{"paper_id":"279dee72-89e8-4b53-952e-2bee48efc317","body_text":"A Thin-Film-Free Electrochromic System Based on Dual Conductive Glass Electrodes and Sodium Tungstate Electrolyte | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article A Thin-Film-Free Electrochromic System Based on Dual Conductive Glass Electrodes and Sodium Tungstate Electrolyte S.M.P.M.K Sanganayaka, E.G.O.D Egodawaththa, H.N.M. Sarangika, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9123105/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Electrochromic devices (ECDs) are widely used in smart windows, displays, and mirrors for dynamic light control, but conventional thin-film electrodes are costly and complex to fabricate. This study presents a film-free electrochromic device that eliminates the need for electrochromic coatings on transparent conductive oxide substrates. The device consists of an acidified sodium tungstate (Na₂WO₄·2H₂O) electrolyte sandwiched between two bare FTO glass electrodes. Upon applying a low voltage of 3 V, a reversible blue coloration forms in situ near the working electrode and disappears when the voltage is removed, restoring transparency. At pH 1.5, when applying 3 V, transmittance measurements reveal an optical modulation of 87.45% and an optical density of 0.96 at 648 nm wavelength, confirming the device's excellent optical performance. The response times for coloration (14 s) and bleaching (35 s) indicate good switching dynamics. The devices show a high coloration efficiency of 66.7 cm 2 /C at 648 nm wavelength. These findings highlight the excellent performance of the device and demonstrate that eliminating the thin-film coating process not only simplifies fabrication but also enables the development of film-free electrochromic devices as high-performance alternatives for next-generation electrochromic applications. Electrochromic Fluorine–doped tin oxide optical modulation optical density coloration efficiency Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Chromism refers to the colour change that occurs due to alterations in the electronic states, such as π electrons and d electrons within a molecule or crystal in response to an external stimulus. Depending on the nature of the stimulus, chromism can be classified into various types, including thermochromism (colour change with temperature), photochromism (colour change with light), and electrochromism (colour change with an electric field) [ 1 ]. Among these, electrochromism has attracted significant attention due to its practical applications. Electrochromism is the phenomenon where the colour or optical properties of a material, such as transmission, reflection, and absorption, undergo a stable and reversible change upon the application of an external voltage[ 2 ]. Electrochromism was first observed in tungsten oxide (WO 3 ) films immersed in sulphuric acid by Kraus in 1953 in an unpublished laboratory report at Balzers AG in Liechtenstein. Electrochromism gained much attention after publication on amorphous and crystalline tungsten oxide films and the development of the first WO 3 -based electrochromic devices between 1969–1973 [ 3 ]. Electrochromic devices (ECDs) are devices that change their colour and optical properties, such as transmittance, reflectance, or absorbance, under the influence of an electrical voltage. ECDs operate based on reversible redox reactions where ions and electrons move within the electrochromic material and alter optical properties[ 4 – 11 ]. Electrochromic devices are recognized as a promising technology across various industries due to their ability to reversibly modulate optical properties in response to an applied potential. Due to their low energy consumption, controllable optical switching, and tuneable coloration properties, these devices are well-suited for a wide range of applications, including smart windows, information displays, light shutters, and variable reflectance mirrors. Conventional electrochromic devices have three major components: a working electrode, an electrolyte, and a counter electrode, as shown in Fig. 1 . It is a “sandwich-type” configuration in which the electrolyte is sandwiched between the working and counter electrode [ 12 – 15 ]. The working electrode of the electrochromic device consists of a thin film of electrochromic material coated on a transparent conductive oxide layer coated glass substrate. Electrolyte is a critical component of an electrochromic device. The electrolyte layer is located between the electrochromic active layer and the ion storage layer. The main roles of electrolytes are allowing the movement of charged ions, and isolating electrodes. Also, it allows the movement of charged ions in a directional manner under the effect of an applied electric field to ensure that the electrochromic layer achieves controllable colour conversion through the redox process of the ions. The electrolyte layer prevents the direct contacting and short-circuiting of the electrochromic layer and ion storage layer by effectively isolating them. The counter electrode of ECD consists of an ion storage layer coated on a transparent conductive oxide layer coated glass substrate. It provides a reversible electrochemical reaction in the device operating in any mode. It stores the charge during the bleaching process[ 16 ]. The counter electrode operates in complementary redox mode to the active electrochromic material[ 17 ]. When a voltage is applied between the working and counter electrode, a distributed electric field is generated. The ions in the electrolyte film migrate uniformly into the (intercalated) electrochromic layer [ 18 ]. The counterflow of electrons happens through the external circuit to balance the charge. This results in variation of electron density in the electrochromic material. Therefore optical properties of the electrochromic device were modulated. When the polarity of the electrodes changes, the ions migrate in the opposite direction (de-intercalated) and the electrochromic device returns to its original state [ 19 ]. The ion transport is easiest for small ions such as protons (H + ) or lithium ions (Li + ). As mentioned previously, conventional electrochromic devices consist of a thin film of electrochromic material coated onto a transparent conductive oxide substrate. Thin film deposition critically influences device performance, durability, and cost. Different thin–film deposition techniques are utilized to produce high-quality electrochromic film. Physical vapour deposition (PVD) methods like sputtering, deposit uniform thin Electrochromic (EC) films by ejecting material via energetic particle collisions. Spin coating involves spreading a precursor solution on a rapidly spinning substrate to form uniform films upon solvent evaporation. Spray coating atomizes droplets using pressurized gas to create thin films, with an airbrush system. Additionally, techniques such as the sol-gel method, electro-deposition, screen printing, inkjet printing, flexographic printing, and blade coating are also employed for electrochromic thin film deposition [ 20 – 24 ]. Each of these technique yield an excellent EC film with enhanced properties. However, they share common drawbacks. These techniques rely on specialized equipment, multi-step fabrication processes, and high-temperature annealing, making them time-consuming, costly, and difficult to scale up. Additionally, challenges such as complex manufacturing, limited scalability, and long-term stability issues like film cracking and delamination further hinder their practical application[ 25 ]. To overcome these limitations in the conventional electrochromic devices, this study explores a novel and simplified approach where no thin film of the electrochromic layer is deposited on the transparent conductive oxide substrate. Here, for the first time, an electrochromic device is prepared by using two bare fluorine-doped tin oxide (FTO) glass substrates as working and counter electrodes, and 0.1 M sodium tungstate solution as electrolyte. This innovative approach eliminates the reliance on traditional thin-film coatings, thereby simplifying the fabrication process and significantly reducing production costs. By addressing key limitations of conventional electrochromic devices such as high material expenses and complex manufacturing steps, this study demonstrates that high-performance electrochromic functionality can be achieved without the need for conventional coating techniques. This advancement paves the way for a more scalable and cost-effective manufacturing route. 2. Experimental 2.1 Materials Sodium tungstate dehydrate (Na 2 WO 4 .2H 2 O, 99.9%) and nitric acid (HNO 3 , 68–70%) were purchased from Sigma Aldrich, and FTO glasses (sheet resistance 12 Ω/sq) were purchases from Soloronix. 2.2 Preparation of an electrolyte The electrolyte for film–free electrochromic devices was prepared using the following procedure. 0.1 M sodium tungstate solution was prepared by dissolving Na 2 WO 4 .2H 2 O powder in deionized water. Then the pH of the solution was adjusted by adding 2 M HNO 3 . 2.3 Fabrication of an electrochromic device In our study, commercially available FTO glasses were used as both the working electrode and counter electrode. ECD configuration with FTO glass / Na 2 WO 4 liquid electrolyte / FTO glass was fabricated. A spacer frame was placed on the top of the one FTO glass, by keeping enough space for electrical contact from the other FTO glass. Then the middle of the spacer film was filled with the electrolyte. The thin-film-free ECD fabrication process is shown in Fig. 2 . 2.4 Identify the optimal pH value and voltage value A series of electrolytes was made with different pH values (pH 1.5, 2, 3, 4, and 5) to investigate the effect of pH on electrochromic performance. Then a series of identical devices were fabricated, and each of them was filled with electrolyte at different pH values. Then constant voltage was applied for each device, and absorbance and transmittance measurements were taken using a UV-visible spectrophotometer (Shimadzu UV 1800). Subsequently, another set of identical devices was fabricated using the electrolyte at optimal pH value. These devices were subjected to varying applied voltages ranging from 0 V to 4 V in 0.5 V increments. Absorbance and transmittance measurements were recorded using a UV-visible spectrophotometer to evaluate the voltage-dependent electrochromic response. 2.5 Electrochromic (EC) measurement An ECD with the configuration of FTO/electrolyte/FTO was fabricated, and the change in the optical transmittance of the ECD was investigated by comparing the UV–visible transmittance spectra in coloured and bleached states in the wavelength range of 400 nm to 900 nm. Cyclic voltammetry studies were carried out using a three-electrode system of computer-controlled Metraohm Autolab (PGSTAT204) in the potential range from − 2.0 V to + 0.5 V with 10 mVs -1 scan rate. The FTO glass, Pt glass, and Ag/AgCl electrodes serve as the working, counter, and reference electrodes, respectively. 0.1 M sodium tungstate solution was used as an electrolyte. The chrono-amperometry test was done to measure the amount of charge involved during the reaction by applying 3 V. 3. Results and Discussion 3.1 Thin film-free electrochromic device performance The influence of electrolyte’s pH on electrochromic behaviour was investigated using a 0.1 M sodium tungstate solution. The pH was adjusted by adding 2 M HNO 3 to achieve pH values of 1.5, 2, 3, 4, and 5. Electrochromic performance was evaluated across these pH levels. No visible coloration was observed at pH 5, 4, or 3, even at an applied voltage of 3 V. However, distinct coloration occurred at pH 1.5 and 2. For electrolyte preparation, sodium tungstate was dissolved in distilled water, producing tungstate ions according to the following reaction (Eq. 1 ). The pH was specifically adjusted to 1.5, as tungstate ions \\(\\left({WO}_{4}^{2-}\\right)\\) are most dominant in the pH range of 1 to 2 [ 26 ]. However, the attempt at pH < 1.5 was unsuccessful, as a white precipitate formed. $${Na}_{2}W{O}_{4}.