Stretchable transparent electrode and method of making the same
By fabricating wavy silver mesh transparent electrodes using inkjet printing, the problems of manufacturing complexity and performance deficiencies of traditional transparent electrodes in flexible and stretchable electronic devices are solved, enabling low-cost, high-performance transparent electrode applications with excellent optoelectronic properties and mechanical flexibility.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-05-23
- Publication Date
- 2026-03-03
AI Technical Summary
Existing transparent electrode materials such as ITO have problems such as complex manufacturing process, high cost, poor stiffness and poor bending resistance in flexible and stretchable electronic devices. Furthermore, traditional composite electrodes cannot simultaneously optimize conductivity and light transmittance.
A multi-layered wavy silver mesh transparent electrode was fabricated using inkjet printing technology. It consists of an elastic substrate and a surface-modified bilayer conductive polymer film, combined with a conductive metal network. The electrode is then embedded into the elastic substrate through a one-step transfer process, avoiding photolithography and chemical etching processes.
A high-performance transparent electrode with low cost and large area fabrication has been achieved, which has excellent photoelectric properties and mechanical flexibility, significantly reduces surface roughness and electrode linewidth, and improves oxidation resistance and tensile strength.
Smart Images
Figure CN115020005B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of flexible electronics, specifically relating to a stretchable transparent electrode and its preparation method. Background Technology
[0002] Flexible and stretchable electronic devices hold immense potential for applications in innovative fields such as human motion detection, healthcare monitoring, and electronic skin. Electrodes are a crucial component of flexible and stretchable electronic devices, and their performance significantly impacts the overall device performance. However, the production of traditional indium tin oxide (ITO) transparent electrodes, widely used in the electronics market, typically involves methods such as magnetron sputtering and physical vapor deposition, which require expensive equipment, complex processes, and high production costs. Furthermore, their inherent stiffness (fracture after 1% strain) and poor bending resistance prevent them from meeting the development requirements of flexible and stretchable electronic devices. Therefore, to meet the demands of future flexible and stretchable devices that are simple to manufacture, low-cost, possess excellent conductivity, mechanical flexibility, and can be fabricated over large areas, it is necessary to address the complex manufacturing processes and poor flexibility of traditional ITO transparent electrodes, thereby developing new alternative routes.
[0003] In recent years, printing technology has attracted much attention due to its advantages such as large patterning area, low cost, multi-functional manufacturing capabilities, and good compatibility with flexible substrates. Among them, inkjet printing / 3D printing technology employs a maskless and contactless method. It is computer-controlled, allowing for the direct creation of precisely positioned design patterns, achieving patterning without templates, and is applicable to various substrates. Furthermore, inkjet printing / 3D printing can save significant amounts of raw materials, reduce costs, and easily achieve large-area production printing, making it a highly promising technology.
[0004] Currently, materials used to fabricate flexible transparent electrodes often include poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), graphene, carbon nanotubes, and metal nanowires. However, these materials exhibit high sheet resistance, and increasing film thickness is typically necessary to improve conductivity. Thicker films, however, absorb light more strongly, reducing transmittance and thus limiting the device's transparency. Metal mesh electrodes, with their advantages of low cost, high conductivity, and high transmittance, offer favorable conditions for fabricating flexible transparent electrodes.
[0005] In light of this, researchers have proposed composites using nanomaterials, conductive polymers, and metal meshes, such as metal nanowires / graphene, carbon nanotubes / metal nanowires, PEDOT:PSS / metal mesh, PEDOT:PSS / metal nanowires, and graphene / metal mesh. However, these composite electrodes currently suffer from drawbacks including high surface roughness, susceptibility to oxidation, high mesh line density, and the inability to simultaneously balance and control conductivity and light transmittance. Metal mesh electrodes, in particular, often feature horizontally and vertically straight mesh lines, which are difficult to buffer stress and exhibit poor stretchability. These factors limit the application of these composite electrodes in flexible optoelectronic devices. Therefore, the fabrication of flexible, stretchable, and transparent electrodes possessing both excellent optoelectronic properties and outstanding mechanical flexibility is crucial and urgent for the development of stretchable electronic devices. Summary of the Invention
[0006] To address the challenges of complex fabrication processes using nanoimprinting and photolithography for metal meshes, the difficulty of stress buffering by existing horizontal and vertical mesh lines, poor tensile strength, poor oxidation resistance and large line height of single metal meshes, and the fact that most current transparent metal mesh electrodes are flexible substrates and cannot be stretched, this invention provides a stretchable transparent electrode and its fabrication method. The high-performance wavy silver mesh stretchable transparent electrode prepared by this method possesses both excellent photoelectric and mechanical tensile properties, providing significant application value for future wearable electronic devices, flexible transparent energy storage devices, and other fields.
