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Abstract
Multifunctional electrodes possess superior properties such as high photoelectric properties and high stability. Laser manufacturing process is one of the widely used method for electrode fabrication. However, the current multifunctional electrode laser manufacturing process suffers from low fabrication speed. Here, we report a high-efficiency laser digital patterning process to fabricate copper-based flexible transparent conducting electrodes. By using a spatially modulated, one single laser spot is modulated into an array of spots with equal intensity, and the fabrication speed can be improved by more than 20 times over the traditional single pulse processing. In addition, copper mesh electrodes with a high photoelectric property have been fabricated. A transparent touch screen panel and multifunctional windows are fabricated with transparent electrodes to demonstrate their use in vehicle defogging, portable heating, and wearable devices.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
In the recent decade, transparent and flexible resistive film heaters have gained great attention due to their wide range of applications in the rapid defogging of outdoor displays and fast-response electric screens in the next-generation devices [1–4]. In particular, for multifunctional window devices, the heating devices often employ electrode materials with characteristics of high transparency, mechanical reliability, and low sheet resistance [5,6]. The indium tin oxide (ITO) has been the most widely used transparent conducting material due to its relatively high transmittance with low sheet resistance [7,8]. Moreover, ITO has prevailed in the market of heat-generating material for the transparent conducting heaters [9,10]. However, ITO suffers from the following natural downsides: its frangibility causing splits upon flexible testing and high-cost due to the limited supply of indium as a rare earth material [11]. Recently, new transparent conducting materials are developed to overcome the drawbacks of the ITO material [12,13].
The electrode materials for heating devices can be divided into two groups: carbon-based materials and metal-based materials [10,14]. The carbon-based materials (e.g., carbon nanotubes and graphene) have good flexibility and can sustain the tension of 100% stress stretching. However, the conductivity and transmittance properties of carbon nanotubes or graphite are much smaller than those of ITO materials [9,15]. The conductivity and transmittance of the metal-based materials (e.g., silver nanowires (AgNWs) and copper nanowires (CuNWs) are 1∼2 orders of magnitude higher than those of the carbon nanotubes [16]. The photoelectric properties of the metal-based materials are typically characterized by low sheet resistance and high transmittance. Both of the sheet resistance and transmittance values are comparable to those of the ITO materials [3,5,17].
Preparation of nanowire materials include selective laser reduction [18] and laser-assisted welding process [19]. However, several drawbacks are reported for the nanowire-based transparent electrode [20]. Due to the low interfacial adhesion, the heating element easily peels off from the substrate, which degrades electrical performance. Though some methods have been reported recently to improve the adhesion, such as nano-welding, pressurization at high temperature and application of the photolithography technology. Nevertheless, this makes the whole process more complex and time-consuming [21]. Furthermore, randomly arranged CuNWs or AgNWs can be fabricated by laser sintering method [22]. But this process is high-cost processes and needs facilities and high precision inkjet printers. This makes it extremely challenging to manufacture flexible heaters at low cost. Thus, some new techniques are desirable to solve these problems.
For these above reasons, the maskless, low-cost and high-resolution patterning techniques to fabricate flexible transparent electrodes at atmospheric pressure has attracted great attention. Metal patterns on flexible substrates not only meet the high transmittance, large area, and low-cost performance for flexible transparent electrodes, but also retain the low resistivity and the ductility of the metal film. However, for oxygen-sensitive metal films, such as Cu, Ni, and other materials, continuous or nanosecond pulsed laser direct ablation processes not only result in an inhomogeneous metal honeycomb structure, but the re-oxidized metal reduces the electrical conductivity of the metal electrodes [11,23]. Besides, laser ablation process can induce the cylindrical ring, droplet finger structures, and the inhomogeneous of compound metallic electrodes, which can increase the leakage of the electronic device. This largely restricts the development of the laser direct ablation process for the fabrication of high-quality flexible transparent electrodes. Compared with the long-pulsed laser-induced metal mesh electrode, the femtosecond laser direct writing ablation (FLDA) process of ultrathin deposition- technique metal films enabled material removal with significantly reduced thermal damage on the underlying flexible polymer substrates. Therefore, the femtosecond laser has an advantage in manufacturing areas [24,25]. However, single Gaussian beams have the disadvantage of low efficiency and low energy utilization in processing. Since femtosecond laser processing of large structures is done by linear scanning point by point, the processing time increases quadratically with the size of the structure. Especially at fixed spot size and laser scanning speed, single-beam laser typically takes a long time to process materials, which is unacceptable in practice and greatly limits the application of femtosecond laser processing. For laser beam modulation, there are lots of technology can be used, such as digital micro-mirror device [26,27] and space light modulator. Spatial light modulators (SLM) are optical modulation devices that have a wide range of applications in information optics. The phase and polarization of Gaussian light can be modulated in space and time by optical or electrical signals in a one-dimensional plane in space-time. The Dammann Grating (DG) is an optically thin, periodic, binary optical element designed to generate a one-or two-dimensional block of equally intense light beam in the light field conversion device [28,29]. By loading a DG phase hologram onto the spatial light modulator, multiple beams generated by a spatial light modulator (SLM) is a novel method to improve the speed of laser fabrication [30].