{2H}_{2}O+{H}_{2}O\\underset{\\begin{array}{c}pH1.5\\\\27{C}^{0}\\end{array}}{\\to}W{O}_{4}^{2-}+2{Na}^{+}$$ 1 In the acidified media (pH = 1.5), tungstate ions, along with H + ions, aid in the production of metatungstic acid. This can be generally represented as \\({\\left(W{O}_{3}\\right)}_{n}.x{H}_{2}O\\) , which is in fact a mixture of homologous compounds different in n (degree of polymerization) and x (number of water molecules). This metatungstic species remains soluble in the acidic aqueous medium and exist dynamic equilibrium with tungstate ions. The equilibrium related to this species can be expressed as following reaction (Eq. 2 ) [ 27 ]. $$n{WO}_{4}^{2-}+2n{H}^{+}+(x-n){H}_{2}O\\leftrightarrow{\\left(W{O}_{3}\\right)}_{n}.x{H}_{2}O$$ 2 Upon applying external voltage, the negatively biased FTO acts as a source of electrons. The Na + and H + ions move toward the negatively biased FTO substrate. They intercalate into the interfacial tungsten oxide from the solution and form a hydrated tungsten blue bronze (Eq. 3). \\(W{O}_{3}.x{H}_{2}O+{zM}^{+}+z{e}^{-1}\\leftrightarrow{M}_{z}W{O}_{3}.{xH}_{2}O\\) (blue bronze) (3) Where M + represents small ions such as H + or Na + . Upon the removal of the applied potential, the intercalated ions undergo de-intercalation. Consequently, \\({M}_{z}W{O}_{3}.{xH}_{2}O\\) returns to \\(W{O}_{3}.x{H}_{2}O\\) leading to completely disappearance of blue coloration. There are no permanent thin film forms of the FTO glass due to the solubility of metatungstic acid species in aqueous electrolyte. This reversible mechanism confirms that the electrochromic response in the present system originates from the in-situ formation of hydrated tungsten bronze species rather than from a pre-deposited solid WO 3 film on a FTO glass. The ability of a substance to absorb light is referred as absorbance. In an electrochromic device, high absorbance is desired in the colored state. As shown in Fig. 3 the device exhibits maximum absorbance at pH 1.5, particularly around the 650 nm wavelength. These findings suggest that pH 1.5 is the optimal condition for maximum electrochromic performance. The higher absorbance observed at 648 nm indicates that the system has a strong optical transition or electronic excitation in this region of the visible spectrum. Ligand-to-metal charge transfer (LMCT) is the dominant mechanism responsible for visible light absorption in the 400–700 nm region in tungstate ions. The peak around 650 nm may correspond to such an LMCT band. A range of voltages from 0 V to 4 V, in 0.5 V increments, was applied to the electrochromic device to determine the optimal voltage for coloration. The corresponding changes in transmittance and absorbance were measured using a UV-Visible spectrophotometer Fig. 4 and Fig. 5 show the variations in absorbance and transmittance, respectively, under different applied potentials. Voltages below 2 V resulted in negligible or delayed color formation. Increasing the voltage to 2.5 V initiated a weak blue coloration. At 3 V, a rapid and intense blue coloration was consistently observed, accompanied by the maximum change in absorbance and minimum transmittance, indicating that 3 V is the optimal operating voltage for effective electrochromic performance. When the applied voltage exceeded 3.5 V, the device exhibited instability, including electrolyte degradation and bubble formation, likely due to water electrolysis or decomposition of electrolyte species. Therefore, 3 V was selected as the optimum voltage, balancing electrolyte stability, response time, and coloration intensity. Figure 6 presents the transmittance spectra for the colored and bleached states under optimized voltage and pH conditions, measured across the wavelength range of 400 to 900 nm. Upon applying 3 V, a blue coloration was observed near the negatively biased electrode. This blue appearance results from the absorption of red light, which corresponds to wavelengths between 620 and 750 nm. Consequently, the optical modulation of transmittance between the colored and bleached states in the 620–750 nm range was calculated using the equation provided below[ 3 ][ 25 ][ 28 ]. $$\\varDelta T={T}_{b}-{T}_{a}$$ 4 Figure 7 shows that optical modulation variation in 620 nm to 750 nm wavelength range. Maximum optical modulation of 87.45% was observed at 648 nm wavelength. Transmittance measurements at 648 nm revealed that the coloured state at 3 V achieved a transmittance of 10.72%, while the transparent state exhibited a transmittance of 98.17%. Another way to quantify the color change between the bleached and colored states is by measuring the change in optical density (∆OD), defined as [ 26 – 28 ]: $$\\varDelta\\text{O}\\text{D}=\\text{log}({\\text{T}}_{b}/{\\text{T}}_{c})$$ 5 where \\({\\text{T}}_{b}\\) and \\({\\text{T}}_{c}\\) represent the transmittance in the bleached and colored states, respectively. At 648 nm, the optical density was found to be 0.96, indicating excellent device performance. This value surpasses those reported for many thin-film-based electrochromic systems, confirming that the liquid-phase coloration mechanism employed here is both effective and efficient. The switching time of the electrochromic device was measured by monitoring the transmittance change at 648 nm, under alternating applied voltages of 3 V (for coloration) and 0 V (for bleaching) over a 60-second period. Figure 8 illustrates the switching behaviour of the device. The coloration time, defined as the time required to reach 90% of full coloration [ 32 ], was determined to be 14 seconds, while the bleaching time, corresponding to 90% of full bleaching, [ 32 ] was 35 seconds. Coloration efficiency (CE) is a key parameter used to evaluate the performance of an electrochromic device. It measures how effectively the device changes its optical density (i.e., how much it darkens or tints) per unit of electrical charge injected or extracted [ 26 – 28 ][ 33 ]. $$CE=\\frac{\\varDelta\\text{O}\\text{D}}{Q}$$ 6 Where, \\(\\varDelta\\text{O}\\text{D}\\) is optical density and Q is amount of charge inserted or extracted. The CE was calculated from the slope of the linear region of the optical density versus charge density curve, as shown in Fig. 9 . The CE of the thin film–free electrochromic device was determined to be 66 cm²/C at a wavelength of 648 nm, which falls within the typical range reported for WO₃-based electrochromic devices ( 30–100 cm²/C ). These results confirm that the film-free electrochromic device can achieve coloration efficiency comparable to conventional devices. To evaluate the stability and repeatability of the device, transmittance variations were recorded during consecutive coloring and bleaching cycles. This was achieved by periodically switching the applied potential between 0 V and 3 V to alternate the device between colored and bleached states. Measurements were taken at 60-second intervals during the coloration process. Figure 10 presents the transmittance changes observed at a wavelength of 648 nm. The device showed noticeable changes in stability during the first three cycles, after which the transmittance stabilized, indicating Fig. 11 : Cyclic Voltammetry (scan rate 10 mVs-1) 3.2 Comparative Analysis of thin-film free electrochromic device with traditional thin film electrochromic device Thin-film-free electrochromic devices represent a promising alternative to traditional counterparts, particularly in applications requiring flexibility, reduced fabrication cost, shorter processing time, and scalability. Despite these advantages, challenges such as long-term stability, material optimization, and commercial viability remain to be addressed. The following tables present a comparative analysis of traditional electrochromic devices and emerging thin-film-free electrochromic devices, with focus on device structure, time consumption, cost and finally device performance. Table 1 Structural comparison of traditional electrochromic devices with novel thin film free electrochromic devices Component Traditional ECD (Thin-Film -Based) Novel ECD (Thin-Film-Free) Working Electrode FTO glass coated with WO 3 or similar EC material Requires thin-film deposition Bare FTO Glass No thin-film deposition needed Counter Electrode FTO glass coated with CeO 2 Require thin-film deposition Bare FTO Glass No thin-film deposition needed Electrolyte Liquid, Gel or Solid Liquid Conventional ECDs typically depend on thin-film-coated electrodes. The working electrode comprises an electrochromic material deposited onto a transparent conductive substrate, while the counter electrode often includes a thin film of Tin oxide (SnO₂) or Cerium oxide (CeO₂) coated on a similar substrate. In contrast, the thin-film-free electrochromic device (TFF-ECD) introduces a novel design that completely eliminates the need for thin-film coatings on both the working and counter electrodes (Table 1 ). In traditional ECDs, color change arises from the insertion of small cations such as H⁺, Li⁺, Na⁺, or K⁺ into the electrochromic material’s lattice under an applied voltage [ 7 , 34 – 39 ]. Conversely, the TFF-ECD demonstrates in situ formation of a blue coloration near the working electrode when a modest voltage is applied across bare FTO electrodes. This simplifies the device architecture and mitigates many fabrication challenges associated with thin-film processes. Fabrication methods play a pivotal role in determining the scalability and commercial viability of ECDs. Traditional thin-film-based devices involve multi-step deposition processes requiring specialized vacuum equipment. The TFF-ECD approach eliminates these deposition steps entirely, substantially reducing both fabrication time and complexity. Table 2 provides a comparative analysis of the fabrication times between conventional thin-film-based and thin-film-free electrochromic devices. Table 2 Comparison of time consumption for device fabrication process Cleaning FTO glasses Traditional ECD (Thin-Film -Based) Novel ECD (Thin-Film-Free) 30–45 min 30–45 min Coating of EC material 1–3 hours Including preparation of solution / slurry + coating 0 min No coating required Annealing / Heat Treatment 1–2 hours Depend on coating method & temperature 0 min No thermal processing needed Preparation of electrolyte 1–2 hours Gel based and solid electrolyte can take longer 45 min Solution preparation and pH adjustment Device Assembly 15–30 min 15–20 min Total Fabrication Time ~ 4–8 hours or much longer Depending on method & materials ~ 1–2 hours The cleaning time for FTO glass remains the same for both device types, as it must be ultrasonically cleaned to remove surface contaminants. In traditional electrochromic devices, thin films are typically deposited on both the counter and working electrodes using techniques such as spin coating, sol-gel processing, sputtering, chemical vapor deposition, and doctor blading. In contrast, TFF-ECDs eliminate the film deposition step entirely, resulting in significant time savings. Additionally, conventional electrochromic films require an annealing process to stabilize their structure, typically involving high temperatures (300–500°C) and lasting 1–2 hours. Thin-film-free devices avoid this step, as no films are deposited. Regarding electrolytes, traditional devices may use liquid, gel, or solid forms. Preparing gel or solid electrolytes requires precise polymerization or solid-state synthesis, which can be time-consuming. In this study, the electrolyte was prepared by dissolving sodium tungstate in distilled water and adjusting the pH with 2 M HNO 3 nitric acid; a process that takes approximately 30 minutes and offers a clear time advantage. The total fabrication time for traditional electrochromic devices can exceed 8 hours, depending on the thin-film deposition technique used. In contrast, TFF-ECD s can be completed within 2 hours, primarily due to the elimination of coating and annealing steps. The final assembly step of sandwiching the electrolyte between the working and counter electrodes requires the same amount of time for both device types. Table 3 Comparison of cost for device fabrication process Cost Traditional EC Device (Thin-Film -Based) Novel EC Device (Thin-Film-Free) Cleaning of FTO/ITO Glasses Medium (Require solvent, ultrasonic bath) Medium (same) FTO/ITO Glasses Medium Medium ( same ) Electrochromic Material High (WO 3 or other EC material needed) None