[0007] To address the problems in the existing technology, the technical solution adopted by this invention is as follows:
[0008] A stretchable transparent electrode includes an elastic substrate and a multilayer flexible transparent conductive film. The multilayer flexible transparent conductive film is a surface-modified bilayer conductive polymer film, and a conductive metal network is deposited on the surface-modified layer. The surface modification is achieved by spin-coating a hydrophobic material layer onto the surface of the bilayer conductive polymer film.
[0009] As an improvement, the elastic substrate is one or more of the following: polydimethylsiloxane (PDMS), hydrogenated styrene-butadiene block copolymer (SEBS), aromatic random copolyester (Ecoflex), topological polymer network hydrogel (TPN), polyvinylidene fluoride (PVDF), or polyurethane acrylate (PUA).
[0010] As an improvement, the hydrophobic material is a cyclohexane solution of octadecyltrichlorosilane (OTS), and the volume ratio of octadecyltrichlorosilane to cyclohexane is 1:10-220.
[0011] As an improvement, the double-layer conductive polymer film is made by spin-coating a layer of ethylene glycol-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (PEDOT: PSS) film onto the surface of a layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film doped with ethylene glycol and surfactant.
[0012] Further improvements include a 6% volume fraction of ethylene glycol and a 1.5% volume fraction of surfactant in the ethylene glycol-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film; and a 6% volume fraction of ethylene glycol in the ethylene glycol-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film.
[0013] A further improvement is that the surfactant is Triton X-100.
[0014] As an improvement, the geometry of the conductive metal network is a wavy network, a horseshoe network, a spiral network, or a kirigami network.
[0015] As an improvement, the conductive metal network is a composite metal network of one or more of gold, silver, copper, aluminum, and nickel.
[0016] The above-mentioned method for preparing a stretchable transparent electrode includes the following steps: Step 1, spin-coating a double layer of conductive polymer onto a substrate; Step 2, chemically modifying the double layer of conductive polymer; Step 3, printing a conductive metal network onto the double layer of conductive polymer; Step 4, transferring the double layer of conductive polymer / conductive metal network onto an elastic substrate to obtain a stretchable transparent electrode.
[0017] As an improvement, the printing in step 3 is completed by inkjet printing, 3D printing, or screen printing.
[0018] Beneficial effects:
[0019] Compared with existing technologies, the present invention provides a stretchable transparent electrode and its preparation method. The stretchable transparent electrode prepared by the method provided by the present invention not only has excellent photoelectric properties but also outstanding mechanical tensile properties, and has good application prospects in the field of flexible stretchable optoelectronic devices. The specific advantages are as follows:
[0020] 1. This invention is based on inkjet printing technology, which eliminates the need for complex processes such as photolithography and / or chemical etching, making it simpler, more cost-effective, more economical in terms of raw materials, and capable of fabricating large-area wavy silver mesh stretched transparent electrodes;
[0021] 2. This invention significantly reduces the linewidth of the silver lines through substrate modification and treatment, effectively improving the photoelectric performance of the wavy silver mesh stretched transparent electrode;
[0022] 3. The present invention employs a one-step transfer process, which makes the surface morphology of the wavy silver mesh stretched transparent electrode smoother and significantly reduces the surface roughness of the electrode. The uniform and smooth morphology of the wavy silver mesh stretched transparent electrode can reduce and avoid leakage current and short-circuit current of optoelectronic devices to a certain extent when applied to optoelectronic devices, which is very beneficial for improving the performance of optoelectronic devices.
