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Abstract
A unique freestanding nickel (Ni) metallic mesh–based electromagnetic interference shielding film has been fabricated though the direct-writing technique and a subsequent selective metal electrodeposited process. The structured freestanding Ni mesh film demonstrates a series of advantages, including ultrathin thickness (2.5-6.0 μm) and ultralight weight (0.23 mg cm−2), extraordinary optoelectronic performance (sheet resistance about 0.24-0.7 Ω sq−1 with transparency of 92%–93%), high figure of merit (18000) and outstanding flexibility as it can withstand folding, rolling and crumpling into various shapes while keeping the conductivity constant. Furthermore, by using this high-performance Ni mesh, an ultrathin, lightweight, freestanding and transparent electromagnetic interference shielding (EMI) film with extraordinary optoelectronic properties (shielding effectiveness about 40 dB with transparency of 92%) is demonstrated in X-band, with no performance attenuation observed even in bending state. This freestanding metallic mesh–structured electrode can be further explored or applied in various potential applications, such as conformal microwave antennas, transparent EMI windows, and wearable electronics.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Electromagnetic radiation pollution, severely exacerbated by the development of modern electronics packed with highly integrated circuits, leads to harmful effects on sensitive precision electronic equipment as well as the living environment for human beings, promoting the research focus on novel high-performance EMI shielding [1–5]. In particular, the transparent EMI shielding is appealing in areas where visual observation is required, e.g., transparent windows for detectors or sensors for space exploration, electronic displays, mobile communication devices, acting as imperative protection components for military and civilian utilities [6,7]. Significantly, with the development of modern electronics toward being flexible and integratable, the EMI shielding film must simultaneously provide high optical transmittance, excellent EMI shielding effectiveness (EMI SE), and meanwhile bendability even twistability which is imperative to adapt to complex shaped or foldable applications [8–12]. To date, various kinds of transparent EMI shielding films with good shielding performance have be demonstrated. Among the novel EMI shielding materials, metal nanowires [13–15] and patterned metal network [16–18] transparent conductive films (TCFs) emerge as better EMI materials than other commercialized indium tin oxide (ITO)-based [19,20] and carbon-based [21–31] films. Han et al. demonstrated a crack-template based silver mesh exhibiting a highly reliable shielding ability in complex service environment [32]. In addition, Jung et al. fabricated a highly stretchable and transparent EMI shielding layer with silver nanowires, meanwhile, the flexible layer can maintain a high EMI SE even under a high tensile strain condition [33]. Despite the high levels of performance and functionality available from these transparent EMI films, they remain substrate-supported which limits their applications nonplanar and irregular surface environment, such as wearable electronics, curved optical devices, etc. [3,8]. Furthermore, the substrate-supported EMI films show pronounced shortcomings on account of the properties of the substrate, such as a high thickness (>50 μm), a low optical transmittance (<92%), poor toughness and susceptibility to high temperature (<140 oC) [34–36].
Undoubtedly, if a freestanding EMI shielding film featured with ultrathin thickness, high transparency, and excellent conductivity is successfully fabricated, the limitations on account of using the supporting substrate can be solved [37,38]. Huang et al. reported ultrathin freestanding silver nanofibers with a transparency of 97% fabricated by a gas assistant solution spinning method [38]. However, the high junction resistance between the nanowires/nanofibers decreases the conductivity of the TCF, and extra processes like high temperature annealing, plasma welding, and mechanical pressing are required to reduce the junction resistance which complicates the fabrication [39]. More importantly, the inherent tradeoff between the optical transmittance and the EMI shielding effectiveness of existing metallic based TCFs are inevitable [17,40,41]. The fabrication of an ultrathin transparent freestanding metallic mesh EMI film, breaking off the tradeoff of the transmittance and EMI SE has never been reported. Thus, it remains a significant technological challenge to develop metallic materials that exhibit all the above-mentioned desirable features simultaneously.
