A fully printed patterned flexible electrochromic film and its preparation method

Abstract

This invention belongs to the field of electrochromic materials technology, specifically relating to a fully printed patterned flexible electrochromic film and its preparation method. The preparation method of the electrochromic film provided by this invention includes the following steps: firstly, conductive ink is inkjet-printed onto the surface of a flexible substrate to form a conductive layer; the conductive ink includes silver nanowires; secondly, protective ink is inkjet-printed onto the surface of the conductive layer to form a protective layer; the protective ink includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid; thirdly, color-changing material ink is inkjet-printed onto the surface of the protective layer to form a color-changing active layer; the color-changing material ink is an electrochromic polymer solution. By using computer-aided inkjet printing, the conductive layer and color-changing active layer materials are directly printed onto the surface of a flexible substrate without a mask or contact, resulting in a flexible electrochromic film with controllable structure, patternability, high repeatability, and personalization.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic materials technology, specifically relating to an electrochromic material and its preparation method. Background Art

[0002] Electrochromism refers to the stable and reversible change in transmittance, reflectance, or absorptivity in the ultraviolet, visible, or near-infrared regions under the influence of an applied electric field. This is visually manifested as a reversible change in the color and transparency of a material. Traditional electrochromic materials mostly use ITO conductive glass as electrodes. However, with the rise of new materials in recent years, such as polymer-based curved curtain wall glass, chameleon-like fabrics, and electronic tags, the fabrication of flexible electrochromic devices using flexible substrates has received wider attention.

[0003] Fabricating electrochromic materials on flexible substrates not only expands the application areas that electrochromic materials on rigid substrates could not reach, but also greatly increases the design freedom of electrochromic materials. However, when using traditional screen printing methods to fabricate electrochromic materials on flexible substrates, the process is complex and it is difficult to control the shape and size of the color-changing pattern. Therefore, how to fabricate high-quality electrochromic films on flexible substrates has become an urgent problem to be solved.

[0004] Currently, most electrochromic devices are fabricated using energy-intensive film-forming methods such as magnetron sputtering, which are difficult to meet new demands such as customized and flexible electrode patterns.

[0005] In view of this, the present invention provides a fully printed patterned flexible electrochromic film and its preparation method. The preparation method provided by the present invention is simple to operate and can precisely control the structure of the conductive layer and the color-changing active layer, thereby obtaining an electrochromic film that can accurately display various patterns.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a fully printed patterned flexible electrochromic film, comprising the following steps:

[0007] A conductive ink is first inkjet printed on the surface of a flexible substrate to form a conductive layer; the conductive ink includes silver nanowires.

[0008] A second inkjet printing process is performed on the surface of the conductive layer to form a protective layer; the protective ink includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid.

[0009] A third inkjet printing process is performed on the surface of the protective layer using color-changing material ink to form a color-changing active layer; the color-changing material ink is an electrochromic polymer solution.

[0010] Preferably, the solvent in the conductive ink is a mixture of isopropanol, ethylene glycol and a wetting agent;

[0011] The mass concentration of silver nanowires in the conductive ink is 0.3-0.6%.

[0012] Preferably, the average length of the silver nanowire is 5–15 μm, and the average diameter of the silver nanowire is 20–30 nm.

[0013] Preferably, the mass concentration of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid in the protective ink is 0.05-0.15%.

[0014] Preferably, the electrochromic polymer includes one or more of polypyrrole, polypyrrole derivatives, polythiophene, polythiophene derivatives, polyaniline / poly(4-styrenesulfonate), and polyaniline derivatives.

[0015] Preferably, the mass concentration of the electrochromic polymer in the electrochromic polymer solution is 0.5–2.0 mg / mL.

[0016] Preferably, the printing voltages of the first inkjet printer, the second inkjet printer, and the third inkjet printer are independently 20-25V;

[0017] The printing frequencies of the first, second, and third inkjet printers are independently 7400–7600 Hz.

[0018] Preferably, the preparation method further includes one or more steps of a first heat treatment, a second heat treatment, and a third heat treatment;

[0019] The first heat treatment is as follows: the product after the first inkjet printing is subjected to a first heat treatment; the temperature of the first heat treatment is 60-80℃, and the holding time of the first heat treatment is 15-20 minutes;

[0020] The second heat treatment is as follows: the product after the second inkjet printing is subjected to a second heat treatment; the temperature of the second heat treatment is 70-85℃, and the holding time of the second heat treatment is 15-20h;

[0021] The third heat treatment is as follows: the product after the third inkjet printing is subjected to a third heat treatment; the temperature of the third heat treatment is 60-70℃, and the heat treatment time is 20-24h.