[0023] 4. The present invention employs a composite strategy and transfer embedding method to effectively reduce the line height of the silver mesh and greatly improve the oxidation resistance of the wavy silver mesh stretched transparent electrode.
[0024] 5. This invention significantly improves the mechanical tensile properties of the wavy silver mesh stretched transparent electrode by combining the wavy structure design with the inherent flexibility of the highly elastic PDMS substrate. Attached Figure Description
[0025] Figure 1 This is a schematic diagram illustrating the fabrication process of the wavy silver mesh stretched transparent electrode of the present invention.
[0026] Figure 2 This is a graph showing the photoelectric performance of the PEDOT:PSS substrate thin film of the present invention.
[0027] Figure 3 The images show a comparison of the mesh line width of the wavy silver mesh stretched transparent electrode according to the present invention. (a) shows the silver mesh lines printed on the unmodified PEDOT:PSS film, and (b) shows the silver mesh lines printed on the surface-modified PEDOT:PSS film.
[0028] Figure 4 This is a graph showing the sheet resistance variation of the wavy silver mesh stretched transparent electrode after the transfer of the present invention.
[0029] Figure 5 This is a graph showing the photoelectric performance of the transparent electrode stretched by the wavy silver mesh after transfer printing according to the present invention.
[0030] Figure 6 The mechanical tensile test curves of the wavy silver mesh stretched transparent electrode, the pure PEDOT:PSS stretched transparent electrode, and the traditional horizontal and vertical silver mesh stretched transparent electrode of the present invention are shown.
[0031] Figure 7 The diagram shows the sheet resistance change curve of the wavy silver mesh stretched transparent electrode of the present invention after cyclic bending. (a) is a diagram of the electrode in the bending state, (b) is a diagram of the electrode returning to the initial state, and (c) is a diagram of the sheet resistance change curve of the electrode after cyclic bending.
[0032] Figure 8The diagram shows the sheet resistance change curves of the wavy silver mesh stretched transparent electrode of the present invention after cyclic stretching. (a) is a diagram of the electrode in the stretched state, (b) is a diagram of the electrode returning to the initial state, and (c) is a diagram of the sheet resistance change curves of the electrode after cyclic stretching. Detailed Implementation
[0033] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.
[0034] Example 1
[0035] Step 1: Preparation of various solutions used in the examples:
[0036] (1) The substrate used in this embodiment is a glass substrate. The glass substrate is ultrasonically cleaned in ethanol and acetone, and then placed in an oven to air dry.
[0037] (2) The original poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT:PSS) solution (pH 1000) was filtered with a water filter with a pore size of 0.45 μm to remove larger PEDOT particles; 6 vol% ethylene glycol (EG) was added to the filtered PEDOT:PSS solution to prepare mixed solution a; and 6 vol% ethylene glycol (EG) and 1.5 vol% surfactant (Triton X-100) were added to the filtered PEDOT:PSS solution to prepare mixed solution b; then, the two mixed solutions were ultrasonically treated for 1-2 min to obtain a homogeneous solution; the PEDOT:PSS solution was purchased from Haraeus;
[0038] (3) Prepare a mixed solution c by mixing octadecyltrichlorosilane (OTS) and the organic solvent n-hexane at a volume ratio of 1:10-220, and place it on a stirrer to obtain a uniformly mixed solution;
[0039] (4) Prepare liquid PDMS (by mixing the "matrix" and "photoinitiator" at a mass ratio of 10:1), and then place it on a mixer to stir evenly so that the matrix and photoinitiator can be mixed more uniformly. Subsequently, place the prepared liquid PDMS in a vacuum drying oven and evacuate to remove air bubbles. The PDMS liquid used in this embodiment is Sylgard 184 from Dow Corning.
