Flexible Transparent Films Research Articles

P‐187: Ultra‐smooth Silver Nanowires Flexible Transparent Electrode for Organic Light Emitting Diodes

Ultra‐smooth, conductive, and uniform flexible transparent composite film is produced by embedding silver nanowires (AgNWs) into polyvinyl butyral(PVB) without high‐temperature/pressure annealing. The sheet resistance of the PVB/AgNWs composite film reaches 25 ohm/sq with a transmittance of 92%.

An All-Transparent Thin Film Flexible Supercapacitor Based on Oblique Angle Deposited NiO Nanowires Arrays

With high power density, fast charging-discharging speed and long cycling life, supercapacitors have been a kind of highly developed novel energy-storage device these years, showing growing performance and various unconventional shapes such as flexible, linear type, stretchable, self-healing, etc. Here, we proposed a rational design of an all-transparent thin film flexible supercapacitor based on oblique angle deposited NiO nanowires arrays. By integrating PET substrate, thin layer of Pt electrode, surround-finger-shape NiO nanowires film and PVA-KOH electrolyte, the as-fabricated supercapacitor has a good flexibility, transparency, and satisfactory energy-storage performance. This supercapacitor showed a high specific capacity of 8 F/cm3, high energy density of 1 mWh/cm3, a power density up to 1.5 W/cm3 and good stability during thousands of bending-recover test and charge-discharge cycles, respectively. This transparent flexible thin film supercapacitor and be used as ingenious energy storage devices for future portable and wearable electronic applications.

Wavelength dependent in-plane birefringence of transparent flexible films determined by using transmission ellipsometry

We introduce a simple method to determine the in-plane birefringence of transparent flexible films by using transmission spectroscopic ellipsometry. The pseudo-ellipsometric constants which can represent their sample azimuthal angle dependent characteristics are introduced. The effect of in-plane birefringence and sample azimuthal angle on the pseudo ellipsometric constants is calculated using Jones matrix formalism, and the observed sample azimuthal angle dependence of measured pseudo-ellipsometric data is well understood. Wavelength dependence of in-plane birefringence is expressed in terms of the Sellmeier dispersion equation. The best fit pseudo-ellipsometric spectra to the measured ones at the sample azimuthal angles of every 15° from 0 to 90° are searched. The dispersion coefficients of the Sellmeier equation and the azimuthal angle of the optic axis are determined for polycarbonate (PC), poly(ethylene naphthalate) (PEN), poly(ethylene terephthalate) (PET), polyimide (PI), and colorless polyimide (CPI) films.

Novel Thermoplastic Cellulose Esters Containing Bulky Moieties and Soft Segments

It is still challenging to convert cellulose into melt-processable materials because natural cellulose, which has a strong hydrogen bonding network, degrades before melting. Herein, a series of novel cellulose-based thermoplastics were successfully designed and fabricated by a simple and efficient homogeneous esterification of cellulose in an ionic liquid. Introducing ester substituents containing both bulky moieties and soft segments can improve the mobility of the cellulose chain, and the glass transition temperatures (Tgs) appeared in the resultant cellulose esters. In particular, when the ester substituents consisted of bulky terminal moiety and soft middle segment, Tgs of the corresponding cellulose esters were relatively low (80–160 °C), indicating these cellulose materials were suitable for melt processing. Accordingly, these thermoplastic cellulose esters can be processed into transparent disks, dumbbells, fibers and flexible films by traditional injection molding, melt extrusion, and hot pressing...

Anisotropic flexible transparent films from remaining wood microstructures for screen protection and AgNW conductive substrate.

Flexible transparent conductive films or substrates prepared from plastics or cellulose are widely used in optoelectronic devices. However, all of these films or substrates are fabricated by complex and expensive methods, which consume much energy and time. In this work, we report for the first time a remarkably facile and effective approach for fabricating flexible transparent films directly from wood. The resulting films exhibit an array of exceptional optical and mechanical properties. The well-aligned cell structures in natural wood are maintained during delignification, leading to anisotropic films with high transparency (≈90% transmittance). These anisotropic films with well-aligned cell structures show mechanical tensile strengths higher than those of the original wood, and can be used as screen protection films for cellphones. Furthermore, ultrathin, highly transparent, and outstandingly conductive films have been prepared from such films and silver nanowires (AgNWs) using the Meyer technique. A conductive film with an optimal area density (341 mg m-2) of AgNWs showed outstanding synergistic properties, with a transmittance of 80% and a sheet resistance of 11 Ω sq-1, equal to the conductivity of ITO. Of importance here is that the low-cost anisotropic transparent wood film shows promising potential for electronics applications in solar cells, flexible displays, and other products.