In this paper, we report a method of fabricating a transparent and flexible 2D copper mesh electrodes. Direct ablation of copper films based on PEN substrates by multiple beams generated by loading DG phase holograms on SLM allows simple, fast and cost-effective direct patterning of copper films into copper meshes electrode without any cumbersome or complex fabrication processes. In addition, the metal coverage of the copper mesh can be easily controlled by simply adjusting the laser scanning speed. Compared with the commercial ITO and copper-based electrodes, we achieved significantly better performance with a sheet resistance of 15.1 Ω/sq, and a transmittance of 91.8% at 550 nm. Besides, the copper mesh electrodes remained stable under multiple harsh conditions, such as bending, squeezing, and heating. Transparent heater based on copper mesh electrode preparation exhibits superior electro-thermal performance at low voltage (less than150 °C at 4 V), rapid thermal response (Maximum temperature reached after 25s), and uniform, stable heating performance (up to 400% strain stretching). But more importantly, the sheet resistance can be easily controlled by the surface metal coverage. Under this condition, the copper mesh heater can precisely respond to the output temperature by just adjusting the sheet resistance of the electrode. The smart window based on copper mesh electrodes can achieve good shielding infrared function, with excellent heat shielding performance. We used 2 W/cm2 of simulated sunlight to irradiate the top of the model cabin, while simultaneously monitoring the temperature in the cabin. By comparing the changes in temperature of different samples, it is found that the higher the metal coverage associate with the better heat shielding effect. The difference in temperature between the sample with metal coverage of 0 and the sample with metal coverage of 0.79 is 5.1 °C. In the demist test, we can control the heater's mist elimination speed directly by controlling the voltage at both ends of the heater and the resistance of the heater itself. The experiment shows that our mist eliminator can complete demist within 60s. The low-cost, ease of fabrication, high stretchability, and sufficient restoring force of the Multifunctional copper mesh electrodes enable their potential applications in the advanced thermal management of next-generation electronics.
2. Experimental section
2.1 Preparation of copper film
Flexible copper metal films were prepared using magnetron sputtering. Approximately 0.5 nm of chromium metal was deposited on a 0.12 mm thick PEN substrate (current 0.1 A, pressure 0.6 Pa, deposition time 5 s), mainly to improve the adhesion of the film, followed by 20 nm of copper metal (current 0.3 A, pressure 0.5 pa, deposition time 160 s).
2.2 Schematics of the FLDA system
The schematic diagram of the setup for manufacturing copper-based flexible transparent conducting electrodes is shown in Fig. 1. Ti: sapphire laser (Model: Mira 900) generates femtosecond pulses. The main laser parameters are 800 nm in the central wavelength, a pulse width of 130 fs, a repetition rate of 1000 Hz, and average output power of 2W. The half-wave and polarizer formed the energy modulation system. A spatial light modulator (SLM; PLUTO2, HOLOEYE, Germany) was used to modulate the laser pulse, which has resolution of 1920 × 1080 pixels and a pixel pitch of 8 µm. The phase of the initial beam is modulated by the SLM, after modulation, the laser beam splits into multiple beams. In the 4f system, combined with the aperture in the middle of the two lenses, and the 0th order beam can be removed. The femtosecond laser was focused with a 5×objective lens (APO, Mitutoyo, Japan, NA = 0.12). Copper mesh electrodes with different metal coverage can be fabricated by FLDA process at different moving speeds of the sample, which was controlled by a linear stage (mode: KBD101 K-Cube, high speed translation of up to 500 mm/s, resolution of 500 nm).