[0040] Step 2: Spin-coat a double layer of conductive polymer onto the substrate:
[0041] (1) The PEDOT:PSS / EG / TritonX-100 mixed solution b prepared in step 1 was spin-coated onto a clean glass substrate. The spin speed was controlled at 1000 rpm, the spin-coating time was 25 s, the temperature was controlled at 120℃, and annealing was performed for 10 min. In this embodiment, the effect of spin-coating a single layer of PEDOT:PSS solution on the photoelectric properties of the transparent thin film electrode of the substrate was investigated (see [link]). Figure 2 );
[0042] (2) The annealed PEDOT:PSS / EG / TritonX-100 / glass substrate was subjected to oxygen plasma treatment with a treatment power of 200 W and a treatment time of 1-2 min. The Plasm-Preen oxygen plasma instrument used in this embodiment was provided by Mycro Technologies, and the oxygen plasma treatment time was controlled to be 1 min 45 s.
[0043] (3) The PEDOT:PSS / EG mixed solution a prepared in step 1 was spin-coated onto the PEDOT:PSS / EG / TritonX-100 / glass substrate in two steps: first, spin-coating at 500 rpm for 5 s, and then at 2000 rpm for 30 s. The spin-coated PEDOT:PSS film was then placed on a heating stage and annealed at 120°C for 10 min. In this embodiment, it was found that only by spin-coating another layer of PEDOT:PSS / EG mixed solution a in the final step of substrate modification can the metal mesh subsequently printed on the substrate effectively reduce the sheet resistance of the overall metal mesh transparent electrode.
[0044] Step 3: Chemical modification of the conductive bilayer polymer:
[0045] The OTS / n-hexane mixed solution c prepared in step 1 was spin-coated onto a PEDOT:PSS film at a rotation speed of 6000 rpm for 20 s. The film was then placed on a hot plate and annealed at 120°C for 3 min. In this embodiment, the volume ratio of OTS to n-hexane was 1:10, and the optimal volume ratio was ultimately determined to be 1:220. The linewidth of the metal mesh transparent electrode was initially 50.621 μm, but after modification with the hydrophobic OTS layer, the linewidth was reduced to 30.372 μm (see [reference needed]). Figure 3 ).
[0046] Step 4: Print a conductive metal network on the dual conductive polymer:
[0047] (1) In this embodiment, the drawing software used to design the wavy mesh is Ai software. Based on the relationship between the pixel pitch and the resolution, the size of the wavy metal mesh is preset to 4 in Ai software. The dot spacing is 15 μm;
[0048] (2) In this embodiment, the printing technology used is inkjet printing.
[0049] The pre-designed wavy grid pattern in (1) is imported into the computer associated with the inkjet printer. The line width of the printed silver line is set to 10 μm, the control dot spacing is set to 15 μm, the printing panel temperature is set to 55 ℃, and the print head pressure is set to 40 V. The inkjet printer used in this embodiment is the Dimatix Materials Printer (DMP 3000) series provided by FUJIFILM, and the nozzle diameter is approximately 20 μm.
[0050] (3) A wavy silver grid was printed on the PEDOT:PSS thin film substrate that had undergone hydrophobic layer treatment in step 3. Subsequently, the printed wavy silver grid electrode was placed on a hot plate and annealed at 120°C for 30 min. The conductive silver ink used in this embodiment was purchased from Advanced Nano Products (ANP) Co., Ltd. (viscosity 10~17 cPs; solid content 30~35%; solvent triethylene glycol monoethyl ether).
[0051] Step 5: Transfer the double-layer conductive polymer / conductive metal network onto the elastic substrate:
[0052] (1) Pour the liquid PDMS prepared in step 1 onto the wavy silver mesh transparent electrode / glass substrate with silicone pads of 0.2 mm thickness attached around the edges;
[0053] (2) Place the electrode from (1) upside down on a clean PET, and then place it in an oven at 90°C for 2 hours to cure.
[0054] (3) The solidified wavy silver mesh / PDMS transparent electrode was peeled off from the glass and PET substrate, thus successfully preparing the wavy silver mesh stretched transparent electrode.
[0055] Examples 2-5:
[0056] The preparation process is the same as in Example 1, except that the spin speed of the PEDOT:PSS / EG / TritonX-100 mixed solution in step 2 (1) is replaced with 1500 rpm, 2000 rpm, 2500 rpm and 3000 rpm respectively.
