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Abstract
Flexible electrochromic devices (ECDs) are a future technology with huge impact on wearable displays, energy saving, and adaptive camouflage. In this work, we used embedded nickel (Ni) mesh transparent electrodes combined with a thin polymer film of poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) to build a multifunctional flexible electrochemical device that integrates the functions of electrochromic and supercapacitor devices. The multi-layer architecture improves the device performance in terms of optical contrast and mechanical strength. Ni-mesh electrodes have a high optical transparency (84.8%), good mechanical flexibility, and low resistance (0.5 Ω/sq), which is conducive to efficient electron injection, benefiting to the response time of the constructed device. The thin polymer film of PEDOT:PSS is an electrochromic (EC) material that also uniformly distributes electrons for a uniform coloration. The fabricated device shows fast response to coloring and bleaching (1.2 and 0.8 s, respectively), an absolute transmittance contrast ratio of 40%, and area capacitance of up to 2.48 mF/cm2. Furthermore, the device exhibits excellent flexibility, and the electrochromic and electrochemical properties of the device are only partially diminished upon folding, which is beneficial for the construction of multifunctional flexible electrochromic devices. With its response time, working stability, and bending ability, our multifunctional device paves the way for the next generation of flexible electronics.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Compared with conventional batteries, supercapacitors have many desirable properties, such as fast charge/discharge rates, high power density, excellent rate performance, and long-term cyclic stability [1–4]. In recent years, significant progress has been made in the theory and practice of supercapacitors. However, supercapacitors with more functions and novel features are still being sought to expand their applications. For example, flexible, stretchable, and wearable supercapacitors have been developed to meet the requirements of portable and wearable electronic devices [5–8]. Electrochromism is the reversible change of the optical properties of a material due to oxidation or reduction upon application of a voltage [9–11]. It has been widely employed in building windows, auto-dimming rearview mirrors, and military camouflage [12–14]. Therefore, it is dense interest to integrate both electrochromic and energy storage properties in one device for multiple applications. Such multifunctional devices are expected to overcome the problems of traditional electrochromic devices that rely on external power sources and have limited application ranges. These devices could be used for energy storage smart windows, which can store energy while regulating lighting and heating in buildings. This ECD-based smart window is valued for its low energy consumption, which can reduce glare or visible/infrared radiation. ECD has a multi-layer structure, which is usually composed of transparent conductive electrodes (TCEs), electrochromic materials, electrolytes, and ion storage layers [15–17]. However, previous reports showed that the performance of ECDs decreases after repeated mechanical deformation and electrochemical cycles. This is mainly due to the fracture of the TCEs caused by mechanical deformation and electrolyte leakage. For this reason, TCEs with high transparency and low sheet resistance are important components for achieving high-performance ECDs [18–20].
Flexible ECDs have been constructed from inorganic EC materials using indium tin oxide (ITO) as the TCE. In addition, solution-processable electroactive aromatic polyimides on ITO flexible substrates have been fabricated as multi-color flexible electrochromic devices [21–9]. However, ITO suffers from inherent brittleness, scarcity of indium, and difficulties in obtaining conformal large-area coatings, which makes it unsuitable for application in extremely flexible and large-area ECDs. A polymer film of PEDOT:PSS with better compatibility with organic EC materials was used to form an all-polymer electrochromic device with better flexibility. However, low electrical conductivity and high redox activity in the working potential window limited its application. A network of silver nanowires was used as a conductive layer in a flexible and stretched electrochromic device [23,24]. The robustness of the Ag nanowire network could be improved by co-assembly with tungsten oxide or carbon nanotube. However, Ag is electrochemically unstable and easily oxidized. Moreover, it requires additional processing procedures, such as UV, thermal reduction or sintering, and protective reduction of the outer coating of the graphene oxide layer, which increase the manufacturing complexity and cost [25–27]. On the other hand, metal grids with the advantages of high transparency, conductivity, and flexibility are emerging as high-performance TCEs for building flexible ECDs, where blooming can be solved with an additional conductive polymer layer. To date, silver and gold grids produced by self-assembly, flexographic printing, and patterned etching technologies have been successfully used to build flexible electrochromic supercapacitors [26–29]. New manufacturing technologies are expected to yield products by batch manufacturing with excellent optoelectronic properties and high-stability metal grids. There is still a great demand for building high performance flexible electrochromic capacitors.
