Metal Nanowire-Coated Metal Woven Mesh for High-Performance

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Metal Nanowire-Coated Metal Woven Mesh for HighPerformance Stretchable Transparent Electrodes Ji Hwan Cho, Dong Joo Kang, Nam-Su Jang, KangHyun Kim, Phillip Won, Seung Hwan Ko, and Jong-Man Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14342 • Publication Date (Web): 03 Nov 2017 Downloaded from http://pubs.acs.org on November 4, 2017

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ACS Applied Materials & Interfaces

Metal Nanowire-Coated Metal Woven Mesh for High-Performance Stretchable Transparent Electrodes Ji Hwan Cho,1 Dong Joo Kang,2 Nam-Su Jang,3 Kang-Hyun Kim,3 Phillip Won,4 Seung Hwan Ko,4 and Jong-Man Kim3,5,* 1

Department of Electronics Engineering, Pusan National University, Busan 46241, Republic of

Korea 2

Department of Nanomechatronics Engineering, Pusan National University, Busan 46241,

Republic of Korea 3

Department of Nano Fusion Technology and BK21 Plus Nano Convergence Technology

Division, Pusan National University, Busan 46241, Republic of Korea 4

Department of Mechanical Engineering, Seoul National University, Seoul 08826, Republic of

Korea 5

Department of Nanoenergy Engineering, Pusan National University, Busan 46241, Republic of

Korea

KEWORDS: metal woven mesh, silver nanowire, dip-coating, stretchable transparent conducting electrode, flexible touch screen panel

ACS Paragon Plus Environment

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ABSTRACT This work presents a new template-assisted fabrication method to obtain stretchable metal grids for high-performance stretchable transparent conducting electrodes (TCEs). Readily accessible metal woven mesh (MWM) is used as a template to make the fabrication process simple, costeffective, reproducible, and potentially scalable by combining it with silver nanowire (AgNW) coating and elastomer filling processes. Stretchable TCEs are made with the AgNW-coated MWM and show remarkable optoelectronic performance with a sheet resistance of ~3.2 Ω/sq and optical transmittance of > 80%, large maximum stretchability of 40%, and electrical and mechanical robustness even under repeated stretching and bending deformations (1000 cycles). The device is demonstrated in a highly flexible touch screen panel that can operate well even in a bent state.


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1. INTRODUCTION Over the past few decades, many efforts have been devoted to developing transparent conductive electrodes (TCEs) with mechanical flexibility and stretchability. Such devices have a wide range of applications in emerging deformable devices, including organic light-emitting diodes,1–5

photovoltaic

devices,2–4,6–8

touch

screen

panels

(TSPs),9–15

heaters,15–18

supercapacitors,19 and smart windows.20 Despite its excellent optoelectronic performance, indium tin oxide (ITO) is not the best material for these applications due to its inherent brittleness and the high-temperature processes required. Therefore, various alternatives have been extensively investigated, such as carbon nanotubes, graphene films, metallic nanostructures, and patterned metal grids, and hybrids.21–29 Metal grid-based flexible and stretchable TCEs have recently gained considerable attention due to the potential for easily optimizing the optoelectronic properties through facile dimensional control and achieving uniform and reproducible fabrication. To date, metal grids have predominantly been fabricated by patterning either metal films1–3,6,7,9–12,16–18,30–34 or conductive nanomaterials4,5,8,13–15,19,20,35–38 into a grid shape on flexible and stretchable substrates. Various lithographic techniques have been used to form etch-masks or molds for patterning metal films into a mesh geometry. Examples include photolithography,11,12,17,30 nanoimprint lithography,1 phase-shift lithography,31 and grain boundary lithography.32,33 Grid-shaped polymeric molds made with soft lithography could be used to create metal film patterns that can be transferred selectively onto flexible substrates.6,7,18 Metal grids could also be fabricated by non-lithographic methods based on cracked templates,9,16 anodized aluminum oxide templates,34 evaporative assembly,2 the breath-figure method,3 and direct laser ablation of metal films.10 Metal grids based on patterned metal films


