A multilayer composite transparent electrode for a flexible substrate and a method of manufacturing the same

Abstract

This invention belongs to the field of flexible electronic materials technology, specifically relating to a multilayer composite transparent electrode for flexible substrates and its fabrication method. The electrode, starting from the surface of the flexible substrate, sequentially comprises a stress buffer layer, a transparent core layer, and an interface optimization layer. The stress buffer layer consists of zinc oxide-tin oxide composite nanoparticles grafted with a silane coupling agent; the transparent core layer is a silver nanowire network with a tin-doped indium oxide shell; and the interface optimization layer is a blended thin film of molybdenum oxide and tungsten oxide formed by controlling the oxygen partial pressure. This invention combines multilayer material design with a low-temperature fabrication process, enabling the electrode to possess high transmittance, low sheet resistance, excellent bending resistance, strong interface adhesion, and high work function characteristics, making it suitable for flexible displays and wearable electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronic materials technology, specifically relating to a multilayer composite transparent electrode for flexible substrates and its preparation method. Background Technology

[0002] With the rapid development of display technology and wearable electronic devices, flexible electronic devices have become an important direction for industrial development due to their bendability, foldability, lightweight and portability. As a core component of flexible displays, touch screens, organic light-emitting diodes (OLEDs), and flexible photovoltaic devices, the performance of transparent electrodes directly affects the optoelectronic characteristics, reliability, and lifespan of these devices.

[0003] Currently, the most widely used transparent electrode material is indium tin oxide (ITO). ITO possesses high transparency and excellent conductivity, but as a ceramic material, it is brittle and lacks flexibility. It is prone to cracking or even fracture when bent or stretched, leading to a sharp deterioration in electrical performance and failing to meet the mechanical reliability requirements of flexible devices. Furthermore, the fabrication of ITO thin films typically requires high-temperature annealing to reduce resistance, but the high-temperature environment causes thermal damage to commonly used flexible polymer substrates, leading to substrate deformation, yellowing, or degradation, severely limiting its application in fully flexible systems.

[0004] To overcome the rigidity of ITO, the industry has begun to research the use of organic conductive polymers as flexible transparent electrode materials, such as poly(3,4-ethylenedioxythiophene)-doped polystyrene sulfonate systems. While these materials possess good flexibility and low-temperature processing characteristics, their overall performance still has significant limitations. On the one hand, organic conductive polymers generally have low conductivity, resulting in high electrode sheet resistance and increased device drive power consumption. On the other hand, their interfacial adhesion with inorganic functional layers is weak, making them prone to delamination or detachment under repeated bending or thermal stress, affecting the mechanical reliability of the device. Furthermore, these materials lack sufficient chemical stability under long-term light exposure and humid heat environments, easily leading to performance degradation and limited lifespan. More importantly, their work function is typically low, resulting in poor energy level matching with common hole transport materials, leading to low carrier injection efficiency, which in turn restricts the photoelectric conversion efficiency and overall performance of the device. Therefore, existing organic conductive polymers still struggle to simultaneously achieve a balance between high conductivity, strong interfacial bonding, good environmental stability, and efficient carrier injection on flexible substrates, requiring further optimization and breakthroughs.

[0005] Therefore, developing a high-performance transparent electrode that combines excellent optoelectronic properties, high flexibility, strong interfacial bonding, good environmental stability, and can be fabricated using low-temperature processes compatible with flexible substrates has become a key issue that urgently needs to be addressed to promote the industrialization of flexible electronics technology. Summary of the Invention

[0006] The purpose of this invention is to provide a multilayer composite transparent electrode for flexible substrates and its preparation method. By designing a multilayer functional thin film with a specific composition and structure, while maintaining excellent light transmittance and flexibility, it significantly improves conductivity, interfacial bonding strength and environmental stability, and achieves a more optimized energy level match with the functional layers of flexible optoelectronic devices, thereby overcoming the shortcomings of existing flexible transparent electrode materials in terms of comprehensive performance.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of the present invention provides a multilayer composite transparent electrode for a flexible substrate, the electrode being attached to the flexible substrate and comprising, in sequence from the surface of the flexible substrate: a stress buffer layer, a transparent core layer, and an interface optimization layer;

[0009] The stress buffer layer is made of zinc oxide-tin oxide composite nanoparticles grafted with 3-aminopropyltriethoxysilane.