No EC material used Coating process High (Requires spin coating, sputtering, etc) None No coating process required Annealing / Heat treatment High (Furnace usage increases cost) None No heat treatment needed Electrolyte Medium Medium ( same ) Assembly & Components Medium Spacer, sealants, labor Medium Same (Similar components used) Total Fabrication Cost High Materials + equipment's + energy Comparatively Low FTO cost is the main contributor The comparison of the cost associated with the device fabrication process of the thin-film based electrochromic devices and the thin-film based electrochromic devices was shown in Table 3 . Traditional ECDs involve a complex, multi-step fabrication process and high-cost materials such as WO 3 and CeO 2 . In contrast, the novel thin film-free approach presented here drastically reduces the costs by eliminating expensive steps like thin film deposition and thermal annealing process. Both traditional and TFF-ECDs rely on FTO or Indium-doped Tin Oxide (ITO) glass as a transparent conductive substrate. Therefore, cost remains the same across both devices. The conventional electrochromic materials require electrochromic materials to prepare a working electrode, and CeO 2 like materials to prepare a counter electrode. The deposition of electrochromic film onto FTO substrate is done through specialized techniques such as sputtering, spin-coating, chemical vapour deposition, and screen printing, etc. Each and every process needs expensive equipment, precise control, and trained labourers. Heat treatment of the coated substrate is essential to enhance the crystallinity and adhesion of the electrochromic film. The annealing process requires a temperature between 300–500 \\(℃\\) for 1–2 hours. These high energy consumption increases the fabrication cost. In contrast, the thin-film-free ECD omits the requirements of electrochromic materials, film deposition methods, and annealing process entirely. This leads to cost and material savings. Both device types should require an electrolyte. Therefore, cost associated with the electrolyte can be the same. However, the cost of preparation of electrolyte for the conventional electrochromic device can be higher, if it uses ionic liquid-like materials. Both ECDs require basic assembly components like spacers and sealant. So the cost associated with the fabrication is the same. When considering all these factors, the cost associated with the total fabrication process is comparatively lower in TFF-ECDs. It makes a TFF-ECD promising for scalable applications. The Table 4 summarizes the performance comparison between conventional ECDs, fabricated using layered working and counter electrodes, and our film-free WO₃-based ECD. Table 4 Comparison of electrochromic performance Working Electrode Applied Voltage (V) T b (s) T c (s) Optical Contrast ( \\(\\varDelta\\) T) Coloration Time (t c ) Bleaching Time (t b ) Coloration Efficiency (cm 2 /C) Ref nWO 3 3.0 72 38 34 10 [ 2 ] AgNW-WO 3 3.0 72 29 43 18 [ 2 ] WO 3 microparticle film -9.0 to 0 76.1 12.5 58.2 [ 31 ] WO 3 nanoparticle film -1.5 to 0 52 10 34.3 [ 31 ] Mesoporous WO 3 film -0.6 to 0.6 75.6 2.4 79.7 [ 31 ] Amorphous WO 3 film -2.5 to 2.5 45.3 17 63 [ 31 ] WO 3 dispersed film -0.9 to 0.9 77.8 15 62.1 [ 31 ] A porous film of WO 3 @ PEO fibers -2 to 1 39.5 1.6 61.4 [ 31 ] Sol-gel titania film + 0.1 to – 1.5 60 55 10 55.9 [ 3 ] Spin-coated WO 3 0 to -1.5 71.3 14 10 40.2 [ 40 ] Slot-die WO 3 0 to -1.5 72.8 12 8.5 38.5 [ 40 ] EFAD printed WO 3 0 to -1.5 72.1 12 9 41.0 [ 40 ] Hydrothermal WO 3 1.28 5.50 [ 41 ] Molybdenum-doped WO 3 56.7 123.5 [ 18 ] WO 3 polycrystalline 76.2 54.8 [ 18 ] TiO 2 62.8 0.98 61.8 30 [ 17 ] NiO nanoparticle 63.6 42.8 [ 18 ] NiO nanosheet 40 63.2 [ 18 ] NiO / Ag / NiO 70 76.6 [ 18 ] Silver nanowire /NiO 15 51.9 [ 18 ] Film free 0 V − 3 V 98.17 10.72 87.45 14 35 66 This paper The performance of the electrochromic device is another important parameter for the scalability of ECDs. Traditional electrochromic devices show optimal modulation in the range of 60–80% and optical density in the range of 0.5–0.8, which depends on the film thickness, morphology, and ion insertion depth. In the thin-film free approach, optical modulation was obtained as 87.5%, and optical density was obtained as 0.96. This is higher than the OD obtained for the conventional electrochromic devices. The coloration efficiency of this novel electrochromic device lies within the range of conventional ECDs. This shows fast coloration but somewhat lower bleaching time. The conventional ECD consists of a thin film of electrochromic material coated electrode. These films can be cracked over time. Due to high-expense coating methods, the scalability of conventional ECDs is limited. However, the thin film-free approach, hasn’t thin film coating there for no degradation happens, and it becomes highly scalable. 4. Conclusions This study presents a novel approach to ECD fabrication by demonstrating reversible electrochromic behavior through a liquid-phase reaction between dual FTO glass substrates, eliminating the need for conventional solid-state electrochromic films. A distinct blue coloration was achieved upon applying 3 V, with the device exhibiting a high optical modulation of 87.5% and an optical density of 0.96 at 648 nm. The coloration efficiency reached 66.7 cm²/C, highlighting efficient charge utilization, while the switching times of 14 s for coloration and 35 s for bleaching confirm favorable electrochemical dynamics. Importantly, the fabrication process entirely bypasses the use of electrochromic materials, thin-film deposition, and thermal treatment, significantly reducing both production cost and time. This thin-film-free architecture not only overcomes key limitations of conventional ECDs but also enables scalable, rapid, and low-cost manufacturing. Overall, the successful development of this liquid-electrolyte-based, film-free ECD offers a promising pathway toward sustainable electrochromic technologies, contributing to enhanced energy efficiency, reduced environmental impact, and advancement of next-generation smart devices. Declarations Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by S.M.P.M.K, H.N.M. , and E.G.O.D. . The first draft of the manuscript was written by S.M.P.M.K, E.G.O.D. and H.N.M. and all authors commented on previous versions of the manuscript. Laboratory facilities were provided by H.M.B.I. and G.M.L.P. All authors read and approved the final manuscript. References Dingari M, Reddy DM, Sumalatha V et al (2020) Recent Studies in Mathematics and Computer Science. 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Mater Today Proc 3:S40–S47. https://doi.org/10.1016/j.matpr.2016.01.006 Yu X, Guo P, Chen J et al (2024) Recent advances in multifunctional electrochromic devices. Responsive Mater 2:1–20. https://doi.org/10.1002/rpm.20240013 Sarangika HNM, Dissanayake MAKL, Senadeera GKR, Karunarathne WGMD (2019) Low cost quasi solid state electrochromic devices based on F-doped tin oxide and TiO2. Mater Today Proc 23:100–104. https://doi.org/10.1016/j.matpr.2019.07.585 Guo Q, Sun C, Li Y et al (2025) Recent Advances of Electrode Materials Applied in an Electrochromic Supercapacitor Device. Molecules 30. https://doi.org/10.3390/molecules30010182 Bourdin M, Mjejri I, Rougier A et al (2020) Nano-particles (NPs) of WO3-type compounds by polyol route with enhanced electrochromic properties. J Alloys Compd 823:1–26. https://doi.org/10.1016/j.jallcom.2020.153690 Chen PW, Chang C, Te, Ko TF et al (2020) Fast response of complementary electrochromic device based on WO3/NiO electrodes. Sci Rep 10:1–12. https://doi.org/10.1038/s41598-020-65191-x Patel M, Ghosh S, Cho S, Kim J (2025) Highly Transparent Spectral Tunable Electrochromic Window Based on Solid-State WO3 Thin Films. Int J Energy Res 2025:. https://doi.org/10.1155/er/8585226 Zhao L, Song S, Li L (2020) Effect of sputtering gas pressure on the performance of WO3 thin films electrochromic device. J Phys Conf Ser 1676. https://doi.org/10.1088/1742-6596/1676/1/012037 Chaudhary A, Pathak DK, Tanwar M et al (2022) Hydrothermally grown nano-WO3 electrochromic film: structural and Raman spectroscopic study. Adv Mater Process Technol 8:970–976. https://doi.org/10.1080/2374068X.2020.1835019 Cho HM, Hwang YJ, Oh HS et al (2025) Recent Advances in Electrochromic Devices: From Multicolor to Flexible Applications. Adv Photonics Res 6. https://doi.org/10.1002/adpr.202400103 Gunathilaka HMBI, Seneviratne VA, Sarangika HNM (2023) Polymer-free gel electrolyte and its application in TiO2-based electrochromic devices. J Appl Electrochem 53:2185–2196. https://doi.org/10.1007/s10800-023-01912-0 Sarangika HNM, Egodawaththa EGOD, Aponsu GMLP (2024) WO3–TiO2 nanostructured thin film prepared by in situ hydrothermal method as the sensing material for liquid petroleum gas (LPG) detection. J Mater Sci Mater Electron 35. https://doi.org/10.1007/s10854-024-13553-w Choi YG, Sakai G, Shimanoe K et al (2002) Preparation of aqueous sols of tungsten oxide dihydrate from sodium tungstate by an ion-exchange method. Sens Actuators B Chem 87:63–72. https://doi.org/10.1016/S0925-4005(02)00218-6 Brzezicki M (2021) A systematic review of the most recent concepts in smart windows technologies with a focus on electrochromics. Sustain 13. https://doi.org/10.3390/su13179604 Ramakrishnan J, Liu T, Zhang F et al (19555) Pr ep rin t n ot pe er re v iew pe er re v Pr ep rin t n ot iew. 1–34 Fabretto M, Vaithianathan T, Hall C et al (2007) Colouration efficiency measurements in electrochromic polymers: The importance of charge density. Electrochem commun 9:2032–2036. https://doi.org/10.1016/j.elecom.2007.05.035 Kwon H, Kim S, Ham M et al (2023) Enhanced Coloration Time of Electrochromic Device Using Integrated WO3@PEO Electrodes for Wearable Devices. Biosensors 13:1–11. https://doi.org/10.3390/bios13020194 Koo BR, Jo MH, Kim KH, Ahn HJ (2020) Multifunctional electrochromic energy storage devices by chemical cross-linking: impact of a WO3·H2O nanoparticle-embedded chitosan thin film on amorphous WO3 films. NPG Asia Mater 12. https://doi.org/10.1038/s41427-019-0193-z Mortimer RJ, Rosseinsky DR, Monk PMS (2015) Electrochromic Materials and Devices. Electrochromic Mater Devices 77:1–638. https://doi.org/10.1002/9783527679850 Rai V, Singh RS, Blackwood DJ, Zhili D (2020) A Review on Recent Advances in Electrochromic Devices: A Material Approach. Adv Eng Mater 22. https://doi.org/10.1002/adem.202000082 (2021) Adhesive electrochromic WO 3 thin films fabricated using a WO 3 nanoparticle-based ink Chan Yang Jeong Faceira B, Teule-gay L, Rignanese G et al (2022) Towards the Prediction of Electrochromic Properties of WO3 Films: Combination of Experimental and Machine Learning Approaches To cite this version : HAL Id : hal-03763753 Towards the Prediction of Electrochromic Properties of WO 3 Films. Combination of Rocca T, Gurel A, Schaming D et al (2024) Multivalent-Ion versus Proton Insertion into Nanostructured Electrochromic WO3 from Mild Aqueous Electrolytes. ACS Appl Mater Interfaces. https://doi.org/10.1021/acsami.4c02152 Physica Status Solidi a – 2022 - Chaudhary - Inorganic-Alone Solid‐State Electrochromic Device for Application as Visible.pdf Shchegolkov AV, Lipkin MS, Komarov FF, Parfimovich ID (2024) Regularities of Obtaining Electrochromic WO3 Films at the Cathode Polarization of the Electrode. Russ J Gen Chem 94:2545–2550. https://doi.org/10.1134/S1070363224090329 Kim KW, Kim YM, Li X et al (2020) Various coating methodologies of WO3 according to the purpose for electrochromic devices. Nanomaterials 10:1–11. https://doi.org/10.3390/nano10050821 Makalesi A, Morkoç Karadeniz S (2021) Novel Synthesis of Good Electrochromic Performance WO3 Nanoplates Grown on Seeded FTO. Eur J Sci Technol 718–722. https://doi.org/10.31590/ejosat Additional Declarations No competing interests reported. Supplementary Files GraphicalAbstract.png Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 07 May, 2026 Reviewers agreed at journal 05 May, 2026 Reviewers invited by journal 05 May, 2026 Editor assigned by journal 22 Mar, 2026 Submission checks completed at journal 16 Mar, 2026 First submitted to journal 14 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-9123105\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":636455628,\"identity\":\"0a12fd2b-db95-4b93-a625-33cb283a6566\",\"order_by\":0,\"name\":\"S.M.P.M.K Sanganayaka\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Sabaragamuwa University of Sri Lanka\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"S.M.P.M.K\",\"middleName\":\"\",\"lastName\":\"Sanganayaka\",\"suffix\":\"\"},{\"id\":636455629,\"identity\":\"17fdda0e-27de-4741-8194-dff25d123ea8\",\"order_by\":1,\"name\":\"E.G.O.D Egodawaththa\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Sabaragamuwa University of Sri Lanka\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"E.G.O.D\",\"middleName\":\"\",\"lastName\":\"Egodawaththa\",\"suffix\":\"\"},{\"id\":636455630,\"identity\":\"6961e819-1c79-4e3e-a2da-b91198ca3a34\",\"order_by\":2,\"name\":\"H.N.M. Sarangika\",\"email\":\"data:image/png;base64,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\",\"orcid\":\"\",\"institution\":\"Sabaragamuwa University of Sri Lanka\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"H.N.M.