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show considerable electrical performance and mechanical stability. This is possible because all the metal lines in the grid architecture are entirely interconnected to one another and typically show good adhesion to substrates. However, many of the approaches require complicated, expensive, or time-consuming fabrication processes, such as micro/nanoscale lithography, highvacuum metal deposition (e.g., evaporation and sputtering), and laser ablation. As an alternative to evaporated or sputtered metal films, percolation networks of conductive nanomaterials have also been used to obtain metal-grid-based TCEs.4,5,8,13–15,19,20,35–38 Several direct printing methods could precisely print nanoparticle inks onto flexible substrates in various patterns, such as inkjet, electrohydrodynamic jet, filamentary, and gravure priting techniques.4,8,19,36,37 However, most printing processes typically take a long time to complete due to the serial process. Metallic nanowires or nanoparticles have been filled in silicon molds with grid-shaped trenches and then transferred onto flexible substrates to fabricate flexible metal grids.13–15 In addition, transparent polymeric molds with trenches filled with metallic nanostructures were also used as flexible and stretchable micro grids without any post-transfer processes.5,20,35,38 Entirely solution-processable trench-filling techniques can be faster and more inexpensive for fabricating flexible and stretchable metal grids compared to the other approaches. Nevertheless, the filling process is quite cumbersome, which hinders large-area and reproducible fabrication. Unlike conventional micro/nanomachining-based strategies, mesh templates made from woven metal fibers could be used for flexible TCEs by directly integrating them in the layers of a device.39–41 This straightforward approach can be greatly helpful for developing various practical flexible optoelectronic devices by making the overall fabrication simple, cost-effective, and potentially scalable. However, there are still some challenges. The choice of material systems for


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the mesh templates is critically limited because the fibers in the mesh should be highly electrically conductive. In addition, the metal fibers should be woven densely to achieve higher electrical conductivity, but this inevitably degrades the optical performance. In this work, we propose a simple yet highly effective way of enhancing the electrical performance of mesh-template-based TCEs without significant degradation in the optical properties. This is achieved by selectively depositing silver nanowires (AgNWs) onto fibers in a metal woven mesh (MWM) template. This simple process can provide new current paths with lower resistance while leaving the total opening area almost unchanged for the passage of incident light. More importantly, the proposed technique can potentially be applied to any kind of mesh templates to obtain a high-performance metal-grid-based TCE, even to non-conductive templates such as cheap polymeric mesh. The AgNW-coated MWM is fully embedded in an elastomeric substrate with the AgNW percolation network exposed at the top surface to fabricate flexible and stretchable TCEs. The resulting TCE shows considerable optoelectronic performance, including a low sheet resistance of ~3.2 Ω/sq with a high optical transmittance of ~80% at a wavelength of 550 nm. The device also shows mechanical robustness against various deformations, such as stretching, bending, and twisting. As a practical demonstration, we successfully use the device as a transparent electrode in a flexible TSP.

2. EXPERIMENTAL DETAILS Synthesis of AgNWs. AgNWs were synthesized using a modified polyol reduction process based on a copper(II) chloride (CuCl2)-mediated approach.42 First, a glass beaker containing 40 mL of ethylene glycol (EG) solution (Daejung Chemical & Metal) was placed in a silicone oil bath, which was heated at 160 °C and magnetically stirred at 360 rpm. After maintaining it for 1


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h, 160 µL of 4 mM CuCl2 (Samchun Chemical) was added, and the solution was heated for 15 min. Then, 10 mL of 9.4 mM silver nitrate (AgNO3; Sigma-Aldrich)/EG and 10 mL of 14.7 mM polyvinyl pyrrolidone (PVP; Alfa Aesar)/EG were injected simultaneously into the CuCl2/EG solution at a rate of ~1.2 mL/min using a two-channel syringe pump (Legato 111, KD Scientific). The mixture was further heated at 160 °C and magnetically stirred at 360 rpm for another 1 h to sufficiently induce the reduction reaction. The synthesized AgNWs were then purified by centrifuging the mixture at 3000 rpm for 10 min in ethanol/deionized (DI) water (1:1 by volume) using a centrifuge (TD4Z-WS, Nasco Korea). After repeating the purification step at least three times, the AgNW solution was prepared by dispersing the purified AgNWs in DI water at a fixed concentration of ~12 mg/mL for the dip-coating process.