[0010] The transparent core layer is a conductive network composed of silver nanowires with a tin-doped indium oxide shell on the surface.

[0011] The interface optimization layer is made of a thin film formed by blending molybdenum oxide and tungsten oxide.

[0012] Furthermore, the thickness of the stress buffer layer is 10~25 nm; the thickness of the transparent core layer is 80~150 nm; and the thickness of the interface optimization layer is 5~12 nm.

[0013] Furthermore, the molar ratio of zinc to tin in the composite nanoparticles is (0.8~1.2):1.

[0014] Furthermore, the material of the stress buffer layer is prepared by the following method:

[0015] (1) Weigh zinc acetate and tin chloride at a zinc-tin molar ratio of (0.8~1.2):1, dissolve them together in ethylene glycol methyl ether, stir, and obtain a mixed salt solution;

[0016] (2) Add oxalic acid solution dropwise to the mixed salt solution to obtain composite nanoparticle precursor sol;

[0017] (3) Add anhydrous ethanol to the precursor sol, and add an amount equivalent to 1.0 molar of the total metal salt. 1.5 times 3 aminopropyltriethoxysilane, reaction 6 Grafting was completed in 10 hours; the resulting product was centrifuged, washed, and 3 grafts were obtained. Zinc oxide of aminopropyltriethoxysilane Tin oxide composite nanoparticles are the material for stress buffer layers.

[0018] The stress buffer layer forms strong chemical bonds with the flexible substrate through organosilane molecules grafted onto its surface, significantly improving interfacial adhesion and preventing interlayer delamination. This layer is constructed using zinc oxide-tin oxide composite nanoparticles, which possess a certain degree of elasticity, effectively absorbing and dispersing localized stresses generated by substrate bending or thermal deformation. Simultaneously, this composite nanostructure achieves physical interlocking at the interface, further suppressing the initiation and propagation of microcracks. Furthermore, its moderate modulus provides a good mechanical transition between the rigid conductive layer and the soft substrate, matching the difference in thermal expansion coefficients between the upper and lower layers, thereby ensuring the structural integrity and electrical reliability of the electrode under dynamic bending conditions.

[0019] Furthermore, the thickness of the tin-doped indium oxide shell is 2-5 nm, wherein the tin doping amount is 8-12 at.%.

[0020] Furthermore, the material of the transparent core layer is prepared by the following method:

[0021] (1) Mix 0.1-0.3 mol / L silver nitrate in ethylene glycol solution with 0.2-0.5 mol / L polyvinylpyrrolidone in ethylene glycol solution and react to obtain silver nanowires; dissolve indium trichloride and tin tetrachloride together in isopropanol at an indium-tin molar ratio of (88-92):(8-12) to prepare a precursor solution with a total metal ion concentration of 0.05-0.15 mol / L;

[0022] (2) Disperse silver nanowires in isopropanol to form a dispersion with a concentration of 1-5 mg / mL; add the precursor solution dropwise to the dispersion, and control the mass ratio of total metal ions to silver nanowires in the precursor solution to be (1:15)-(1:25); after the addition is complete, react at 120-150℃ for 4-8 hours.

[0023] (3) After the reaction is complete, the product is centrifuged, washed and dried to obtain silver nanowires with a tin-doped indium oxide shell, which is the core layer material.

[0024] The transparent core layer constructs a three-dimensional conductive network using silver nanowires, achieving a balance between high light transmittance and low sheet resistance with extremely low coverage. A uniformly coated indium tin oxide shell effectively isolates silver from direct contact with the environment, inhibiting silver oxidation and sulfide formation, significantly improving long-term stability. This shell also serves as an interface transition layer, improving the adhesion and ohmic contact between the silver nanowires and adjacent functional layers. Furthermore, it buffers stress through its own deformation during bending, protecting the silver nanowires from breakage and maintaining the integrity of the conductive network.