\",\"middleName\":\"\",\"lastName\":\"Sarangika\",\"suffix\":\"\"},{\"id\":636455633,\"identity\":\"7d52b812-1488-475c-8d5b-68ad484c84c1\",\"order_by\":3,\"name\":\"G.M.L.P. Aponsu\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Sabaragamuwa University of Sri Lanka\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"G.M.L.P.\",\"middleName\":\"\",\"lastName\":\"Aponsu\",\"suffix\":\"\"},{\"id\":636455636,\"identity\":\"f4bbfa63-346a-4b7a-8f4e-532c0b789f92\",\"order_by\":4,\"name\":\"H.M.B.I Gunathilake\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Industrial Technology Institute, Colombo, Sri Lanka\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"H.M.B.I\",\"middleName\":\"\",\"lastName\":\"Gunathilake\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2026-03-14 13:56:00\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-9123105/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-9123105/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":109157879,\"identity\":\"9af6d06f-7c01-43ae-8327-c08662fc8354\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:40\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":256930,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSchematic Representation of Electrochromic Device\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/111000438eb4d17f9d88d904.png\"},{\"id\":109157880,\"identity\":\"d7afe6d1-5d97-4670-bb8f-5d19e80488cf\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:40\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":607286,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSchematic diagram of the process of thin-film free electrochromic device\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/ecc619615557d9a93ae96ae7.png\"},{\"id\":109157881,\"identity\":\"1a9594be-a040-40e6-b86e-9c31a847713b\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:41\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1051225,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSpectra of different pH values under 3V of applied potential\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/48576b9ccff28184d8962257.png\"},{\"id\":109157882,\"identity\":\"2ed8ccdd-bae4-4466-95f3-626f1c683fe0\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:41\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1161965,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eAbsorbance spectra of different applied potentials for the electrolyte with pH 1.5\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/ce582a84a812f5d466fd0277.png\"},{\"id\":109205110,\"identity\":\"85508bfd-aa9b-4689-9169-71c599170e3b\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 15:03:24\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":121839,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eTransmittance spectra of different applied potentials for the electrolyte with pH 1.5\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/3c5204523893bc2b8ba3ea7b.png\"},{\"id\":109205434,\"identity\":\"32c8f5c0-8113-4b38-8902-a28dc7aaa472\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 15:04:46\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":389452,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eTransmittance spectra Curves for colored (3 V) and bleached states (0 V)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/5f35cb4533c0c552863fffa5.png\"},{\"id\":109157886,\"identity\":\"3f62ef9d-5414-4fbd-a3c0-b9eb7b732b04\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:41\",\"extension\":\"png\",\"order_by\":7,\"title\":\"Figure 7\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1014712,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eOptical modulation spectrum for optimal conditions\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.7.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/939326c54885104e665f42aa.png\"},{\"id\":109157888,\"identity\":\"2bbe6c6f-310a-4c88-8e12-cc5af69d5210\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:41\",\"extension\":\"png\",\"order_by\":8,\"title\":\"Figure 8\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1016749,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eTransmittance variation monitored at wavelength of 650 nm, obtained by applying voltage of 3 V (Coloration) and 0 V (bleaching) 60 s each\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.8.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/2646f34bc910d4111f615fb8.png\"},{\"id\":109205249,\"identity\":\"bf4c5f8f-e870-4ff3-8143-f4050e8590c4\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 15:03:53\",\"extension\":\"png\",\"order_by\":9,\"title\":\"Figure 9\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":919877,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eOptical density vs charge density under 3 V applied potential\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.9.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/07c1f032ec9d805085cc29b3.png\"},{\"id\":109157889,\"identity\":\"9af774f9-e906-4487-b49c-8c90f42d75cf\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:41\",\"extension\":\"png\",\"order_by\":10,\"title\":\"Figure 10\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1408549,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eKinetics measurements\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.10.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/90a488c4f6e9ed718249be47.png\"},{\"id\":109157890,\"identity\":\"98b1e289-7f22-4c54-b759-7cc7a236356c\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 07:00:41\",\"extension\":\"png\",\"order_by\":11,\"title\":\"Figure 11\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1058160,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eCyclic Voltammetry (scan rate 10 mVs-1)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig.11.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/aee7f6eb013da1a5158ac2de.png\"},{\"id\":109207300,\"identity\":\"54c366bd-2704-41a7-af8b-e4c532712065\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 15:19:13\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":9345273,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/655babf5-2e09-4249-8f05-2509fdeeff18.pdf\"},{\"id\":109205259,\"identity\":\"b8a81666-d76e-4cee-bb27-e5cf9ec135fd\",\"added_by\":\"auto\",\"created_at\":\"2026-05-13 15:03:55\",\"extension\":\"png\",\"order_by\":1,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":505060,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"GraphicalAbstract.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9123105/v1/6dfbdce82dc0ac3f6705d624.png\"}],\"financialInterests\":\"No competing interests reported.\",\"formattedTitle\":\"A Thin-Film-Free Electrochromic System Based on Dual Conductive Glass Electrodes and Sodium Tungstate Electrolyte\",\"fulltext\":[{\"header\":\"1. Introduction\",\"content\":\"\\u003cp\\u003eChromism refers to the colour change that occurs due to alterations in the electronic states, such as π electrons and d electrons within a molecule or crystal in response to an external stimulus. Depending on the nature of the stimulus, chromism can be classified into various types, including thermochromism (colour change with temperature), photochromism (colour change with light), and electrochromism (colour change with an electric field) [\\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e]. Among these, electrochromism has attracted significant attention due to its practical applications. Electrochromism is the phenomenon where the colour or optical properties of a material, such as transmission, reflection, and absorption, undergo a stable and reversible change upon the application of an external voltage[\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eElectrochromism was first observed in tungsten oxide (WO\\u003csub\\u003e3\\u003c/sub\\u003e) films immersed in sulphuric acid by Kraus in 1953 in an unpublished laboratory report at Balzers AG in Liechtenstein. Electrochromism gained much attention after publication on amorphous and crystalline tungsten oxide films and the development of the first WO\\u003csub\\u003e3\\u003c/sub\\u003e-based electrochromic devices between 1969\\u0026ndash;1973 [\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eElectrochromic devices (ECDs) are devices that change their colour and optical properties, such as transmittance, reflectance, or absorbance, under the influence of an electrical voltage. ECDs operate based on reversible redox reactions where ions and electrons move within the electrochromic material and alter optical properties[\\u003cspan additionalcitationids=\\\"CR5 CR6 CR7 CR8 CR9 CR10\\\" citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e]. Electrochromic devices are recognized as a promising technology across various industries due to their ability to reversibly modulate optical properties in response to an applied potential. Due to their low energy consumption, controllable optical switching, and tuneable coloration properties, these devices are well-suited for a wide range of applications, including smart windows, information displays, light shutters, and variable reflectance mirrors.\\u003c/p\\u003e \\u003cp\\u003eConventional electrochromic devices have three major components: a working electrode, an electrolyte, and a counter electrode, as shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e. It is a \\u0026ldquo;sandwich-type\\u0026rdquo; configuration in which the electrolyte is sandwiched between the working and counter electrode [\\u003cspan additionalcitationids=\\\"CR13 CR14\\\" citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e15\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe working electrode of the electrochromic device consists of a thin film of electrochromic material coated on a transparent conductive oxide layer coated glass substrate. Electrolyte is a critical component of an electrochromic device. The electrolyte layer is located between the electrochromic active layer and the ion storage layer. The main roles of electrolytes are allowing the movement of charged ions, and isolating electrodes. Also, it allows the movement of charged ions in a directional manner under the effect of an applied electric field to ensure that the electrochromic layer achieves controllable colour conversion through the redox process of the ions. The electrolyte layer prevents the direct contacting and short-circuiting of the electrochromic layer and ion storage layer by effectively isolating them. The counter electrode of ECD consists of an ion storage layer coated on a transparent conductive oxide layer coated glass substrate. It provides a reversible electrochemical reaction in the device operating in any mode. It stores the charge during the bleaching process[\\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e]. The counter electrode operates in complementary redox mode to the active electrochromic material[\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eWhen a voltage is applied between the working and counter electrode, a distributed electric field is generated. The ions in the electrolyte film migrate uniformly into the (intercalated) electrochromic layer [\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e]. The counterflow of electrons happens through the external circuit to balance the charge. This results in variation of electron density in the electrochromic material. Therefore optical properties of the electrochromic device were modulated. When the polarity of the electrodes changes, the ions migrate in the opposite direction (de-intercalated) and the electrochromic device returns to its original state [\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e]. The ion transport is easiest for small ions such as protons (H\\u003csup\\u003e+\\u003c/sup\\u003e) or lithium ions (Li\\u003csup\\u003e+\\u003c/sup\\u003e).