Flexible Transparent Conductive Electrodes Research Articles

Facile Nanowelding Process for Silver Nanowire Electrodes Toward High‐Performance Large‐Area Flexible Organic Light‐Emitting Diodes

AbstractDespite considerable interest, uniform and robust flexible transparent conducting electrodes (FTCEs) that can be seamlessly integrated and used for highly efficient large‐area flexible oganic light‐emitting diodes (OLEDs) remain elusive. In this study, a large‐area fabrication of uniform transparent electrodes for high‐performance flexible OLEDs by exploiting the rapid nanowelding process of silver nanowires (AgNWs) onto polyethylene terephthalate substrate under Xe‐lamp irradiation and mechanical pressing treatment is reported. The performance of AgNWs FTCEs is significantly enhanced by applying the Xe‐lamp beam irradiation for 5 s and subsequent compression at 20 MPa for 15 s, achieving a low sheet resistance of 26.5 Ω sq−1, a high transmittance of 95.2% (at 550 nm), and very smooth surfaces with root‐mean‐square of 5.4 nm. Meanwhile, the nanowelded AgNWs FTCEs maintain excellent electrical conductivity (only a 2.96% increase in ΔR/R0) after 1000 bending cycles. The resulting AgNWs FTCEs‐based green phosphorescent OLED achieves an unprecedented external quantum efficiency (EQE) of 23.7% and a current efficiency as high as 81.5 cd A−1. Benefiting from the uniform properties for resulting AgNWs FTCEs, the fabricated flexible OLED with a large area of 25 × 25 mm2 still retains a high EQE of 22.2% and a current efficiency of 78.0 cd A−1.

Scalable one-step synthesis of reduced graphene oxide: Towards flexible transparent conductive films and active supercapacitor electrodes

The reduced graphene oxide (rGO) thin films have attracted much attention in flexible electronic devices and supercapacitors (SCs). However, the chemical reduction mechanism of GO needs to be clarified, and the one-step process at low temperatures for preparing high-quality rGO thin films from GO dispersions is still blank in the research field. Here, we propose a one-step operation to spray GO dispersions onto substrate or current collector under a hydroiodic acid (HI) atmosphere while simultaneously achieving the preparation of rGO thin films. This pioneering metal-free, transfer-free, fast, low-temperature, environmentally friendly, and scalable spraying technology enables large-scale production of high-quality rGO. This method realizes the preparation of highly conductive and high transmittance rGO thin films on flexible polyimide and polyethylene terephthalate substrates, as well as the preparation of rGO thin films on current collectors as SCs electrodes. Density functional theory calculations show that oxygen-containing functional groups on the surface of GO exhibit a stronger adsorption energy for HI, and have a low energy barrier during reduction by HI. Ab initio molecular dynamics simulated the possible reduction reaction path between GO and HI at 90 °C, demonstrating that HI molecules can effectively reduce GO. Furthermore, the sheet resistance of the transparent conductive film created using the method developed in this study reaches approximately 1000 Ω/sq (80 % transparency), and the specific capacitance of the SCs electrode film created in this method is 433.2 F/g (5 mV/s, 1 M H2SO4). Our study not only validates the efficacy of the one-step synthesis method for rGO thin films but also provides theoretical insights into the underlying reaction mechanism. This work holds significant promise for advancing applications in various electronics by facilitating large-scale production of high-quality rGO thin films.

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.

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.

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 Conductive Robust Carbon Nanotube Networks for Strong Buckypapers and Transparent Electrodes

AbstractWhile individual single‐wall carbon nanotubes (SWCNTs) have remarkable strength and electrical conductivity, SWCNT networks fabricated from dispersions have inferior properties due to nanotube bundling, limiting the potential applications of SWCNT materials. Herein, a common dye molecule (purpurin) is used to exfoliate SWCNTs via noncovalent functionalization and to fabricate SWCNT materials by a simple solution‐based process. The advantageous noncovalent interactions result in efficient exfoliation and metallic SWCNT enrichment, affording SWCNT materials with high mechanical robustness and electrical conductivity. This method is used to prepare mechanically robust SWCNT films and flexible transparent conductive electrodes.

Flexible Transparent Conductive Electrodes: Unveiling Growth Mechanisms, Material Dimensions, Fabrication Methods, and Design Strategies.

