Flexible Transparent Electrodes Research Articles

Evaporation-induced self-assembled ultrathin AgNW networks for highly conformable wearable electronics

The flexibility and stability of transparent electrodes play a crucial role in the growing popularity of flexible devices, especially in potential wearable electronics. To date, various solution-coating techniques have been developed for fabricating silver nanowire (AgNW) flexible bioelectronics. However, achieving the orderly distributed patterns of AgNW without undesirable aggregations still poses a grand challenge. Here, an approach to realize regular patterned ultrathin AgNW networks on a freestanding electrospun PVDF-TrFE frame by evaporation-induced self-assembly is proposed. The patterning mechanism of evaporating AgNW colloidal suspension is investigated from experimental and theoretical analysis. The influence of evaporation-induced flow inside colloidal freestanding membranes on forming regular square hole-shaped arrays, selective deposition of AgNW, and aligning them along the artificial pinning array are addressed. Owing to the orderly arrangement of AgNW networks, the resultant flexible electrode achieves ultrathin thickness (about 5 μm), high optical transmittance (87.8%), and low sheet resistance (8.4 Ω·sq−1) with a relatively low dosage of AgNW (9 μg·cm−2). The electrode exhibits excellent durability during cyclic bending (50,000 times) and stretching (50% strain). The resistance remains virtually unchanged during 200 days in everyday environments. Furthermore, the excellent conformability and breathability of the flexible transparent electrode attached to the human skin demonstrates its potential application as an e-skin sensor. Our findings reliably urge a simple approach to underscore better outcomes with effective patterns by self-assembly of AgNW for highly conformal wearable electronics.

Encapsulation of Flexible Transparent Electrodes Based on Indium Zinc Tin Oxide with Highly Transparent and Mechanically Robust Polymer Dielectrics

This study was aimed at comprehensively investigating the utility of PMMA and CYTOP as encapsulation layers for flexible transparent electrodes composed of indium zinc tin oxide (IZTO). Optical modeling and experimental techniques were combined to assess the viability of PMMA and CYTOP as encapsulation materials. Optical modeling suggested that PMMA and CYTOP are well-suited for IZTO encapsulation. Subsequent experiment confirmed that the transmittance values of IZTO-films remained unaffected when encapsulated with PMMA and CYTOP. To examine the influence of encapsulation on mechanical resilience, all film, including untreated IZTO and IZTO treated with PMMA/CYTOP, were subjected to 20,000 bending cycles. The mechanical stability and optical properties of the IZTO film were considerably enhanced when encapsulated with these insulating materials. The improvement in transmittance was attributable to the lower refractive index of PMMA and CYTOP. Furthermore, scanning electron microscopy images demonstrated that the remarkable flexibility of PMMA and CYTOP effectively prevented the formation of cracks on the IZTO film, underscoring their pivotal role in enhancing the mechanical robustness of IZTO. In summary, this research highlights the potential of PMMA and CYTOP as efficient encapsulation materials for IZTO-based flexible transparent electrodes, offering dual benefits in terms of optical performance and mechanical durability.

Electroless silver plating combined with laser direct writing technology: For the fabrication of flexible silver mesh transparent electrodes

Ultra-thin metal meshes are emerging as potential candidates for ln2O3 (ITO) due to their mechanical properties, excellent flexibility and optoelectronic properties. However, the manufacturing of high-performance metal meshes is often accompanied by thin-layer metal deposition processes such as sputtering deposition and vacuum evaporation, as well as the combination of imprinting templates, which increases the complexity of the process and production costs. Herein, we have established a finite element theoretical calculation model for predicting the optoelectronic performance of metal meshes and propose a method based on electroless plating silver combined with laser direct writing to prepare high-quality Ag meshes. It provides a way to achieve rapid and economical production of Ag mesh transparent electrodes. The ultra-thin Ag mesh exhibits excellent transmittance (90.2 % at 550 nm), the transmittance is close to 95 % above the 600 nm wavelength band and the sheet resistance is 13.0 Ω/sq. Furthermore, The Ag mesh exhibits excellent mechanical flexibility, indicated by the fact that the resistance is almost unchanged after 5000 bending cycles.