[0025] Furthermore, the molar ratio of molybdenum to tungsten in the interface optimization layer is (1:3) to (3:1).

[0026] Furthermore, the material of the interface optimization layer is prepared by the following method:

[0027] (1) Molybdenum trioxide (MoO3) powder and tungsten trioxide (WO3) powder are mixed at a molar ratio of molybdenum to tungsten of (1:3) to (3:1), ground, pressed into shape, and sintered to obtain composite ceramic target material;

[0028] (2) Using a composite ceramic target as the sputtering source, magnetron sputtering deposition is performed in a mixed atmosphere containing argon and oxygen at a substrate temperature of 80-120℃. During the deposition process, the volume partial pressure of oxygen in the mixed gas is adjusted to 10%-30% to form a blended thin film of molybdenum oxide and tungsten oxide.

[0029] (3) After deposition, the film is annealed to obtain the material of the interface optimization layer.

[0030] The interface optimization layer is co-deposited by controlling the oxygen partial pressure (10%-30%), enabling molybdenum oxide and tungsten oxide to form a blended structure with a high work function. This layer has good energy level matching with the upper organic functional material, which can significantly reduce the hole injection barrier and improve device efficiency. At the same time, the blended thin film structure formed under these conditions is dense, which can effectively block water and oxygen and enhance the mechanical strength and bending resistance of the electrode.

[0031] A second aspect of this invention provides a method for fabricating a multilayer composite transparent electrode for a flexible substrate, comprising the following steps:

[0032] (1) The flexible substrate is cleaned and then subjected to oxygen plasma treatment;

[0033] (2) A dispersion of zinc oxide-tin oxide composite nanoparticles grafted with 3-aminopropyltriethoxysilane was prepared and coated on the surface of the treated flexible substrate. Then, it was dried and cured at 80-120℃ to form a stress buffer layer.

[0034] (3) Disperse silver nanowires with tin-doped indium oxide shells on their surface in an organic solvent to obtain conductive ink. Coat the conductive ink onto the surface of the stress buffer layer and heat-treat it at 100-150℃ to form a transparent core layer.

[0035] (4) Using magnetron sputtering, a composite ceramic target material of molybdenum oxide and tungsten oxide is deposited on the surface of the transparent core layer to form an interface optimization layer, thus obtaining the multilayer composite transparent electrode.

[0036] Further, in step (4), the substrate temperature is 80-120℃ during deposition, the working gas is a mixture of argon and oxygen, wherein the oxygen volume partial pressure is 10%-30%, and after deposition, it is annealed at 150-200℃ in an oxygen-containing atmosphere to form an interface optimization layer.

[0037] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0038] 1. By designing a multi-layer composite structure of "stress buffer layer - transparent core layer - interface optimization layer", a synergistic effect of mechanical adaptation, high-efficiency conductivity and interface energy level regulation is achieved, and the overall performance is better than that of single material or simple stacked electrode.

[0039] 2. The surface chemical grafting treatment of composite nanoparticles in the stress buffer layer significantly enhances the interfacial bonding force between the electrode and the flexible substrate, effectively suppresses delamination and crack generation during bending, and improves the mechanical reliability of the electrode.

[0040] 3. The transparent core layer uses a silver nanowire network coated with an indium oxide shell, which achieves low sheet resistance while maintaining high light transmittance, and the shell protection enhances the oxidation resistance and environmental stability of the silver nanowires.

[0041] 4. The interface optimization layer forms a dense structure with a high work function by depositing a molybdenum / tungsten oxide blend film by controlling the oxygen partial pressure. This optimizes the energy level matching with the upper functional material, thereby improving the hole injection efficiency.

[0042] 5. The overall preparation process is compatible with low-temperature processes, suitable for heat-sensitive flexible polymer substrates, with a wide process window, which is conducive to achieving large-area uniform preparation and has good industrialization prospects. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Unless otherwise specified, all raw materials used in the examples are commercially available products.

[0045] Example 1

[0046] This embodiment provides a multilayer composite transparent electrode for flexible substrates, the preparation method of which includes the following steps:

[0047] (1) Flexible substrate pretreatment: A 125 μm thick polyethylene terephthalate (PET) film was selected as the flexible substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 15 minutes each, followed by drying with nitrogen. The cleaned PET substrate was placed in an oxygen plasma treatment instrument and treated at 100 W power for 2 minutes to improve its surface energy.

