Flexible Energy Devices Research Articles

A Porous and Interconnected Polypyrrole Film with High Conductivity and Ion Accessibility as Electrode for Flexible All‐Solid‐State Supercapacitors

AbstractNanoporous electrodes with high electrical conductivity and good mechanical properties are attractive for high‐performance flexible supercapacitors. In this work, we report a flexible polypyrrole (PPy) film electrode synthesized by a modified versatile vapor‐phase polymerization (VPP) strategy. Differing from conventional VPP protocols that are likely to form smooth polymer films, it could easily engineer the PPy film with porous and interconnected structure by simply optimizing the concentration of oxidant and the polymerization time. The film electrode showed an exceptionally high electrical conductivity up to 94 S cm−1. The unique porous PPy films constructed by interconnected electronic/ionic conductive networks achieved a specific capacitance of 494 F g−1(corresponding to 836 mF cm−2) at a current density of 1 A g−1. The fabricated all‐solid‐state supercapacitor device with the PPy electrodes exhibited a specific capacitance of 300 F g−1 at 1 A g−1 and a high energy density of 26.67 kW kg−1. The high electrochemical performance and outstanding mechanical properties present the film electrode promising potential for flexible energy devices in various applications.

Low temperature ZnO/TiOx electron-transport layer processed from aqueous solution for highly efficient and stable planar perovskite solar cells

Owing to the low temperature processability and high charge carrier mobility, ZnO has been successfully employed in perovskite solar cells (PSCs) to act as the electron transport layer. Even so, because of the poor ZnO/perovskite interface chemical stability, achieving highly efficient and stable PSCs is still challenging the researchers. Therefore, the optimization of ZnO/perovskite interface by proper surface passivation has been developed for highly efficient PSCs. In this work, an environmentally friendly low-temperature aqueous solution-processed TiOx was applied on the aqueous solution-processed ZnO surface to promote the ZnO/perovskite interface stabilization and the interface charge recombination reduction. High performance PSCs with over 19% efficiency and relatively good stability were finally obtained. This low temperature aqueous solution-processed ZnO/TiOx route is simple and scalable, and facilities the future commercialization of perovskite based photovoltaic technology. Meanwhile, it is also compatible with the flexible energy devices.

Milli-Watt Power Harvesting from Dual Triboelectric and Piezoelectric Effects of Multifunctional Green and Robust Reduced Graphene Oxide/P(VDF-TrFE) Composite Flexible Films.

For a variety of mechanical energy harvesting as well as biomedical device applications, flexible energy devices are useful which require the development of environment-friendly and robust materials and devices. In this manuscript, we demonstrate a lead-free, facile, low-cost, sol-gel-processed reduced graphene oxide (rGO)/P(VDF-TrFE) nanocomposite with multipurpose capability demonstration as a piezoelectric nanogenerator (PENG) and hybrid piezoelectric triboelectric nanogenerator (HPTENG) devices. The structural analysis of the materials shows that the interactions between the rGO and P(VDF-TrFE) matrix help in breaking the centrosymmetry of rGO, resulting in a strong enhancement in the piezoelectric, ferroelectric, and triboelectric properties of composites over pristine P(VDF-TrFE) films. In the case of PENG, the composite devices showed >22 times improvement in the piezoelectric output voltage over the pristine P(VDF-TrFE) PENG device with the highest output voltage of 89.7 V for the 0.5 wt % rGO composite. Also, HPTENG devices based on composite films generated an average VOC of 227 V, much higher than the pristine P(VDF-TrFE)-based devices. Maximum output power densities measured were 0.28 W/cm3 and 0.34 mW/cm3 for hybrid piezoelectric-triboelectric and piezoelectric devices, respectively. The triboelectric devices demonstrated lighting of 45 blue light-emitting diodes directly, connected in series, by harvesting mechanical energy generated by repeated finger tapping. The study highlights the promise of rGO/P(VDF-TrFE) composites for PENG and HPTENG devices with dramatically improved electrical output.

Silk-Based Advanced Materials for Soft Electronics.

