength and high electrical conductivity, and therefore can serve as an ideal freestanding flexible electrode for electrochemical devices. Furthermore, the functionalization of graphene with IL (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate) not only increases the electroactive surface area of a graphene-based nanohybrid paper electrode, but also improves the adhesion and dispersion of metal nanoparticles on the paper surface. These unique attributes, combined with the merits of an ultrasonic-electrodeposition method, lead to the formation of PtPd alloy nanoparticles on IL-graphene paper with high loading, uniform distribution, controlled morphology and favourable size. Consequently, the resultant nanohybrid paper electrode exhibits remarkable catalytic activity as well as excellent cycle stability and improved anti-poisoning ability towards electrooxidation of fuel molecules such as methanol and ethanol. Furthermore, for nonenzymatic electrochemical sensing of some specific biomarkers such as glucose and reactive oxygen species, the nanohybrid paper electrode shows high selectivity, sensitivity and biocompatibility in these bio-catalytic processes, and can be used for real-time tracking hydrogen peroxide secretion by living human cells. All these features demonstrate its promising application as a versatile nanohybrid electrode material in flexible and lightweight electrochemical energy conversion and biosensing systems such as bendable on-chip power sources, wearable/implantable detectors and in vivo micro-biosensors.

Fiber-based multifunctional nickel phosphide electrodes for flexible energy conversion and storage

Fiber-based multifunctional nickel phosphide electrodes have been successfully prepared by facile electrodeposition of nickel nanoparticle arrays on a commercial carbon fiber followed by low-temperature phosphidation. With the synergistic effect from the hierarchically porous structure and chemical compositions, the resultant electrodes exhibit excellent performance for overall water-splitting electrocatalysis and flexible supercapacitors.

Al/C/MnO2 sandwich nanowalls with highly porous surface for electrochemical energy storage

Hierarchical materials supported on metal substrates present promising applications in flexible energy storage and conversion devices. Compared to Au, Ag, Cu, Ni, Ti, W and their alloys, Al, the most abundant metal in the crust has been less used in supercapacitors due to its high activity which makes it unstable in acid and base electrolytes. In this paper, we explore a novel Al/C/MnO2 sandwich structured material for the first time for supercapacitor. Owing to the highly porous and open surface structure and the highly conductive Al/C double core current collector on nanoscale, the Al/C/MnO2 sandwich nanowall arrays supported on Al foil show excellent capacitance performance with a maximum area specific capacitance of 1008.3 mF cm−2 and a high energy density of 35.2 μWh cm−2 at 2 mA cm−2. Moreover, a supercapacitor device with 4 supercapacitors connected in series can power a LED lamp. The present study demonstrates a novel electrode architecture based on Al foil with remarkably high area specific capacitance and stability for promising supercapacitor applications. Our strategy provides a new approach to the fabrication of hierarchical electrode materials from Al metal (could also be extend to other metal substrates) for supercapacitors and other energy storage and conversion devices.

Flexible MoS2 Field-Effect Transistors for Gate-Tunable Piezoresistive Strain Sensors.

Atomically thin molybdenum disulfide (MoS2) is a promising two-dimensional semiconductor for high-performance flexible electronics, sensors, transducers, and energy conversion. Here, piezoresistive strain sensing with flexible MoS2 field-effect transistors (FETs) made from highly uniform large-area films is demonstrated. The origin of the piezoresistivity in MoS2 is the strain-induced band gap change, which is confirmed by optical reflection spectroscopy. In addition, the sensitivity to strain can be tuned by more than 1 order of magnitude by adjusting the Fermi level via gate biasing.

Molecular Engineering of Zinc Phthalocyanine Sensitizers for Efficient Dye-Sensitized Solar Cell