Fabrication of AgNW-MWM-based stretchable TCEs. MWM template made of stainless steel micro fibers was coated with AgNWs using a simple dip-coating method. The MWM template was pressed at 20 MPa for 1 h using a commercially available pressing machine (QM900S, Qmesys) to reduce the gaps between the fibers. The template was then dipped in the AgNW solution and maintained at 70 °C until the DI water fully evaporated, leaving AgNWs on the top surface of the template. The AgNW-coated MWM (AgNW-MWM) was then bonded to a sacrificial dry film resist (DFR; FF-1030, Kolon) at 95 °C under slightly pressurized conditions using a roll laminator (Excelam 355Q, GMP). The laminating process was conducted with the AgNW-coated side of the AgNW-MWM facing the DFR to expose the highly conductive AgNW network on the top surface of the device after removing the sacrificial film. Polydimethylsiloxane prepolymer (PDMS; Sylgard 184 kit, Dow corning) was mixed with a curing agent at a weight ratio of 10:1 and gently poured onto the bonded AgNW-MWM/DFR


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system. The system was then maintained in a vacuum desiccator for 40 min to remove all the air bubbles and allow the AgNW-MWM to fully embed in the PDMS matrix. After thermally curing at 95 °C for 40 min in a convection oven (ON-11E, Jeio tech), the stretchable TCE was prepared by fully dissolving the sacrificial DFR in a solution containing 0.75 M sodium hydroxide (NaOH) at room temperature, and thereby leaving the AgNW-coated template in the PDMS matrix.

Characterization. The morphology of the MWM template, AgNW-MWM, and AgNWMWM-based stretchable TCEs was investigated using a field-emission scanning electron microscope (FESEM; S7400, Hitachi) and an optical microscope (OM; BX60M, Olympus) equipped with a charge-coupled device (CCD) camera module. The detailed surface profiles of the fabricated stretchable TCEs were observed using an atomic force microscope (AFM; XE-100, Park systems) and a laser interferometric profiler (NV-1000, Nanosystem). The sheet resistance of the device was characterized by a two-probe method.35,43 The electrical resistance (R) of the device was first measured using a digital multimeter (34465A, Keysight technologies), and the sheet resistance (Rs) was then calculated by the equation Rs = R × (w/l), where w and l are the width and length of the device, respectively. The optical transmittance of the device was measured using an ultraviolet-visible (UV-vis) spectrophotometer (LAMBDA 365, PerkinElmer) with an integrating sphere at a wavelength ranging from 400 to 800 nm. The optoelectronic properties were measured from at least five identical devices. Stretching, twisting, and bending tests were conducted by applying mechanical loads to the device using a computer-controlled automatic stand (JSV-H100, JISC) and a custom-made mechanical jig. The electrical resistance was monitored in real time during the tests using a


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digital multimeter. A tape test was performed by repeatedly attaching and detaching adhesive tape (810D, 3M) to the top surface of the device using the motorized stand while recording the electrical resistance every 10 cycles until 100 cycles.

3. RESULTS AND DISCUSSION The TCE fabrication is illustrated in Figure 1(a). The overall process is cost-effective and can be potentially scaled up to a large area due to the abundance and easy accessibility of the MWM template, as shown in Figure S1(a) in the Supporting Information (SI). The proposed approach can thus be used as an efficient way to obtain high-performance flexible and stretchable TCEs for practical device applications. Figure 1(b) shows a digital image of the fabricated stretchable TCE, which is highly flexible and transparent. The magnified OM image in Figure 1(c) indicates that the mesh architecture can be maintained stably even after experiencing the entire process while keeping almost the same geometric uniformity as the as-prepared MWM template (Figure S1(b) in the SI). This characteristic is greatly helpful for obtaining uniform optoelectronic performance over the whole device area by enabling similar conductor-to-window ratios per unit area, regardless of the location. Figure 2(a) shows the sequential changes in the surface morphology of the MWM template due to repeated AgNW coating for up to five cycles. The AgNWs used for the coating process had an average length of ~12.1 µm and diameter of ~279.8 mm, as shown in Figure S2 in the SI. The clean surface of the as-prepared template was conformally covered with AgNWs during coating, and the AgNW percolation network gradually became denser as the number of coats increased.