Fig. 1. Schematic illustration of the experimental system of multiple-beam femtosecond laser processing on the metal copper film based on SLM. The inserted picture is a schematic diagram of multi-beam (2 × 2) processing.
2.3. Electro-thermal and defogging performances of the copper mesh heater
A four-probe system (Suzhou Jingge, ST-2258C, China) was used to measure the resistance of the copper mesh. In order to test the mechanical flexibility, copper foil (ELCOAT P-100, Japan) was attached to both ends of the sample. The changes in electrical properties were recorded with a high-precision digital multimeter (DDM7510, USA). An infrared (IR) camera (FLIR, FLIR ONE Pro, USA) was used to monitor thermal performances and capture images. In the defogging test, the thermal properties of the copper mesh on quartz glass and PEN substrate (20mm × 20mm) were measured. The DC voltage is provided by a power supply unit (Maksun, MT152D, China). In the defogging test, the copper foil-attached sample was stored in a refrigerator at the temperature of 4°C for 30 minutes to form water mist on the entire film.
2.4. General characterization
An optical microscope (Olympus BX60) is used to directly observe the surface morphology of the sample in the process of processing. Scanning electron microscopy (SEM: Quanta-FEI) and atomic force microscopy (AFM: Seiku Instruments SPI4000/SPA-400 system) were used to characterize the morphology of the copper mesh electrodes. The transmittance data were measured using a spectrophotometer (PerkinElmer Lambda 950).
3. Results and discussion
In this work, by loading the DG phase hologram on the spatial light modulator, one single laser spot is modulated into an array of spots with equal intensity. First, the beam profile after the phase modulation is validated experimentally. The phase hologram is drawn according to the turning point of the numerical solution of the DG, as shown in Fig. 2(a1-a6). After modulated by the phase hologram on the SLM, the laser spots are shown in Fig. 2(b1-b6), and the corresponding optical image is shown in Fig. 2(c1-c6). Besides, by modulating the relative phase, 25 parallel beams with different distributions can also be generated. It is demonstrated that this simple laser digital patterning process based on a spatially modulated femtosecond laser beam can improve the processing efficiency more than 20 times than the traditional single pulse processing.
Fig. 2. (a) Phase holograms calculated by Dammann Grating theory. (b) Multiple-beam observed by laser profiler. (c) The optical images of copper thin film after the corresponding multiple-beam ablation.
After the FLDA process, the irradiated areas of the copper thin film are ablated away from the substrate, whereas the un-ablated areas still adhere to the substrate, resulting in higher transparency while maintaining the good electrical conductivity of copper. The “NBU” metal patterned was fabricated via the proposed method, as shown in Fig. 3(a). In this experiment, the surface morphology of the patterned copper mesh layer is critically important to obtain high-performance electrodes. The surface morphology of the copper mesh electrodes on a PEN substrate is analyzed using SEM and AFM. Figure 3(b) ((i-iv) present mesh electrode with different areal density areas, and the SEM images show a distinct contrast between ablated circle hole and copper film. This indicates that the femtosecond laser successfully clears away the copper in the irradiated areas, while the non-irradiated copper film can be used as an electrode. The distribution of the hole arrays can be adjusted by changing the multiple-beam distributions, as shown in Fig. 3(a) (i-iv). The thickness of the film electrode measured by AFM is about 20 nm. After laser irradiation, there is no obvious protrusions and melting trace on the edges of the holes, demonstrating the superiority of femtosecond laser processing, as shown in Fig. 3(b). As shown in Fig. 3(c), Using copper mesh transparent electrode with ITO as counter electrode a four-wire resistive touch screen panel (TSP) was fabricated, and the functionality of the TSP is confirmed by writing “NBU” characters on the device.
Fig. 3. (a) A character “NBU” shows the control ability of the laser direct ablation process. (b) (i-iv) Optical image of fabricated rectangular patterns on ultrathin Cu films with different areal densities of 0.68, 0.62, 0.52, and 0.4. (c) AFM images of the Copper FTCEs. (d) Photographs of the four-wire resistive TSP and demonstration by writing the letters “NBU” on the flexible transparent touch screen.