Effect of Graphene-EC on Ag NW-Based Transparent Film Heaters: Optimizing the Stability and Heat Dispersion of Films.

To optimize the performance of silver nanowire (Ag NW) film heaters and explore the effect of graphene on a film, we introduced poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and graphene modified with ethyl cellulose (graphene-EC) into the film. The high-quality and well-dispersed graphene-EC was synthesized from graphene obtained by electrochemical exfoliation as a precursor. The transparent film heaters were fabricated via spin-coating. With the assistance of graphene-EC, the stability of film heaters was greatly improved, and the conductivity was optimized by adjusting the Ag NW concentration. The film heaters exhibited a fast and accurate response to voltage, accompanied by excellent environmental endurance, and there was no significant performance degradation after being operated for a long period of time. These results indicate that graphene-EC plays a crucial role in optimizing film stability and heat dispersion in the film. The Ag NW/PEDOT:PSS-doped graphene-EC film heaters show a great potential in low-cost indium-tin-oxide-free flexible transparent electrodes, heating systems, and transparent film heaters.

Hybrid Ag nanowire transparent conductive electrodes with randomly oriented and grid-patterned Ag nanowire networks

To improve the electrical properties of silver nanowire (Ag NW) transparent conductive electrodes (TCEs), the density of Ag NW networks should be increased, to increase the number of percolation paths. However, because of the inverse relationship between optical transmittance and electrical resistivity, the optical properties of Ag NW TCEs deteriorate with increasing density of the Ag NW network. In this study, a hybrid Ag NW electrode composed of randomly oriented and grid-patterned Ag NW networks is demonstrated. The hybrid Ag NW electrodes exhibit significantly improved sheet resistances and slightly decreased transmittances compared to randomly oriented Ag NW networks. Hybrid Ag NW TCEs show excellent mechanical flexibilities and durabilities in bending tests with a 5 mm radius of curvature. Moreover, flexible transparent film heaters (TFHs) based on the hybrid Ag NW electrodes show elevated maximum temperatures relative to TFHs based on randomly oriented Ag NW electrodes, when operated at the same input voltages.

Low roughness silver nanowire flexible transparent electrode by low temperature solution-processing for organic light emitting diodes

Highly smooth, conductive, and uniform flexible transparent composite film is produced by embedding silver nanowires (AgNWs) into polymer without high-temperature annealing. The insert of poly (vinyl alcohol) (PVA) layer enhances the hydrophilicity of the substrate surface and avoids the agglomeration of AgNWs. The thick junctions between nanowires are welded to the same height as a single wire by mechanical pressing, resulting in a great increase of the electrical conductivity and low surface roughness. The sheet resistance of the PVA/AgNW composite film reaches 3 Ω/sq with a transmittance of 83%, and does not show obvious change after tape test and substrate bending, suggesting good adhesion of AgNWs to the substrate and excellent flexibility. The composite film possesses better stability of resisting the chemical corrosion than conventional annealed-AgNW film. The scattering of AgNWs can break the waveguide mode and the total internal reflection, which consequently enhances the out-coupling efficiency in an organic light emitting diode (OLED). Flexible OLED employing the PVA/AgNW composite film as anode on polyethylene naphthalate (PEN) substrate presents a current efficiency improvement of 27% compared to controlled ITO-anode device with same structure, demonstrating its exciting prospect for applications in flexible optoelectronics.

Transparent Electrodes Based on Silver Nanowire Networks: From Physical Considerations towards Device Integration

The past few years have seen a considerable amount of research devoted to nanostructured transparent conducting materials (TCM), which play a pivotal role in many modern devices such as solar cells, flexible light-emitting devices, touch screens, electromagnetic devices, and flexible transparent thin film heaters. Currently, the most commonly used TCM for such applications (ITO: Indium Tin oxide) suffers from two major drawbacks: brittleness and indium scarcity. Among emerging transparent electrodes, silver nanowire (AgNW) networks appear to be a promising substitute to ITO since such electrically percolating networks exhibit excellent properties with sheet resistance lower than 10 Ω/sq and optical transparency of 90%, fulfilling the requirements of most applications. In addition, AgNW networks also exhibit very good mechanical flexibility. The fabrication of these electrodes involves low-temperature processing steps and scalable methods, thus making them appropriate for future use as low-cost transparent electrodes in flexible electronic devices. This contribution aims to briefly present the main properties of AgNW based transparent electrodes as well as some considerations relating to their efficient integration in devices. The influence of network density, nanowire sizes, and post treatments on the properties of AgNW networks will also be evaluated. In addition to a general overview of AgNW networks, we focus on two important aspects: (i) network instabilities as well as an efficient Atomic Layer Deposition (ALD) coating which clearly enhances AgNW network stability and (ii) modelling to better understand the physical properties of these networks.