In this work, we constructed a flexible multifunctional smart window based on an embedded Ni grid electrode fabricated by laser direct-writing technology, selective electroplating, and UV nanoimprinting and exhibited an up-scalable surface area. This Ni-mesh electrode had a high transmittance (84.8%), high flexibility, an extremely low sheet resistance (0.5 Ω/sq), and can be used as an auxiliary pattern for effective electron injection. The PEDOT:PSS layer extended the electric field across the film. The electric field was homogeneous and underwent reversible redox reactions for electrochemical purposes. Tungsten oxide (WO3) was introduced to the ECD as cathode electrochromic material with good color-switch performance and good mechanical bendability. The WO3 gel was fabricated through a sol-gel process, which has the advantages of low cost and easy fabrication. Due to the synergistic effects of the highly conductive Ni-mesh electrode and the electrochromic material WO3, the constructed multifunctional smart window exhibited fast coloring and bleaching response speed (1.2 and 0.8 s, respectively), area capacitance of up to 2.48 mF/cm2, and support of the folding and bending process. The Ni-mesh TCE and WO3 nanocomposite-based flexible ECD showed excellent electrochromic performance, making it a promising candidate for smart window, energy storage, and multifunctional electronic devices.
2. Experimental section
2.1 Fabrication of Ni-mesh transparent electrode by confined electroplating
The fabrication of transparent Ni-mesh TCE included three steps of laser direct-writing, selective electroplating, and UV nanoimprinting. First, the grid pattern was written into the photoresist on the pre-processed ITO substrate by laser direct-writing technology. The line width can be as narrow as 4 µm and different grid patterns (hexagon, square, and random) could be realized. Then, Ni metal was selectively filled into the photoresist microgrooves by an electroplating process, and the exposed patterned ITO region was used as a patterned plated electrode. Subsequently, the photoresist was removed, and a UV-curable resin (D10, Phichem) was drop cast onto the substrate. Then, a flexible polyethylene terephthalate (PET) film (thickness: ∼120 µm) was fixed to the UV-curable resin. Finally, the UV resin was cured by UV irradiation (1000 mW/cm2, Led Lamplic) for 25 s, and the PET substrate was peeled off from the ITO substrate to obtain the Ni grid electrode embedded in the cured resin.
2.2 Fabrication of lithium chloride/polyvinyl alcohol (LiCl/PVA) gel electrolyte
LiCl (1.1 g, Beijing Innochem) was added to 120 mL of deionized water, and the resulting solution was magnetically stirred for 15 min. Subsequently, PVA (12 g, Shanghai Aladdin Biochem) was added to the solution, and the resulting mixture was magnetically stirred at 90 °C for 2 h until a homogeneous and transparent solution was obtained. Finally, the solution was placed into a vacuum oven for 1 h at room temperature to remove air bubbles.
2.3 Preparation of WO3 by a sol-gel method
First, 30% concentration of hydrogen peroxide (H2O2, 20 mL, Shanghai Aladdin Biochem) was added dropwise to tungsten powder (W, 5 g, Shanghai Aladdin Biochem), and the resulting solution was placed in an ice water bath and magnetically stirred for 3–4 h. Subsequently, the solution was kept in a vacuum drying box for 1 h to facilitate solution layering. Absolute ethyl alcohol (C2H6O, 3 g, Shanghai Aladdin Biochem) was added dropwise to the supernatant, followed by heating and stirring at 60 °C for 20 min. After standing for 2 h and filtering, a tungsten oxide solution was obtained.