In order to determine the balance between transmittance and sheet resistance by altering the metal coverage, we depict the relationship between sheet resistance and metal coverage, as shown in Fig. 4(a). The metal coverage is defined as the ratio of the metal area after ablation to the total area. In this experiment, the copper mesh electrode after FLDA processing still maintains an excellent electrical performance (15.1 Ω/sq) even if the metal coverage is low (0.37). Here, copper flexible transparent conductive electrodes (FTCEs) are fabricated by single-step FLDA of the copper film under atmospheric conditions. In this case, the lower metal coverage (0.37) of the copper mesh electrode not only maintains the high-class conductivity of copper but also has the superiority of the higher transparency.
Fig. 4. (a) Sheet resistance of the Copper patterning electrode as a function of Copper metal coverage and the comparison of sheet resistance and metal coverage with the literature of Copper mesh and Ag plastic foil. (b) Substrate-based transmittance spectra of the Copper mesh-type electrodes on PEN with different metal coverage. (c) Substrate-based transmittance at 550 nm versus the sheet resistance at different metal coverage and a comparison with recently reported transparent conducting electrodes, including our samples, Au mesh, Ag mesh, Cu mesh, Ni mesh, AgNi mesh, Au nanowires, Ag nanowires, hierarchical metal meshes (HMG), PEDOT: PSS, SCNI, and SRCN.
Figure 4(b) shows the relationship between transmittance and metal coverage rate in the wavelength range of 350 to 800 nm. It is found that the best transmission at a wavelength of 550 nm, and it depends on the metal of coverage the copper mesh from 65% (metal coverage = 1) to 91.8% (metal coverage = 0.37). Therefore, the 20 nm copper FTCEs demonstrate high optical transmission (91.8% at 550 nm) and low sheet resistance (15.1 Ω/sq). These data include the transmittance of both the copper layer and PEN substrate. This successful fabrication confirms that the clean circle-shape arrays and these key manufacture steps can be effectively reduced to a micron range. Moreover, the copper mesh electrode exhibits an excellent property in the coordination between transmission and resistance, as illustrated in Fig. 4(c). By comparing our results with recently reported works including metal meshes [2,11], metal nanowires [31–33], PEDOT: PSS [34], single-wall carbon nanotubes (SCNT) [35], and scaffold-reinforced conductive network (SRCN) [36], the Cu mesh electrode present excellent photoelectric properties as shown in Fig. 4(c). Compared with similar metallic copper-based electrodes, the photovoltaic properties of this FTEs are better than those of other electrodes (Cu NWs, Cu mesh). The optoelectronic properties are comparable to those of silver mesh FTE. However, copper has similar electrical and thermal conductivity compared to silver, and is 90 times cheaper. In addition, this method is a low-cost manufacturing method without using any dangerous chemical reagents. Therefore, the Cu mesh has a considerable competitive advantage.
To determine the durability of the copper mesh electrodes, bending cycles and tape adhesion were tested, as shown in Figs. 5(a)-(d). The test sample of a 2 cm × 3 cm copper mesh with a metal coverage of 0.37 (sheet resistance: 15.1 Ω/sq, transmission: 91.8% at 550 nm) is prepared as illustrated in Fig. 5(a). The transparent copper mesh on the PEN is used as an electrode in the circuit, and a red LED is connected under an applied voltage of 5 V. Moreover, the relative change in resistance (ΔR/R0) was only about 2%, suggesting that it remains high stability during bending. As shown in Fig. 5(b), the gluing intensity is tested using a 2 cm × 3 cm copper mesh with 0.65 metal coverage. After peeling 500 times, the resistance of the copper mesh gradually increased (the rate of change was less than 5%). In order to compare the flexibilities of this film, the variation of resistance is measured after tensile and compressive bending cycles, as shown in Figs. 5(c),(d). With the increasing of bending curvatures up to 250 m-1 and 500 m-1, the resistance of the copper meshes film increase less than 1% for both tensile and compressive loading.
Fig. 5. (a) Variation in resistance of Copper FTCEs of the number of repeated bending to a radius of 6.5 mm. (b) 3 M tape test result showing robust adhesion. (c),(d) The variation of resistance of different curvatures, tensile and compression loading, respectively. (e) Resistance and temperature change of the flexible copper mesh electrode as a function of the bending angle ranging from 0° to 90°. The inset shows IR images and schematics of the copper mesh electrode during bending.