Flexible transparent conductive electrodes (FTCEs) constitute an indispensable component in state-of-the-art electronic devices, such as wearable flexible sensors, flexible displays, artificial skin, and biomedical devices, etc. This review paper offers a comprehensive overview of the fabrication techniques, growth modes, material dimensions, design, and their impacts on FTCEs fabrication. The growth modes, such as the "Stranski-Krastanov growth," "Frank-van der Merwe growth," and "Volmer-Weber growth" modes provide flexibility in fabricating FTCEs. Application of different materials including 0D, 1D, 2D, polymer composites, conductive oxides, and hybrid materials in FTCE fabrication, emphasizing their suitability in flexible devices are discussed. This review also delves into the design strategies of FTCEs, including microgrids, nanotroughs, nanomesh, nanowires network, and "kirigami"-inspired patterns, etc. The pros and cons associated with these materials and designs are also addressed appropriately. Considerations such as trade-offs between electrical conductivity and optical transparency or "figure of merit (FoM)," "strain engineering," "work function," and "haze" are also discussed briefly. Finally, this review outlines the challenges and opportunities in the current and future development of FTCEs for flexible electronics, including the improved trade-offs between optoelectronic parameters, novel materials development, mechanical stability, reproducibility, scalability, and durability enhancement, safety, biocompatibility, etc.

Stability improvement of N-GQDs/AgNWs/PET based flexible electrochromic device for smart window application

The design and development of cost-effective and highly stable flexible transparent conductive electrodes (f-TCEs) is crucial for various optoelectronic applications. Herein, we report the fabrication of nitrogen-doped graphene quantum dot (N-GQD)-protected silver nanowire (AgNWs)-modified polyethylene terephthalate (PET) electrodes as f-TCEs (N-GQDs/AgNWs/PET). Furthermore, we fabricated flexible electrochromic devices (ECDs) for smart window applications using N-GQD/AgNW/PET as the f-TCE. The presence of N-GQDs on the AgNW/PET electrode improved the stability of the developed N-GQD/AgNW/PET-based flexible ECDs. The N-GQDs/AgNWs/PET-based flexible ECDs demonstrated an excellent coloration efficiency (ȠCE) of 42.7 cm2C−1 with an optical contrast of 45.4 %. Additionally, they demonstrated fast coloring and bleaching times of 6.9, and 5.7 s, respectively.

Synthesis, Properties, and Application of Ultrathin and Flexible Tellurium Nanorope Films: Beyond Conventional 2D Materials.

Nanomaterials that can be easily processed into thin films are highly desirable for their wide range of applicability in electrical and optical devices. Currently, Te-based 2D materials are of interest because of their superior electrical properties compared to transition metal dichalcogenide materials. However, the large-scale manufacturing of these materials is challenging, impeding their commercialization. This paper reports on ultrathin, large-scale, and highly flexible Te and Te-metal nanorope films grown via low-power radiofrequency sputtering for a short period at 25°C. Additionally, the feasibility of such films as transistor channels and flexible transparent conductive electrodes is discussed. A 20 nm thick Te-Ni-nanorope-channel-based transistor exhibits a high mobility (≈450 cm2 V-1 s-1 ) and on/off ratio (105 ), while 7 nm thick Te-W nanorope electrodes exhibit an extremely low haze (1.7%) and sheet resistance (30 Ω sq-1 ), and high transmittance (86.4%), work function (≈4.9eV), and flexibility. Blue organic light-emitting diodes with 7 nm Te-W anodes exhibit significantly higher external quantum efficiencies (15.7%), lower turn-on voltages (3.2V), and higher and more uniform viewing angles than indium-tin-oxide-based devices. The excellent mechanical flexibility and easy coating capability offered by Te nanoropes demonstrate their superiority over conventional nanomaterials and provide an effective outlet for multifunctional devices.

Fabrication Technologies of Flexible Transparent Electrodes for Supercapacitors: Recent Advances and Perspectives

Flexible transparent portable electronic products provide substantial support for the rapid development of the intelligent era. Flexible transparent supercapacitors (FTSCs) are considered the most promising energy storage devices due to their exceptional electrochemical performance, outstanding mechanical flexibility, and high optical transmittance. However, it is difficult to balance their mechanical flexibility and optical transmittance. The key to reconciling the contradiction is to fabricate flexible transparent conductive electrodes (FTCEs) with excellent mechanical flexibility and optical transmittance by combining the characteristics of manufacturing technologies and electrode materials. In this review, the characteristics of advanced FTCEs manufacturing technologies and their applications in FTSCs are systematically summarized. First, the device structure, working mechanism, and basic performance of FTSCs are briefly introduced. Second, the manufacturing characteristic and principle of different FTCEs preparation technologies are mainly described, including vacuum filtration, coating, deposition, printing, and layer‐by‐layer assembly. Next, the device structure and design principle of multifunctional FTSCs are demonstrated in detail. Finally, the challenges and prospects of applying FTCEs manufacturing technology to construct FTSCs are proposed.