2.4 Assembly of the ECD
A solution of PEDOT:PSS (10 mL, 0.8 wt% PEDOT, 0.5 wt% PSS, Heraeus Deutschland GmbH & Co.) was added to ethylene glycol (0.7 g, Shanghai Aladdin Biochem) and a surfactant (Triton-X100, 0.025 g, Shanghai Aladdin Biochemistry) to form a stable mixture after sonication for 15 min. The Ni-mesh TCE was treated with a plasma machine to improve the hydrophilicity of the surface, and two pieces of the Ni-mesh TCE were spin-coated with the prepared PEDOT:PSS mixture at a speed of 3000 rpm for 30 s, followed by heating at 60 °C. Then, the first film was formed by annealing under the plate for 10 min. Subsequently, one piece of the Ni-mesh TCE was spin-coated at 3000 rpm for a second deposition of the PEDOT:PSS mixed solution with a spin-coating time of 30 s, followed by annealing under a hot plate at 60 °C for 30 min for evaporation of the solution and improvement of the morphology. Another piece of Ni-mesh TCE was spin-coated with a tungsten oxide solution at a speed of 2000 rpm for 30 s and left at room temperature for 30 min. The PVA/LiCl gel was then drip-casted on Ni grids with PEDOT:PSS. After standing at room temperature for 10 h until solidification of the electrolyte, the two Ni grids were assembled.
2.5 Characterization
Surface morphology and elemental composition of the Ni grid electrode/PEDOT:PSS composite film were analyzed using a field emission scanning electron microscope (FE-SEM; JEOL, JSM-5400, USA). The thickness of the spin-coated PEDOT:PSS film and the sheet resistance of the plated Ni-mesh TCE were measured by a step profiler (XP-200, Ambios Technology) and a four-point probe (CMT SR2000, A.I.T.), respectively. Electrochromic properties and electrochemical behavior were measured using a UV-VIS spectrophotometer (Specord 210 PLUS, Analytik Jena AG) and an electrochemical workstation (CHI 760E, Shanghai CH Instrument), respectively.
The specific capacitance of the electrochromic supercapacitors used in our work was determined by the area capacitance according to the following formula:
where CA represents the areal capacitance of the electrode, I(t) is the current density measured during cyclic voltammograms (CV) testing, ΔV is the potential range value, and A is the electrode area (2 cm ×1.5 cm). In addition, electrochemical impedance spectroscopy (EIS) was performed under the open circuit potential of a sinusoidal signal in the voltage range of 0.01 Hz to 100 kHz and an amplitude of 10 mV.The coloration efficiency (CE) is an important indicator for the comprehensive evaluation of electrochromic supercapacitors. CE is defined as the change in optical density (ΔOD) per unit charge (ΔQ) inserted into (or extracted from) the electrochromic device. It can be calculated according to the following formulas:
where Tb and Tc are the transmittance in the bleaching and coloring states, respectively.3. Results and discussion
The structure of flexible ECD is shown in Fig. 1(a). It consists of a highly efficient Ni-mesh TCE for electron injection, a PEDOT:PSS/WO3 layer for electrochemical reactions, and a PVA/LiCl gel layer for ion transportation, ion storage, and counterion conduction. The thickness of the Ni-mesh TCE was about 2 µm, and it was embedded in the UV resin on the flexible substrate. Its height difference to the upper surface of the UV resin is very small, resulting in super high robustness. In addition, the organic properties of other films ensure good mechanical flexibility and interfacial compatibility, which is conducive to the reliable operation of the device under repeated bending or conformal adhesion. Figure 1(b) shows the SEM image of the Ni-mesh TCE in the substrate. The random grid pattern had a line width of 5 µm and a period of 150 µm. The grid pattern and line distribution can be designed and implemented as required. The low aspect ratio of the metal makes the Ni grid transparent, providing high transmittance. Figure 1(c) shows a cross-sectional SEM image of the PEDOT:PSS/WO3 composite film, revealing the delamination of PEDOT:PSS and WO3 and the thickness of each layer of about 300 nm. The combination of PEDOT:PSS and WO3 not only increase the electrochemical performance but also support the color change of tungsten due to the uniform distribution of electrons on the entire plane. At the same time, PEDOT:PSS inhibited the blooming effect of the Ni-mesh TCE, as shown in Fig. 1(d). Energy dispersive spectroscopy (EDS) analysis of the element distribution of the Ni-mesh TCE/PEDOT:PSS/WO3 composite electrode showed a random grid-like distribution of Ni, an even distribution of W on the plate, and S that was related to PEDOT:PSS. The transmittance spectra of Ni-mesh TCE, ITO glass, and flexible ITO/PET are shown in Fig. 1(e). The Ni-mesh TCE exhibited a high optical transmittance (84%), ITO glass had a similar transmittance of over 80%. However, the flexible ITO/PET showed a significant decrease in optical transmittance, which may impede an application of the flexible ITO/PET as high-performance electrochromic device. Furthermore, the sheet resistance of the Ni-mesh TCE was only 0.5 Ω/sq, which is advantageous for manufacturing high-quality electrochromic capacitors. Figure 1(f) shows the dependence of the bending times of Ni-mesh TCE and flexible ITO/PET on the change of the sheet resistance. With increasing number of bending times, the thin-layer square resistance of the Ni-mesh TCE remained basically unchanged, while the thin-layer square resistance of the flexible ITO/PET increased significantly, which reveals an advantageous bending resistance of the Ni-mesh TCE. This demonstrates the advantages of the Ni-mesh TCE for flexible ECDs. Figure 1(g) shows the manufacturing procedure of transparent Ni mesh electrodes, which contains spin-coating photoresist on ITO glass, laser direct writing, developer processing, electrodepositing Ni, and removing photoresist.
Fig. 1. (a) Illustration of the flexible ECD. (b) SEM image of a Ni grid electrode (scale bar: 200 µm). The inset is a magnified SEM image of the Ni grid TCE (scale bar: 5 µm). (c) Cross-sectional SEM image of the composite PEDOT:PSS/WO3 film (scale bar: 1 µm). (d) EDS mapping of Ni, W, and S elements in the composite Ni-mesh TCE/PEDOT:PSS film. (e) Transmission spectrum of Ni-mesh TCE (black), ITO glass (red), and flexible ITO/PET (blue) in the UV-Vis-NIR range. The inset shows the maple leaf pattern behind the Ni-mesh TCE. The red dotted line area is a photography of the Ni-mesh TCE. (f) Dependence of the sheet resistance of the Ni-mesh TCE (blue) and the flexible ITO/PET (red) on the number of bending times when the bending radius was 8 mm. (g) The manufacturing procedure of Ni transparent mesh electrodes containing laser direct-writing, developer processing, electrodepositing Ni, and removing photoresist.
Figure 2 demonstrates the electrochemical properties of Ni mesh-based ECDs. Figure 2(a) shows the CV curve of the device versus Ag/AgCl reference electrode in a potential window of 0–0.8 V at scan rates of 0.01, 0.05, 0.1, 0.5, 1, and 2 V/s. The almost rectangular CV curve demonstrates the excellent electrochemical properties of the ECDs, such as excellent charge storage characteristics and fast response. This shape is well maintained even at a scan rate of 2 V/s. Figure 2(b) shows that after 10,000 charge-discharge cycles, the retention rate of the capacitor was 92%. The surface capacitance calculated by Eq. (1) reached 2.5 mF/cm2 at a scan rate of 0.01 V/s. As the scan rate increased to 2 V/s, the area capacitance per decreased to 0.82 mF/cm2, which may be due to the good electrochemical stability of PEDOT:PSS and the good packing effect of the Ni-mesh TCE as a current collector. Because of the sandwich design of the upper and lower layers of the ECDs, the gel electrolyte was sealed in the device without significant air contact. In addition, the frequency response in the frequency range of 0.01 to 100 kHz was measured by EIS, as shown in Fig. 2(c). The Nyquist plot exhibits a semicircle and a diagonal line. The semicircle represents the impedance of the electrochemical reaction of the Ni-mesh TCE, and the diagonal line reflects the ion diffusion process of the active material in the electrode. A small semicircle is correlated with a small charge transfer resistance, while a large slope is correlated with a high electrochemical capacitance and a fast ion diffusion rate. Figure 2(d) shows the charge-discharge curves (GCD) of ECDs in a voltage range of 0 - 0.8 V at current densities of 0.1, 0.15, 0.2, 0.3, and 0.5 mA/cm2. All GCD curves exhibited linear distributions, approximately symmetric triangular shapes, and a non-negligible voltage drop, which fully illustrated the good capacitance behavior of the ECDs. As the current density increased, the charge-discharge time decreased from 13.8 to 2.1 s.