[0057] Example 6:
[0058] The preparation process was the same as in Example 1, except that in step 2 (1), the number of spin-coated PEDOT:PSS / EG / Triton X-100 mixed solution layers was replaced with a double layer. In this example, the effect of spin-coated double-layer PEDOT:PSS solution on the photoelectric properties of the substrate transparent thin film electrode was investigated (see [link to relevant documentation]). Figure 2 Therefore, a spin-coating method was adopted to apply a two-layer PEDOT:PSS solution, and the spin speed was controlled at 1000 rpm.
[0059] Examples 7-10:
[0060] The preparation process is the same as in Example 6, except that the spin speed of the PEDOT:PSS / EG / TritonX-100 mixed solution in step 2 (1) is replaced with 1500 rpm, 2000 rpm, 2500 rpm and 3000 rpm respectively.
[0061] Examples 11-15:
[0062] The preparation process is the same as in Example 1, except that the volume ratio of OTS to n-hexane in step 3 is replaced with 1:50, 1:100, 1:150, 1:200 and 1:220, respectively.
[0063] Example 16
[0064] The light transmittance of the wavy silver mesh stretched transparent electrode was characterized by ultraviolet spectrophotometry; the electrical conductivity of the wavy silver mesh stretched transparent electrode was characterized by a four-probe sheet resistance meter.
[0065] This embodiment investigated the sheet resistance changes of multiple transferred stretched wavy silver mesh transparent electrodes (see [reference]). Figure 4 It is evident that printing a corrugated silver mesh on a PEDOT:PSS thin film substrate significantly reduces sheet resistance and improves the conductivity of the corrugated silver mesh stretched transparent electrode. Furthermore, the sheet resistance of the electrode does not change significantly after transfer, indicating that the one-step transfer method employed in this invention successfully transfers the electrode, preserving the electrode material and maintaining its conductivity to a great extent. The optimal combined photoelectric performance of the corrugated silver mesh stretched transparent electrode after transfer, considering both conductivity and light transmittance, is: a sheet resistance of 29.85 Ω sq. -1 The corresponding transmittance at 550 nm is ~81.94% (see [reference]). Figure 5 ).
[0066] Example 17
[0067] The sheet resistance changes of pure PEDOT:PSS stretched transparent electrode, horizontal and vertical silver mesh stretched transparent electrode, and wavy silver mesh stretched transparent electrode under tensile strain were characterized using a tensile testing instrument and a four-probe sheet resistance meter. The pure PEDOT:PSS stretched transparent electrode and the horizontal and vertical silver mesh stretched transparent electrode were prepared according to the preparation method of the wavy silver mesh stretched transparent electrode in Example 1.
[0068] In this embodiment, to demonstrate the advantages of the present invention in terms of mechanical tensile properties compared to pure PEDOT:PSS stretched transparent electrodes and traditional horizontal and vertical silver mesh stretched transparent electrodes, the tensile properties of the three were compared and investigated (see [reference]). Figure 6 Comparing the changes in resistance under stretching of the three types of stretched transparent electrodes, the changes in resistance under stretching are as follows: wavy silver mesh stretched transparent electrode < horizontal and vertical silver mesh stretched transparent electrode < PEDOT:PSS stretched transparent electrode. The wavy silver mesh stretched transparent electrode of this invention has the best mechanical tensile properties.
[0069] Example 18
[0070] The sheet resistance variation of the wavy silver mesh stretched transparent electrode under cyclic bending was characterized using a stretching instrument and a four-probe sheet resistance meter.
[0071] This embodiment tests the cyclic bending of a wavy silver mesh stretched transparent electrode (see [reference]). Figure 7 In the test, the sheet resistance of the stretched corrugated silver mesh transparent electrode was measured after 5000 cyclic bends. After approximately 1500 cyclic bends, the sheet resistance remained almost identical to the initial value. A more significant increase in sheet resistance only occurred after more than 2000 cyclic bends, but the change remained small compared to the initial value. After 5000 repeated bends, the sheet resistance increased by less than double compared to the original value, demonstrating the excellent bending resistance of the corrugated silver mesh stretched transparent electrode.