Ecofriendly Cellulose Substrate‐Based Flexible Transparent Electrode for Flexible Organic Solar Cells with Efficiency Over 18%

Flexibility is a key advantage of organic solar cells (OSCs), and the power conversion efficiencies (PCEs) of flexible OSCs (FOSCs) are primarily constrained by flexible transparent electrodes (FTEs). While much attention has been devoted to the study of conductive layers on FTEs, the importance of flexible substrates in influencing the properties of FTEs and the performance of FOSCs is often overlooked. In this study, an FTE is developed using an eco‐friendly ethyl cellulose (EC) substrate and silver nanowires (AgNWs) as the conductive electrode. The FTE exhibits a high transmittance of up to 88% at 550 nm and a low sheet resistance of 17.65 Ω/□. Consequently, FOSCs based on the EC/PI FTEs achieve a remarkable PCE of 18.05%, comparable to that on the rigid ITO substrate. The flexible devices also demonstrate excellent bending and peeling durability even under extreme bending conditions.

Silver Nanowires (AgNWs) Post-Treatment Effect in Application of Flexible Transparent and Conductive Electrodes: A Mini Review

Transparent flexible electrodes (TFEs) are extremely crucial for expanding flexible and wearable electronic devices. Silver nanowires (AgNWs) have been extensively investigated as an alternative to replace Indium Tin Oxide (ITO) as a commercial TFE due to their high conductivity, transparency, and flexibility. AgNWs have replaced ITO-based electrodes as the preferred approach in flexible, transparent, and conductive electrodes (FTCE). AgNWs outperform other materials, such as Reduced Graphene Oxide (RGO), ceramic material, Carbon Nanotubes (CNT), and conductive polymers, in terms of electrical conductivity, transmittance, flexibility, and low sheet resistance. Numerous techniques, including as electrospinning, spray coating, spin coating, and doctor blades, are used to use AgNWs as flexible substrates. Seed-based growth and template-assisted synthesis are two fundamental synthesis techniques that could be used to generate AgNWs. However, poor adhesiveness, and thermal and electrical stability, begin to be bottlenecks for AgNWs as high deployment in a variety of devices. So AgNWs synthesis process began to shift to other methods, such as wet chemical and polyol. In this paper, short and clear summary of various advances including post-treatment methods such as UV radiation, microwave, sonication, quenching, and so on is conducted to be one step forward to test mechanical properties and to improve AgNWs performance.

Opto-electrochemical variation with gel polymer electrolytes in transparent electrochemical capacitors for ionotronics

Advanced flexible ionotronic devices have found excellent applications in the next generation of electronic skin (e-skin) development for smart wearables, robotics, and prosthesis. In this work, we developed transparent ionotronic-based flexible electrochemical capacitors using gel electrolytes and indium tin oxide (ITO) based transparent flexible electrodes. Different gel electrolytes were prepared using various salts, including NaCl, KCl, and LiCl in a 1:1 ratio with a polyvinyl alcohol (PVA) solution and compared its electrochemical performances. The interaction between gel electrolytes and ITO electrodes was investigated through the development of transparent electrochemical capacitors (TEC). The stable and consistent supply of ions was provided by the gel, which is essential for the charge storage and discharge within the TEC. The total charge contribution of the developed TECs is found from the diffusion-controlled mechanism and is measured to be 4.59 mC cm−2 for a LiCl/PVA-based gel. The prepared TEC with LiCl/PVA gel electrolyte exhibited a specific capacitance of 6.61 mF cm−2 at 10 μA cm−2. The prepared electrolyte shows a transparency of 99% at 550 nm and the fabricated TEC using LiCl/PVA gel exhibited a direct bandgap of 5.34 eV. The primary benefits of such ionotronic-based TEC development point to its potential future applications in the manufacturing of transparent batteries, electrochromic energy storage devices, ionotronic-based sensors, and photoelectrochemical energy storage devices.

Tri-system integration in metal-oxide nanocomposites via in-situ solution-processed method for ultrathin flexible transparent electrodes

For stable operation of ultrathin flexible transparent electrodes (uFTEs), it is critical to implement effective risk management during concurrent multi-loading operation of electrical bias and mechanical folding cycles in high-humidity environments. Despite extensive efforts in preparing solution-processed uFTEs with cost-effective and high-throughput means, achieving in-situ nano-adhesion in heterogeneous metal-oxide nanocomposites remains challenging. In this work, we observed by serendipity liquid-like behaviour of transparent metal-oxide-semiconductor zinc oxide nanoparticles (ZnONPs) onto silver nanowires (AgNWs) developed by in-situ solution processed method (iSPM). This enabled us to address the long-standing issue of vulnerability in the nanocomposite caused by the interface of dissimilar materials between AgNWs and ZnONPs, resulting in a remarkably improved multi-loading operation. Importantly, substrate-integrated uFTEs constituted of the metal-oxide nanocomposite electrode semi-embedded in the polymer matrix of greatly thin <0.5 μm thickness is successfully demonstrated with the smooth surface topography, promoted by the tri-system integration including (i) AgNW-AgNW, (ii) ZnONP-ZnONP, and (iii) AgNW-ZnONP systems. Our finding unveils the complex interfacial dynamics associated with the heterogeneous interface system between AgNWs and ZnONPs and holds great promise in understanding the in-situ nano-adhesion process and increasing the design flexibility of next generation solution-processed uFTEs.