Fig. 2. Electrochemical performance of flexible ECDs. (a) Typical cyclic voltammograms (CV) of ECDs at scan rates of 0.01, 0.05, 0.1, 0.5, 1, and 2 V/s. (b) Capacitance retention and charge-discharge characteristics of ECDs. The inset shows the measured capacitance per area of the ECDs as a function of the scan rate. (c) Imaginary impedance Z” and real impedance Z’ (Nyquist diagram) in the frequency range of 0.1 Hz to 10 kHz. The inset shows the enlarged part of the low-frequency region. (d) Potential change of supercapacitors with the time (GCD graph) at different current densities.
With the high transmittance, low square resistance, and good bending resistance of the Ni-mesh TCE in combination with the good electrochromic characteristics of the PEDOT:PSS/WO3 double-stacked active material, a device with good electrochromic performance was obtained. Many factors affect the electrochromic performance of the device, and the applied voltage is one of the most important factors. The transmission spectrum is provided in Fig. 3(a). The absorption of the EC material and the transmittance of the device can be continuously adjusted. At a working voltage of 1.8 V, the maximum transmittance change at 675 nm was 40%, indicating compatibility and superiority of the Ni-mesh TCE in these ECDs. Figure 3(b) shows the electrochromic switching behavior of the device at 650 nm upon application of a voltage of 1.8 V for 3 s and -1.8 V for 3 s over 5 cycles with alternately changing optical transmittance. Figure 3(c) shows that the colored time to reach 90% of the highest contrast was 1.2 s, and the corresponding bleached time was 0.8 s, which is superior to the characteristics of most of the electrochromic devices based on ITO electrodes. This may be because the Ni-mesh TCE directly provided an electron transfer channel, resulting in an increased electron transfer rate. At the same time, PEDOT:PSS was used as a capacitive active material to further increase the electron transfer rate. The CE is an important indicator for evaluating the efficiency of electrochromic devices. A high CE value indicates that the electrochromic device has a higher optical contrast during charge insertion or extraction. According to the calculation of the slope, the CE value of the electrochromic supercapacitor was 124.1 cm2/C (Fig. 3(d)). Figure 3(e) shows that the transmission increased with the number of color change cycles. After 500 cycles, the transmittance gradually decreased from 40.2% to 31.5% (corresponding to about 78.3% contrast retention). Furthermore, the working characteristics increased further with the number of cycles, which may be due to the evaporation of the liquid electrolyte in the gel during long-term cycling. Figure 3(f) shows a photograph of the device in its colored and bleached state.
Fig. 3. Electrochromic performance of the ECDs. (a) Transmission spectra of the ECDs in different colored states. (b) Switching characteristics of the ECDs for the coloring and bleaching voltages of -1.8 and 1.8 V, respectively. (c) Optical responses for coloring and bleaching steps. (d) Variation of the optical density (OD) of the ECDs versus the charge density (Q). (e) Transmittance of the ECDs at 675 nm as a function of the number of operation cycles at the bleaching and coloring states. (f) Photographs of the device at different coloration voltages.