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The optoelectronic properties of the AgNW-MWMs were investigated by measuring the sheet resistances and optical transmittances. Figure 2(b) shows the changes in sheet resistance as a function of the number of coats. The sheet resistance of the as-prepared MWM template with a fiber diameter of ~50 µm and fiber-to-fiber distance of ~800 µm was 12.5 ± 1.7 Ω/sq. This low value resulted from the high electrical conductivity of the template woven with metallic fibers. After the first AgNW coating, the sheet resistance decreased considerably to 7.2 ± 1.7 Ω/sq, which means that electrons predominantly flow through the more conductive AgNW film rather than the metallic fiber. In addition, the AgNW coating would also be helpful for reducing the sheet resistance by connecting metallic fibers at the intersection regions and thereby enhancing the electrical property. The sheet resistance gradually decreased to 3.2 ± 1.2 Ω/sq with three coats. This occurred because the AgNW percolation network became much denser with more coats and allowed more electrons to flow through the new current paths. However, after three coats, the electrical performance of the AgNW-MWM was almost constant, regardless of further coat applications. This means that the AgNWs coated on the MWM template were sufficiently dense after three coats to achieve the lowest sheet resistance, as shown in the SEM images in Figure 2(a). Importantly, the exponential decrease in resistance of the device with the increased number of coats implies that the thickness of the AgNW layer is quite uniform for each coating time because the change in resistance predominantly depends on the change in thickness of the AgNW layer with respect to the fixed mesh geometry. The optical performance of the AgNW-MWM according to the number of AgNW coats was investigated by measuring the optical transmittance at a wavelength of 550 nm, as shown in Figure 2(c). The full spectral transmittance for each model are also provided in Figure S3 in the


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SI. The as-prepared MWM template had a high optical transmittance of 90.4 ± 0.2 %. Interestingly, the transmittances of the AgNW-MWMs exhibited a maximum deviation of only ~2.5% from the as-prepared template, regardless of the number of coats. This is supported by the diameters of the metallic fibers remaining almost constant with little change in the window sizes even after several AgNW coats (Figure 2(a)). Digital images in the inset of Figure 2(c) show that AgNW-MWMs demonstrate similar visibility regardless of the coating cycles. As the result, a high transmittance of 88.5 ± 0.1 % was achieved with three coats of AgNWs. The three-coat AgNW-MWMs were used to fabricate stretchable TCEs for their excellent optoelectronic performance. Figure 3(a) and (b) show top-view and cross-sectional SEM images of a fabricated stretchable TCE. The AgNW-MWM was stably embedded in the PDMS matrix with the highly conductive AgNW film exposed at the top surface. For practical applications, the AgNW film should adhere to the template with enough strength to prevent delamination during use. This characteristic was investigated using the cyclic tape test, as shown in Figure S4 in the SI. The initial resistance of the device was stably maintained without significant degradation for up to 100 cycles of the tape test. The SEM images in the inset of Figure S4 in the SI also support this by clearly showing that the surface morphology is almost the same as the initial state, even after 100 cycles. To evenly expose the AgNW film and achieve the uniform surface conductivity, the AgNWMWM should be tightly laminated onto the sacrificial DFR film before being embedded in PDMS matrix. However, the heat and pressure imposed during the laminating process eventually generate rough topography on the device surface by causing the AgNW-coated fibers to protrude from the surface. Figure 3(c) shows the cross-sectional profile measured in a region where two AgNW-coated metallic fibers cross each other. The maximum protrusion height is ~5 µm in this