Multilayer ordered silver nanowire network films by self‐driven climbing for large‐area flexible optoelectronic devices

AbstractSilver nanowire (AgNW) networks hold great promises as next‐generation flexible transparent electrodes (FTEs) for high‐performance flexible optoelectronic devices. However, achieving large‐area flexible AgNW network electrodes with low sheet resistance, high optical transmittance, and a smooth surface remains a grand challenge. Here, we report a straightforward and cost‐effective roll‐to‐roll method that includes interface assembly/wetting‐induced climbing transfer, nanowelding, and washing processess to fabricate flexible ordered layered AgNW electrodes with high network uniformity. By manipulating the stacking number of the interfacially assembled AgNW monolayer, we can precisely tailor and balance the transparency and the conductivity of the electrodes, achieving an exceptional Figure of Merit (FoM) value of 862. Moreover, the ordered layered structure enhances surface smoothness, compared with randomly arranged structures. To highlight the potential of these ordered layered AgNW network electrodes in flexible optoelectronic devices, we successfully employ them as highly sensitive strain sensors, large‐area flexible touch screens, and flexible smart windows. Overall, this work represents a substantial advance toward high‐performance FTEs over large areas, opening up exciting opportunities for the development of advanced optoelectronic devices.image

Fabrication of surface embedded silver cellulose-based flexible transparent electrodes by self-assembly

Fabrication of surface embedded silver cellulose-based flexible transparent electrodes by self-assembly

Flexible Transparent Electrode Based on Ag Nanowires: Ag Nanoparticles Co-Doped System for Organic Light-Emitting Diodes.

Flexible organic light-emitting diodes (FOLEDs) have promising potential for future wearable applications because of their exceptional mechanical flexibility. Silver nanowire (Ag NW) networks are the most promising candidates to replace indium tin oxide (ITO), which is limited by its poor bendability. In this study, three different methods including methanol impregnation, argon plasma treatment, and ultraviolet radiation were used to reduce the junction resistance of Ag NWs to optimize the flexible transparent electrodes (FTEs); which were prepared using Ag NWs and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS). Then, the optoelectronic properties of the FTEs were further improved by using a co-doped system of silver nanowires and silver nanoparticles (Ag NPs), the structure of which consisted of PET/Ag NWs: Ag NPs/PEDOT: PSS/DMSO. The largest FOM value of 1.42 × 10-2 ohm-1 and a low sheet resistance value of 13.86 ohm/sq were obtained using the optimized FTEs. The prepared FOLED based on the optimized FTEs had a luminous efficiency of 6.04 cd/A and a maximum EQE of 1.92%, and exhibited no observed decline in efficiency when reaching maximum luminance. After 500 bending tests, the luminance still reached 82% of the original value. It is demonstrated that the FTEs prepared via the co-doped system have excellent optoelectronic properties as well as high mechanical stability.

Construction of 3D Patterns Through Modified Electrochemical Replication and Transfer

AbstractAs the development of flexible electronics continuously progresses, so does the demand for fabricated 3D electrodes via patterning technology. Electrochemical replication and transfer (ERT) has emerged as an efficient patterning technique, which deposits materials of interest on a predefined template via electroplating and subsequently transfers them onto target substrates. ERT can pattern large‐area 2D electrodes on nontraditional substrates whilst maintaining adequate flexibility, stretchability, and complex surface structures. This study extends the capability of ERT from 2D into 3D patterning. Via the rational design of a 3D SiO2/Si template, in which conductive Si trenches or holes are patterned with insulating SiO2 banks, electroplating of materials only occurs in the exposed Si surfaces so that both continuous and isolated 3D patterns with high aspect ratios up to 4:1 are realized. 3D‐ERT offers a high‐throughput and low‐cost approach to fabricating high Figure of Merit (&gt;30 000) flexible transparent electrodes. Also, the application of 3D‐ERT in constructing highly sensitive, and self‐powered pressure sensors is showcased.