[0022] Preferably, the flexible substrate comprises a polyester film or polytetrafluoroethylene.

[0023] The present invention also provides an electrochromic thin film prepared according to the preparation method described above, comprising a stacked flexible substrate, a silver nanowire conductive layer, a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid protective layer, and an electrochromic polymer color-changing active layer.

[0024] This invention provides a method for preparing a fully printed patterned flexible electrochromic film, comprising the following steps: first inkjet printing of conductive ink on the surface of a flexible substrate to form a conductive layer; the conductive ink includes silver nanowires; second inkjet printing of protective ink on the surface of the conductive layer to form a protective layer; the protective ink includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid; and third inkjet printing of a color-changing material ink on the surface of the protective layer to form a color-changing active layer; the color-changing material ink is an electrochromic polymer solution. This invention obtains a controllable, patternable, highly repeatable, and personalized electrochromic film by preparing a conductive layer, a protective layer, and a color-changing active layer through inkjet printing. This invention uses computer-aided control of inkjet printing equipment to directly print the conductive layer, protective layer, and color-changing active layer materials onto the surface of a flexible substrate without a mask or contact, forming a high-precision electrochromic film. The preparation method provided by this invention is not only simple to operate, has high material utilization and low manufacturing cost, but also can quickly and flexibly use full printing to spray personalized products, achieve higher wiring density and precision, and has unparalleled advantages in terms of large area, flexibility, low cost and green environmental protection. Attached Figure Description

[0025] Figure 1 SEM image of the conductive layer prepared in Example 1;

[0026] Figure 2 This is a SEM image of the film after the protective layer was formed in Example 1. Detailed Implementation

[0027] This invention provides a method for preparing a fully printed patterned flexible electrochromic film, comprising the following steps:

[0028] A conductive ink is first inkjet printed on the surface of a flexible substrate to form a conductive layer; the conductive ink includes silver nanowires.

[0029] A second inkjet printing process is performed on the surface of the conductive layer to form a protective layer; the protective ink includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid.

[0030] A third inkjet printing process is performed on the surface of the protective layer using color-changing material ink to form a color-changing active layer; the color-changing material ink is an electrochromic polymer solution.

[0031] This invention involves inkjet printing conductive ink onto the surface of a flexible substrate to form a conductive layer. In this invention, the flexible substrate preferably comprises a polyester film (PET film) or a polytetrafluoroethylene (PTFE) film, more preferably a polyester film. In this invention, the conductive ink includes silver nanowires, the average length of which is preferably 5–15 μm, more preferably 8–13 μm; the average diameter of which is preferably 20–30 nm, more preferably 23–27 nm. This invention preferably adjusts the length and diameter of the silver nanowires according to the size of the nozzle of a microelectronic printer used for inkjet printing.

[0032] In this invention, the mass concentration of silver nanowires in the conductive ink is preferably 0.3-0.6%, more preferably 0.35-0.5%. In this invention, the solvent in the conductive ink is preferably a mixture of isopropanol, ethylene glycol, and a wetting agent. In this invention, the wetting agent is preferably a polyether-modified polysiloxane. In this invention, the volume ratio of isopropanol to ethylene glycol is preferably 13-17:10, more preferably 15:10; the volume ratio of ethylene glycol to the wetting agent is preferably 10:0.004-0.004, more preferably 10:0.005.

[0033] In this invention, the printing voltage of the first inkjet printer is preferably 20-25V, more preferably 22-24V; the printing frequency of the first inkjet printer is preferably 7400-7600Hz, more preferably 7500Hz; and the number of nozzles in the first inkjet printer is preferably 7-16, more preferably 8-12. In this invention, the number of layers in the first inkjet printer is preferably 5-7, more preferably 5-6. This invention regulates the photoelectric properties of the silver nanowire conductive network by controlling the number of layers in the first inkjet printer. In this invention, as the number of inkjet-printed layers increases from 5 to 7, the sheet resistance of the silver nanowire film decreases from 156Ω / sq to 47Ω / sq, and the transmittance of the film at 550nm decreases from 84.2% to 79.1%.

[0034] The present invention preferably uses a flexible electronic printer for the first inkjet printing.