Soft bioelectronics that could be integrated with soft and curvilinear biological tissues/organs have attracted multidisciplinary research interest from material scientists, electronic engineers, and biomedical scientists. Because of their potential human health-related applications, soft bioelectronics require stringent demands for biocompatible components. Silk, as a kind of well-known ancient natural biopolymer, shows unique combined merits such as good biocompatibility, programmable biodegradability, processability into various material formats, and large-scale sustainable production. Such unique merits have made silk popular for intensive design and study in soft bioelectronics over the past decade. Due to the development of fabrication techniques in material processing and progress in research, silk has been engineered into a variety of advanced materials including silk fibers/textiles, nanofibers, films, hydrogels, and aerogels. Natural and regenerated silk materials can also be transformed into intrinsically nitrogen-doped and electrically conductive carbon materials, due to their unique molecular structure and high nitrogen content. The rich morphologies and varied processing options for silk materials can furnish transformed carbon materials with well-designed structures and properties. The favorable and unique material merits of silk materials and silk-derived carbon materials offer potential applications in soft electronics. Based on commercial silk fibers/textiles and the availability of re-engineered silk materials with versatile technological formats, functional soft electronics have been explored with silk as flexible biosupports/biomatrixes or active components. These soft systems include bioresorbable electronics, ultraconformal bioelectronics, transient electronics, epidermal electronics, textile electronics, conformal biosensors, flexible transistors, and resistive switching memory devices. Silk-derived carbon materials with rationally designed morphologies and structures have also been developed as active components for wearable sensors, electronic skins, and flexible energy devices, which provide novel concepts and opportunities for soft electronics. In this Account, we highlight the unique hierarchical and chemical structure of natural silk fibers, the fabrication strategies for processing silk into materials with versatile morphologies and into electrically conductive carbon materials, as well as recent progress in the development of silk-based advanced materials (silk materials and silk-derived carbon materials) for soft bioelectronics. The design and functionality of soft electronics developed with commercial silk fibers/textiles, re-engineered silk materials, and silk-derived carbon materials as biosubstrate/matrix and active components is introduced in detail. We further discuss future challenges and prospects for developing silk-based soft bioelectronics for wearable healthcare systems. By leveraging the unique advantages of silk-based advanced materials, the design and construction strategy for flexible electronics, as well as the potential of flexible electronics for conformable and intimate association with human tissues/organs, silk-based soft bioelectronics should have a significant impact on diverse healthcare fields.

Recent advances in the physics of polymer systems

Recent advances in the physics of polymer systems

In situ tensile fracturing of multilayer graphene nanosheets for their in-plane mechanical properties

The excellent mechanical properties of single- and few-layer graphene have been well-quantified and evidenced by computational methods and local indentation measurements. However, there are less experimental reports on the in-plane mechanical properties of multilayer graphene sheets, despite many practical applications in flexible electronic and energy devices (e.g. graphene flexible electronic display, battery, and storage devices) are actually based on these thicker nanosheets. Here, in-plane fracture behaviors of multilayer graphene nanosheets with thicknesses between ∼10 and 300 nm (∼10–1000 layers) are characterized and quantified by in situ scanning electron microscopy and transmission electron microscopy under tensile loading. We found that, generally, the fracture strengths of graphene nanosheets decrease as the thickness (or layers) increases; however, the fracture strain of thinner graphene sheets is less than that of thicker sheets. The fracture process of the thicker nanosheets includes the initial flattened stage, the stable elastic stage, and the rapid fracture with brittle characteristics, while the thinner nanosheets show obvious delamination between the atomic layers at fracture. This work provides critical experimental insights into the tensile fracture behavior of multilayer two-dimensional materials and a better understanding on their realistic mechanical performance for potential flexible device and composite applications.

Monolithic integration of flexible lithium-ion battery on a plastic substrate by printing methods

Energy storage devices with flexible form factor have become critical components of wearable electronic systems. Inspired by methods of monolithic integration in the microelectronics fabrication process, we propose a planar flexible full-solid-state lithium-ion battery (FSLB) architecture and a layer-by-layer stencil printing assembly method for fabricating batteries on polyethylene terephthalate (PET) substrate. FSLBs use quasi-solid electrolyte based on LiTFSI and ultraviolet (UV)-curable ethoxylated trimethylolpropane triacrylate (ETPTA) polymeric matrix in combination with Li4Ti5O12 (LTO)/LiFePO4 (LFP)-based electrodes. Excellent mechanical flexibility (< 10 mm bending radius) can be achieved. The electrochemical characteristics of electrolyte, including ion conductivity, physical stability during room-temperature and tender assembly processes, are promising. A complete thin film-shape FSLB demonstrated working operation both under planar and bending conditions. The unique architecture and assembly processes open new ways for planar flexible devices to be integrated with flexible energy devices.