Large Scale Self-Assembly of Smectic Nanocomposite Films by Doctor Blading versus Spray Coating: Impact of Crystal Quality on Barrier Properties

Flexible transparent barrier films are required in various fields of application ranging from flexible, transparent food packaging to display encapsulation. Environmentally friendly, waterborne polymer–clay nanocomposites would be preferred but fail to meet in particular requirements for ultra high water vapor barriers. Here we show that self-assembly of nanocomposite films into one-dimensional crystalline (smectic) polymer–clay domains is a so-far overlooked key-factor capable of suppressing water vapor diffusivity despite appreciable swelling at elevated temperatures and relative humidity (R.H.). Moreover, barrier performance was shown to improve with quality of the crystalline order. In this respect, spray coating is superior to doctor blading because it yields significantly better ordered structures. For spray-coated waterborne nanocomposite films (21.4 μm) ultra high barrier specifications are met at 23 °C and 50% R.H. with oxygen transmission rates (OTR) < 0.0005 cm3 m–2 day–1 bar–1 and water vapor ...

P‐134: Flexible Transparent Electrode Film with a Continuous Ag Nanofiber Network Embedded Structure for Flexible OLEDs

We report a flexible and high‐performance TCE/substrate platform by introducing electro‐spun Ag nanofiber (AgNF) and glass‐fabric reinforced hybrimer (GFRHybrimer) with high transparency and robustness. A single‐line network of AgNF, which already has a conductive path without junction, can provide high transparency and low sheet resistance, simultaneously. Moreover, GFRHybrimer matrix enhances the thermal stability of the AgNF TCE and mechanical durability of the composite film with smooth surface topography. To confirm the reliability and durability, we fabricated OLED on the AgNF/GFRHybrimer composite film and demonstrated the availability of the composite film for the next generation opto‐electronics.

Flexible transparent and conductive films of reduced-graphene-oxide wrapped silver nanowires

A novel hybrid material based on silver nanowires (AgNWs) and reduced graphene oxide (rGO) wrapped network structure is prepared. AgNWs/rGO films are fabricated by simple filtrating a graphene oxide and AgNWs mixture solution which is well-dispersed in ethylene glycol with sodium dodecylbenzene sulfonate as a stabilizing agent. Compared to the single materials of rGO or AgNWs, the formation of this hybrid material has a low sheet resistance (15.33Ω/sq) and high transparency (80.1% at 550nm). In addition, the hybrid AgNWs/rGO film prepared by a facile fabrication approach also shows a high flexibility and prominent stability, which is suitable for flexible electronics applications.

Plasticized Polymer Interlayer for Low-Temperature Fabrication of a High-Quality Silver Nanowire-Based Flexible Transparent and Conductive Film.

Silver nanowires (AgNWs) are one of the most promising materials to replace commercially available indium tin oxide in flexible transparent conductive films (TCFs); however, there are still numerous problems originating from poor AgNW junction formation and improper AgNW embedment into transparent substrates. To mitigate these problems, high-temperature processes have been adopted; however, unwanted substrate deformation prevents the use of these processes for the formation of flexible TCFs. In this work, we present a novel poly(methyl methacrylate) interlayer plasticized by dibutyl phthalate for low-temperature fabrication of AgNW-based TCFs, which does not cause any substrate deformation. By exploiting the viscoelastic properties of the plasticized interlayer near the lowered glass-transition temperature, a monolithic junction of AgNWs on the interlayer and embedment of the interconnected AgNWs into the interlayer are achieved in a single-step pressing. The resulting AgNW-TCFs are highly transparent (∼92% at a wavelength of 550 nm), highly conductive (<90 Ω/sq), and environmentally and mechanically robust. Therefore, the plasticized interlayer provides a simple and effective route to fabricate high-quality AgNW-based TCFs.

High quality transparent conductive Ag-based barium stannate multilayer flexible thin films

Transparent conductive multilayer thin films of silver (Ag)-embedded barium stannate (BaSnO3) structures have been deposited onto flexible polycarbonate substrates by magnetron sputtering at room temperature to develop an indium free transparent flexible electrode. The effect of thicknesses of Ag mid-layer and barium stannate layers on optical and electrical properties were investigated, and the mechanisms of conduction and transmittance were discussed. The highest value of figure of merit is 25.5 × 10−3 Ω−1 for the BaSnO3/Ag/BaSnO3 multilayer flexible thin films with 9 nm thick silver mid-layer and 50 nm thick barium stannate layers, while the average optical transmittance in the visible range from 380 to 780 nm is above 87%, the resistivity is 9.66 × 10−5 Ω · cm, and the sheet resistance is 9.89 Ω/sq. The change rate of resistivity is under 10% after repeated bending of the multilayer flexible thin films. These results indicate that Ag-based barium stannate multilayer flexible thin films can be used as transparent flexible electrodes in various flexible optoelectronic devices.