\\u003c/p\\u003e \\u003cp\\u003eAs mentioned previously, conventional electrochromic devices consist of a thin film of electrochromic material coated onto a transparent conductive oxide substrate. Thin film deposition critically influences device performance, durability, and cost. Different thin\\u0026ndash;film deposition techniques are utilized to produce high-quality electrochromic film. Physical vapour deposition (PVD) methods like sputtering, deposit uniform thin Electrochromic (EC) films by ejecting material via energetic particle collisions. Spin coating involves spreading a precursor solution on a rapidly spinning substrate to form uniform films upon solvent evaporation. Spray coating atomizes droplets using pressurized gas to create thin films, with an airbrush system. Additionally, techniques such as the sol-gel method, electro-deposition, screen printing, inkjet printing, flexographic printing, and blade coating are also employed for electrochromic thin film deposition [\\u003cspan additionalcitationids=\\\"CR21 CR22 CR23\\\" citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR24\\\" class=\\\"CitationRef\\\"\\u003e24\\u003c/span\\u003e]. Each of these technique yield an excellent EC film with enhanced properties. However, they share common drawbacks. These techniques rely on specialized equipment, multi-step fabrication processes, and high-temperature annealing, making them time-consuming, costly, and difficult to scale up. Additionally, challenges such as complex manufacturing, limited scalability, and long-term stability issues like film cracking and delamination further hinder their practical application[\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eTo overcome these limitations in the conventional electrochromic devices, this study explores a novel and simplified approach where no thin film of the electrochromic layer is deposited on the transparent conductive oxide substrate. Here, for the first time, an electrochromic device is prepared by using two bare fluorine-doped tin oxide (FTO) glass substrates as working and counter electrodes, and 0.1 M sodium tungstate solution as electrolyte.\\u003c/p\\u003e \\u003cp\\u003eThis innovative approach eliminates the reliance on traditional thin-film coatings, thereby simplifying the fabrication process and significantly reducing production costs. By addressing key limitations of conventional electrochromic devices such as high material expenses and complex manufacturing steps, this study demonstrates that high-performance electrochromic functionality can be achieved without the need for conventional coating techniques. This advancement paves the way for a more scalable and cost-effective manufacturing route.\\u003c/p\\u003e\"},{\"header\":\"2. Experimental\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.1 Materials\\u003c/h2\\u003e \\u003cp\\u003eSodium tungstate dehydrate (Na\\u003csub\\u003e2\\u003c/sub\\u003eWO\\u003csub\\u003e4\\u003c/sub\\u003e.2H\\u003csub\\u003e2\\u003c/sub\\u003eO, 99.9%) and nitric acid (HNO\\u003csub\\u003e3\\u003c/sub\\u003e, 68\\u0026ndash;70%) were purchased from Sigma Aldrich, and FTO glasses (sheet resistance 12 Ω/sq) were purchases from Soloronix.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.2 Preparation of an electrolyte\\u003c/h2\\u003e \\u003cp\\u003eThe electrolyte for film\\u0026ndash;free electrochromic devices was prepared using the following procedure. 0.1 M sodium tungstate solution was prepared by dissolving Na\\u003csub\\u003e2\\u003c/sub\\u003eWO\\u003csub\\u003e4\\u003c/sub\\u003e.2H\\u003csub\\u003e2\\u003c/sub\\u003eO powder in deionized water. Then the pH of the solution was adjusted by adding 2 M HNO\\u003csub\\u003e3\\u003c/sub\\u003e.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec5\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.3 Fabrication of an electrochromic device\\u003c/h2\\u003e \\u003cp\\u003eIn our study, commercially available FTO glasses were used as both the working electrode and counter electrode. ECD configuration with FTO glass / Na\\u003csub\\u003e2\\u003c/sub\\u003eWO\\u003csub\\u003e4\\u003c/sub\\u003e liquid electrolyte / FTO glass was fabricated. A spacer frame was placed on the top of the one FTO glass, by keeping enough space for electrical contact from the other FTO glass. Then the middle of the spacer film was filled with the electrolyte. The thin-film-free ECD fabrication process is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e\\n\\u003ch3\\u003e\\u003c/h3\\u003e\\n\\u003cdiv id=\\\"Sec7\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.4 Identify the optimal pH value and voltage value\\u003c/h2\\u003e \\u003cp\\u003eA series of electrolytes was made with different pH values (pH 1.5, 2, 3, 4, and 5) to investigate the effect of pH on electrochromic performance. Then a series of identical devices were fabricated, and each of them was filled with electrolyte at different pH values. Then constant voltage was applied for each device, and absorbance and transmittance measurements were taken using a UV-visible spectrophotometer (Shimadzu UV 1800). Subsequently, another set of identical devices was fabricated using the electrolyte at optimal pH value. These devices were subjected to varying applied voltages ranging from 0 V to 4 V in 0.5 V increments. Absorbance and transmittance measurements were recorded using a UV-visible spectrophotometer to evaluate the voltage-dependent electrochromic response.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec8\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.5 Electrochromic (EC) measurement\\u003c/h2\\u003e \\u003cp\\u003eAn ECD with the configuration of FTO/electrolyte/FTO was fabricated, and the change in the optical transmittance of the ECD was investigated by comparing the UV\\u0026ndash;visible transmittance spectra in coloured and bleached states in the wavelength range of 400 nm to 900 nm. Cyclic voltammetry studies were carried out using a three-electrode system of computer-controlled Metraohm Autolab (PGSTAT204) in the potential range from \\u0026minus;\\u0026thinsp;2.0 V to +\\u0026thinsp;0.5 V with 10 mVs\\u003csup\\u003e-1\\u003c/sup\\u003e scan rate. The FTO glass, Pt glass, and Ag/AgCl electrodes serve as the working, counter, and reference electrodes, respectively. 0.1 M sodium tungstate solution was used as an electrolyte. The chrono-amperometry test was done to measure the amount of charge involved during the reaction by applying 3 V.\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"3. Results and Discussion\",\"content\":\"\\u003cdiv id=\\\"Sec10\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.1 Thin film-free electrochromic device performance\\u003c/h2\\u003e \\u003cp\\u003eThe influence of electrolyte\\u0026rsquo;s pH on electrochromic behaviour was investigated using a 0.1 M sodium tungstate solution. The pH was adjusted by adding 2 M HNO\\u003csub\\u003e3\\u003c/sub\\u003e to achieve pH values of 1.5, 2, 3, 4, and 5. Electrochromic performance was evaluated across these pH levels. No visible coloration was observed at pH 5, 4, or 3, even at an applied voltage of 3 V. However, distinct coloration occurred at pH 1.5 and 2. For electrolyte preparation, sodium tungstate was dissolved in distilled water, producing tungstate ions according to the following reaction (Eq.\\u0026nbsp;\\u003cspan refid=\\\"Equ1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e). The pH was specifically adjusted to 1.5, as tungstate ions \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\left({WO}_{4}^{2-}\\\\right)\\\\)\\u003c/span\\u003e\\u003c/span\\u003e are most dominant in the pH range of 1 to 2 [\\u003cspan citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e26\\u003c/span\\u003e]. However, the attempt at pH\\u0026thinsp;\\u0026lt;\\u0026thinsp;1.5 was unsuccessful, as a white precipitate formed.\\u003cdiv id=\\\"Equ1\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ1\\\" name=\\\"EquationSource\\\"\\u003e\\n$${Na}_{2}W{O}_{4}.{2H}_{2}O+{H}_{2}O\\\\underset{\\\\begin{array}{c}pH1.5\\\\\\\\27{C}^{0}\\\\end{array}}{\\\\to}W{O}_{4}^{2-}+2{Na}^{+}$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e1\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eIn the acidified media (pH\\u0026thinsp;=\\u0026thinsp;1.5), tungstate ions, along with H\\u003csup\\u003e+\\u003c/sup\\u003e ions, aid in the production of metatungstic acid. This can be generally represented as \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\({\\\\left(W{O}_{3}\\\\right)}_{n}.x{H}_{2}O\\\\)\\u003c/span\\u003e\\u003c/span\\u003e, which is in fact a mixture of homologous compounds different in n (degree of polymerization) and x (number of water molecules). This metatungstic species remains soluble in the acidic aqueous medium and exist dynamic equilibrium with tungstate ions. The equilibrium related to this species can be expressed as following reaction (Eq.\\u0026nbsp;\\u003cspan refid=\\\"Equ2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e) [\\u003cspan citationid=\\\"CR27\\\" class=\\\"CitationRef\\\"\\u003e27\\u003c/span\\u003e].\\u003cdiv id=\\\"Equ2\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ2\\\" name=\\\"EquationSource\\\"\\u003e\\n$$n{WO}_{4}^{2-}+2n{H}^{+}+(x-n){H}_{2}O\\\\leftrightarrow{\\\\left(W{O}_{3}\\\\right)}_{n}.x{H}_{2}O$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e2\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eUpon applying external voltage, the negatively biased FTO acts as a source of electrons. The Na\\u003csup\\u003e+\\u003c/sup\\u003e and H\\u003csup\\u003e+\\u003c/sup\\u003e ions move toward the negatively biased FTO substrate. They intercalate into the interfacial tungsten oxide from the solution and form a hydrated tungsten blue bronze (Eq.\\u0026nbsp;3).\\u003c/p\\u003e \\u003cp\\u003e \\u003cspan class=\\\"InlineEquation\\\"\\u003e \\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(W{O}_{3}.x{H}_{2}O+{zM}^{+}+z{e}^{-1}\\\\leftrightarrow{M}_{z}W{O}_{3}.{xH}_{2}O\\\\)\\u003c/span\\u003e \\u003c/span\\u003e (blue bronze) (3)\\u003c/p\\u003e \\u003cp\\u003eWhere M\\u003csup\\u003e+\\u003c/sup\\u003e represents small ions such as H\\u003csup\\u003e+\\u003c/sup\\u003e or Na\\u003csup\\u003e+\\u003c/sup\\u003e. Upon the removal of the applied potential, the intercalated ions undergo de-intercalation. Consequently, \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\({M}_{z}W{O}_{3}.{xH}_{2}O\\\\)\\u003c/span\\u003e\\u003c/span\\u003e returns to \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(W{O}_{3}.x{H}_{2}O\\\\)\\u003c/span\\u003e\\u003c/span\\u003e leading to completely disappearance of blue coloration. There are no permanent thin film forms of the FTO glass due to the solubility of metatungstic acid species in aqueous electrolyte. This reversible mechanism confirms that the electrochromic response in the present system originates from the in-situ formation of hydrated tungsten bronze species rather than from a pre-deposited solid WO\\u003csub\\u003e3\\u003c/sub\\u003e film on a FTO glass.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe ability of a substance to absorb light is referred as absorbance. In an electrochromic device, high absorbance is desired in the colored state. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e the device exhibits maximum absorbance at pH 1.5, particularly around the 650 nm wavelength. These findings suggest that pH 1.5 is the optimal condition for maximum electrochromic performance. The higher absorbance observed at 648 nm indicates that the system has a strong optical transition or electronic excitation in this region of the visible spectrum. Ligand-to-metal charge transfer (LMCT) is the dominant mechanism responsible for visible light absorption in the 400\\u0026ndash;700 nm region in tungstate ions. The peak around 650 nm may correspond to such an LMCT band.