Design of conductive pattern on recycled paper

PurposeIn the current study, the authors prepared conductive nano-structured thin films composed of copper on the surface of the printed paper using a magnetron sputtering system. Furthermore, the printability of conductive films for the sake of re-using printed paper and its additional applications were also investigated.Design/methodology/approachPaper-based electronic devices have been the matter of intense interest because of their easy accessibility, lightweight, low cost, biodegradable, recyclable and ecofriendliness. Furthermore, these devices are inexpensive compared to other substrates. Nowadays, flexible energy and electronic devices made of the paper substrate are receiving a significant interest because of the issue of sustainable energy production from the environment. One of the most reliable techniques for the deposition of thin films and creating conductive patterns on the paper is magnetron sputtering.FindingsThe printed and coated printed papers were evaluated with X-ray powder diffraction, scanning electron microscopy with energy-dispersive (SEM-EDX), four-point probe conductivity and spectroscopic measurements.Practical implicationsThe paper investigates the printability of conductive paper attributable to its second application.Originality/valueThe authors prepared conductive nanostructured copper-based thin films on the surface of the printed paper. They recovered and reused the paper as a root of raw material due to the environmental issue.

A facile method to conduct 3D self-supporting Co-FeCo/N-doped graphene-like carbon bifunctional electrocatalysts for flexible solid-state zinc air battery

The rapid development of wearable and portable electronics is triggering a lot of researches on flexible energy device. Flexible zinc-air batteries (ZABs) with high bifunctional oxygen electrocatalytic activity and superb flexible can be employed as promising power supplies to fulfill these novel electronic devices. Considering the major challenges to the flexible ZABs such as low power density, poor energy efficiency and unsatisfactory mechanical stability, we propose a novel plasma-assistance strategy to prepare highly foldable self-supporting air-electrodes based on nitrogen-doped carbon layer encapsulated Co and FeCo nanoparticles hybrid nanowire arrays (Co-FeCo/N-G). The obtained Co-FeCo/N-G air-electrode show superior oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) activity. Thus, the flexible ZABs using Co-FeCo/N-G air-electrode achieve a high open circuit voltage of 1.419 V. Furthermore, it exhibits an outstanding peak power density of 82 mW cm−2, a small discharge-charge voltage gap of 0.61 V at 1 mA cm−2 and long-term durability. Specially, the flexible Co-FeCo/N-G ZAB displays excellent mechanical stability under large deformation conditions, which can be folded into 180° without obvious decay of its performance. Thereby, our work offers a unique insight into design of highly flexible air electrodes with favorable electrocatalytic activity for emerging wearable and portable electronics.

Thermally etched porous carbon cloth catalyzed by metal organic frameworks as sulfur hosts for lithium–sulfur batteries

Activated carbon cloth (CC) plays vital roles in the fabrication of flexible energy devices, structured supports for catalysts, and CO2 capturer, etc. In terms of the conventional processing methods of activated CC, KOH and CO2 are the representative activation agents. Based on the idea of waiving the use of concentrated alkali and specialty gases, we demonstrate herein a highly efficient and previously unreported method of CC activation with a two-step procedure: homogeneous growth of metal organic frameworks (MOFs) on CC and subsequent activation catalyzed by the MOF derivatives. During pyrolysis, the MOF structures are transformed into Co3O4 particles, which react with carbon, leading to etching of the carbon fiber. This method can be used to form activated CC with coexistence of micropores, mesopores, and macropores. With the benefit of such hierarchical and unique structures, a free-standing sulfur-impregnated porous CC electrode demonstrates obvious advantages over CC-supported sulfur melt or sulfur slurry electrodes, which demonstrates great feasibility of MOF catalyzing porosification of CC for practical applications. This reported method not only broadens the scope of application of MOFs, it could also be further used to create hierarchical structures on other carbonaceous materials in various fields.

3D Interlaced Networks of VO(OH)2 Nanoflakes Wrapped with Graphene Oxide Nanosheets as Electrodes for Energy Storage Devices

The evolution of newfangled electrode materials with excellent properties has gained tremendous attention in order to meet the requirements applied to flexible energy devices. Vanadium oxides have ...