Herein, we demonstrate the realization of a freestanding, ultrathin, lightweight, mechanically robust, and transparent Ni metallic mesh-based EMI shielding film though the direct-writing technique followed by a selective metal electrodeposited process, providing simplicity and fully controllable flexibility to regulate the sheet resistance and meanwhile maintaining the transmittance unchanged, which is attributed to the confinement properties of the patterned microgrooves generated from the laser direct-writing technique. Regulation of the sheet resistance can be easily attained just by monitoring the thickness of the Ni metallic mesh layer, and in this way, the EMI SE of the Ni mesh film can be further improved without an obvious influence on the transmittance, breaking off the tradeoff of both. The ultrathin freestanding Ni mesh contributes to excellent flexibility, folding or even attaching to three-dimensional shapes with ignorable degradation of the EMI shielding efficiency. It also allows a free permeation of gas and liquid molecules, such as oxygen, moisture, etc., showing excellent air permeability. This Ni mesh films are characterized with extraordinary optoelectronic properties: a sheet resistance of 0.24-0.7 Ω sq−1, a transparency about 92%-93%, and a high EMI about 40 dB shielding efficiency in 8.2-12.4 GHz frequency range (X-band) for plane and crooked Ni-mesh films. Above all, the high-performance Ni-mesh EMI film processing excellent electrical conductivity, high EMI SE, outstanding transmittance and mechanical properties are promising EMI materials for practical applications.
2. Experimental section
2.1 Fabrication of freestanding Ni mesh film
ITO glass substrates (∼6 Ω sq−1, South China Xiang Science & Technology, China) were cleaned with a scouring pad, liquid detergent, and deionized water, and were subsequently dried at 90 ℃ for 30 min. The photoresist (AZ-4620, USA) was spin-coated at 2000 rpm for 30 s to reach a thickness of 9.6 μm on the pre-cleaned ITO glass at room temperature. Next, the photoresist layer was patterned by the laser direct-writing technique and the relief grooves of the photoresist were generated after the development [42]. Then Ni was selectively deposited in the grooves on exposed ITO glass regions to form the patterned Ni mesh film. 150 mL Ni plating solution composed of 4 g Ni(SO3NH2)2·4H2O, 0.6 g NiCl2·6H2O, and 0.3 g HBO3 in distilled water, was used for the electroplating deposition. A plating set-up (China Electronics Technology Group Corporation, DDT-3) is used in the process. The thickness of the deposited Ni mesh can be controlled by the electroplating time, and three different thicknesses of 2.5, 4, and 6 μm correspond to an electroplating time of 300, 400, and 500 s, respectively, at a constant cathode current density of 0.5 A/cm2 at the temperature of 55 ℃. The samples were placed in sodium hydroxide solution (20 wt ‰) for 5 min to fully remove the photoresist, followed by the rinsing of the samples with clean water, which leaves the bare metal grid film on the ITO glass substrate. Finally, the metal mesh was peeled off from the ITO glass substrate with the assistance of a tweezer, and an ultrathin, lightweight, freestanding Ni mesh was obtained.
2.2 Characterizations
The morphology of the samples was characterized using an S-3400N scanning electron micro-scope (FESEM: JEOL, JSM-5400, USA) and a 3D laser confocal microscopy (Keyence, VK 9700). The sheet resistance of the fabricated samples was measured using a four-point probe (ST2263). Optical transmission spectra and haze factors were recorded using a Lambda 750 UV–VIS spectrometer (Perkin Elmer, USA). Computer simulation technology (CST) Microwave Studio software is used to analyze the microwave shielding effectiveness of the proposed freestanding Ni mesh film. The EMI shielding effectiveness was recorded by an Agilent N5230C PNA Network Analyzer and a calibration kit WR-90 in the frequency range of 8.2-12.4 GHz (X-band).
3. Results and discussion
3.1 Sample preparation
The fabrication process of the freestanding Ni-mesh mainly includes four steps, which are illustrated in Fig. 1(a). First, a photoresist layer with a thickness of 9.6 μm was obtained by spin-coating onto a pre-cleaned ITO glass. Then, the patterned micro-trenches on the photoresist layer was generated by the laser direct-writing technique [42], and the patterned ITO glass surface in the mesh grooves was exposed after the development of the photoresist. Following on, the Ni metal was electrodeposited inside the predefined micro mesh grooves though the selective electrodeposition, and the deposition time was carefully controlled to obtain the Ni metallic mesh layer with a desired thickness. Thanks to the space confinement of the micro-grooves, the Ni mesh only grow inside them without a broadening in the linewidth. Lastly, the ultrathin, freestanding, and transparent Ni mesh conductive films were finally accomplished after being peeled off from the ITO glass substrate. For all the obtained samples, the width of the Ni line is fixed on 5 μm with the thickness ranging from 2.5 to 6.0 μm. Therefore, the sheet resistance can be adjusted in a wide range while keeping the transmittance of the Ni mesh film almost unchanged. This provides a facile way to regulate the conductivity and optical transparency of the Ni mesh separately just by controlling the deposited time period, breaking the tradeoff of both.