\\u003c/p\\u003e \\u003cp\\u003eA range of voltages from 0 V to 4 V, in 0.5 V increments, was applied to the electrochromic device to determine the optimal voltage for coloration. The corresponding changes in transmittance and absorbance were measured using a UV-Visible spectrophotometer Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e and Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e show the variations in absorbance and transmittance, respectively, under different applied potentials.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eVoltages below 2 V resulted in negligible or delayed color formation. Increasing the voltage to 2.5 V initiated a weak blue coloration. At 3 V, a rapid and intense blue coloration was consistently observed, accompanied by the maximum change in absorbance and minimum transmittance, indicating that 3 V is the optimal operating voltage for effective electrochromic performance. When the applied voltage exceeded 3.5 V, the device exhibited instability, including electrolyte degradation and bubble formation, likely due to water electrolysis or decomposition of electrolyte species. Therefore, 3 V was selected as the optimum voltage, balancing electrolyte stability, response time, and coloration intensity.\\u003c/p\\u003e \\u003cp\\u003eFigure\\u0026nbsp;6 presents the transmittance spectra for the colored and bleached states under optimized voltage and pH conditions, measured across the wavelength range of 400 to 900 nm. Upon applying 3 V, a blue coloration was observed near the negatively biased electrode. This blue appearance results from the absorption of red light, which corresponds to wavelengths between 620 and 750 nm. Consequently, the optical modulation of transmittance between the colored and bleached states in the 620\\u0026ndash;750 nm range was calculated using the equation provided below[\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e][\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e][\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e].\\u003cdiv id=\\\"Equ3\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ3\\\" name=\\\"EquationSource\\\"\\u003e\\n$$\\\\varDelta T={T}_{b}-{T}_{a}$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e4\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eFigure\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e shows that optical modulation variation in 620 nm to 750 nm wavelength range. Maximum optical modulation of 87.45% was observed at 648 nm wavelength. Transmittance measurements at 648 nm revealed that the coloured state at 3 V achieved a transmittance of 10.72%, while the transparent state exhibited a transmittance of 98.17%.\\u003c/p\\u003e \\u003cp\\u003eAnother way to quantify the color change between the bleached and colored states is by measuring the change in optical density (∆OD), defined as [\\u003cspan additionalcitationids=\\\"CR27\\\" citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e26\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e]:\\u003cdiv id=\\\"Equ4\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ4\\\" name=\\\"EquationSource\\\"\\u003e\\n$$\\\\varDelta\\\\text{O}\\\\text{D}=\\\\text{log}({\\\\text{T}}_{b}/{\\\\text{T}}_{c})$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e5\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003ewhere \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\({\\\\text{T}}_{b}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e and \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\({\\\\text{T}}_{c}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e represent the transmittance in the bleached and colored states, respectively.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eAt 648 nm, the optical density was found to be 0.96, indicating excellent device performance. This value surpasses those reported for many thin-film-based electrochromic systems, confirming that the liquid-phase coloration mechanism employed here is both effective and efficient.\\u003c/p\\u003e \\u003cp\\u003eThe switching time of the electrochromic device was measured by monitoring the transmittance change at 648 nm, under alternating applied voltages of 3 V (for coloration) and 0 V (for bleaching) over a 60-second period. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e8\\u003c/span\\u003e illustrates the switching behaviour of the device. The coloration time, defined as the time required to reach 90% of full coloration [\\u003cspan citationid=\\\"CR32\\\" class=\\\"CitationRef\\\"\\u003e32\\u003c/span\\u003e], was determined to be 14 seconds, while the bleaching time, corresponding to 90% of full bleaching, [\\u003cspan citationid=\\\"CR32\\\" class=\\\"CitationRef\\\"\\u003e32\\u003c/span\\u003e] was 35 seconds.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eColoration efficiency (CE) is a key parameter used to evaluate the performance of an electrochromic device. It measures how effectively the device changes its optical density (i.e., how much it darkens or tints) per unit of electrical charge injected or extracted [\\u003cspan additionalcitationids=\\\"CR27\\\" citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e26\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e][\\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e33\\u003c/span\\u003e].\\u003cdiv id=\\\"Equ5\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ5\\\" name=\\\"EquationSource\\\"\\u003e\\n$$CE=\\\\frac{\\\\varDelta\\\\text{O}\\\\text{D}}{Q}$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e6\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eWhere, \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\varDelta\\\\text{O}\\\\text{D}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e is optical density and Q is amount of charge inserted or extracted.\\u003c/p\\u003e \\u003cp\\u003eThe CE was calculated from the slope of the linear region of the optical density versus charge density curve, as shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig8\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003e. The CE of the thin film\\u0026ndash;free electrochromic device was determined to be 66 cm\\u0026sup2;/C at a wavelength of 648 nm, which falls within the typical range reported for WO₃-based electrochromic devices \\u003cb\\u003e(\\u003c/b\\u003e30\\u0026ndash;100 cm\\u0026sup2;/C\\u003cb\\u003e).\\u003c/b\\u003e These results confirm that the film-free electrochromic device can achieve coloration efficiency comparable to conventional devices.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cem\\u003eTo evaluate the stability and repeatability of the device, transmittance variations were recorded during consecutive coloring and bleaching cycles. This was achieved by periodically switching the applied potential between 0 V and 3 V to alternate the device between colored and bleached states. Measurements were taken at 60-second intervals during the coloration process.\\u003c/em\\u003e Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e10\\u003c/span\\u003e \\u003cem\\u003epresents the transmittance changes observed at a wavelength of 648 nm. The device showed noticeable changes in stability during the first three cycles, after which the transmittance stabilized, indicating\\u003c/em\\u003e Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig10\\\" class=\\\"InternalRef\\\"\\u003e11\\u003c/span\\u003e: Cyclic Voltammetry (scan rate 10 mVs-1)\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec11\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.2 Comparative Analysis of thin-film free electrochromic device with traditional thin film electrochromic device\\u003c/h2\\u003e \\u003cp\\u003eThin-film-free electrochromic devices represent a promising alternative to traditional counterparts, particularly in applications requiring flexibility, reduced fabrication cost, shorter processing time, and scalability. Despite these advantages, challenges such as long-term stability, material optimization, and commercial viability remain to be addressed. The following tables present a comparative analysis of traditional electrochromic devices and emerging thin-film-free electrochromic devices, with focus on device structure, time consumption, cost and finally device performance.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 1\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eStructural comparison of traditional electrochromic devices with novel thin film free electrochromic devices\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"3\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eComponent\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eTraditional ECD\\u003c/p\\u003e \\u003cp\\u003e(Thin-Film -Based)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eNovel ECD\\u003c/p\\u003e \\u003cp\\u003e(Thin-Film-Free)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eWorking Electrode\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eFTO glass coated with WO\\u003csub\\u003e3\\u003c/sub\\u003e or similar EC material\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eRequires thin-film deposition\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eBare FTO Glass\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo thin-film deposition needed\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCounter Electrode\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eFTO glass coated with CeO\\u003csub\\u003e2\\u003c/sub\\u003e\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eRequire thin-film deposition\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eBare FTO Glass\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo thin-film deposition needed\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eElectrolyte\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eLiquid, Gel or Solid\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLiquid\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eConventional ECDs typically depend on thin-film-coated electrodes. The working electrode comprises an electrochromic material deposited onto a transparent conductive substrate, while the counter electrode often includes a thin film of Tin oxide (SnO₂) or Cerium oxide (CeO₂) coated on a similar substrate. In contrast, the thin-film-free electrochromic device (TFF-ECD) introduces a novel design that completely eliminates the need for thin-film coatings on both the working and counter electrodes (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e). In traditional ECDs, color change arises from the insertion of small cations such as H⁺, Li⁺, Na⁺, or K⁺ into the electrochromic material\\u0026rsquo;s lattice under an applied voltage [\\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e7\\u003c/span\\u003e, \\u003cspan additionalcitationids=\\\"CR35 CR36 CR37 CR38\\\" citationid=\\\"CR34\\\" class=\\\"CitationRef\\\"\\u003e34\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR39\\\" class=\\\"CitationRef\\\"\\u003e39\\u003c/span\\u003e]. Conversely, the TFF-ECD demonstrates in situ formation of a blue coloration near the working electrode when a modest voltage is applied across bare FTO electrodes. This simplifies the device architecture and mitigates many fabrication challenges associated with thin-film processes.\\u003c/p\\u003e \\u003cp\\u003eFabrication methods play a pivotal role in determining the scalability and commercial viability of ECDs. Traditional thin-film-based devices involve multi-step deposition processes requiring specialized vacuum equipment. The TFF-ECD approach eliminates these deposition steps entirely, substantially reducing both fabrication time and complexity. Table\\u0026nbsp;\\u003cspan refid=\\\"Tab2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e provides a comparative analysis of the fabrication times between conventional thin-film-based and thin-film-free electrochromic devices.