[0035] This invention prepares a conductive layer through a first inkjet printing process, which can obtain a controllable, patternable, and highly repeatable silver nanowire conductive network without the need for subsequent etching processes. It also solves the problems of controllability and repeatability of the silver nanowire conductive network.

[0036] In this invention, the process after the first inkjet printing preferably includes: subjecting the inkjet-printed product to a first heat treatment; the temperature of the first heat treatment is preferably 60-80°C, more preferably 65-75°C; the holding time of the first heat treatment is preferably 15-20 min, more preferably 16-18 min.

[0037] The present invention dries the first inkjet-printed product by means of a first heat treatment to remove the solvent.

[0038] After obtaining the conductive layer, the present invention performs a second inkjet printing of the protective ink on the surface of the conductive layer to form a protective layer. In the present invention, the protective ink includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS); the mass concentration of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid in the protective ink is preferably 0.05-0.15%, more preferably 0.05-0.08%. In the present invention, the protective ink preferably also includes a wetting agent, which is preferably a polyether-modified polysiloxane. In the present invention, the mass concentration of the wetting agent in the protective ink is preferably 0.01-0.05%, more preferably 0.01-0.03%.

[0039] In this invention, the preparation method of the protective ink preferably includes the following steps: dissolving poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid and a wetting agent in water to obtain the protective ink. In this invention, the water is preferably deionized water. In this invention, the dissolution is preferably carried out under stirring conditions. This invention does not have special requirements for the stirring, as long as complete dissolution is achieved.

[0040] In this invention, the printing voltage of the second inkjet printer is preferably 20-25V, more preferably 22-24V; the printing frequency of the second inkjet printer is preferably 7400-7600Hz, more preferably 7500Hz; the number of nozzles in the second inkjet printer is preferably 7-16, more preferably 8-12. In this invention, the number of layers in the second inkjet printer is preferably 1-4 layers, more preferably 2-3 layers.

[0041] The present invention preferably utilizes a flexible electronic printer for the second inkjet printing.

[0042] In this invention, the process after the second inkjet printing preferably includes: subjecting the printed product to a second heat treatment; the temperature of the second heat treatment is preferably 70-85°C, more preferably 75-80°C; and the holding time of the second heat treatment is preferably 15-20 hours, more preferably 16-18 hours.

[0043] The present invention dries the second inkjet-printed product by means of a second heat treatment to remove the solvent.

[0044] In this invention, the protective layer can prevent the flexible substrate and conductive layer from being oxidized or corroded; at the same time, the protective layer can improve the adhesion of the color-changing active layer and the conductive layer, thereby improving the bending resistance of the electrochromic material.

[0045] After obtaining the protective layer, the present invention utilizes a color-changing material ink to perform a third inkjet printing on the surface of the protective layer to form a color-changing active layer. In this invention, the color-changing material ink is an electrochromic polymer solution; the electrochromic polymer preferably includes one or more of polypyrrole, polypyrrole derivatives, polythiophene, polythiophene derivatives, polyaniline / poly(4-styrene sulfonate) (PANI / PSS), and polyaniline derivatives, more preferably one or more of polypyrrole, polythiophene, and polyaniline / poly(4-styrene sulfonate). In this invention, when the electrochromic polymer consists of two or more of the above-mentioned specific substances, the present invention has no special requirements on the ratio of the specific substances, and any ratio can be used. In this invention, the mass concentration of the electrochromic polymer in the electrochromic polymer solution is preferably 0.5–2.0 mg / mL, more preferably 0.5–0.7 mg / mL. The present invention has no special requirements on the solvent in the electrochromic polymer solution, as long as it can dissolve the electrochromic polymer. The present invention preferably adjusts the concentration of the electrochromic polymer solution according to the inkjet printing equipment.

[0046] In this invention, the printing voltage of the third inkjet printing is preferably 20-25V, more preferably 22-24V; the printing frequency of the third inkjet printing is preferably 7400-7600Hz, more preferably 7500Hz; and the number of nozzles in the third inkjet printing is preferably 7-16, more preferably 8-12. In this invention, the number of layers in the third inkjet printing is preferably 4-10, more preferably 5-7. This invention controls the electrochromic performance by adjusting the number of layers in the third inkjet printing. In this invention, the more layers of the color-changing active layer, the more uniform the deposition of the color-changing active layer, and the clearer and more obvious the color change after applying electricity. However, the number of color-changing active layers cannot be too high, because the more color-changing layer material, the greater the current required for color change. However, the conductivity of the nano-silver wire electrode cannot be particularly high, because higher conductivity requires more deposited silver wires, which leads to a decrease in light transmittance. The color change of the electrochromic device is also affected by the light transmittance of the electrode.