Wax-shaped wettability assisted patterning of silver nanowires on various substrates as transparent, flexible, or stretchable electrodes

With the rapid development of flexible and wearable devices, flexible transparent conductive electrodes are highly demanded. However, there is no available technology that can pattern emerging electric materials (e.g., silver nanowires (AgNWs)) on versatile substrates in large scale to achieve high performance in different aspects on demands, such as transparency, flexibility, stretchability, and biocompatibility. Here, a wax-shaped wetting/dewetting (WSWD) method is demonstrated to pattern AgNWs networks into transparent conductive circuits ranging from tens of micrometers to centimeters on various substrates. For instance, the AgNWs coatings patterned on polyethylene terephthalate (PET) films achieve high electrical conductivity and optical transparency up to 73%, and a stable resistance (CV < 0.1%) after cyclic bending (>200 times); the AgNWs coatings patterned into polydimethylsiloxane (PDMS) microchannels exhibit good durability after cyclic bending (>200 times) and stretching (30% strain). Finally, the flexible AgNWs coatings are used as wearable transparent heaters applied to the human finger joint and wrist, which are thermally stable and safe (42 °C < T < 50 °C for 3 min) under cyclic bending. Thus, this method provides a simple, low-cost, green, and versatile means for fabricating transparent conductive electrodes, which can be applied to optoelectronic, wearable, and healthcare devices.

Smooth, Chemically Altered Nucleating Platform for Abrupt Performance Enhancement of Ultrathin Cu-Layer-Based Transparent Electrodes.

Rapid advances in flexible optoelectronic devices necessitate the concomitant development of high-performance, cost-efficient, and flexible transparent conductive electrodes (TCEs). This Letter reports an abrupt enhancement in the optoelectronic characteristics of ultrathin Cu-layer-based TCEs via Ar+-mediated modulation of the chemical and physical states of a ZnO support surface. This approach strongly regulates the growth mode for the subsequently deposited Cu layer, in addition to marked alteration to the ZnO/Cu interface states, resulting in exceptional TCE performance in the form of ZnO/Cu/ZnO TCEs. The resultant Haacke figure of merit (T10/Rs) of 0.063 Ω-1, 53% greater than that of the unaltered, otherwise identical structure, corresponds to a record-high value for Cu-layer-based TCEs. Moreover, the enhanced TCE performance in this approach is shown to be highly sustainable under severe simultaneous loadings of electrical, thermal, and mechanical stresses.

Aluminum-Doped Zinc Oxide Improved by Silver Nanowires for Flexible, Semitransparent and Conductive Electrodes on Textile with High Temperature Stability.

In order to facilitate the design freedom for the implementation of textile-integrated electronics, we seek flexible transparent conductive electrodes (TCEs) that can withstand not only the mechanical stresses encountered during use but also the thermal stresses of post-treatment. The transparent conductive oxides (TCO) typically used for this purpose are rigid in comparison to the fibers or textiles they are intended to coat. In this paper, a TCO, specifically aluminum-doped zinc oxide (Al:ZnO), is combined with an underlying layer of silver nanowires (Ag-NW). This combination brings together the advantages of a closed, conductive Al:ZnO layer and a flexible Ag-NW layer, forming a TCE. The result is a transparency of 20-25% (within the 400-800 nm range) and a sheet resistance of 10 Ω/sq that remains almost unchanged, even after post-treatment at 180 °C.

Transparent and Stretchable Electromagnetic Interference Shielding Film with Fence-like Aligned Silver Nanowire Conductive Network.

Flexible transparent conductive electrodes (TCEs) that can be used as electromagnetic interference (EMI) shielding materials have a great potential for use as electronic components in optical window and display applications. However, development of TCEs that display high shielding effectiveness (SE) and good stretchability for flexible electronic device applications has proven challenging. Herein, this study describes a stretchable polydimethylsiloxane (PDMS)/silver nanowire (AgNW) TCE with a fence-like aligned conductive network that is fabricated via pre-stretching method. The fence-like AgNW network endowed the PDMS/AgNW film with excellent optoelectronic properties, i.e., low sheet resistance of 7.68Ωsq-1 at 73.7% optical transmittance, thus causing an effective EMI SE of 32.2dB at X-band. More importantly, the fence-like aligned AgNW conductive network reveals a high stability toward tensile deformation, thus gives the PDMS/AgNW film stretch-stable conductivity and EMI shielding property in the strain range of 0-100%. Typically, the film can reserve ≈70% or 80% of its initial EMI SE when stretching at 100% strain or stretching/releasing (50% strain) for 128 cycles, respectively. Additionally, the film exhibits a low-voltage driven and stretchable Joule heating performance. With these overall performances, the PDMS/AgNW film should be well suited for use in flexible and stretchable optical electronic devices.