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab2\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 2\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eComparison of time consumption for device fabrication process\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"3\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003eCleaning FTO glasses\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eTraditional ECD\\u003c/p\\u003e \\u003cp\\u003e(Thin-Film -Based)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eNovel ECD\\u003c/p\\u003e \\u003cp\\u003e(Thin-Film-Free)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e30\\u0026ndash;45 min\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e30\\u0026ndash;45 min\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCoating of EC material\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1\\u0026ndash;3 hours\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eIncluding preparation of solution / slurry\\u0026thinsp;+\\u0026thinsp;coating\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e0 min\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo coating required\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAnnealing / Heat Treatment\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1\\u0026ndash;2 hours\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eDepend on coating method \\u0026amp; temperature\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e0 min\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo thermal processing needed\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003ePreparation of electrolyte\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1\\u0026ndash;2 hours\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eGel based and solid electrolyte can take longer\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e45 min\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eSolution preparation and pH adjustment\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eDevice Assembly\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e15\\u0026ndash;30 min\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e15\\u0026ndash;20 min\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003eTotal Fabrication Time\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e~\\u0026thinsp;4\\u0026ndash;8 hours or much longer\\u003c/b\\u003e\\u003c/p\\u003e \\u003cp\\u003e\\u003cem\\u003eDepending on method \\u0026amp; materials\\u003c/em\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e~\\u0026thinsp;1\\u0026ndash;2 hours\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe cleaning time for FTO glass remains the same for both device types, as it must be ultrasonically cleaned to remove surface contaminants. In traditional electrochromic devices, thin films are typically deposited on both the counter and working electrodes using techniques such as spin coating, sol-gel processing, sputtering, chemical vapor deposition, and doctor blading. In contrast, TFF-ECDs eliminate the film deposition step entirely, resulting in significant time savings.\\u003c/p\\u003e \\u003cp\\u003eAdditionally, conventional electrochromic films require an annealing process to stabilize their structure, typically involving high temperatures (300\\u0026ndash;500\\u0026deg;C) and lasting 1\\u0026ndash;2 hours. Thin-film-free devices avoid this step, as no films are deposited. Regarding electrolytes, traditional devices may use liquid, gel, or solid forms. Preparing gel or solid electrolytes requires precise polymerization or solid-state synthesis, which can be time-consuming. In this study, the electrolyte was prepared by dissolving sodium tungstate in distilled water and adjusting the pH with 2 M HNO\\u003csub\\u003e3\\u003c/sub\\u003enitric acid; a process that takes approximately 30 minutes and offers a clear time advantage. The total fabrication time for traditional electrochromic devices can exceed 8 hours, depending on the thin-film deposition technique used. In contrast, TFF-ECD s can be completed within 2 hours, primarily due to the elimination of coating and annealing steps. The final assembly step of sandwiching the electrolyte between the working and counter electrodes requires the same amount of time for both device types.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab3\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 3\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eComparison of cost for device fabrication process\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"3\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCost\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eTraditional EC Device\\u003c/p\\u003e \\u003cp\\u003e(Thin-Film -Based)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eNovel EC Device\\u003c/p\\u003e \\u003cp\\u003e(Thin-Film-Free)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCleaning of FTO/ITO Glasses\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMedium\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003e(Require solvent, ultrasonic bath)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eMedium\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003e(same)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eFTO/ITO Glasses\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMedium\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eMedium \\u003cb\\u003e(\\u003c/b\\u003e\\u003cb\\u003esame\\u003c/b\\u003e\\u003cb\\u003e)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eElectrochromic Material\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003e(WO\\u003c/b\\u003e\\u003csub\\u003e\\u003cb\\u003e3\\u003c/b\\u003e\\u003c/sub\\u003e \\u003cb\\u003eor other EC material needed)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eNone\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo EC material used\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCoating process\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003e(Requires spin coating, sputtering, etc)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eNone\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo coating process required\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAnnealing / Heat treatment\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003e(Furnace usage increases cost)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eNone\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eNo heat treatment needed\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eElectrolyte\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMedium\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eMedium \\u003cb\\u003e(\\u003c/b\\u003e\\u003cb\\u003esame\\u003c/b\\u003e\\u003cb\\u003e)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAssembly \\u0026amp; Components\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMedium\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eSpacer, sealants, labor\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eMedium\\u003c/p\\u003e \\u003cp\\u003e\\u003cem\\u003eSame\\u003c/em\\u003e \\u003cb\\u003e(Similar components used)\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eTotal Fabrication Cost\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eMaterials\\u0026thinsp;+\\u0026thinsp;equipment's\\u0026thinsp;+\\u0026thinsp;energy\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eComparatively Low\\u003c/p\\u003e \\u003cp\\u003e\\u003cb\\u003eFTO cost is the main contributor\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe comparison of the cost associated with the device fabrication process of the thin-film based electrochromic devices and the thin-film based electrochromic devices was shown in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e. Traditional ECDs involve a complex, multi-step fabrication process and high-cost materials such as WO\\u003csub\\u003e3\\u003c/sub\\u003e and CeO\\u003csub\\u003e2\\u003c/sub\\u003e. In contrast, the novel thin film-free approach presented here drastically reduces the costs by eliminating expensive steps like thin film deposition and thermal annealing process. Both traditional and TFF-ECDs rely on FTO or Indium-doped Tin Oxide (ITO) glass as a transparent conductive substrate. Therefore, cost remains the same across both devices.\\u003c/p\\u003e \\u003cp\\u003eThe conventional electrochromic materials require electrochromic materials to prepare a working electrode, and CeO\\u003csub\\u003e2\\u003c/sub\\u003e like materials to prepare a counter electrode. The deposition of electrochromic film onto FTO substrate is done through specialized techniques such as sputtering, spin-coating, chemical vapour deposition, and screen printing, etc. Each and every process needs expensive equipment, precise control, and trained labourers. Heat treatment of the coated substrate is essential to enhance the crystallinity and adhesion of the electrochromic film. The annealing process requires a temperature between 300\\u0026ndash;500 \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(℃\\\\)\\u003c/span\\u003e\\u003c/span\\u003efor 1\\u0026ndash;2 hours. These high energy consumption increases the fabrication cost. In contrast, the thin-film-free ECD omits the requirements of electrochromic materials, film deposition methods, and annealing process entirely. This leads to cost and material savings. Both device types should require an electrolyte. Therefore, cost associated with the electrolyte can be the same. However, the cost of preparation of electrolyte for the conventional electrochromic device can be higher, if it uses ionic liquid-like materials. Both ECDs require basic assembly components like spacers and sealant. So the cost associated with the fabrication is the same. When considering all these factors, the cost associated with the total fabrication process is comparatively lower in TFF-ECDs. It makes a TFF-ECD promising for scalable applications.\\u003c/p\\u003e \\u003cp\\u003eThe Table\\u0026nbsp;\\u003cspan refid=\\\"Tab4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e summarizes the performance comparison between conventional ECDs, fabricated using layered working and counter electrodes, and our film-free WO₃-based ECD.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab4\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 4\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eComparison of electrochromic performance\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"9\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c6\\\" colnum=\\\"6\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c7\\\" colnum=\\\"7\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c8\\\" colnum=\\\"8\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c9\\\" colnum=\\\"9\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eWorking Electrode\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eApplied Voltage (V)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eT\\u003csub\\u003eb (s)\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eT\\u003csub\\u003ec (s)\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eOptical Contrast (\\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\varDelta\\\\)\\u003c/span\\u003e\\u003c/span\\u003eT)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003eColoration Time\\u003c/p\\u003e \\u003cp\\u003e(t\\u003csub\\u003ec\\u003c/sub\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003eBleaching Time (t\\u003csub\\u003eb\\u003c/sub\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003eColoration Efficiency\\u003c/p\\u003e \\u003cp\\u003e(cm\\u003csup\\u003e2\\u003c/sup\\u003e/C)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003eRef\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003enWO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e3.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e72\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e38\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e34\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e10\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAgNW-WO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e3.