[0047] The present invention preferably utilizes a flexible electronic printer for third inkjet printing.

[0048] In this invention, the third inkjet printing process preferably further includes: subjecting the printed product to a third heat treatment; the temperature of the third heat treatment is preferably 60-70°C, more preferably 60-65°C; the holding time of the third heat treatment is preferably 20-24 hours, more preferably 22-24 hours.

[0049] This invention dries the product after the third inkjet printing process by a third heat treatment to remove the solvent.

[0050] This invention employs inkjet printing to print transparent conductive circuit patterns of silver nanowires onto the surface of a PET film. A poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid protective layer is then printed onto the silver nanowire transparent conductive circuit pattern. Finally, a color-changing active layer is formed on the surface of the protective layer using inkjet printing, resulting in a patterned flexible electrochromic film. The entire preparation process of the flexible electrochromic film utilizes inkjet printing technology, allowing for direct computer-aided design of the circuit pattern. This process is simple, flexible in design, and convenient in fabrication. Furthermore, printing low-concentration PEDOT:PSS onto the silver nanowire network structure not only prevents the silver nanowire electrodes from being oxidized and corroded but also improves the adhesion between the conductive layer and the organic color-changing active layer, enhancing the bending resistance of the flexible electrochromic film. In this invention, inkjet printing technology allows for on-demand printing. It utilizes piezoelectric pulses to control the printhead to eject microdroplets and accurately deliver them to any designated location, meeting the need for flexible design and fabrication of customized electrodes, while also offering advantages such as low raw material consumption.

[0051] The present invention also provides an electrochromic material prepared according to the preparation method described above, comprising a layered flexible substrate, a silver nanowire conductive layer, a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid protective layer, and an electrochromic polymer color-changing active layer.

[0052] The electrochromic film provided by this invention has the characteristics of fast response speed and good stability.

[0053] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] Inkjet printing of conductive layers with silver nanowires: A 0.35% (w / w) aqueous solution of silver nanowires was used as the conductive ink, wherein the average length of the silver nanowires was 10 μm and the average diameter of the silver nanowires was 25 nm; Five layers were inkjet printed on the surface of a polyester film using a Flexible Electronics Printer. The printing voltage was 21 V, the number of nozzles was 8, and the printing frequency was 7500 Hz. After inkjet printing, the conductive layer was kept at 80 °C for 15 min to obtain the conductive layer.

[0056] Inkjet printing of PEDOT:PSS protective layer: PEDOT:PSS and polyether-modified polysiloxane were dissolved in deionized water to obtain protective ink; the mass concentration of PEDOT:PSS in the protective ink was 0.05%, and the mass concentration of polyether-modified polysiloxane was 0.01%; three layers were inkjet printed on the conductive layer surface using a Flexible Electronics Printer. The inkjet printing voltage was 21V, the number of nozzles was 8, and the printing frequency was 7500Hz. After inkjet printing, the layer was kept at 70℃ for 20 hours to obtain the protective layer.

[0057] Inkjet printing of color-changing active layer: A polyaniline / poly(4-styrene sulfonate) (PANI / PSS) solution with a mass concentration of 0.5 mg / mL was used as the color-changing material ink; five layers were inkjet printed on the protective layer surface using a Flexible Electronics Printer. The inkjet printing voltage was 21V, the number of nozzles was 8, and the printing frequency was 7500Hz. After inkjet printing, the layer was kept at 60℃ for 22 hours to form the color-changing active layer, thus obtaining the electrochromic material.

[0058] Example 2

[0059] Electrochromic films were prepared according to the method of Example 1, except that the mass concentration of PEDOT:PSS in the protective ink was 0.08%, and a PANI / PSS solution with a mass concentration of 0.7 mg / mL was used as the color-changing material ink.

[0060] Example 3

[0061] Electrochromic films were prepared according to the method of Example 1, except that six conductive layers were printed using inkjet printing, and a PANI / PSS solution with a mass concentration of 0.7 mg / mL was used as the color-changing material ink.