Fig. 1. (a) The schematic illustration of the fabrication process of the freestanding Ni mesh conductive film. (b) The characterizations of freestanding Ni metallic mesh: (i) large-scaled, (ii) high optical transparency, (iii), (iv) flexible and (v), (vi) lightweight properties. (c) (i) The weight of a scaled 10×10 cm2 Ni mesh film with 4.0 μm thickness, (ii) a 100 g weight and (iii) the mechanical property of the Ni mesh film. (d) SEM images with different scale bar.
3.2 Characterization
The ultrathin freestanding Ni mesh film with a thickness of several micrometers shows excellent transparency and flexibility as demonstrated in Fig. 1(b). The metallic mesh fabrication method can be scaled up to the large area, and a 10×10 cm2 Ni mesh film is obtained, as shown in Fig. 1(b-i). The freestanding Ni mesh film is completely transparent that the flower can be seen clearly through it [Fig. 1(b-ii)]. And meanwhile it exhibits excellent flexibility so that can be uniformly attached to complex shaped objects without any gap, such as the flower stem and the grape [Figs. 1(b-iii) and (b-iv)] and even can stand upon the setaria viridis with sides dropping down naturally [Fig. 1(b-v)], which mainly attributes to its freestanding structure nature. Moreover, when the Ni mesh film was placed on the Albizia julibrissin, the flower filaments can even sustain their original state without any visible damage [Figs. 1(b-vi)], delivering its ultralight features. For a 4.0 μm thickness Ni mesh film with an area of 10×10 cm2, it only weighs 23.1 mg [Fig. 1(c-i)] showing an area density of 0.23 mg cm−2, while this lightweight Ni mesh still can sling a 100 g weight [Fig. 1(c-ii)], more than 4000 times of the Ni mesh own weight. When the weight was laid down, the Ni mesh film appears intact without any deformation, which was attributed to the firm texture of the Ni mesh [Fig. 1(c-iii)].
It can be further confirmed from the scanning electronic microscopy (SEM) images of our obtained Ni mesh conductive film, as depicted in Fig. 1(d), that high density and well-shaped Ni lines resulting from selective electrodeposition form highly uniform and naturally interconnected networks over the large area. Additionally, three-dimensional (3D) confocal microscope images in Fig. 2 show the morphological characterizations of the Ni mesh film at different stages of the preparation procedures. Figures 2(a)–2(c) display the microscope images of the micro-grooves in the photoresist layer, micro-grooves filled with Ni through selective metal electrodeposition, and the bare Ni mesh after dissolving the photoresist layer, respectively. Figures 2(d)–2(f) depict the cross-sectional profiles of the microgrooves corresponding to the fabrication steps in Figs. 2(a)–2(c). The pattered micro-grooves in the photoresist layer are with a depth of 9.6 μm and a width of 5.0 μm [Fig. 2(d)], then deposited Ni in those grooves partially decreased the groove depth to 5.6 μm [Fig. 2(e)], corresponding to the gained bare Ni mesh with a thickness around 4.0 μm [Fig. 2(f)]. By controlling the deposition time, the Ni mesh samples obtained here possess various thicknesses, whose SEM images are shown in Fig. 2(g), revealing the thickness of the Ni film of about 2.5 μm, 4.0 μm, and 6.0 μm, respectively. It is noteworthy that the width of the Ni line is always fixed at 5.0 μm, owing to the confinement effect of the pattered micro-grooves. It is further guaranteed that the transmittance cannot be affected by the adjustment of the sheet resistance of the Ni mesh film, which solves the contradiction of the traditional optical-electrical performance. Especially, the cross-section SEM images of single Ni line in Fig. 2(g) indicate that the electrodeposited process generates a highly dense, smooth, and uniform Ni mesh layer, which possess outstanding qualities like high thermal stability, corrosion resistance and mechanical robustness. For the superior performances above, the ultrathin, lightweight, freestanding, transparent, and flexible Ni mesh can be conformal to any arbitrary shaped objects, adapting to different applications.
Fig. 2. The 3D confocal microscope images of the formation process of Ni mesh. (a) Photoresist patterning, (b) Ni electrodepositing, (c) bare Ni mesh, and (d)-(f) line profile of the Ni line in different processes. (g) Profile and cross-sectional SEM images of the freestanding Ni mesh with various thicknesses of 2.5 μm, 4.0 μm, and 6.0 μm, respectively.