Dye-sensitized solar cells (DSSCs) have been expected as low-cost, lightweight, and flexible energy conversion devices. To date, the highest conversion efficiency above 12 % has been achieved with p-conjugated macrocyclic zinc porphyrin sensitizer YD2-o-C8 using cobalt polypyridine redox shuttles. Designed p-conjugated macrocycles such as porphyrins and phthalocyanines have attracted special attention as versatile molecular platforms of highly efficient dyes for DSSCs. While a lot of porphyrin-based sensitizers have been designed and synthesized to enhance the conversion efficiency in DSSCs, the efficiencies of DSSCs employing red/near-IR absorbing phthalocyanine-based sensitizers had not been impressive due to their strong tendency to aggregate and the lack of directionality of electron transfer in the excited states. To overcome these drawbacks of phthalocyanine-based sensitizers, several approaches such as steric suppression of aggregation, electronic push-pull structures through asymmetrical substitutions, and optimization of adsorption sites have been reported. Recently, we showed that the structural modification of peripheral bulky substituents and adsorption site around the phthalocyanine core induced the improvement of incident photon-to-current efficiency (IPCE), and thereby achieved a solar-to-electric power-conversion efficiency (PCE) of 5.9% from solar cells employing PcS18 under one sun condition. However, while the maximum value of IPCE was more than 80 %, the values around 520 nm was about 30 %. Since the absorption coefficient of the sensitizers at the wavelength is very low, in order to increase the efficiency, higher dye adsorption density is desired. This can be done by decreasing the molecular size. In addition to IPCE spectrum, open circuit voltage of the PcS18 cell was not high. This could be improved by modifying the size of peripheral substituents attached to the phthalocyanine core to cover the TiO2 surface by the dye molecules. In this presentation, we examine the effect of the length and number of alkoxy groups around the phthalocyanine moiety on the photovoltaic properties. We now expect the alkoxy groups to have three functions, preventing aggregation, filling the space among dyes on TiO2 surface and increasing dye adsorption density. We found that an asymmetrical zinc phthalocyanine (ZnPc) PcS20 bearing propoxy groups in the 2 and 6 positions of peripheral phenoxy units showed a record PCE value of 6.4 % under simulated air mass 1.5 global sunlight.

Flexible, transferable, and thermal-durable dye-sensitized solar cell photoanode consisting of TiO₂ nanoparticles and electrospun TiO₂/SiO₂ nanofibers.

Flexible dye-sensitized solar cells (DSSCs) often face the dilemma of the high temperature sintering of TiO2 photoanode to achieve superior performance and low thermal durability of the flexible substrate. Herein, we report a photoanode that combines the flexibility and high-temperature durability, which circumvents the long-standing challenge in flexible photoanode of DSSC. A hybrid mat consisting of anatase-phased TiO2 nanofibers and structurally amorphous SiO2 nanofibers is first prepared via the method of dual-spinneret electrospinning followed by pyrolysis. The hybrid fibrous mat is then impregnated with binder-free TiO2 nanoparticles and sintered at 480 °C to form a flexible composite photoanode for DSSC. The DSSC based on this composite photoanode achieves a power conversion efficiency of 6.74 ± 0.33% on FTO/glass substrate. Device characterization and phototransient measurement, dye-loading experiment, and structural characterization indicate that, in the composite photoanode, the TiO2 nanoparticles enhance the dye loading, the TiO2 nanofibers improve the electron transport, and the SiO2 nanofibers provide the mechanical strength/flexibility. The freestanding composite mat of TiO2 nanoparticles and electrospun TiO2/SiO2 nanofibers, as well as the preparation methods reported herein, not only is ideal for flexible DSSCs, but also can be applied for a broad range of flexible and low-cost energy conversion devices.

Nanotube liquid crystal elastomers: photomechanical response and flexible energy conversion of layered polymer composites

Elastomeric composites based on nanotube liquid crystals (LCs) that preserve the internal orientation of nanotubes could lead to anisotropic physical properties and flexible energy conversion. Using a simple vacuum filtration technique of fabricating nanotube LC films and utilizing a transfer process to poly (dimethyl) siloxane wherein the LC arrangement is preserved, here we demonstrate unique and reversible photomechanical response of this layered composite to excitation by near infra-red (NIR) light at ultra-low nanotube mass fractions. On excitation by NIR photons, with application of small or large pre-strains, significant expansion or contraction of the sample occurs, respectively, that is continuously reversible and three orders of magnitude larger than in pristine polymer. Schlieren textures were noted in these LC composites confirming long range macroscopic nematic order of nanotubes within the composites. Order parameters of LC films ranged from Soptical = 0.51–0.58 from dichroic measurements. Film concentrations, elastic modulus and photomechanical stress were all seen to be related to the nematic order parameter. For the same nanotube concentration, the photomechanical stress was almost three times larger for the self-assembled LC nanotube actuator compared to actuator based on randomly oriented carbon nanotubes. Investigation into the kinetics of photomechanical actuation showed variation in stretching exponent β with pre-strains, concentration and orientation of nanotubes. Maximum photomechanical stress of ∼0.5 MPa W−1 and energy conversion of ∼0.0045% was achieved for these layered composites. The combination of properties, namely, optical anisotropy, reversible mechanical response to NIR excitation and flexible energy conversion all in one system accompanied with low cost makes nanotube LC elastomers important for soft photochromic actuation, energy conversion and photo-origami applications.

