WO2023236327A1

WO2023236327A1 - Flexible electrochromic film and preparation method therefor

Info

Publication number: WO2023236327A1
Application number: PCT/CN2022/107893
Authority: WO
Inventors: 弗罗恩阿恩; 卡尔奥古斯丁; 斯凯宁阿尔伯特; 胡小文; 周国富
Original assignee: 克莱梅得科技有限公司; 深圳市国华光电科技有限公司
Priority date: 2022-06-10
Filing date: 2022-07-26
Publication date: 2023-12-14
Also published as: CN115185107A

Abstract

A flexible electrochromic film and a preparation method therefor. The electrochromic film sequentially comprises, from bottom to top, a substrate, a conductive heating layer and a thermochromic coating; raw materials for the conductive heating layer comprise a conductive material and ink containing a polymer binder; the thermochromic coating is based on a photonic material or a thermochromic material; there is at least one conductive heating layer. The flexible electrochromic film based on the thermochromic coating and the adjustment of electrothermally driven optical characteristics has high transparency, and can be manufactured by means of an extensible coating technique, and a roll-to-roll production mode can be implemented.

Description

Flexible electrochromic film and preparation method thereof

Technical field

The invention relates to the field of organic optoelectronics, and in particular to a flexible electrochromic film and a preparation method thereof.

Background technique

Thermochromic devices can change their optical properties when exposed to thermal stimuli and have broad potential in a variety of applications, including sensors, smart windows, and anti-counterfeiting labels. Although its optical properties change automatically in response to thermal fluctuations, devices that respond through electrical manipulation may be more user-friendly. A quick and efficient way to do this is to use electrothermal stimulation, which causes an increase in temperature when a current or voltage is applied to a conductive system; the heat generated depends on the current flowing through the conductor, allowing precise control of the electrothermal stimulation. Therefore, thermally sensitive systems can be equipped with heating elements that can exceed the initial thermal response caused by ambient temperature, even allowing for localized heating when using patterned electrodes. Although research in electrothermally driven photonic devices holds great promise, one of the major challenges in this field is the development of highly flexible, transparent systems that can display multi-color tuning, which is attractive for display and window applications.

Most reports on electrochromic devices use thermochromic dyes or polymers, which can only switch between colored, colorless, or an intermediate state between the two states when electrothermal stimulation is applied. Due to lower optical quality, these systems are limited to non-transparent devices. However, recent advances have enabled electrothermally driven structural color-tunable systems, but these systems are limited to rigid, transparent or flexible, opaque device structures. Furthermore, generalization to large-area applications remains quite difficult due to the need for scalable processes. To establish electrothermally driven polychromatic photonic systems with high transparency and flexibility, integrated heaters with limited impact on the above characteristics should be used.

Transparent heaters consist of a thin film conductive layer that effectively induces Joule heating when a current or voltage is applied to the surface area of the conductive layer, resulting in a rapid, controllable heating rate. Currently, transparent conductive oxides, especially indium tin oxide, are the most important conductive materials for making transparent heaters, but their use is limited due to their limited mechanical flexibility. After intensive research, a variety of conductive materials have been developed that can be used as energy-saving heaters. Silver nanowires (AgNWs) have attracted special attention in this field because their integrated transparent heaters combine high optical transparency with low sheet resistance through their permeable network. Furthermore, these metallic nanowires can be solution-processed on plastic substrates, allowing the fabrication of flexible heaters through a variety of processes, such as spray coating, screen printing, and inkjet printing. Integrating metal nanowires into devices requires good adhesion between the substrate and the nanowires, so polymeric materials can be added to such inks to form an encapsulating film after deposition to promote uniform heating.