3.3 Optical diffraction
For the application of the EMI shielding film in the optical imaging domain, uniform illumination is crucial in ensuring the imaging quality while the light beam penetrates through the metal mesh. As a matter of fact, only zeroth-order diffraction is useful in imaging and observation [43]. However, the stray light caused by high-order diffraction spots is one important defect of the metal mesh film, which causes deceptive targets and covers up real detection objects, thus reducing the image quality through the optical windows [44]. To surmount the effect of high-order diffraction, a random grid has been introduced to the mesh pattern owning to its concentration of zeroth-order diffraction energy.
In order to explore the diffraction characteristics of different mesh patterns, three mesh arrangements have been fabricated and investigated, in order of the square, the honeycomb and the random grid configuration, as depicted in Figs. 3(a-i)–3(a-iii). The stray light distributions of various mesh arrangements are analyzed by a digital imaging method based on Fourier optics. Figures 3(b-i)–3(b-iii) graphically illustrate the simulation results of beam intensity distribution through the Ni metal grid film with regard to the mesh arrangements in Figs. 3(a-i)–3(a-iii). The 3D intensity distributions of diffraction patterns in accordance with the 2D diffraction distributions are further clarified in Figs. 3(c-i)–3(c-iii), from which the intensity distribution of stray light can be more intuitive. The high-order diffraction of a square arranged mesh is mainly distributed in a cross shape, and it evolves to a double cross pattern in the honeycomb mesh pattern. The high stray light intensity attenuates the zeroth-order distribution energy, causing a degradation of the imaging quality and duplicated false images. The stray light energy from high-order diffractions by the random mesh is greatly attenuated as compared with that from the square or honeycomb arranged mesh, which indicates the good optical performance of such structured EMI windows.
Fig. 3. Diffraction pattern analysis of the Ni mesh film with different grid arrangements. (a) Different arrangements of (i) square, (ii) honeycomb and (iii) random grid grids. (b) Diffraction spectrograms of (i) square, (ii) honeycomb and (iii) random arranged grids. (c) The 3D intensity profiles of diffraction spots related to (i) square, (ii) honeycomb and (iii) random arranged grid, respectively.
3.4 Optical and electrical properties
The optical and electrical properties of the prepared freestanding Ni mesh were first characterized by measuring the values of the visible light transmittance and the sheet resistance. The Ni mesh with different thicknesses (random distribution of the mesh with the spacing ranging from 120 to 150 μm) all exhibit excellent optical performance, with transmittance up to 92%-93% in the whole visible spectrum of 380-780 nm, as shown in Fig. 4(a). As we know, the transmittance of the metallic mesh film is dependent upon the filling factor (FF) which is defined by W/(W + G), where W is the width of the mesh and G is the mesh spacing [45]. For the freestanding Ni mesh, the transmittance is only decided by the occupation of the Ni metal grids, excluding the influenced of the substrate. The transmittance (T) of the Ni-mesh can be described as the following formula [17]:
Here we use the average mesh spacing of the randomly arranged Ni mesh to calculate the transmittance, and the obtained value is about 93.4%. Meanwhile, the measured transmittance value of the 2.5-μm-thick Ni mesh achieved 93% at the wavelength of 550 nm [Fig. 4(a)], which is in accordance with the calculated value. With the thickness increasing, the transmittance decreased slightly, from 93% to 92%, while the haze increased from 1.3% to 2%, mainly caused by the increased scattering at greater thickness Ni grids. Owing to the low occupancy of the Ni line (only 3%), the freestanding Ni mesh not only exhibits high transparency and low density, but also provides excellent permeable properties. Place the freestanding Ni mesh on a holder, it allows a free permeation of gas and liquid molecules, such as oxygen, moisture, etc., as revealed in Visualization 1 and Visualization 2. The smoke rose up through the freestanding Ni mesh without any block, and meanwhile, the water filtered through the mesh straightly, paving a way for the EMI shielding application in wearable electronics.Fig. 4. Characterization of the freestanding Ni mesh film with various thicknesses. (a) Transmittance, and (b) sheet resistance on the left and FoMs on the right for the freestanding Ni mesh film with a thickness of 2.5 μm, 4.0 μm and 6.0 μm, respectively. (c) Comparison of the FoMs of the Ni mesh film in this work with other reported transparent metal meshes. Normalized sheet resistance changes versus (d) various bending radii, (e) the number of repeated bending cycles, and (f) different applied strain ratios for the Ni mesh film at the thickness of 2.5 μm, 4.0 μm and 6.0 μm, respectively.