In order to prove the practical application of the copper mesh as an electrode for the transparent heater, a copper mesh film with a size of 2 cm × 3 cm under a two-terminal side-contact construction is employed. The temperature of the smart copper mesh flexible heater varies with the bending angle (0° to 90°), as shown in Fig. 5(e). The variation of resistance of the flexible heater is low, even if the bending angle is up to 90°. Thus, compared with the common photo-lithographically fabricated, vacuum deposited, and drop casted NW percolation meshes [31–33], the fabricated copper FTCEs not only have higher transparency and maintain good electrical conductivity but also maintain excellent mechanical properties.
In demonstrating the practicability of the high thermal stability of the copper mesh electrodes, the smart electrodes are applied to an adjustable transparent heater. The mechanical and thermal stability tests of the copper mesh heaters are shown in Fig. 6. The copper heaters are used as conductors in the array circuit to light up the LEDs, as shown in Fig. 6(a). Under 9V DC voltage, the LEDs light-emitting array remains unchanged after a period of time, and the temperature of the transparent heater is 65.6 °C. It is indicated that the transparent electrode after the DC voltage has good conductivity. In addition, under different types of mechanical deformations such as bending and torsion tests, the electro-thermal performance of heater shows higher stability, as shown in Fig. 6(b). In this experiment, an IR camera was used to record the temperature changes of the sample in the different DC voltages (3 V to 15 V). In Fig. 6(c), a macro view of the surface temperature distribution was obtained. At a DC voltage of 15 V, the flexible copper heater with the sheet resistance value of 15.1 Ω/sq exhibits the maximum temperature of approximately 103.8 °C. Besides, the temperature distribution of the heating zone is uniform. In the meantime, Fig. 6(d) shows the temperature distribution of the heater over time for different DC voltages (3 V to 15 V). The temperature of the sample surface rises rapidly after the voltage is applied and reaches a maximum temperature after approximately 25 s. Subsequently, the temperature stabilizes at the maximum value and falls rapidly after the voltage is switched off. This shows that the heater has good heating performance. As shown in Fig. 6(e), the time-dependent surface temperature is repeatedly switched from 0 to 10 V every 80 s, and the repeatability of the flexible heater is studied under the heating/cooling test of more than 10 cycles. During the cycling tests, the temperature reaches the same value when voltage is applied, and the surface temperature is stable. Furthermore, the temperature response is relatively fast in the process of repeatability testing, which has far-reaching significance for smart windows and thermochromic applications. In this condition, the excellent stability of the flexible copper heater coupled with simple, cheap, and reproducible manufacturing makes it valuable for the functional flexible heater applications.
Fig. 6. Electro-thermal performance of the heater. (a) LED lighting array circuit with flexible transparent electrodes. (b) Thermal images of stretchable transparent heater affixed on hand. (c) Temperature distribution image of the heater using an infrared camera at an electrical input of 3 V, 6 V, 9 V, 12 V, 15 V. (d) The behaviors of the heater at various applied voltages (3, 6, 9, 12, 15 V). (e) Variations in the temperature of a copper mesh electrode and an ITO electrode on PEN film as a function of the number of cycles of repeated voltage on (10 V) and off (0 V).
Next, we focused on the influence of sheet resistance on flexible copper mesh heaters and the changing trend of time-temperature of the copper mesh transparent heaters under different sheet resistances. Figure 7(a) shows the curve of the temperature of flexible copper heaters that have different sheet resistance with time under various bias voltages. For the sheet resistance of 8.7 Ω/sq copper mesh, the operating temperatures of the copper heater can be adjusted from 27.3 to 151.9 °C with different biases (0 V to 4.5 V), respectively. In order to give a visual demonstration of the effect of the sheet resistance on heater power, a patterned copper mesh on the PEN substrate with the transparent letters “NBU” is fabricated, as shown in the insert image of Fig. 7(a). The temperature distribution of copper mesh with different sheet resistance under 3 V applied voltage is illustrated in Fig. 7(b). Clearly, for copper mesh transparent heaters with different square resistances, the temperature rises rapidly and reaches an equilibrium value within 50 s. The heat generated by the heater in a certain period of time is related to the resistance of the heater. The maximum temperature value decreases with the increase of sheet resistance, which is determined by the metal coverage of the copper mesh, as shown in Fig. 7(c). Under the same applied voltage, the lower resistance can produce more thermal energy, which results in a higher temperature on the surface of the heater device. In this case, the operating temperature of the copper mesh heater can be easily controlled by the surface metal coverage (sheet resistance), and the copper mesh heater can precisely respond to the output temperature with even small different sheet resistances.