All-solution-processed flexible semitransparent organic solar cells based on sprayed silver nanowire composites as top electrodes

Solution processable transparent top electrodes with good conductivity and high transmittance play a critical role in developing highly efficient semitransparent organic solar cells (ST-OSCs). Herein, a simple low-temperature spray-coating method is proposed to fabricate silver nanowires/zinc oxide nanoparticles (AgNWs/ZnO) composite electrodes. The effects of coverage of ZnO nanoparticles on optoelectronic properties and surface morphologies of the composites are systemically investigated. Compared to the pristine AgNWs, the AgNWs/ZnO composite layer exhibits improved electrical conductivity due to the filling of nanoparticles as well as the capillary force caused during the volatilization of ZnO dispersion. A low sheet resistance of 8.3 Ω/ and a high transmittance of 78.91 % at 550 nm are achieved in the optimized AgNWs/ZnO composite films with excellent thermal and mechanical stabilities. By using the spray-coated AgNWs composite as the top electrode, the PM6:N3 based ST-OSCs prepared on ITO/glass substrate attain a power conversion efficiency (PCE) of 10.88 % and an average transmittance (AVT) of 28.80 % due to the enhanced charge extraction and suppressed trap-assisted recombination. Moreover, fully solution-processed ST-OSCs are fabricated based on AgNWs/ZnO top electrodes, achieving a PCE of 9.01 % and an AVT of 27.8 %. It provides a simple and effective strategy to fabricate transparent flexible top electrodes and may pave the way towards all-solution-processed highly efficient ST-OSCs.

Mechanical Durability and Flexibility in Perovskite Photovoltaics: Advancements and Applications.

The remarkable progress in perovskite solar cell (PSC) technology has witnessed a remarkable leap in efficiency within the past decade. As this technology continues to mature, flexible PSCs (F-PSCs) are emerging as pivotal components for a wide array of applications, spanning from powering portable electronics and wearable devices to integrating seamlessly into electronic textiles and large-scale industrial roofing. F-PSCs characterized by their lightweight, mechanical flexibility, and adaptability for cost-effective roll-to-roll manufacturing, hold immense commercial potential. However, the persistent concerns regarding the overall stability and mechanical robustness of these devices loom large. This comprehensive review delves into recent strides made in enhancing the mechanical stability of F-PSCs. It covers a spectrum of crucial aspects, encompassing perovskite material optimization, precise crystal grain regulation, film quality enhancement, strategic interface engineering, innovational developed flexible transparent electrodes, judicious substrate selection, and the integration of various functional layers. By collating and analyzing these dedicated research endeavors, this review illuminates the current landscape of progress in addressing the challenges surrounding mechanical stability. Furthermore, it provides valuable insights into the persistent obstacles and bottlenecks that demand attention and innovative solutions in the field of F-PSCs.

Research on Flexible Transparent Conductive Electrodes Based on Ultra-Thin Ag in the Form of Grain Boundary with IZO Layer

In this paper, we investigated a transparent conductive electrode (TCE) that satisfies electrical, optical, and mechanical properties, formed by depositing ultra-thin Ag metal in the form of a random grain boundary with an indium zinc oxide (IZO) layer on a PET substrate. Commonly used ITO electrodes are brittle and difficult to apply to flexible devices. In contrast, IZO-based electrodes are mechanically flexible and can be used as flexible TCE, and have high electrical and optical properties. A 90 nm thick IZO electrode has a transmittance of 90.2% at a wavelength of 460 nm and a sheet resistance of 29.5 ohm/sq. In particular, Ag metal was deposited in the form of an atypical metal island using an RF magnetron sputtering system. At 3 nm there were few metal clusters in the form of islands, and many void channels were formed, resulting in high sheet resistance as well as a decrease in optical transmittance. However, about 5 nm thickness, the number of void channels decreased and the optical path changed, improving the electrical and optical properties. Results showed that the sheet resistance was reduced to 19.8 ohm/sq, and the transmittance was also increased to 91.1%. The mechanical properties were also found to be the same for conventional IZO and Ag/IZO TCE.