Additionally, the sheet resistance of the Ni mesh film can be substantially adjusted with a modulation in the Ni layer thickness, as given by Fig. 4(b). An extremely low sheet resistance of 0.24 Ω sq−1 was achieved for the 6-μm-thick Ni mesh, and the optical transmittance at the wavelength of 550 nm still reached 91.9%. Furthermore, the influence of the metal thickness on the overall properties of the Ni mesh film can be judged by the figure of merit (FoM), the ratio of electrical conductance to optical conductance (${\sigma _{dc}}$/${\sigma _{opt}}$), as defined by the following formula [16,17]:
3.5 Mechanical properties
Our ultrathin freestanding Ni mesh electrodes are bendable, stretchable and foldable. Stability of their electrical conductivity under deformation is a critical issue for the attachment on the complex shaped surfaces [16]. The normalized variation of the sheet resistance is used as the function of mechanical actions, either bending the film down to a radius of 3 mm, 2 mm, 1 mm [Fig. 4(d)] or repetitively bending the film to radii of 3 mm, 2 mm, 1 mm for 2000 times [Fig. 4(e)]. On examining the freestanding Ni mesh film after both bending regimes, the normalized variation of sheet resistance is almost unchanged, predicting no obvious degradation in the electrical conductivity. And meanwhile, the Ni mesh film with different thicknesses all exhibit excellent mechanical durability, which mainly attributes to their substrate-free and the metallic mesh structure. Additionally, the stretchability of the Ni mesh electrodes are examined with strain of 5%, 10%, 15%, 20%, 25%, 30%, respectively, as illustrated in Fig. 4(f). For the 2.5-μm-thick Ni mesh film, the sheet resistance kept the same until cracks are generated when the strain is up to 30%, but the cracked mesh still maintains a constant electrical conductivity. The 4.0 μm thick Ni mesh exhibits the highest stability with almost no difference when undergoing continued strain among the three Ni mesh electrodes. It is noteworthy that the random arrangement of the metal grids is not specially designed for stretching, but it can still withstand a 30% stretch while ensuing the good electrical conductivity, delivering that the Ni mesh film can be attached to arbitrary shaped objects. This remarkable Ni mesh stability is attributed to its freestanding nature, furthermore, the highly stable conductivity under bending, cyclic bending and stretching makes it a qualified flexible, transparent, and conductive film for flexible optoelectronic device applications.
3.6 EMI shielding effectiveness
The ability of a material to attenuate the unwanted incident electromagnetic radiation is termed as EMI SE [49–51]. The total EMI SE (SET) is defined as the logarithmic ratio of incident EM wave power (Pi) to transmitted EM wave power (Pt) as expressed by the following formula [52]:
In view of the EMI shielding for metallic based film, the EMI shielding is mainly caused by reflection, and the SET can be described by the Simon formulation as [53]: Where f (MHz) is the frequency, σ (S cm−1) is the electrical conductivity and t (cm) is the thickness of the EMI shielding. It is obvious that the total SE is strongly dependent on the electrical conductivity σ of the shielding materials. Thanks to the selective electrodeposited process, the freestanding Ni mesh films have extremely low sheet resistances (i.e., 0.7, 0. 4 and 0.24 Ω sq−1 for 2.5, 4 and 6 μm thickness Ni mesh, respectively). High conductivity of materials generally leads to high EMI SE, and such highly conductive freestanding Ni mesh films could be utilized as efficient EMI shielding materials.To evaluate the EMI SE of those freestanding Ni mesh films, a vector network analyzer in the frequency of 8.2-12.4 GHz (X-band) is employed. Figure 5(a) shows the measured EMI SE spectra of transparent freestanding Ni mesh films with different thicknesses in the X-band frequency range. The EMI SE of the Ni mesh films exhibit similar tendency, whose values decrease gradually along with the increasing frequency. The EMI SE values of the 6-μm-thick Ni mesh film decrease from 41 to 38 dB with the frequency increases from 8.2 to 12.4 GHz, whereas the values of the 2.5-μm-thick Ni mesh film decline from 37 to 35 dB. We illustrate that the Ni mesh film with increased thickness performs better in EMI shielding, attributing to the gradually increased electric conductivity. The simulated data further confirms our experimental results, as shown in Fig. 5(b), in which the electric conductivity corresponds to calculated ones at different thicknesses. The EMI SE decreases with the increase of the working frequency, which is in accordance with the measured results, but the calculated EMI SE value is about 6 dB higher than the measured one.