To obtain thermochromic devices, one can utilize inorganic nanocrystals, organic dyes, or hydrogels that undergo phase transitions upon temperature fluctuations. Photonic structures based on hydrogels or block copolymers can also be used to achieve thermochromic responses. Another class of materials commonly used to achieve thermochromic structural color changes is cholesteric liquid crystals (CLC). Due to the periodic helical structure of liquid crystal molecules, CLC can reflect circularly polarized light in a specific wavelength range and specific chirality. The central wavelength of the reflection band depends on the pitch length, which is defined by the periodicity of the superimposed spiral. When using thermochromic CLC mixtures, the initial reflection color can be changed by shortening or widening the pitch length due to the reorganization of the helices upon heating and cooling. Thermochromic CLC coatings can be obtained through a variety of methods, such as polymer dispersed liquid crystals (PDLC), side chain or main chain liquid crystal polymers, or by creating individual substrate units. In the PDLC method, a heat-sensitive low molecular weight liquid crystal mixture is encapsulated in droplets and added to a polymer binder to obtain a strong thermochromic coating. Microcapsules containing thermochromic CLC materials can also be prepared. These microcapsules can be mixed with a curable binder and used as a coating. Thermochromic liquid crystalline polymer systems, such as polysiloxane-based systems or backbone oligomers, can also be coated directly on rigid or flexible substrates. These systems often require the addition of a polymer network or the application of a topcoat to produce a mechanically robust coating system. This protective topcoat can also be obtained through directionally controlled photoinduced phase separation (PIPS). In this system, the polymerizable monomer is partially incompatible with the non-reactive liquid crystal and migrates to the coating-air interface during the photopolymerization process to form a hard topcoat. Ultimately, an acrylic polymer topcoat forms, protecting the underlying thermochromic, non-reactive CLC portion.

The existing technology includes a variety of electrothermal-driven color-changing systems. Currently, these devices, which change their optical properties through electrothermal stimulation, lack flexibility or transparency due to their structure. For example, films containing thermochromic pigments can be applied to patterned electrodes to locally heat the film when a voltage is applied. Despite demonstrating flexibility, such systems are not suitable for transparent applications due to the lower optical quality due to the absorbance properties of the pigments. Furthermore, these pigments are limited to changes between colored and non-colored opaque states, making multicolor adjustment impossible. In addition, polymers containing thermochromic fluorescent moieties or that display color changes through thermally induced conformational changes can also be used. These polymers can be coated around conductive fibers or printed as inks on conductive electrodes. However, these polymers can only switch between two color states and, like thermochromic pigments, lack the optical qualities for use in transparent devices.

To achieve electrothermal color tuning, thermochromic photonic systems such as photonic block copolymers, elastic inverse opals, and cholesteric liquid crystals can be used. These materials display reflective structural colors that can be changed into various colors by temperature changes or electrothermal stimulation. Despite the variety of electrothermally driven photonic devices, current systems are limited to rigid, transparent or flexible, opaque device forms. However, combining the flexibility and transparency of electrochromic photonic devices remains challenging due to poor mechanical or optical properties of one or more layers in multilayer devices. When these materials are applied to a rigid substrate such as glass with conductive electrodes, an electrothermal response may be produced. Although these materials have been used to fabricate transparent electrothermally driven color-changing devices, they have not yet been applied to flexible substrates, thus limiting the scope of applications of these systems. Some examples show electrothermally driven photonic color-changing devices on flexible substrates, but these devices are opaque and cannot be prepared using coating techniques that enable large-area applications. For example, fabrication using complex pixel structures, multi-layer spin-coating processes, or including photonic inverse opal hydrogels that require deposition in molds and chemical etching steps.

And so far, such thermochromic coatings have never been integrated with transparent conductive heating layers on flexible substrates to induce electrothermal modulation of optical properties and create electrochromic flexible thin film devices.

Therefore, there is an urgent need to find a technical solution to solve the technical problems in this field.

Contents of the invention

The technical solution of the present invention discloses a flexible electrochromic film based on a thermochromic coating and electrothermally driven optical property adjustment. It has high transparency, can be manufactured through scalable coating technology, and can realize roll-to -roll production method. The invention also discloses a method for preparing the above-mentioned flexible electrochromic film.

An object of the present invention is to provide a flexible electrochromic film, which sequentially includes a substrate, a conductive heating layer and a thermochromic coating from bottom to top;

in,

The raw materials of the conductive heating layer include conductive materials and inks containing polymer binders;

The raw materials of the thermochromic coating include thermochromic materials;

The conductive heating layer is at least one layer.

Preferably, the polymer binder may be, but is not limited to, one or more of polyvinyl alcohol, polyvinyl butyral or polyimide.

Further, the substrate is selected from a flexible film, and the optional object of the flexible film is selected from one or more of polyethylene terephthalate, bidirectionally oriented polypropylene or polycarbonate.

Further, in the conductive heating layer, the conductive material is selected from one or more of metal nanomaterials, carbon nanomaterials, graphene materials, and ITO materials.

The shape or form of the above-mentioned materials may be, but is not limited to, granular, tubular, strip, linear, etc. The above metals may be, but are not limited to, gold, silver, copper, aluminum, platinum, iron, or an alloy of two or more of the above metals.