[0062] The conductive layer prepared in Example 1 was examined by scanning electron microscopy, and the SEM image was obtained, as shown below. Figure 1 As shown. By Figure 1 As can be seen, the silver nanowires overlap each other to form a conductive network.

[0063] The conductive layer-protective layer prepared in Example 1 was examined by scanning electron microscopy, and the SEM image was obtained, as shown below. Figure 2 As shown. By Figure 2 As can be seen, the surfaces of the interlocking silver nanowires are covered with a PEDOT:PSS film.

[0064] The electrochromic properties of the electrochromic films prepared in Examples 1-3 were tested using an electrochemical workstation. A three-electrode system was used, with the electrochromic film as the working electrode, a silver wire as the reference electrode, and a platinum wire as the counter electrode. The three electrodes were fixed in a cuvette. A 1 mol / L H₂SO₄ solution was used as the electrolyte solution for cyclic voltammetry and chronoamperometry to analyze the coloring and fading times of the electrochromic films. The electrochemical stability of the electrochromic films was analyzed under the conditions of a scanning potential range of -1.6 to 1.2 V, a scanning speed of 50 mV / s, and 100 scans. The results are listed in Table 1.

[0065] Table 1. Electrochromic properties of the electrochromic films prepared in Examples 1-3

[0066] Example Electrochromic properties Example 1 Coloring time is 2 seconds, fading time is 2.5 seconds, color change is fast, and cycle stability is good. Example 2 Coloring time is 2 seconds, fading time is 2.8 seconds, color change is fast, and cycle stability is good. Example 3 Coloring time is 2 seconds, fading time is 3.2 seconds, color change is fast, and cycle stability is good.

[0067] As can be seen from the data in Table 1, the electrochromic thin film prepared by this invention has the characteristics of fast response time and good stability.

[0068] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a fully printed patterned flexible electrochromic film, comprising the following steps: A conductive ink is first inkjet printed on the surface of a flexible substrate to form a conductive layer; the conductive ink includes silver nanowires; the flexible substrate is a polyester film. A second inkjet printing process is performed on the surface of the conductive layer to form a protective layer; the protective ink includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid. A third inkjet printing process is performed on the surface of the protective layer using a color-changing material ink to form a color-changing active layer; the color-changing material ink is an electrochromic polymer solution. The conductive ink contains silver nanowires with a mass concentration of 0.3-0.6%, and the first inkjet printing layer has 5-7 layers; the average length of the silver nanowires is 5-15 μm, and the average diameter of the silver nanowires is 20-30 nm. The printing voltage of the first inkjet printer is 20-25V; The printing frequency of the first inkjet printer is 7400-7600Hz.

2. The preparation method according to claim 1, characterized in that, The solvent in the conductive ink is a mixture of isopropanol, ethylene glycol, and a wetting agent.

3. The preparation method according to claim 1, characterized in that, The protective ink contains 0.05–0.15% poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid by mass concentration.

4. The preparation method according to claim 1, characterized in that, The electrochromic polymer includes one or more of polypyrrole, polypyrrole derivatives, polythiophene, polythiophene derivatives, polyaniline / poly(4-styrene sulfonate), and polyaniline derivatives.

5. The preparation method according to claim 1 or 4, characterized in that, The electrochromic polymer solution has a mass concentration of 0.5–2.0 mg / mL.

6. The preparation method according to claim 1, characterized in that, The printing voltages for the second and third inkjet printing are independent, ranging from 20 to 25V. The printing frequencies of the second and third inkjet printers are independently 7400–7600 Hz.

7. The preparation method according to claim 1 or 6, characterized in that, The preparation method further includes one or more steps of a first heat treatment, a second heat treatment, and a third heat treatment; The first heat treatment is as follows: the product after the first inkjet printing is subjected to a first heat treatment; the temperature of the first heat treatment is 60-80℃, and the holding time of the first heat treatment is 15-20 minutes; The second heat treatment is as follows: the product after the second inkjet printing is subjected to a second heat treatment; the temperature of the second heat treatment is 70-85℃, and the holding time of the second heat treatment is 15-20h; The third heat treatment is as follows: the product after the third inkjet printing is subjected to a third heat treatment; the temperature of the third heat treatment is 60-70℃, and the heat treatment time is 20-24h.

8. An electrochromic thin film prepared by the preparation method according to any one of claims 1 to 7, comprising a stacked flexible substrate, a silver nanowire conductive layer, a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid protective layer, and an electrochromic polymer color-changing active layer.

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