Fig. 5. EMI SE of fabricated Ni mesh films. (a) The measured EMI SE of plane Ni mesh films in X-band, (b) the theoretically calculated EMI SE of plane Ni mesh films, (c) the EMI SE of spherical Ni mesh films. (d) The EMI SE curves of the Ni mesh film with a thickness of 4 μm with different curvatures, 0.45 cm−1, 0.65 cm−1, and 1 cm−1, respectively. (e) The EMI SE variation of a 4.0 μm thickness Ni mesh film with different bending cycles. (f) A comparison of the EMI SE versus transmittance characteristic of the measured sample with various flexible transparent EMI films in literature.
Furthermore, to adapt to complex 3D objects, such as nonplanar and irregular surfaces, the influence of bending curvatures of freestanding Ni mesh films on EMI SE has been investigated. According to Fig. 5(c), it is apparent that the EMI SE value variation trend of the spherical Ni mesh film with a curvature of 0.3 cm−1 is in accordance with the complanate one. At the same frequency, SE is only 1 dB lower for the spherical Ni mesh film, in which the inappreciable gap can be ignored. In addition, as shown in Fig. 5(d), the EMI SE performance of the freestanding 4.0-μm-thick Ni mesh film with different curvatures of 0.45 cm−1, 0.65 cm−1, and 1 cm−1 was also tested, respectively. At the same frequency, EMI SE value decreases slightly with the decrease of the curvature radius, and the overall difference among them is within 1 dB. Compared with the flat Ni mesh film, the decrease in EMI SE of the curved Ni mesh films is within 3 dB, which can fully meet the requirements of the EMI shielding in complex topography. It is noteworthy that the freestanding Ni mesh here can maintain the high mechanical stability after being bended for thousands of cycles, and simultaneously hold high EMI SE values. As depicted in Fig. 5(e), when bended for 500 cycles, 1000 cycles, and 1500 cycles at a curvature radius of 0.45 cm−1 for the 4.0-μm-thick Ni mesh, it also can keep almost the same EMI SE compared to the initial value before bending. To make a comparison with the metallic shielding materials in the recently reported works [8,10,12,17,32,33,54,55], as presented in Fig. 5(f), where the EMI SE and the transparency properties of our freestanding Ni mesh films are all superior to those reported. An important finding is that the inherent conflict between optical transmittance and EMI SE exists in other shielding materials is broken in our Ni mesh films, originating from the fabrication process which can regulate the electric conductivity while maintaining the transmittance approximately unchanged. The extraordinary EMI performance of the freestanding Ni mesh film under complex surface shapes indicates its wide application prospects in conformal transparent EMI windows, attributing to the ultrathin and random grid configuration nature.
4. Conclusion
In conclusion, we demonstrate an ultrathin, lightweight, freestanding Ni mesh film that are fabricated by the direct-writing technique with a selective metal electrodeposited process, exhibiting excellent transparency, flexibility and conductivity towards high performance EMI windows. The patterned micro-grooves provide restriction for the Ni deposition, which allows continuously regulating of the sheet resistance of the Ni mesh film while maintaining the transmittance approximately unchanged. This provides a platform for engineering the FoM of the transparent metallic mesh conductive film, breaking off the confliction of the transparency and conductivity. Free from the substrate, the freestanding lightweight Ni mesh film (density of 0.23 mg cm−2) exhibits extraordinary optoelectronic performance (FoM ∼18000, sheet resistance about 0.24 Ω sq−1 with transparency of 92%), an outstanding EMI shielding efficiency ∼40 dB in X-band and high mechanical flexibility (can be attached, folded, stretched, and crumpled into any shapes with almost no performance degradation). Therefore, the controlled, solution-processable and potentially scalable production of the ultrathin, lightweight, freestanding metallic mesh structured transparent electrode presented here offers a new paradigm for developing transparent EMI devices.
Funding
National Natural Science Foundation of China (61405133); Natural Science Foundation of Jiangsu Province (BK20181166); Natural Science Research of Jiangsu Higher Education Institutions of China (18KJB510040).
Disclosures
The authors declare that there are no conflicts of interest related to this article.
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