ECDs made of Ni-mesh TCE have also achieved great success in terms of mechanical flexibility. In order to demonstrate the potential of the devices for wearable electronics, the switching effect at different bending radii of 8, 10, and 13 mm has been studied, as shown in Fig. 4(a). In terms of optical contrast and response time, ECDs have reached a satisfactory level. As the bending radius increased, the optical contrast decreased only about 4%, and the response time remained almost unchanged. As shown in Fig. 4(b), when the bending radius was 8 mm, the characteristic absorption peak remained unchanged after 1000 bending cycles. Although the intensity and the optical contrast decreased, the performance was still satisfactory. The decrease in optical contrast may be due to the uneven shedding of the gel electrolyte and the PEDOT:PSS/WO3 layer during bending, which ultimately led to the degradation of device performance. This effect could be prevented by changing the PET substrate and controlling the thickness of the ionic electrolyte. Similarly, the excellent mechanical flexibility of ECDs is not only reflected in their electrochromic properties but also in their electrochemical properties. As shown in Fig. 4(c), when the bending radii were 8, 10, and 13 mm, the CV of the ECDs at the scan rate of 0.5 V/s exhibited no significant decline compared with those without bending. In addition, the device also showed good mechanical flexibility in repeated bending experiments. As shown in Fig. 4(d), at a bending radius of 8 mm, 1000 bending cycles, and a scan rate of 0.5 V/s, the area capacitance was slightly lower, and the amplitude was about 5%. These characteristics meet the requirements of wearable electronics for smart devices, which is mainly due to the excellent mechanical stability of the Ni-mesh TCE and PEDOT:PSS/WO3 double-stacked active material. Therefore, flexible ECDs based on Ni-mesh TCE have good mechanical flexibility and electrochromic and electrochemical properties with promising potential for application in wearable color-changing and energy storage dual-functional devices.
Fig. 4. Mechanical flexibility of the electrochromic supercapacitors. (a) Switching performance of the ECDs at bending radii of 8, 10, and 13 mm. (b) Switching behavior of the ECDs at 675 nm after 0, 500, and 1000 bending cycles. (c) Typical CV of ECDs at bending radii of 8, 10, and 13 mm. (d) Typical CV of ECDs at a scan rate of 0.5 V/s after 0, 500, and 1000 bending cycles.
4. Conclusion
In summary, we propose a flexible multifunctional electrochromic device based on Ni-mesh TCE that simultaneously functions as smart electrochromic device and energy storage device. Compared with previously reported flexible electrochromic devices based on ITO or silver nanowires, the Ni-mesh TCE has the advantages of high electrical conductivity, high light transmittance, high mechanical flexibility, and high oxidation stability, allowing for the fabrication of new devices with high performance. The fabricated electrochromic device has a transmittance contrast of 40%, a coloring time of -1.8 V at 1.2 s, and a bleaching time of 0.8 s at 1.8 V. It has a good conformal adhesion, and the number of bending cycles is 1000. These features enable the fabrication of highly flexible and reliable electrochromic devices with the potential for wearable electronics.
Funding
National Natural Science Foundation of China (61974100); the National Science Foundation of the Jiangsu Higher Education Institutions of China (20KJA480002).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data will be made available on request.
References
1. L. Niu, T. Z. Wu, M. Chen, L. Yang, J. J. Yang, Z. X. Wang, A. A. Kornyshev, H. L. Jiang, S., Bi, and G. Feng, “Conductive Metal-Organic Frameworks for Supercapacitors,” Adv. Mater. 34(52), 2200999 (2022). [CrossRef]
2. J. Park, J., Lee, and W. Kim, “Redox-Active Water-in-Salt Electrolyte for High-Energy-Density Supercapacitors,” ACS Energy Lett. 7(4), 1266–1273 (2022). [CrossRef]
3. A. Baburaj, H. Gullapalli, A. B. Puthirath, D. Salpekar, J. Joyner, S. Kosolwattana, R. Vajtai, B., Ganguli, and P. M. Ajayan, “Stacked on-chip supercapacitors for extreme environments,” J. Mater. Chem. A 10(24), 12900–12907 (2022). [CrossRef]
4. M. R. Islam, S. Afroj, K. S., Novoselov, and N. Karim, “Smart Electronic Textile-Based Wearable Supercapacitors,” Adv. Sci. 9(31), 2203856 (2022). [CrossRef]
5. S. S. Lee, K. H. Choi, S. H., Kim, and S. Y. Lee, “Wearable Supercapacitors Printed on Garments,” Adv. Funct. Mater. 28(11), 1705571 (2018). [CrossRef]
6. Y. Z. Zhao, Q. D. Liang, S. M. Mugo, L. J. An, Q., Zhang, and Y. Y. Lu, “Self-Healing and Shape-Editable Wearable Supercapacitors Based on Highly Stretchable Hydrogel Electrolytes,” Adv. Sci. 9(24), 2201039 (2022). [CrossRef]
7. Y. Q. Jiang, K. Ma, M. L. Sun, Y. Y. Li, and J. P. Liu, “All-Climate Stretchable Dendrite-Free Zn-Ion Hybrid Supercapacitors Enabled by Hydrogel Electrolyte Engineering,” Energy Environ. Mater. 0, 1–8 (2022).