Invited Presentation: Electrolyte Breakthrough to Advance Flexible Batteries

Flexible batteries have garnered a great deal of attention as a promising power source for versatile-shaped electronic devices including bendable smart phones, roll-up displays and wearable electronics, which play crucial roles in facilitating the advent of wearable electronics era. One formidable challenge for development of the flexible batteries arises from difficulties in securing solid-state electrolytes with reliable electrochemical/mechanical properties. Currently available liquid electrolytes show good electrochemical performance suitable for practical applications, however, they often suffer from safety failures due to unwanted leakage problems and flammable characteristics. Moreover, liquid electrolytes limit choices in cell design due to their fluidic attributes, which essentially require the use of separator membranes and packaging canisters with fixed dimension in cell assembly. These shortcomings of liquid electrolytes motivate us to develop advanced solid-state electrolytes that can easily conform to complex-structured substrates such as three-dimensional (3D) electrodes and also ensure sufficient mechanical deformability for reliable use.Herein, as electrolyte breakthrough to advance flexible batteries, a new class of bendable, shape-conformable and thermally-stable composite polymer electrolyte is demonstrated and also its potential application to flexible batteries featuring shape diversity is explored. More notably, the composite polymer electrolyte can be directly writable and printable onto complicated/contoured electrodes, without the aid of processing solvents. The unique structural/compositional designs and well-tuned rheological properties, in collaboration with direct UV-assisted nanoimprint lithography, allow for successful fabrication of solid-state composite polymer electrolytes in geometries that lie far beyond those accessible with conventional electrolytes. As an alternative electrolyte to exceed conventional carbonate-based liquid electrolytes, plastic crystal electrolytes (PCEs) have been investigated. The PCEs, which are composed of lithium salts and plastic crystals bearing good solvation capability, are characterized with unusual thermal stability and ionic transport behaviors. Among various plastic crystal candidates, succinonitrile (SN) is known to show excellence in thermal stability and ionic transport due to high boiling point and structural defects (i.e., trans-gauche isomerism) of plastic crystal phase. Despite of these advantageous characteristics, application of the PCEs to flexible batteries is staggered due to their poor mechanical properties. Most of PCEs are excessively plastic and even more show liquid-like behavior at room temperature. In this talk, we present a wide variety of material strategies to improve the physicochemical properties (in particular, focusing on mechanical flexibility) of SN-based PCEs, which are mainly devoted to integrating with functional polymer matrix that serves as a mechanical framework. The structural design concept demonstrated herein for the synthesis of plastic crystal polymer electrolytes can be suggested as a versatile and scalable electrolyte platform to bring unprecedented opportunities in progress of next-generation flexible energy storage/conversion devices. References Keun-Ho Choi, Sung-Ju Cho, Se-Hee Kim, Yo Han Kwon, Je Young Kim, Sang-Young Lee, "Thin, deformable, and safety-reinforced plastic crystal polymer electrolytes for high-performance flexible lithium-ion batteries", Adv. Funct. Mater. online published.Sang-Young Lee, Keun-Ho Choi, Yo Han Kwon, Hye-Ran Jung, Heon-Cheol Shin, Je Young Kim, "Progress in flexible energy storage and conversion systems, with a focus on cable-type lithium ion battery", Energy Environ. Sci. 2013, 6, 2414. (featured as a back cover image).Eun-Hye Kil, Keun-Ho Choi, Hyo-Jeong Ha, Sheng Xu, John A. Rogers, Mi Ri Kim, Young-Gi Lee, Kwang-Man Kim, Kuk Young Cho, Sang-Young Lee, "Imprintable, bendable, and shape-conformable polymer electrolytes for versatile-shaped lithium-ion batteries", Adv. Mater. 2013, 25, 1395. (featured as a back cover image).

Air-stable n-type colloidal quantum dot solids.

Colloidal quantum dots (CQDs) offer promise in flexible electronics, light sensing and energy conversion. These applications rely on rectifying junctions that require the creation of high-quality CQD solids that are controllably n-type (electron-rich) or p-type (hole-rich). Unfortunately, n-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure. Here we report high-performance, air-stable n-type CQD solids. Using density functional theory we identify inorganic passivants that bind strongly to the CQD surface and repel oxidative attack. A materials processing strategy that wards off strong protic attack by polar solvents enabled the synthesis of an air-stable n-type PbS CQD solid. This material was used to build an air-processed inverted quantum junction device, which shows the highest current density from any CQD solar cell and a solar power conversion efficiency as high as 8%. We also feature the n-type CQD solid in the rapid, sensitive, and specific detection of atmospheric NO2. This work paves the way for new families of electronic devices that leverage air-stable quantum-tuned materials.