Fig. 7. (a) The temperature augmentation of copper mesh heaters recorded by an IR camera from 0 to 4.5 V (0.5 V every 60 s) with different sheet resistances. (Inset) Top view IR photograph of a patterned Copper FTCEs, scale bar: 1 cm. (b) Temperature variations of the Copper mesh with different sheet resistance values as a function of time at 3 V. (c) Fitting diagram of copper transparent film heaters changing with sheet resistances.
The functional test application of smart glass was carried out, and the integrated demonstration of heat shielding and defogging was done, respectively. As shown in Fig. 8(a), the transmittance of copper FTCE has been tested at a wavelength of 400 nm-2500 nm by using a spectrophotometer. For a sample with a metal coverage of 0.41, the transmittance for visible light is above 75%. For the electrode with a metal coverage of 0.41, the transmittance in visible band is above 75%. In the infrared band, the transmittance for infrared light gradually decreases compares with that of visible band, this means that the Cu mesh electrode has a higher transmittance for visible light than that of infrared light. It is fully proved that the FTCE could be practically applied to heat shielding. We used 2 W/cm2 of simulated sunlight to irradiate the top of the model cabin, while simultaneously monitoring the temperature in the cabin. The temperature change curve is shown in Fig. 8(b). By comparing the data in this Fig, it is found that the higher the metal coverage associate with the better heat shielding effect. The maximum temperature difference can reach 5.1°C Moreover, we demonstrate the defogging by using the copper FTCE to replace a common demister. Figure 8(c) shows a demonstration of the copper FTCE function as a defogging window. Three different sheet resistances of copper FTCE (20 mm × 20 mm × 1 mm) are placed into a refrigerator with a temperature of 4 °C for 30 min, and then taken them out and use 4 VDC voltage heater heating. The copper FTCE with the highest metal coverage (0.79) can remove the mist in just 20 s, and the defogging time of copper FTCE with the lowest metal coverage (0.37) needs 60 s. The letter under the copper FTCE can be clearly observed after heating for 15 s, and the spray on the heater almost goes after heating for 60 s, which indicated that the temperature and the heat flux are proportional.
Fig. 8. (a) Visible to infrared transmittance with respect to copper mesh smart windows under different metal coverage. The inset shows that the model house monitors the temperature change of the functional windows with different metal coverage. (b) The indoor air temperature of the four sets of samples under simulated sunlight changes with time. (c) Defogging test of three different sheet resistance Copper mesh heaters. SEM images are listed on the left, and defogging images are on the right (scale bar: 30µm). Images on the left side of the red line are mist not entirely removed (transparent electrode with the highest metal coverage (0.79) can remove the mist in just 20 s, and the defogging time of Copper FTCE with the lowest metal coverage (0.41) needs 60 s).
4. Conclusion
In summary, a flexible, transparent, and lightweight copper mesh heater fabricated by the multiple-beam parallel femtosecond laser direct ablation process is reported. Firstly, the electrical, optical, mechanical stabilities, and thermal of the copper mesh flexible transparent electrodes are investigated. The obtained copper mesh electrode exhibits a low sheet resistance (15.1 Ω/sq) with high transmittance (91.8%). The copper mesh electrode exhibits remarkable mechanical flexibility under 10,000 bending cycles at a bending radius of 6.5 mm and during tape-pull tests. Moreover, due to the outstanding electrical and first-rank thermal conductivity of copper, the temperature of the copper mesh-based heater can rapidly reach up to more than 151.9 °C at a DC voltage of 4 V with negligible changes in saturation temperature. The fog is completely removed, and the university logo below became clearly visible after 30 s (metal coverage: 0.77). In addition, the flexible copper mesh conducting panels are successfully applied for touch screen panels and high-performance transparent electrical heaters. These results demonstrate that copper meshes are a viable alternative to ITO electrodes and are excellent potential candidates for applications in electronic devices and transparent flexible heaters.
Funding
National Key Research and Development Program of China (2022YFE0199100); Natural Science Foundation of Shandong Province (ZR2022MF030); Natural Science Foundation of Zhejiang Province (LY21F050002).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
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