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case. It is worth noting that the surface topography of the device can be reduced further through optimization of the laminating conditions. A very smooth surface was found in the window area of the device, as shown in the AFM analysis results in Figure 3(d) and Table S1 in the SI, which is greatly helpful for achieving low-loss transmission of incident light. Figure 3(e) shows the optoelectronic performance of the AgNW-MWM before and after being embedded in PDMS matrix. The electrical properties of the embedded AgNW-MWM were almost not changed. However, the optical properties degraded by ~8.7% compared to the asprepared AgNW-MWM due to the PDMS filling the open spaces. Nevertheless, the stretchable TCE still exhibited excellent sheet resistance (Rs) of ~3.2 Ω/sq and optical transmittance (T) of > 80%. More importantly, the optoelectronic performance of the device can be easily controlled by simply using MWM templates with different geometric parameters such as the fiber diameter and fiber-to-fiber distance. To demonstrate this, three different models of MWM templates were used to fabricate stretchable TCEs, as shown in Figure 3(f). The detailed dimensions are provided in Table S2 in the SI. The opening area (OA) is defined as the ratio of the window area to the total area. The optical transmittance of the device was gradually increased with increasing OA by allowing more light to pass through the window regions. The full spectral transmittances for the devices are provided in Figure S5 in the SI. The increase in OA also leads to a gradual reduction of the sheet resistance because the templates with larger OA have larger fiber diameters and fiber-to-fiber distances, as summarized in Table S2 in the SI. This clearly suggests the possibility of further optimization of the optoelectronic performance in a simple manner. After embedding it in PDMS matrix, the AgNW-MWM could be stably stretched with tensile strains applied in both the orthogonal and diagonal directions, as shown in Figure S6 in the SI.


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Furthermore, the deformed shapes of the devices almost completely recovered to their initial states when released thanks to the elastic restoring force of the PDMS in the open spaces of the AgNW-MWM. Figure 4(a) shows the normalized resistance of the fabricated stretchable TCE when stretched in the orthogonal direction. The device could be stretched to ɛ = 20% in the orthogonal direction without failure. This is probably due to straightening along the stretching direction of the woven fibers, which initially have a zigzag shape. This process is schematically illustrated in Figure S7 in the SI. The normalized resistance of the device gradually increased with the tensile strain in the orthogonal direction, but electrical failure did not occurred at up to ɛ = 20%, as shown in Figure 4(a). To examine the strain-dependent electrical characteristics, the morphological changes of the device surface were investigated according to the applied strain using SEM (Figure 4(b)). When stretched to ɛ = 20%, channel-like cracks occurred on the AgNW film in regions where the upper and lower fibers are bridged by the AgNW film (AgNW bridge), as shown in the middle SEM image in Figure 4(b). This is explained by the strain predominantly concentrating on the AgNW bridges during the straightening process of the fibers after stretching. This also implies that the gradual increase in the sheet resistance was caused by the gradual loss of the current paths in the AgNW bridges with increasing applied strain. Interestingly, even when the AgNW bridges were broken by being exposed to high strain (i.e., ɛ = 20%), the device still exhibited relatively good electrical performance, as shown in Figure 4(a). This is probably resulted from the fact that electrons can flow through the metallic fibers underlying the AgNW film instead of the broken paths, which makes the device electrically robust even at high strains. When released, many of the channel-like cracks closed up (rightmost SEM image in Figure 4(b)). This suggests that many of the broken current paths recovered due to