[0072] Example 19
[0073] The sheet resistance variation of the wavy silver mesh stretched transparent electrode under cyclic stretching was characterized using a stretching instrument and a four-probe sheet resistance meter.
[0074] This embodiment demonstrates a cyclic stretching test on a wavy silver mesh stretched transparent electrode (see [reference]). Figure 8The sheet resistance of a wavy silver mesh stretched transparent electrode was tested after 5000 cyclic stretching cycles (with a fixed stretching amount of 50%). After multiple 50% stretching cycles, the sheet resistance of the wavy silver mesh stretched transparent electrode showed a continuous increasing trend, and the increase in sheet resistance also exhibited a regular upward trend. However, after 2000 cyclic stretching cycles, the wavy silver mesh stretched transparent electrode still maintained relatively considerable conductivity.
[0075] This invention utilizes a simple and low-cost inkjet printing technology to design and fabricate a wavy silver mesh stretched transparent electrode. The photoelectric properties of the electrode are controlled by adjusting the number of composite conductive film layers and the mesh linewidth and spacing. Rs 29.85 Ω sq -1 , T The electrode exhibits excellent mechanical flexibility and tensile strength (100% tensile strain) through a combination of a corrugated design and a highly elastic substrate (81.94%). A one-step transfer process embeds the corrugated silver mesh into the surface of the PDMS elastic substrate, giving the electrode excellent oxidation resistance. This stretchable transparent electrode replaces traditional ITO transparent electrodes and provides a feasible technical solution for the innovation of flexible and stretchable electronic devices.
Claims
1. A method for producing a stretchable transparent electrode, characterized by, The stretchable transparent electrode comprises an elastic substrate and a multilayer flexible transparent conductive film, wherein the multilayer flexible transparent conductive film is a double-layer conductive polymer film which is surface-modified, and a conductive metal network is deposited on the surface-modified layer. The surface modification is a layer of hydrophobic material which is spin-coated on the surface of the double-layer conductive polymer film; the preparation method of the stretchable transparent electrode comprises the following steps: Step 1, spin-coating a double-layer conductive polymer on a substrate; Step 2, chemically modifying the double-layer conductive polymer; Step 3, printing a conductive metal network on the double-layer conductive polymer; Step 4, transferring the double-layer conductive polymer / conductive metal network to an elastic substrate to obtain the stretchable transparent electrode; the double-layer conductive polymer film is a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film which is spin-coated with a layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) doped with ethylene glycol and Triton X-100 on the surface of a layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) doped with ethylene glycol.
2. The method of claim 1, wherein the method further comprises, The elastic substrate is a composite of one or more of polydimethylsiloxane, hydrogenated styrene-butadiene block copolymer, aromatic random copolyester, topological polymer network hydrogel, polyvinylidene fluoride, or polyurethane acrylate.
3. The method of claim 1, wherein the method further comprises: The hydrophobic material is a cyclohexane solution of octadecyltrichlorosilane, and the volume ratio of octadecyltrichlorosilane to cyclohexane is 1:10-220.
4. The method of claim 1, wherein the method further comprises, The volume fraction of ethylene glycol in the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film doped with ethylene glycol and Triton X-100 is 6%, and the volume fraction of surfactant is 1.5%; the volume fraction of ethylene glycol in the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film doped with ethylene glycol is 6%.
5. The method of claim 4, wherein the method further comprises, The surfactant is Triton X-100.
6. The method of claim 1, wherein the stretchable transparent electrode is prepared by the steps of: The geometric structure of the conductive metal network is a wavy network, a horseshoe-shaped network, a spiral-shaped network, or a paper-cut pattern network.
7. The method of claim 1, wherein the method further comprises, The conductive metal network is a composite metal network of one or more of gold, silver, copper, aluminum, and nickel.
8. The method of claim 1, wherein the stretchable transparent electrode is prepared by the steps of: The printing in Step 3 is completed by inkjet printing, 3D printing, or screen printing.