Preferably, the conductive material may include, but is not limited to, silver nanowires, gold particles, graphene particles, etc.

Further, the thermochromic material is selected from the group consisting of cholesteric liquid crystals, photonic block copolymers, photonic particle arrays, photonic inverse opal structures, and distributed Bragg reflectors;

The thermochromic material is selected from thermochromic inorganic materials.

Further, the conductive heating layer is continuous.

Further, the conductive heating layer is patterned.

Further, the base is flexible.

Further, the flexible electrochromic film further includes an additional layer, and the additional layer is selected from one or more of an adhesive layer or a protective topcoat.

Another object of the present invention is to provide a method for preparing the above-mentioned flexible electrochromic film. The preparation method includes the following steps:

Preparation of thermochromic coatings

S1. Mix photonic materials or thermochromic materials, acrylic acid derivatives and photoinitiators, heat the reaction, and obtain an intermediate;

S2. Apply the above intermediate on the conductive heating layer and perform photocuring.

The acrylate derivatives described in the present invention can be, but are not limited to, monoacrylate and diacrylate. The monoacrylate can be, but is not limited to: methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate; the diacrylate can be, but is not limited to: ethylene glycol diacrylate, diacrylate Propylene glycol diacrylate, methyl diacrylate, ethyl diacrylate.

The photoinitiator described in the present invention is generally an initiator commonly used in free radical polymerization of acrylic derivatives, such as benzoyl peroxide.

Further, in S1, the photonic material is made by mixing nematic liquid crystal and chiral dopant.

Further, in S2, the application method is selected from coating, rod coating, spin coating, knife coating, slot die coating, knife coating, reverse roller coating, transfer roller coating, spray coating, gravure printing, One or more of flexographic printing, offset printing, and screen printing.

Further, in S2, the photocuring step is: in an inert atmosphere, first cure the intermediate with an ultraviolet intensity of about 1.5mW/cm ² for 10-20 minutes; and then cure it with an ultraviolet intensity of about 20mW/cm ² 5-10min.

The invention has the following beneficial effects:

The technical solution of the present invention discloses a flexible electrochromic film based on a thermochromic coating and electrothermal driven optical property adjustment, which has high transparency; can be manufactured through scalable coating technology, and can realize roll-to-roll The production method has broad industrialization prospects.

Description of the drawings

Figure 1 shows the structure and working principle of the flexible electrochromic film according to Embodiment 1 of the present invention.

Figure 2(a) shows a schematic diagram of the flexible electrochromic film according to Embodiment 1 of the present invention;

Figure 2(b) shows the transmission spectrum of the electrochromic film of the flexible electrochromic film in Embodiment 1 of the present invention;

Figure 2(c) shows a voltage-temperature-wavelength schematic diagram of the flexible electrochromic film according to Embodiment 1 of the present invention.

Figure 3 shows the process and structural diagram of patterning a flexible electrochromic film.

Figure 4 shows the electrothermal response diagram of L1-L3 in Test Example 2.

Figure 5(a)-(b) respectively show the steady-state temperature of the PVA coating on the top of the conductive silver nanowire when the same voltage (U=4V or U=5V) amplitude is applied to the conductive silver nanowire pattern.

Figure 6(a)-(b) respectively show the reflection colors produced when the thermochromic PDLC coating on top of the conductive substrate is non-selectively heated (a: red, T=30=; b: green, T= 34 non);

Figures 6(c)-(e) respectively show that the localized reflected color is caused by electrothermal heating, depending on which conductive circuit is turned on.

Figures 6(f)-(g) respectively show that color patterns can be achieved by applying current on multiple conductive silver nanowire circuits.

Detailed ways

The concept of the present invention and the technical effects produced will be clearly and completely described below with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without exerting creative efforts are all protection scope of the present invention. Unless specifically mentioned, the reagents, materials or preparation methods used in the examples of the present invention should be regarded as commonly used methods in this technical field.

Example 1

A flexible electrochromic film, its structure from bottom to top is as shown in Table 1 below:

Table 1 Structure and related parameters of the flexible electrochromic film of Example 1

Among them, in the above structure, the conductive heating layer is continuous, and its raw materials are silver nanowires and ink containing polyvinyl alcohol as a polymer binder (TranDuctive N15, Genesink).