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the high elasticity of the PDMS. After experiencing high strain (ɛ = 20%), the electrical resistance of the device increased by ~42.8% compared to the as-prepared state. This was presumably due to incomplete closure of the channel-like cracks upon releasing. Nevertheless, the new initial resistance of the device was still low (< 10 Ω). Figure 4(c) shows the normalized resistance of the device under strain applied in the diagonal direction. The device showed much larger stretchability than the orthogonal direction. This occurred because the MWM template can be stretched further in the diagonal direction by deforming into a rhombus shape while two fibers rotate around an intersection point as strain is applied. This process is illustrated in Figure S6(b) in the SI. Unlike stretching in the orthogonal direction, the AgNW bridges were broken in a way that the cracks gradually propagate from one end in this case. Thus, the resistance change was ~53.9% smaller than that obtained with stretching in the orthogonal direction. The AgNW bridges were completely opened when stretched to ɛ = 40% (middle SEM image in Figure 4(d)). However, the device still functioned well without electrical failure because alternative current paths can be provided by the electrically conductive MWM template. When the cracks in the AgNW bridges closed up upon release, the initial resistance of the device returned to the ~42.1% higher value, which is similar to the behavior in the orthogonal case (Figure 4(c)). Figure S8(a) and (b) in the SI show sequential SEM images of the AgNW bridges in the initial, stretched, and released states under ɛ = 10% and 20% strains in the orthogonal and diagonal directions. For strain below the critical point where channel-like cracks occur, the AgNWs in the bridge regions were still sufficiently interconnected to each other with enough density to maintain sufficient current paths. This leads to more stable and reversible electrical performance.


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The electrical performance of the device was thus stably maintained even under 1000 stretching/releasing cycles in the orthogonal (ɛ = 10%) and diagonal (ɛ = 20%) directions, as shown in Figure 4(e). In addition, SEM images in Figure S9 in the SI indicate that the surface morphology of the device was also stably kept even after the cyclic tests. The stretchable TCEs were also found to be electrically robust against other types of mechanical deformations, such as bending and twisting. Figure 4(f) shows the normalized resistance of the device as a function of the bending radius (Rb). The maximum change in resistance was only ~1.4% upon extreme bending (Rb = ~0.4 mm). Moreover, the device was also highly stable for numerous bending cycles, showing constant electrical resistance and surface morphology over 1000 cycles with a minimum bending radius of ~3 mm, as shown in Figure S10 in the SI. Figure 4(g) shows that the device can also be twisted up to 90º without considerable change in the resistance. These results indicate that the device is highly appropriate for applications in flexible and stretchable devices. To demonstrate the practical potential of the device, the AgNW-MWM-based stretchable TCEs were used as a top electrode in a conventional four-wire resistive TSP module. The flexible TSP was simply designed with an architecture in which two TCEs are vertically assembled with intermediate insulating spacers, as schematically illustrated in Figure 5(a). Prior to the assembly process, four pieces of copper tape were applied to both ends of each TCE so that the locations where touch events occurred could be detected precisely by constructing a four-wire configuration, as shown in Figure 5(b). After connecting the fabricated flexible TSP to control software, its practicality was successfully demonstrated by writing the initials of our institution (“P”, “N”, and “U”), as shown in Figure 5(c). An ITO-coated PET sheet was employed as a bottom electrode. However, the


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brittleness of ITO films would critically hinder their use in flexible devices. In contrast to the AgNW-MWM-based stretchable TCEs, the electrical resistance of the ITO/PET sheet easily failed in the bending test and largely increased as the bending radius decreased, as shown in Figure S11 in the SI. To demonstrate a TSP with greater mechanical and electrical stability, we replaced the ITO/PET bottom electrode with the TCEs and verified the performance stability by successfully writing the letters “abc” on the bent screen, as shown in Figure 5(d). The experimental results clearly confirm that the proposed stretchable TCEs can have many applications in flexible and stretchable electronics due to their excellent optoelectronic performance, high stretchability, mechanical and electrical robustness, and simple, low-cost, and reproducible fabrication.

4. CONCLUSION In summary, we have proposed a simple but highly efficient way of developing highperformance flexible and stretchable TCEs. Readily accessible MWM templates were coated with AgNWs and embedded in PDMS matrix in a method that is cost-effective and scalable. The fabricated stretchable TCEs exhibited a low sheet resistance of ~3.2 Ω/sq and high optical transmittance of > 80% at a wavelength of 550 nm. In addition, high stretchability (ɛ = 20% and 40% in the orthogonal and diagonal directions, respectively) and considerable reversibility were achieved while retaining good electrical performance due to the unique opening-and-closing mechanism of AgNW cracks on the electrically conductive MWM template. The device was also electrically and mechanically stable even under repeated stretching and bending for up to 1000 cycles. Finally, the usability was demonstrated by applying the device in a TSP module and successfully operating it in flat and bent states.