Solution-processed multifunctional transparent conductive films based on long silver nanowires/polyimide structure with highly thermostable and antibacterial properties

The optical, electrical, thermal and antibacterial properties of AgNW/PI composite films.

Flexible grid-mesh electrodes fabricated by electroless copper plating on corona-treated PET substrates and coating with graphene for transparent film heaters

Graphene-coated Cu mesh electrodes for transparent flexible film heaters have been successfully fabricated on corona-treated PET substrates via solution processes.

Successful entrapment of carbon dots within flexible free-standing transparent mesoporous organic-inorganic silica hybrid films for photonic applications

The effective entrapment of Carbon dots (CDs) into a polymer-silica hybrid matrix, formed as free standing transparent flexible films, is presented. The composite's synthesis, characterization, device application and properties -mechanical, thermal and optical- are being provided and discussed. CDs of 3nm mean size with strong photoluminescence are embedded into a silica matrix during the sol-gel procedure, using tetraethyl orthosilicate as the precursor and F127 triblock copolymer as the structure directing agent under acidic conditions. The final hybrid nanostructure forms free standing transparent films that show high flexibility and long term stable CDs luminescence indicating the protective character of the hybrid matrix. It is crucial that the photoluminescence of the hybrid's CDs is not seriously affected after thermal treatment at 550°C for 30min. Moreover, the herein reported hybrid is demonstrated to be suitable for the fabrication of advanced photonic structures using soft lithography processes due to its low shrinkage and distortion upon drying, both attributable to its porosity. Finally, it is reported that addition of F127 ethanolic solution in aqueous solution of CDs induces a blue-shift of their photoluminescence.

Micropatterning of lanthanide complex species onto self-cracking flexible transparent films and their photophysical properties

Based on lanthanide optical materials, flexible and transparent luminescent films have been fabricated based on self-cracking micro-pattern on polydimethylsiloxane (PDMS) substrates. The morphology and photoluminescence were studied based on the self-assembly structures. The corresponding intra-molecular energy transfer and photophysical properties were evaluated. Results demonstrated that both lanthanide complex and phosphors could be well controlled and stamped onto the designed cracking micropatterns with red or green emissions. The effects of pH value changes on the luminescent features of the films, as well as its influence on europium complex have been extensively studied. Investigation on transmittance and mechanical properties indicated that the optical and structural quality of such functional films will be potentially useful in the novel design of light-emitting devices or for sensing applications.

Large-scale synthesis of AgNWs with ultra-high aspect ratio above 4000 and their application in conductive thin film

Large-scale, uniform silver nanowires (AgNWs) with diameter of 30 nm and ultra-high aspect ratio up to 4000 were obtained by adding Cu2+ and Fe3+ to the AgNWs synthesis. AgNWs were longer at higher concentration of Cu2+ and better uniformity in the presence of both Fe3+ and Cu2+. Finding indicate that by simply controlling Cu2+/Fe3+ molar ratios in the reaction process, the high yield (98%), ultra-high aspect ratio (over 4000) and large-scale (over 50 g per pot) production of AgNWs can be obtained. Additionally, embedding the ultra-high aspect ratio AgNWs into polyvinyl alcohol (PVA) matrices, novel AgNWs@PVA flexible transparent conductor films (TCFs) with high-electrical conductivity performance was fabricated. This method improved the production efficiency of ultra-high aspect ratio AgNWs and could be applied to high performance TCFs; thus having major commercial implications.

Metallic Nanowires and Their Application

Metallic nanowire films, especially silver nano-wires (AgNWs) and copper nanowires (CuNWs), with a random mesh structure have attracted considerable attention as high-performance flexible transparent films to replace the traditional, expensive, and brittle indium tin oxide films. These films have been widely used in displays, touchscreens, and solar cells to achieve next-generation electronics that can be bent, stretched, compressed, twisted, and deformed into complex, nonplanar shapes but maintain good conductive performance, reliability, and integration. Recent researches have indicated that the application of metallic nanowires has been accelerated due to these promising properties. This paper reviews the wet-chemical synthesis of AgNWs and CuNWs, fabrication and posttreatment of nanowire films, as well as their applications as conductive materials in some devices. It provides a latest overview of metallic nanowires and exhibits the developing prospects of high-performance conducting materials for future flexible and wearable optoelectronic devices.