The raw material of the thermochromic coating is the photonic material cholesteric liquid crystal. This cholesteric liquid crystal is transformed from a nematic liquid crystal with a smectic phase.

The preparation method of the flexible electrochromic film of the above embodiment 1 is as follows:

P1. On PET (Melinex 506, thickness 100μm) substrate, gravure printing (specific preparation method is: printing speed of 0.5m/s, anilox roller force of 250N, anilox roller speed of 50%, and ink transfer Before going to the PET substrate, the anilox roller needs to undergo 3 pre-ink cycles) a layer of ink based on silver nanowires (<1wt%) containing polyvinyl alcohol as the polymer binder and cured in a 90°C oven for 5 minutes Evaporate the organic solvent to form a conductive heating layer to obtain a substrate (thickness <50 nm) containing the conductive heating layer;

P2. Apply an appropriate amount of conductive epoxy glue (Chemtronics, CW2400) to both edges of the substrate containing the conductive heating layer to ensure good electrical contact;

P3. Provide an input voltage to the above-mentioned substrate containing the conductive heating layer, so that the substrate containing the conductive heating layer generates Joule heat and increases the temperature in a stepwise manner. The input voltage values are set to 2, 4, 6, 8 and 10V respectively. Correspondingly, the steady-state temperature of the substrate containing the conductive heating layer reaches 25, 32, 40, 51 and 62°C respectively within 30S. Increasing temperature will cause the resistance of the conductive heating layer to decrease. In order to prevent the silver nanowires from melting at high temperatures, the temperature should not exceed 120°C;

In addition, step P3 in Embodiment 1 can be performed once, twice and three times respectively to obtain one, two and three conductive heating layers respectively. The more conductive heating layers, the lower the corresponding resistance. For example, the resistance of two conductive heating layers is approximately 11.8±0.2Ωsq ^-1 ; while the resistance of three conductive heating layers is approximately 7.4±0.04Ωsq ^-1 ;

P4. Preparation of thermochromic coating

S1. Mix the photonic material nematic liquid crystal (Merck MLC 2138) (35wt%) and the chiral dopant (Merck S811) (15wt%) to obtain a precursor;

S2. Add photoinitiator (Ciba Irgacure 651) (0.5wt%), stilbene diacrylate (5wt%) and isobornyl methacrylate (44.5wt%) to the above precursor (50wt%), and heat to Stir for 30 minutes at 40°C to obtain the intermediate; during the heating process, since the nematic liquid crystal is heated and changes into cholesteric liquid crystal, a temperature-responsive material can be formed on the conductive heating layer;

S3. Use a wire bar coater with a gap height of 80 μm to bar-coat the above-mentioned intermediate on the conductive heating layer as a rough coating. In order to induce polymerization to induce phase separation and form a rigid topcoat, the rough coating is placed at 54 ℃ of nitrogen environment with 1.5mW/cm ² ultraviolet light (light source equipment: EXFO Omnicure S2000) intensity for 20 minutes; then, curing again under the condition of 20mW/cm ² (light source equipment: EXFO Omnicure S2000) for 5 minutes to obtain thermally induced Color-changing coating (approximately 25-30μm), which is done to induce light-induced phase separation and form a rigid topcoat.

Among them, for the specific chemical structure of stilbene diacrylate, please refer to the literature (Nature, 2002, 417, 55-58)

Relevant tests: Conduct an electrochromic test on the flexible electrochromic film obtained in Example 1 above.

When the applied voltage to the flexible electrochromic film increases from 0V to 3V, the reflection band of the electrochromic film appears at around 850nm; further, when the applied voltage increases to 6.5V, the reflection band of the electrochromic film shifts blue. to about 450nm. The above process is reversible when the thermochromic material is in the cholesteric phase. At this time, after the external voltage is removed, the electrochromic film will return to its original colorless state;

When the applied voltage further increases to 7.5V, the temperature of the electrochromic film rises above the cholesteric-isotropic transition temperature (about 60°C), and the color change is irreversible at this time.

The electrothermal-induced reflection band can be retained upon bending, showing stable electrothermal performance.

Figure 1 shows the structure and working principle of a flexible electrochromic film according to Embodiment 1 of the present invention, and its conductive heating layer has a high degree of transparency. A conductive heating layer is applied on top of the substrate; the integrated heater is in contact with a thermochromic coating applied on the conductive heating layer. When a current is applied to the system (U _on ), modulation of the optical properties of the thermochromic coating can be observed.