Stability of Silver-Nanowire-Based Flexible Transparent Electrodes under Mechanical Stress

Flexible transparent electrodes are integral to the advancement of flexible optoelectronic devices such as flexible displays and solar cells. However, indium tin oxide (ITO), a traditional material used in transparent electrodes, exhibits a significant increase in resistance under mechanical stress, which limits the long-term stability of flexible devices. Here, we prepare various types of silver nanowire (AgNW)-based transparent electrodes and investigate their stability in terms of electrical resistance and optical transmittance under compressive and tensile stresses. Under compressive stress, ITO on a polyethylene terephthalate (PET) substrate exhibits a significantly high electrical resistance of &gt;3000 Ω after 1000 stress cycles, while the AgNW-coated electrode on a PET film exhibits a relatively smaller resistance of &lt;1200 Ω. The AgNW-embedded electrode in a UV-curable polymer matrix (NOA63 or NOA71) exhibits an even lower electrical resistance of &lt;450 Ω because AgNWs can easily maintain their network. A similar trend is observed under tensile stress. The AgNW-embedded electrode shows the highest resistance stability, whereas the ITO on the PET substrate shows the poorest stability. The optical transmittance is comparable regardless of the type of stress or electrode used. This superior stability of the AgNW-based electrodes, realized by integrating it with a polymer matrix, is promising for the development of durable and high-performance flexible optoelectronic devices.

Flexible transparent Ag NW micromesh electrode with enhanced electrical and thermal properties for multifunctional smart panel applications

With the advent of next-generation smart panels, it is highly desirable to integrate multiple functions for application in intelligent buildings, human–machine interfaces, art exhibitions, etc.

One‐step elaboration of flexible transparent conductive electrodes from silver nanowires/polymer nanocomposites

AbstractA new simplified low temperature deposition method to manufacture flexible transparent conductive electrodes (FTCE) based on conductive polymer composite filled with silver nanowires (AgNWs) was investigated. Polyurethane/AgNWs composite was deposed on a poly(ethylene terephthalate) substrate as a conductive paint in a thin layer lower than 2 μm. The high aspect ratio nanowires influence on the electrical behavior is followed with surface resistivity and optical transparency experiments. The best compromise was obtained with a conductive layer filled with 2.84 vol.% of AgNWs; it exhibits a surface resistivity of 143 Ω/sq with 73% in transmittance. These transparent conductive composites processing in one step with good touching manipulation resistance demonstrate the real interest for this kind of FTCEs technology without indium tin oxide.

Effects of copper metal organic decomposition ink on properties of single-walled carbon nanotube based flexible transparent electrodes

The effects of copper metal organic decomposition (Cu MOD) ink on the electrical and mechanical properties of SWCNT-based flexible transparent electrodes were investigated. In particular, we designed and demonstrated Cu MOD ink as bonding agents between oxidized SWCNT (Ox-SWCNT) and the polyethylene terephthalate (PET) substrate. PET substrates were surface-treated via plasma etching, and ultraviolet/ozone (UV/O3) treatment was conducted for enhancing the dispersion of SWCNTs. Subsequently, spray coating of numerous times with Ox-SWCNT dispersion and once with Cu MOD ink was applied to the PET substrates at low temperatures. In this way, a robust, flexible, and transparent Ox-SWCNT/Cu@PET composite electrode was fabricated. The as-prepared Ox-SWCNT/Cu@PET composite electrode exhibited good properties, with a sheet resistance of 483.9 Ω/sq and transmittance of 82.1%. Even after 10000 bending cycles and 100 peel-off times, the resistance was only increased by factors of 1.07 and 1.12, respectively, confirming good mechanical robustness. In addition, the electrode exhibited excellent environmental stability; its electrical resistance was only increased by a factor of 1.35 after subjected to harsh environmental conditions (85 °C, 85% relative humidity) for 48 h. These results indicate that the Ox-SWCNT/Cu@PET composite electrodes are promising for wide application as FTCEs.

Stability enhancement and patterning of silver nanowire networks by conformal TiO2 coating for flexible transparent conductive electrodes

Stability enhancement and patterning of silver nanowire networks by conformal TiO2 coating for flexible transparent conductive electrodes

Highly durable and flexible transparent electrode on PET based on copper and cupronickel multilayer

Multilayer grid electrodes consisting of Cu0.7Ni0.3/Cu/Cu0.7Ni0.3 utilize the high conductivity of Cu to realize low electrical resistance and the high corrosion resistance of CuNi to improve reliability. The effect of thickness of outer CuNi layer on corrosion resistance and visibility was investigated. Samples prepared with 2 μm line width on PET having grid mesh side length of 300 μm, and 60° internal angle with 280 nm thickness showed a transmittance of 90.1% at 550 nm and sheet resistance of 2.4 Ω/□ after grid pattern formation. The low process temperature enabled electrode formation on thin substrate, 23 μm-thick PET and accomplish highly durable and flexible electrode on PET. The superior bending properties showed no change in sheet resistance after 200 000 cycles of outer/inner fatigue bending tests at 3 mm radius of curvature. Additionally, the potential for foldable usage was further supported by demonstrating the ability to form electrodes on both sides of the film.