Crystallization-induced properties from morphology-controlled organic crystals.

During the past two decades, many materials chemists have focused on the development of organic molecules that can serve as the basis of cost-effective and flexible electronic, optical, and energy conversion devices. Among the potential candidate molecules, metal-free or metal-containing conjugated organic molecules offer high-order electronic conjugation levels that can directly support fast charge carrier transport, rapid optoelectric responses, and reliable exciton manipulation. Early studies of these molecules focused on the design and synthesis of organic unit molecules that exhibit active electrical and optical properties when produced in the form of thin film devices. Since then, researchers have worked to enhance the properties upon crystallization of the unit molecules as single crystals provide higher carrier mobilities and exciton recombination yields. Most recently, researchers have conducted in-depth studies to understand how crystallization induces property changes, especially those that depend on specific crystal surfaces. The different properties that depend on the crystal facets have been of particular interest. Most unit molecules have anisotropic structures, and therefore produce crystals with several unique crystal facets with dissimilar molecular arrangements. These structural differences would also lead to diverse electrical conductance, optical absorption/emission, and even chemical interaction properties depending on the crystal facet investigated. To study the effects of crystallization and crystal facet-dependent property changes, researchers must grow or synthesize crystals of highly conjugated molecules that have both a variety of morphologies and high crystallinity. Morphologically well-defined organic crystals, that form structures such as wires, rods, disks, and cubes, provide objects that researchers can use to evaluate these material properties. Such structures typically occur as single crystals with well-developed facets with dissimilar molecular arrangements. Recently, researchers have proposed several approaches for the vapor and solution phase synthesis of high quality organic crystals with various morphologies. In this Account, we focus on methodologies for the synthesis of various organic- and metal-containing highly conjugated molecular crystals. We also examine the new optical and chemical properties of these materials. In addition, we introduce recent experimental results demonstrating that high crystallinity and specific molecular arrangements lead to crystallization-induced property changes. We believe that the understanding of the crystallization-induced property changes in organic crystals will provide both fundamental knowledge of the chemical processes occurring at various interfaces and opportunities for researchers to take advantage of crystallization-induced property changes in the development of high-performance organic devices.

Design methodology for flexible energy conversion systems accounting for dynamic performance

This article presents a methodology to help in the definition of the optimal design of power generation systems. The innovative element is the integration of requirements on dynamic performance into the system design procedure. Operational flexibility is an increasingly important specification of power systems for base- and part-load operation. Thus, it is crucial to discard, in an early phase of the design process, plant configurations which feature unacceptable dynamic performance. The test case is the preliminary design of an off-grid power plant serving an off-shore platform where one of the three gas turbines is combined with an organic Rankine cycle turbogenerator to increase the overall energy efficiency. The core of the procedure is a stationary model, capable of performing the on-design thermodynamic cycle calculation, and the design of the components of the system. The results of these simulations are used within the framework of a multi-objective optimization procedure to identify a number of equally optimal system configurations. A dynamic model of each of these systems is automatically parameterized, by inheriting its parameters values from the design model. Dynamic simulations allow then to discriminate among the initial set of solutions, thus providing the designs that also comply with dynamic requirements.

Thermoelectric Properties and Thermal Stability of PEDOT:PSS Films on a Polyimide Substrate and Application in Flexible Energy Conversion Devices

In this study, we investigated the flexibility and thermal stability of films consisting of a complex of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) cast onto a polyimide substrate. We also prepared a PEDOT:PSS-based flexible device for thermoelectric energy conversion. The thermal stability of a PEDOT:PSS film was evaluated by measuring the Seebeck coefficient (S) and electrical conductivity (σ) for 30 heating and cooling cycles at 330 K to 380 K. Furthermore, the durability of the PEDOT:PSS film was examined by heating at 353 K in air for 4000 h. The approximate values of S and σ were 14 μV K−1 and 600 S cm−1, respectively. These values were almost the same before and after repeated bending treatments (10,000 times, radius of curvature 10 mm). In addition, the S and σ values for the PEDOT:PSS film were nearly constant during the heating cycle treatments. In the durability test, σ gradually decreased with increasing heating time (7% at 300 h, 17% at 3600 h). Thus, it was found that PEDOT:PSS films have both flexibility and mechanical toughness as well as relatively good thermal stability in air up to 3600 h. The maximum electric power for the PEDOT:PSS-based flexible device was 0.334 μW at ΔT = 100 K. These results for the power-generating properties of the flexible device are consistent with values calculated from the properties of the constituent materials.