Figure 2(a) shows a schematic diagram of the flexible electrochromic film according to Embodiment 1 of the present invention. It can be seen that a flexible, transparent silver nanowire/PET heater induces reflection band movement under electrical stimulation. In the absence of electrical stimulation (U _off ), the transparent foil remains colorless at room temperature but can display reflective color when voltage is applied (U _on );

Figure 2(b) shows the transmission spectrum of the electrochromic film of the flexible electrochromic film of Embodiment 1 of the present invention, showing the electrothermal-induced reflection band movement when adjusting the input voltage;

Figure 2(c) shows a voltage-temperature-wavelength schematic diagram of the flexible electrochromic film of Example 1 of the present invention, showing the reflection band deflection when changing the voltage amplitude (blue) or heating the sample with a hot plate (red) Shift comparison.

Example 2

In this embodiment, first, two methods, gravure printing and rod coating, are tried to prepare the conductive heating layer of the flexible electrochromic film.

(1) Gravure printing method:

Apply Kapton tape (thickness = 50 μm) to the substrate surface to create a patterned conductive circuit (the width of the three conductive lines are set to L1 = 7 mm, L2 = 4 mm, and L3 = 2 mm, respectively, and separated by Kapton tape); on PET (Melinex 506, thickness 100μm) substrate, gravure printing (specific preparation method: printing speed of 0.5m/s, anilox roller force of 250N, anilox roller speed of 50%, and transfer the ink to the PET substrate Previously, the anilox roller required 3 pre-ink cycles) a layer of ink based on silver nanowires (<1wt%) containing polyvinyl alcohol as polymer binder and cured in a 90°C oven for 5 min to evaporate the organic solvent ; Thereby, the area without tape is filled with ink, and after drying, a conductive heating layer is formed to obtain a substrate containing a conductive heating layer (thickness <50nm); finally, the tape is removed. The relevant processes and structures are shown in Figure 3.

The above steps can be performed multiple times to reduce the resistance of the conductive heating layer.

The resistances of the conductive heating layers prepared by gravure printing were recorded as R1-R3 respectively, and the resistances R1-R3 of L1-L3 after each printing were tested respectively. The obtained resistance data are shown in Table 2.

Table 2 Data of the resistance R1-R3 of the conductive heating layer after each printing of L1-L3

导电线conductive thread	宽度(mm)Width(mm)	R1(Ω)R1(Ω)	R2(Ω)R2(Ω)	R3(Ω)R3(Ω)
L1 L1	77	175175	7676	3333
L2 L2	44	320320	107107	5757
L3 L3	22	780780	295295	143143

Combining Table 2 and Figure 4, it can be seen that after three repeated subsequent gravure printing steps, R3 produces resistances of 33Ω, 57Ω and 143Ω respectively.

The reduction in the width of the conductive lines leads to an increase in resistance. Therefore, when voltage is applied to conductive patterns with different resistances, the temperature rise of the thinnest circuit (i.e., with the highest resistance) is smaller, and the electrothermal response is accordingly less significant. , the relevant electrothermal response is shown in Figure 4.

In order to study the electrothermal heating performance of each conductive circuit of L1-L3, a 15wt% aqueous solution containing polyvinyl alcohol (Merck, Mw=9.000-10.000g/mol, 80% hydrolysis) was drop-cast on the top of the patterned substrate. The deposited polyvinyl alcohol solution was left to dry to form a transparent coating (thickness = 120 μm). Each conductive line can be driven individually, allowing for localized heating when voltage is applied. When the conductive patterns were passed individually by current, they reached different steady-state temperatures. This is caused by resistance bias, for example the conductive pattern with the lowest resistance will show the highest steady-state temperature, as shown in Figure 5.

(2) Rod coating method

Kapton tape was attached to a 36 μm black PET (Tenolan OCN0003, 100 μm thickness) substrate to form a mask. Use silver nanowire ink (Transductive N15, Genesink) to conduct a bar coating (gap height = 80 μm) on the substrate, and then dry to form a thin film. After a single coating step, the resistance of the conductive lines is controlled in the range of 25-40Ω. Compared to gravure printing, lower resistance is achieved after a single coating step due to the larger volume deposited on the substrate during rod coating.

Then, further, a thermochromic emulsion was applied on the conductive heating layer obtained by the above-mentioned rod coating (gap height = 80 μm) method.