Flexible, stripe-patterned organic solar cells and modules based on multilayer-printed Ag fibers for smart textile applications

Rapid advancement in the fabrication technologies of stripe/fiber-shaped optoelectronic devices has driven the performance of smart textile electronics to a new height. In the development of high-performance smart textile electronics, indium tin oxide (ITO)-free flexible transparent conductive electrodes (TCEs) are particularly desirable because they offer superior flexibility and lower manufacturing cost than the brittle ITO-based counterparts. Herein, we innovatively combine spin-coating and three-dimensional direct-ink writing (three-dimensional-DIW) techniques to develop large-area (5 × 5 cm2) PEDOT:PSS/Ag-fibers hybrid TCEs (denoted as DIW-TCEs) for application in flexible organic solar cells (OSCs). Through a multilayer printing strategy, high aspect-ratio Ag-fibers are successfully deposited on top of the planar PEDOT:PSS film. The resulting DIW-TCEs, when fully embedded in a colorless polyimide substrate, exhibit excellent electrical conductivity (sheet resistance ∼ 4 Ω/□), superior optical transmittance, and mechanical flexibility. One-dimensional stripe-patterned OSCs (stripe-OSCs) based on DIW-TCEs achieved power conversion efficiency of 9.3% and 8.2% at an active area of 0.11 cm2 and 0.31 cm2, respectively. For real-life application, a flexible power module was constructed using eight stripe-OSCs. When attached on textile, the module successfully lit up a commercial light-emitting diode upon photocharging. The unique DIW-TCE fabricated herein can be the ITO-free alternative for the production of smart textile electronics.

Large‐Area Smooth Conductive Films Enabled by Scalable Slot‐Die Coating of Ti3C2Tx MXene Aqueous Inks

AbstractLarge‐area flexible transparent conductive electrodes (TCEs) featuring excellent optoelectronic properties (low sheet resistance, Rs, at high transparency, T) are vital for integration in transparent wearable electronics (i.e., antennas, sensors, supercapacitors, etc.). Solution processing (i.e., printing and coating) of conductive inks yields highly uniform TCEs at low cost, holding great promise for commercially manufacturing of transparent electronics. However, to formulate such conductive inks as well as to realize continuous conductive films in the absence of percolation issue are quite challenging. Herein, the scalable slot‐die coating of Ti3C2Tx MXene aqueous inks is reported for the first time to yield large‐area uniform TCEs with outstanding optoelectronic performance, that is, average DC conductivity of 13 000 ± 500 S cm−1. The conductive MXene nanosheets are forced to orientate horizontally as the inks are passing through the moving slot, leading to the rapid manufacturing of highly aligned MXene TCEs without notorious percolation problems. Moreover, through tuning the ink formulations, such conductive MXene films can be easily adjusted from transparent to opaque as required, demonstrating very low surface roughness and even mirror effects. These high‐quality, slot‐die‐coated MXene TCEs also demonstrate excellent electrochemical charge storage properties when assembled into supercapacitors.

High-performance copper nanowire electrode for efficient flexible organic light-emitting diode

Highly conductive and robust polyvinyl alcohol/copper nanowire (PVA/CuNW) flexible transparent conductive electrode (FTCE) is fabricated via a simple and low-cost process at room temperature. The CuNW film is formed on a mixed cellulose ester (MCE) membrane by vacuum filtration. Subsequently, the flowing glacial acetic acid (GAA)-toluene solution passes through them to remove the oxide layer without damaging nanowires. The final PVA/CuNW FTCE is constructed by embedding the treated CuNWs into a pre-prepared PVA binding layer on the polyethylene terephthalate (PET) substrate, which presents excellent conductivity with a low sheet resistance of 46.2 Ω / s q and a high transparency of 90.5% at 550 nm. Meanwhile, the chemical and mechanical stability have been significantly enhanced compared with the bare CuNW FTCE attributed to the protective effect of the PVA binding layer. A flexible phosphorescent OLED device using such PVA/CuNW FTCE as the anode exhibits a current efficiency of 26.4 cd/A at 1000 cd/m 2 , which is comparable to that of the reference device (27.1 cd/A) based on indium tin oxide anode on glass, indicating its high potential for application in flexible optoelectronics. • Highly conductive PVA/CuNW electrodes are fabricated at room temperature. • The electrode shows excellent optoelectronic properties. • Low roughness as well as significantly enhanced chemical and mechanical stability has been achieved. • The flexible OLED device using PVA/CuNW exhibits high luminance and efficiency.