8. M. S. Kolathodi, A. Akbarinejad, C. Tollemache, P. K. Zhang, and J. Travas-Sejdic, “Highly stretchable and flexible supercapacitors based on electrospun PEDOT:SSEBS electrodes,” J. Mater. Chem. A 10(39), 21124–21134 (2022). [CrossRef]
9. C. Gu, A. B. Jia, Y. M. Zhang, and S. X. A. Zhang, “Emerging Electrochromic Materials and Devices for Future Displays,” Chem. Rev. 122(18), 14679–14721 (2022). [CrossRef]
10. J. W., Kim and J. M. Myoung, “Flexible and Transparent Electrochromic Displays with Simultaneously Implementable Subpixelated Ion Gel-Based Viologens by Multiple Patterning,” Adv. Funct. Mater. 29(13), 1808911 (2019). [CrossRef]
11. H. C. Moon, C. H. Kim, T. P., Lodge, and C. D. Frisbie, “Multicolored, Low-Power, Flexible Electrochromic Devices Based on Ion Gels,” ACS Appl. Mater. Interfaces 8(9), 6252–6260 (2016). [CrossRef]
12. Y. L. Zhai, J. H. Li, S. Shen, Z. J. Zhu, S. Mao, X. Xiao, C. Z. Zhu, J. G. Tang, X. Q., Lu, and J. Chen, “Recent Advances on Dual-Band Electrochromic Materials and Devices,” Adv. Funct. Mater. 32(17), 2109848 (2022). [CrossRef]
13. X. Ren, S. Y. Hu, Z. F. Jia, T. T. Qin, Y. M. Sui, F. C. Wang, W. S., Pan, and C. Yang, “A Self-Packageable and Tailorable Electrochromic Device based on the “Blood-Coagulation” Mechanism,” Adv. Funct. Mater. 32(39), 2206127 (2022). [CrossRef]
14. H. Gong, W. Z. Li, G. X. Fu, Q. Q. Zhang, J. B. Liu, Y. H., Jin, and H. Wang, “Recent progress and advances in electrochromic devices exhibiting infrared modulation,” J. Mater. Chem. A 10(12), 6269–6290 (2022). [CrossRef]
15. A. Aliprandi, T. Moreira, C. Anichini, M. A. Stoeckel, M. Eredia, U. Sassi, M. Bruna, C. Pinheiro, C. A. T. Laia, S., Bonacchi, and P. Samori, “Hybrid Copper-Nanowire-Reduced-Graphene-Oxide Coatings: A “Green Solution” Toward Highly Transparent, Highly Conductive, and Flexible Electrodes for (Opto) Electronics,” Adv. Mater. 29(41), 1703225 (2017). [CrossRef]
16. P. Kanninen, N. D. Luong, L. H. Sinh, I. V. Anoshkin, A. Tsapenko, J. Seppala, A. G., Nasibulin, and T. Kallio, “Transparent and flexible high-performance supercapacitors based on single-walled carbon nanotube films,” Nanotechnology 27(23), 235403 (2016). [CrossRef]
17. T. K. Rao, Y. L. Zhou, J. Jiang, P., Yang, and W. G. Liao, “Low dimensional transition metal oxide towards advanced electrochromic devices,” Nano Energy 100, 107479 (2022). [CrossRef]
18. H. Lee, S. Hong, J. Lee, Y. D. Suh, J. Kwon, H. Moon, H. Kim, J., Yeo, and S. H. Ko, “Highly Stretchable and Transparent Supercapacitor by Ag-Au Core-Shell Nanowire Network with High Electrochemical Stability,” ACS Appl. Mater. Interfaces 8(24), 15449–15458 (2016). [CrossRef]