Recent Advances in Growth and Modification of Graphene‐Based Energy Materials: From Chemical Vapor Deposition to Reduction of Graphene Oxide

AbstractGraphene is recognized as the next generation of energy materials due to its spectacular physical properties. Meanwhile, there are diverse synthetic methods toward graphene, and these methods have unique advantages to impel graphene to be suitable for different energy devices. Chemical vapor deposition and reduction of graphene oxide are classical methods for preparing graphene with various lattice structures and layer numbers, resulting in the tunability of graphene properties, whereby the synthetic methods have significant effects on energy device performances. Therefore, this review pays close attention to the discrepancies of graphene‐based materials prepared by these two methods for use in solar cells, rechargeable batteries, and electrocatalysis for hydrogen evolution. Furthermore, the modifications of graphene are introduced to offset the weaknesses of synthetic methods. Then, the review introduces graphene‐based flexible energy devices because graphene prepared by these two methods shows similarity in their mechanical stability. Finally, other synthetic methods are shortly highlighted to explain the importance of these two methods. The analyses for the discrepancies and similarity of graphene‐based materials in classical energy devices from the aspect of synthesis are beneficial to guide the preparation and modifications of graphene for maximizing its application and promote practical usage in the future.

Ni-Co-N hybrid porous nanosheets on graphene paper for flexible and editable asymmetric all-solid-state supercapacitors

Great attention has been drawn to flexible and portable electronic devices, so it is important to develop flexible energy-storage devices. In this study, the porous Ni-Co-N nanosheets on flexible graphene paper (GP) are prepared by surface nitridation of NiCo2O4 nanosheets. Compared with NiCo2O4/GP, Ni3N/GP and CoN/GP, Ni-Co-N/GP shows superior performance in terms of specific capacitance of 960 F/g (48.1 mF/cm2) at 4 A/g, rate performance (86% capacitance retention) and cycle life (the capacitance retention reaches 95% over 5000 cycles). The paper-based all-solid-state asymmetric supercapacitors (SCs) are manufactured based on Ni-Co-N/GP and chemical oxidized GP (graphene oxide paper, GOP), which exhibits excellent bendability, flexibility, editability. The flexible energy device shows an outstanding specific energy of 4.78 mWh/cm3 and excellent cycle life (89% capacitance retention after 8000 cycles).

Interface engineering of low temperature processed all-inorganic CsPbI2Br perovskite solar cells toward PCE exceeding 14%

All-inorganic perovskite CsPbI2Br has received much attention recently due to its suitable bandgap and excellent thermal stability. Herein, we demonstrated a low temperature solution process to obtain high quality CsPbI2Br films and fabricate devices with a facile n-i-p structure (ITO/SnO2/CsPbI2Br/Spiro-OMeTAD/MoO3/Ag), in which MoO3 was introduced as interfacial layer that led to high efficient charge extraction and suppressed carrier recombination. As a result, the champion cells exhibited a relatively high power conversion efficiency of 14.05% and superb fill factor of 81.5%. More importantly, unencapsulated PSCs with MoO3 interfacial layers showed outstanding stabilities with retaining 80% of initial PCE with thermal treatment at 85 °C for 140 min in ambient air, 80% of initial PCE under continuous illumination for 120 min in ambient air, and 89% of initial PCE after being stored in N2 glove-box over 60 days. Meantime, it should be mentioned that all interlayers and active layer were processed at temperature below 160 °C, and hence, this fabrication technique is promising for flexible energy devices and future commercialization.

Flexible gasochromic films with favorable high temperature resistance and energy efficiency

Flexible gasochromic solar energy devices have received extensive attention in recent years. It is difficult to prepare flexible gas chromogenic films by traditional methods. In practical application, with the rise of temperature, the performance of the conventional gasochromic film decreases significantly and is even completely unusable. Therefore, it is necessary to develop gasochromic films with good high temperature resistance. Photo-deposition, a simple method to prepare porous tungsten oxide gasochromic film using tungsten hexachloride and ethanol was reported. We developed this facile method to prepare the flexible edge-sharing WO3 gasochromic films on Polyethylene terephthalate (PET). The WO3 films prepared by this method on glass can keep the high porosity after heated at 250 °C and also can keep the fast speed of the gasochromic (tc,90%=22 s and tb=4 s) after 300 cycles. In addition, the gasochromic films still can be homogeneous extraordinarily after folded 180 degrees for 100 times. Finally, we also demonstrate a flexible tent consist of WO3 gasochromic films by this way which is a possible use of the film we proposed by coating on PET.

Flexible Energy Harvester Based on Poly(vinylidene fluoride) Composite Films.