Shape Dependence of Silver Nanowires on Synthesis Conditions and it’s Effect on the Optical and Electrical Properties

As the market share of optoelectronic devices grows yearly, the transparent conductive electrodes that guarantee device performance subsequently gain attention. In order to solve the cost issue of the most commonly commercialised transparent conductive electrodes (indium tin oxide) and the problem that they cannot be used in portable wearable devices, flexible carbon-based hybrid nanomaterials are considered as an alternative. But, it still suffers the complicated synthesis process. Thus, silver nanowire (AgNW) is regarded as the most promising material with advantages of the facile synthesis process, high conductivity and transparency. The synthesis conditions and AgNW morphology are believed to be vital for their optical and electrical properties. This research investigated the effect of synthesis conditions (capping agent molecular weight and compositions, reaction temperature and the stirring rate) and discussed the connection between the optical transmission and electrical resistance of coated films fabricated by AgNW with various morphology. Results show that heavier capping agents with more viscous solutions are more favourable for long wire growth, and mixed capping agent solutions can achieve higher aspect ratios. Both relatively low reaction temperature and no stirring could prevent silver particles nucleation and agglomeration, achieving longer nanowires. The AgNW-coated film by nanowires with longer lengths could have more advantages in the trade-off between conductivity and transparency for better performance. This article illustrates and explains the influence of factors in the synthesis process on its morphology and functionality, creating more possibilities for the development and application of flexible transparent conductive electrodes.

Foldable Perovskite Solar Cells and Modules Enabled by Mechanically Engineered Ultrathin Indium‐Tin‐Oxide Electrodes

AbstractFlexible transparent conducting electrodes (TCEs) play a critical role when achieving highly flexible perovskite solar cells (PSCs) for potential applications such as wearable, portable, and aerospace power sources. Despite extensive exploration of electrode materials and substrate engineering, there have been few reports on flexible PSCs with both satisfactory performance and flexibility. Here, highly conductive indium‐tin‐oxide (ITO) based ultrathin TCEs are developed for highly efficient, and foldable perovskite solar cells and modules. By introducing an additional aluminum oxide (AlOx) layer to the substrate, deformation‐free ITO‐based ultrathin (≈10 µm) TCEs are successfully fabricated. A champion flexible perovskite solar cell and module using ultrathin TCEs achieve efficiencies of 19.16% and 13.26% (aperture areas of 0.078 and 16 cm2), respectively, outperforming reference devices using commercial high‐performing flexible TCEs. The modules maintain 100% and 92% of their initial performance after 10 000 bending cycles with a radius of 1 and 0.5 mm, respectively, which is unprecedented on module scale.

High aspect ratio copper nanowires and copper nanoparticles decorated by reduced graphene oxide for flexible transparent conductive electrodes

Copper nanowires (CuNWs) have been widely used in flexible electronics and optoelectronic devices. However, the large contact resistance and poor stability limit their practical applications in optoelectronic devices. Herein, the high aspect ratio CuNWs and uniform ultra-small copper nanoparticles (CuNPs) were grown in-situ on the reduced graphene oxide (rGO) to form copper/reduced graphene oxide (Cu/rGO) nanocomposite by a one-step hydrothermal method. Graphene oxide, which converted to rGO in the synthesis, played an essential role in forming the high aspect ratio CuNWs (L/D ≈ 1666) and the dispersed ultra-small CuNPs (diameter ≈ 2 nm). The photoelectric properties of rGO/Cu/rGO flexible transparent conductive electrodes, assembled by Cu/rGO nanocomposite and outer layer rGO, reduced from graphene oxide by sodium borohydride solution, can be extended over 65 h at 60 °C in air. The high aspect ratio CuNWs and ultra-small CuNPs decorated by rGO resulted in a good bending resistance. This approach is anticipated as an effective strategy to solve problems with oxidation of CuNWs and promote their various applications in flexible optoelectronic devices.