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ASSOCIATED CONTENT Supporting Information. Digital and OM images of MWM template (Figure S1), SEM image and length and diameter distributions of the synthesized AgNWs (Figure S2), full spectral transmittance of AgNW-MWMs with different AgNW coating cycles (Figure S3), normalized resistance of the AgNW-MWM-based stretchable TCE under repeated taping tests for up to 100 cycles (Figure S4), full spectral transmittance of the AgNW-MWM-based stretchable TCEs prepared using templates with different opening areas (Figure S5), sequential SEM images of the device when stretched and released in the orthogonal (ɛ = 20%) and diagonal (ɛ = 40%) directions (Figure S6), schematic illustrations of cross-sectional geometries of metal fibers in the initial and orthogonally stretched states (Figure S7), sequential SEM images of the device when stretched and released in the orthogonal (ɛ = 10%) and diagonal (ɛ = 20%) directions (Figure S8), SEM images of the device after the cyclic stretching tests (Figure S9), normalized resistance of the AgNW-MWM-based stretchable TCE as a function of bending for up to 1000 cycles (Figure S10), normalized resistance of the ITO/PET sheet as a function of bending radius (Figure S11), statistical roughness parameters examined on the window region of the device using the AFM (Table S1), detailed dimensions of MWM templates with different opening areas (Table S2). This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]


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ACKNOWLEDGEMENT This

research

was

supported

by

the

Basic

Science

Research

Program

(No.

2015R1A2A2A01004038 and No. 2017R1A2B3005706) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning.

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Figure 1. Fabrication of AgNW-MWM-based stretchable TCE. (a) schematic illustration of the fabrication process, (b) digital image of the fabricated device, scale bar: 20 mm, and (c) magnified OM image of metal grids on the device, scale bar: 500 µm.


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Figure 2. Fabrication and performance measurements of AgNW-MWM. (a) SEM images of AgNW-MWMs with different AgNW coating cycles, scale bars: 100 µm, and (b) sheet resistance and (c) optical transmittance of the fabricated AgNW-MWMs at a wavelength of 550 nm as a function of the number of AgNW coats (inset: digital images of the AgNW-MWMs processed with different coating cycles, scale bar: 20 mm).


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Figure 3. Fabrication and performance measurements of AgNW-MWM-based stretchable TCE. (a) top-view, scale bars: 1 mm, 50 µm (inset) and (b) cross-sectional SEM images of the fabricated device, scale bars: 1 mm, 100 µm (inset), (c) cross-sectional profile along line A-A’ marked in the inset (inset: top-view 3D profiling image on the region where two metallic fibers cross each other), (d) AFM image of the window region marked in (a), (e) comparison of optoelectronic performance of the AgNW-MWM before and after embedding in PDMS matrix, and (f) variations in optoelectronic performance of the devices prepared with AgNW-MWMs with different opening areas.


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Figure 4. Electrical robustness of AgNW-MWM-based stretchable TCE under various mechanical deformations. (a), (c) sheet resistance and (b), (d) sequential SEM images of the device when stretched and released in the orthogonal ((a), (b)) and diagonal ((c), (d)) directions, scale bars: 50 µm, (e) cyclic responses of the device under 1000 stretching/releasing cycles with a maximum strain of 10% (orthogonal) and 20% (diagonal), and normalized resistance of the device as a function of (f) bending radius and (g) twisting angle (inset: digital images of the devices being tested).


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Figure 5. Flexible TSP application. (a) schematic illustration of the TSP architecture, (b) digital image of the fabricated flexible TSP, scale bar: 30 mm, and sequential digital images of the TSP while writing letters on the screen in (c) flat and (d) bent states.


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TABLE OF CONTENTS GRAPHIC


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Metal Nanowire-Coated Metal Woven Mesh for High-Performance

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