Advances and challenges for flexible energy storage and conversion devices and systems

To meet the rapid development of flexible, portable, and wearable electronic devices, extensive efforts have been devoted to develop matchable energy storage and conversion systems as power sources, such as flexible lithium-ion batteries (LIBs), supercapacitors (SCs), solar cells, fuel cells, etc. Particularly, during recent years, exciting works have been done to explore more suitable and effective electrode/electrolyte materials as well as more preferable cell configuration and structural designs to develop flexible power sources with better electrochemical performance for integration into flexible electronics. An overview is given for these remarkable contributions made by the leading scientists in this important and promising research area. Some perspectives for the future and impacts of flexible energy storage and conversion systems are also proposed.

Themed issue on flexible energy storage and conversion

Themed issue on flexible energy storage and conversion

Thermoelectric Properties of Transition Metal Deposited MWCNT Buckypaper

In this work, we report the preparation of transition metal deposited flexible multiwalled carbon nanotube buckypaper for thermoelectric applications. MWCNT buckypaper prepared by dispersion and filtration method was then deposited with the transition metals such as silver (Ag) and copper (Cu) by the electrodeposition method. We measured the voltage yield of Ag and Cu-doped buckypaper by making the temperature gradient along the sample. We established the temperature dependent Seebeck coefficient for Ag and Cu-doped buckypaper and found significant increase in the S(T). It is also revealed that remarkable rise in the value of S(T) and output voltage by connecting 3-sheets of BP in series. Here we determined the enhancement of Seebeck coefficient by increasing the number of BP sheets, thereby improving the thermoelectric efficiency. Furthermore, these paper-like CNT films show good flexibility, which makes them possible to be widely applied in various flexible energy conversion devices.

Fine tuning of the PCDTBT-OR:PC71BM blend nanoscale phase separation via selective solvent annealing toward high-performance polymer photovoltaics

Solution-processable polymer solar cells show great promise for providing a cost-effective route to create lightweight and flexible solar energy conversion devices. The photoactive layer comprising the conjugated polymer donor and fullerene derivative acceptor must be optimized to form bicontinuous nanoscale phase separation in order for efficient exciton dissociation and charge collection due to the short exciton diffusion length of organic semiconductors. The donor polymer poly[9-(heptadecan-9-yl)-9H-carbazole- 2,7-diyl-alt-(5,6-bis(hexyloxy)-4,7-di(thiophen-2- yl)benzo[c][1,2,5]thiadiazole)-5,5-diyl] (PCDTBT-OR) has a deeper highest occupied molecular orbital level compared to its counterpart PCDTBT, and shows promise in increasing the open-circuit voltage and power conversion efficiency (PCE) of polymer solar cells. The phase separation evolution of the PCDTBT-OR:PC71BM blend with various weight ratios under tetrahydrofuran (THF) vapor annealing and its influence on the photovoltaic performance is investigated in detail. It is found that THF vapor annealing can promote the acceptor PC71BM aggregation from the donor PCDTBT-OR matrix to form nanoscale donor/acceptor phase separation for efficient exciton dissociation and charge collection depending on the donor/acceptor weight ratio and the annealing time. The THF vapor-annealed PCDTBT-OR:PC71BM solar cells exhibit remarkable enhancement, with a PCE of 7.01% compared to 3.25% of the as-cast solar cells with the same active layer thickness. This work provides a general methodology to construct nano-interpenetrating networks for homogeneous polymer/fullerene blends and is potentially applicable to the roll-to-roll manufacturing of polymer solar cells.

Highly Conductive and Flexible Paper of 1D Silver-Nanowire-Doped Graphene

A novel architecture of graphene paper is proposed to consist of "1D metallic nanowires/defect-free graphene sheets". Highly conductive and flexible papers of 1D silver nanowires (Ag NWs) and chemical vapor deposition (CVD) graphene sheets as an example were fabricated by a simple filtration method. CVD graphene paper possesses much higher electrical conductivity of 1097 S/cm, compared with other reported carbon-related papers (graphene, carbon nanotube, etc.). With the addition of Ag NWs to form Ag NWs/graphene paper, the electrical conductivity is further improved up to 3189 S/cm, even higher than ∼2000 S/cm of bulk graphite. Ag NWs/graphene papers have very good flexibility with the only <5% loss of electrical conductivity over 500 times mechanical bending. Highly conductive composite papers have potential in high-performance, flexible energy conversion and storage devices.