In these days, we are facing emerging energy crisis due to depletion of fossil fuels. Therefore, renewable energy which is based on wind energy, mechanical force energy, microwave energy and vibrations energy have attracted a lot of attentions. Piezoelectric energy harvesting is one of the promising renewable energy sources. As the use portable electronic devices increases, the need for portable renewable energy sources further increases. Especially, piezoelectric materials can be the best selection due to their robust properties. In this research, piezoelectric composites were prepared and investigated for piezoelectric energy harvesting applications. In this study, two types of flexible energy harvesters, 0.36BS-0.64PT-PVDF composite and PVDF film, were prepared and analyzed. Due to its high Curie temperature and low lead content, BS-PT is expected to be a substitute for PZT in the near future. The composite materials based on the PVDF and 0.36BS-0.64PT film showed higher open circuit voltage (0.73 V) than PVDF film (0.49 V). Also, the stored voltage of 0.36BS-0.64PT-PVDF composite film was 330 nJ which is 5.68 times higher than 58 nJ for PVDF films. By introducing the piezoelectric BS-PT ceramics, 0.36BS-0.64PT-PVDF composite film shows the enhanced performance such as open circuit voltage, energy and dielectric constant compared with those of PVDF materials. It seems that 0.36BS-0.64PT-PVDF composite film is more suitable for flexible energy device.

Nanoimprint lithography for the manufacturing of flexible electronics

Flexible electronics have received considerable attention in academies and industries for their promising applications in enormous fields, such as flexible displays, wearable sensors, artificial skins, and flexible energy devices. Challenges remain in developing a flexible and scalable manufacturing method to facilitate the fabrication of multi-functional structures in a flexible electronic system. Nanoimprint lithography is a high resolution and low-cost approach to fabricate nanostructures over a large area. This paper reviews recent progress of nanoimprint lithography and its applications in flexible electronics. The basic principles, classification, research focus, and critical issues of nanoimprint lithography are elaborated. Then, the advantages of nanoimprint lithography are demonstrated in several typical applications related to flexible electronics, including conductive films, optoelectronic devices, flexible sensors, energy harvesting and storage devices, and bioinspired electronic devices. Finally, the challenges and perspectives of nanoimprint lithography in flexible electronic systems are discussed.

Highly porous structured polyaniline nanocomposites for scalable and flexible high-performance supercapacitors.

Recently, flexible energy devices have been used to power up portable electronics such as E-skins, smart clothes, and bendable displays. However, the usage of rigid and inactive components in electrode materials limits the application in flexible energy devices. Here, we report a novel method to fabricate porous polyaniline composites (Pt_CPPy/PANI:CSA) using Pt decorated carboxyl polypyrrole nanoparticles (Pt_CPPyNPs) as a nucleating agent for electrodes of supercapacitors. The specific capacitance and electrical conductivity of the Pt_CPPy/PANI:CSA film are 325.0 F g-1 and 814 S cm-1, respectively, which are much higher than those of the pristine PANI:CSA film. Furthermore, the porous PANI:CSA composites exhibit excellent rate capability and cycling stability as the pores in the PANI structure enhance the active surface area between PANI and the ions of the electrolytes. This unique fabrication technique is an effective approach for preparing large scale highly porous polyaniline nanomaterials for diverse electrochemical applications.

Photo-responsive heterojunction nanosheets of reduced graphene oxide for photo-detective flexible energy devices

Ultrasonication-assisted delamination and assembly of transition metal dichalcogenides with graphene for heterogeneous nanosheets used in photo-sensitive wearable energy devices.

Stretchable/flexible silver nanowire Electrodes for energy device applications.

Research on sustainable and high-efficiency energy devices has recently emerged as an important global issue. These devices are now moving beyond the form of a bulk, rigid platform to a portable, flexible/stretchable format that is easily available in our daily lives. Similar to the development of an active layer for the production of next-generation energy devices, the fabrication of flexible/stretchable electrodes for the easy flow of electrons is also very important. Silver nanowire electrodes have high electronic conductivity even in a flexible/stretchable state due to their high aspect ratio and percolation network structures compared to conventional electrodes. Herein, we summarize the research in the field of flexible/stretchable electronics on energy devices fabricated using silver nanowires as the electrodes. Additionally, for a systematic presentation of the current research trends, this review classifies the surveyed research efforts into the categories of energy production, storage, and consumption.