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e72\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e29\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e43\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e18\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eWO\\u003csub\\u003e3\\u003c/sub\\u003e microparticle film\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e-9.0 to 0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e76.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e12.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e58.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eWO\\u003csub\\u003e3\\u003c/sub\\u003e nanoparticle film\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e-1.5 to 0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e52\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e10\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e34.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eMesoporous WO\\u003csub\\u003e3\\u003c/sub\\u003e film\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e-0.6 to 0.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e75.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e2.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e79.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAmorphous WO\\u003csub\\u003e3\\u003c/sub\\u003e film\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e-2.5 to 2.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e45.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e17\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e63\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eWO\\u003csub\\u003e3\\u003c/sub\\u003e dispersed film\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e-0.9 to 0.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e77.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e15\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e62.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eA porous film of WO\\u003csub\\u003e3\\u003c/sub\\u003e @ PEO fibers\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e-2 to 1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e39.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e1.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e61.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eSol-gel titania film\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e+\\u0026thinsp;0.1 to \\u0026ndash; 1.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e60\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e55\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e10\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e55.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eSpin-coated WO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0 to -1.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e71.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e14\\u003c/p\\u003e 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nanosheet\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e40\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e63.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eNiO / Ag / NiO\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e70\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e76.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eSilver nanowire /NiO\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e15\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e51.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e[\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e]\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003eFilm free\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e0 V \\u0026minus;\\u0026thinsp;3 V\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e98.17\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e10.72\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e87.45\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e14\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e35\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e66\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003eThis paper\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe performance of the electrochromic device is another important parameter for the scalability of ECDs. Traditional electrochromic devices show optimal modulation in the range of 60\\u0026ndash;80% and optical density in the range of 0.5\\u0026ndash;0.8, which depends on the film thickness, morphology, and ion insertion depth. In the thin-film free approach, optical modulation was obtained as 87.5%, and optical density was obtained as 0.96. This is higher than the OD obtained for the conventional electrochromic devices. The coloration efficiency of this novel electrochromic device lies within the range of conventional ECDs. This shows fast coloration but somewhat lower bleaching time.\\u003c/p\\u003e \\u003cp\\u003eThe conventional ECD consists of a thin film of electrochromic material coated electrode. These films can be cracked over time. Due to high-expense coating methods, the scalability of conventional ECDs is limited. However, the thin film-free approach, hasn\\u0026rsquo;t thin film coating there for no degradation happens, and it becomes highly scalable.\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"4. Conclusions\",\"content\":\"\\u003cp\\u003eThis study presents a novel approach to ECD fabrication by demonstrating reversible electrochromic behavior through a liquid-phase reaction between dual FTO glass substrates, eliminating the need for conventional solid-state electrochromic films. A distinct blue coloration was achieved upon applying 3 V, with the device exhibiting a high optical modulation of 87.5% and an optical density of 0.96 at 648 nm. The coloration efficiency reached 66.7 cm\\u0026sup2;/C, highlighting efficient charge utilization, while the switching times of 14 s for coloration and 35 s for bleaching confirm favorable electrochemical dynamics.\\u003c/p\\u003e \\u003cp\\u003eImportantly, the fabrication process entirely bypasses the use of electrochromic materials, thin-film deposition, and thermal treatment, significantly reducing both production cost and time. This thin-film-free architecture not only overcomes key limitations of conventional ECDs but also enables scalable, rapid, and low-cost manufacturing.\\u003c/p\\u003e \\u003cp\\u003eOverall, the successful development of this liquid-electrolyte-based, film-free ECD offers a promising pathway toward sustainable electrochromic technologies, contributing to enhanced energy efficiency, reduced environmental impact, and advancement of next-generation smart devices.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003ch2\\u003eAuthor Contribution\\u003c/h2\\u003e\\u003cp\\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by S.M.P.M.K, H.N.M. , and E.G.O.D. . The first draft of the manuscript was written by S.M.P.M.K, E.G.O.D. and H.N.M. and all authors commented on previous versions of the manuscript. Laboratory facilities were provided by H.M.B.I. and G.M.L.P. All authors read and approved the final manuscript.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\u003cli\\u003e\\u003cspan\\u003eDingari M, Reddy DM, Sumalatha V et al (2020) Recent Studies in Mathematics and Computer Science. Recent Stud Math Comput Sci 3 3. \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.9734/bpi/rsmcs/v3\\u003c/span\\u003e\\u003cspan address=\\\"10.9734/bpi/rsmcs/v3\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eAn DK, Jeon SJ (2024) Improved Coloration Efficiency and Stability of WO3 Electrochromic Devices by the Addition of Silver Nanowires. 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Eur J Sci Technol 718\\u0026ndash;722. \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.31590/ejosat\\u003c/span\\u003e\\u003cspan address=\\\"10.31590/ejosat\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"journal-of-applied-electrochemistry\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"jach\",\"sideBox\":\"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)\",\"snPcode\":\"10800\",\"submissionUrl\":\"https://submission.nature.com/new-submission/10800/3\",\"title\":\"Journal of Applied Electrochemistry\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"em\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false},\"keywords\":\"Electrochromic, Fluorine–doped tin oxide, optical modulation, optical density, coloration efficiency\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-9123105/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-9123105/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eElectrochromic devices (ECDs) are widely used in smart windows, displays, and mirrors for dynamic light control, but conventional thin-film electrodes are costly and complex to fabricate. This study presents a film-free electrochromic device that eliminates the need for electrochromic coatings on transparent conductive oxide substrates. The device consists of an acidified sodium tungstate (Na₂WO₄\\u0026middot;2H₂O) electrolyte sandwiched between two bare FTO glass electrodes. Upon applying a low voltage of 3 V, a reversible blue coloration forms in situ near the working electrode and disappears when the voltage is removed, restoring transparency. At pH 1.5, when applying 3 V, transmittance measurements reveal an optical modulation of 87.45% and an optical density of 0.96 at 648 nm wavelength, confirming the device's excellent optical performance. The response times for coloration (14 s) and bleaching (35 s) indicate good switching dynamics. The devices show a high coloration efficiency of 66.7 cm\\u003csup\\u003e2\\u003c/sup\\u003e/C at 648 nm wavelength. These findings highlight the excellent performance of the device and demonstrate that eliminating the thin-film coating process not only simplifies fabrication but also enables the development of film-free electrochromic devices as high-performance alternatives for next-generation electrochromic applications.\\u003c/p\\u003e\",\"manuscriptTitle\":\"A Thin-Film-Free Electrochromic System Based on Dual Conductive Glass Electrodes and Sodium Tungstate Electrolyte\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2026-05-13 07:00:06\",\"doi\":\"10.21203/rs.3.rs-9123105/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2026-05-07T21:39:39+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"88855391039906839956335125764334662405\",\"date\":\"2026-05-05T06:50:12+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"\",\"date\":\"2026-05-05T04:29:02+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorAssigned\",\"content\":\"\",\"date\":\"2026-03-22T15:16:44+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"checksComplete\",\"content\":\"\",\"date\":\"2026-03-16T08:28:59+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"submitted\",\"content\":\"Journal of Applied Electrochemistry\",\"date\":\"2026-03-14T13:45:47+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"journal-of-applied-electrochemistry\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"jach\",\"sideBox\":\"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)\",\"snPcode\":\"10800\",\"submissionUrl\":\"https://submission.nature.com/new-submission/10800/3\",\"title\":\"Journal of Applied Electrochemistry\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"em\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false}}],\"origin\":\"\",\"ownerIdentity\":\"91d8e739-1d00-4964-8cf0-20abf3fe20ac\",\"owner\":[],\"postedDate\":\"May 13th, 2026\",\"published\":true,\"recentEditorialEvents\":[{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2026-05-07T21:39:39+00:00\",\"index\":11,\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"88855391039906839956335125764334662405\",\"date\":\"2026-05-05T06:50:12+00:00\",\"index\":10,\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"6\",\"date\":\"2026-05-05T04:29:02+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"under-review\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2026-05-13T07:00:07+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2026-05-13 07:00:06\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-9123105\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-9123105\",\"identity\":\"rs-9123105\",\"version\":[\"v1\"]},\"buildId\":\"XKTyCvWXoU3ODBz1xrDgd\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}