The relevant steps are: the thermochromic emulsion consists of a heat-sensitive cholesteric liquid crystal mixture dispersed in a PVA-based solution (15wt% aqueous solution) in the form of droplets (the mixture is composed of nematic liquid crystal (Merck E7, 70wt%) and hand The dopant (Merck S811, 30wt%) is dispersed in the form of droplets in a solution (15wt%) of PVA (80% hydrolyzed) and dried after rod coating to form a temperature-responsive polymer dispersed liquid crystal (PDLC). ) coating (thickness 12-18μm).

Relevant tests: The following tests were performed on the flexible electrochromic film prepared by the rod coating method in Example 2.

Colorful patterns are created through localized heating induced by patterned conductive circuits. The flexible substrate was patterned with conductive lines of the same width (3 mm).

Encapsulating cholesteric liquid crystal droplets with PVA adhesive can display reflective color changes when the temperature changes. When an external heater (hot plate) is used to heat the final device, reflective color appears in the PDLC coating when the smectic-cholesteric phase transition (29°C) temperature is exceeded.

At 30°C, all areas coated with emulsion on the substrate surface turned red, and at 34°C, they turned green (Figure 6(a)-Figure 6(b)). When a current is applied to a single conductive line, localized heating occurs, heating only the PDLC coating on top of that conductive circuit. Depending on the activated conductive circuit, reflective colors appear in different PDLC coatings (Figure 6(c)-Figure 6(e)). The small changes in applied voltage are due to slightly different ohmic resistances of the silver nanowire circuits. Finally, multiple conductive lines can be processed simultaneously (Figure 6(f)-(g)). When the appropriate voltage amplitude is applied to each conductor, the same reflected color is obtained. The reflected color is red-shifted near the edge of the PDLC coating. This is because the width of the PDLC coating is larger than the width of the silver nanowires, causing cooling near the edge of the PDLC coating. Therefore, these systems can also be used to monitor temperature distribution, allowing small temperature changes to be represented by different reflection colors (red = 30°C, green = 34°C, blue = 36°C).

The above-mentioned embodiments of the present invention are merely examples to clearly illustrate the present invention, and are not intended to limit the implementation of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. An exhaustive list of all implementations is neither necessary nor possible. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

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Claims

A flexible electrochromic film, characterized in that the flexible electrochromic film includes a substrate, a conductive heating layer and a thermochromic coating from bottom to top;

in,

The raw materials of the conductive heating layer include conductive materials and inks containing polymer binders;

The thermochromic coating is based on photonic materials or thermochromic materials;

The conductive heating layer is at least one layer.
The flexible electrochromic film according to claim 1, characterized in that the substrate is selected from a flexible film, and the optional object of the flexible film is selected from polyethylene terephthalate, bidirectionally oriented polypropylene or One or more types of polycarbonates.
The flexible electrochromic film according to claim 1, wherein in the conductive heating layer, the conductive material is selected from one or more of metal nanomaterials, carbon nanomaterials, graphene materials, and ITO materials.
The flexible electrochromic film according to claim 1, wherein the photonic material is selected from the group consisting of cholesteric liquid crystals, photonic block copolymers, photonic particle arrays, photonic inverse opal structures, and distributed Bragg reflectors;

The thermochromic material is selected from thermochromic inorganic materials.
The flexible electrochromic film according to claim 1, wherein the conductive heating layer is continuous.
The flexible electrochromic film of claim 1, wherein the conductive heating layer is patterned.
The flexible electrochromic film according to claim 1, characterized in that the flexible electrochromic film further includes an additional layer, the additional layer is selected from one or more of an adhesive layer or a protective topcoat. .
The preparation method of the flexible electrochromic film according to any one of claims 1 to 7, characterized in that the preparation method of the flexible electrochromic film includes the following steps:

Preparation of thermochromic coatings

S1. Mix photonic materials or thermochromic materials, acrylic acid derivatives and photoinitiators, heat the reaction, and obtain an intermediate;

S2. Apply the above intermediate on the conductive heating layer and perform photocuring.
The method for preparing a flexible electrochromic film according to claim 8, wherein in S1, the photonic material is made by mixing nematic liquid crystal and a chiral dopant.
The method for preparing a flexible electrochromic film according to claim 8, wherein in S2, the application method is selected from the group consisting of coating, rod coating, spin coating, knife coating, slot die coating, and doctor blade coating. One or more of coating, reverse roller coating, transfer roller coating, spray coating, gravure printing, flexographic printing, offset printing, and screen printing.