19. S. Lin, X. P. Bai, H. Y. Wang, H. L. Wang, J. N. Song, K. Huang, C. Wang, N. Wang, B. Li, M., Lei, and H. Wu, “Roll-to-Roll Production of Transparent Silver-Nanofiber-Network Electrodes for Flexible Electrochromic Smart Windows,” Adv. Mater. 29(41), 1703238 (2017). [CrossRef]
20. D. D. Li, W. Y. Lai, Y. Z., Zhang, and W. Huang, “Printable Transparent Conductive Films for Flexible Electronics,” Adv. Mater. 30(10), 1704738 (2018). [CrossRef]
21. T. G. Yun, M. Park, D. H. Kim, D. Kim, J. Y. Cheong, J. G. Bae, S. M., Han, and I. D. Kim, “All-Transparent Stretchable Electrochromic Supercapacitor Wearable Patch Device,” ACS Nano 13(3), 3141–3150 (2019). [CrossRef]
22. R. T. Ginting, M. M., Ovhal, and J. W. Kang, “A novel design of hybrid transparent electrodes for high performance and ultra-flexible bifunctional electrochromic-supercapacitors,” Nano Energy 53, 650–657 (2018). [CrossRef]
23. J. Jung, H. Cho, R. Yuksel, D. Kim, H. Lee, J. Kwon, P. Lee, J. Yeo, S. Hong, H. E. Unalan, S., Han, and S. H. Ko, “Stretchable/flexible silver nanowire electrodes for energy device applications,” Nanoscale 11(43), 20356–20378 (2019). [CrossRef]
24. C. Lee, Y. Oh, I. S. Yoon, S. H. Kim, B. K., Ju, and J. M. Hong, “Flash-induced nanowelding of silver nanowire networks for transparent stretchable electrochromic devices,” Sci. Rep. 8(1), 2763 (2018). [CrossRef]
25. K., Mallikarjuna and H. Kim, “Highly Transparent Conductive Reduced Graphene Oxide/Silver Nanowires/Silver Grid Electrodes for Low-Voltage Electrochromic Smart Windows,” ACS Appl. Mater. Interfaces 11(2), 1969–1978 (2019). [CrossRef]
26. T. F. Qiu, B. Luo, M. H. Liang, J. Ning, B. Wang, X. L., Li, and L. J. Zhi, “Hydrogen reduced graphene oxide/metal grid hybrid film: towards high performance transparent conductive electrode for flexible electrochromic devices,” Carbon 81, 232–238 (2015). [CrossRef]
27. R. R. Sondergaard, M. Hosel, M., Jorgensen, and F. C. Krebs, “Fast printing of thin, large area, ITO free electrochromics on flexible barrier foil,” J. Polym. Sci. 51(2), 132–136 (2013). [CrossRef]
28. Y. Kim, H. Shin, M. Han, S. Seo, W. Lee, J. Na, C., Park, and E. Kim, “Energy Saving Electrochromic Polymer Windows with a Highly Transparent Charge-Balancing Layer,” Adv. Funct. Mater. 27(31), 1701192 (2017). [CrossRef]
29. Y. H. Liu, J. L. Xu, X. Gao, Y. L. Sun, J. J. Lv, S. Shen, L. S., Chen, and S. D. Wang, “Freestanding transparent metallic network based ultrathin, foldable and designable supercapacitors,” Energy Environ. Sci. 10(12), 2534–2543 (2017). [CrossRef]