[0048] (2) Preparation and formation of stress buffer layer:

[0049] (i) Dissolve 1.098 g zinc acetate (Zn(CH3COO)2·2H2O) and 1.128 g tin chloride (SnCl4·5H2O) together in 50 mL ethylene glycol methyl ether and stir at 70 °C until completely dissolved to obtain a mixed salt solution.

[0050] (ii) Under stirring, 20 mL of ethylene glycol methyl ether solution containing 1.26 g of oxalic acid (H2C2O4·2H2O) was slowly added dropwise to the above mixed salt solution. After the addition was complete, the reaction was continued at 70 °C for 3 hours to obtain the composite nanoparticle precursor sol.

[0051] (iii) 70 mL of anhydrous ethanol and 2.21 mL of 3-aminopropyltriethoxysilane (APTES, equivalent to 1.2 times the total molar amount of the metal salt) were added to the precursor sol, and the mixture was refluxed at 80 °C for 8 hours under nitrogen protection. After the reaction was completed, the product was separated by centrifugation, washed three times with anhydrous ethanol, and finally redispersed in 50 mL of anhydrous ethanol to obtain a dispersion of zinc oxide-tin oxide composite nanoparticles grafted with APTES.

[0052] The above dispersion was spin-coated onto the PET substrate treated in step (1) at a speed of 3000 rpm for 30 seconds. It was then dried and cured on a hot plate at 100°C for 10 minutes to form a stress buffer layer with a thickness of about 15 nm.

[0053] (3) Preparation and formation of the transparent core layer:

[0054] (i) 40 mL of 0.2 mol / L silver nitrate (AgNO3) ethylene glycol solution was mixed with 100 mL of 0.3 mol / L polyvinylpyrrolidone (PVP) ethylene glycol solution, and the mixture was stirred in an oil bath at 130 °C for 2 hours. After the reaction was completed, the mixture was allowed to cool naturally, centrifuged, and washed three times with anhydrous ethanol to obtain silver nanowire powder.

[0055] 0.88 mmol of indium trichloride (InCl3) and 0.12 mmol of tin tetrachloride (SnCl4) were dissolved together in 10 mL of isopropanol to prepare a precursor solution with a total metal ion concentration of 0.1 mol / L.

[0056] (ii) Take 10 mg of the above silver nanowires and disperse them in 10 mL of isopropanol. While stirring, slowly add 1 mL of precursor solution to the silver nanowire dispersion. Transfer the mixture to a hydrothermal reactor lined with polytetrafluoroethylene and react at 135 °C for 6 hours.

[0057] (iii) After the reaction is completed, the mixture is centrifuged, washed with isopropanol and deionized water in sequence, and finally dried in a vacuum drying oven at 70°C to obtain silver nanowire powder with a tin-doped indium oxide shell on the surface.

[0058] The silver nanowire powder was dispersed in ethanol to prepare a conductive ink with a concentration of 2 mg / mL. This ink was spin-coated onto the surface of a stress buffer layer at 2000 rpm for 30 seconds. Subsequently, it was heat-treated on a hot plate at 120°C for 15 minutes to form a transparent core layer with a thickness of approximately 100 nm.

[0059] (4) Formation of the interface optimization layer:

[0060] (i) Weigh, mix and grind molybdenum trioxide (MoO3) and tungsten trioxide (WO3) powders at a molar ratio of 1:1, cold press them into shape, and sinter them at 900°C for 2 hours in an argon atmosphere to obtain a composite ceramic target.

[0061] (ii) Place the sample with the transparent core layer on the sample stage of the magnetron sputtering equipment and evacuate to a background vacuum of less than 5.0 × 10⁻⁶. -4 After Pa, a mixture of argon and oxygen is introduced, with the oxygen volume partial pressure controlled at 20% and the working pressure at 0.5 Pa. The sample stage is heated to 100℃, and a composite ceramic target is used as the cathode, with a target power density of 3 W / cm². 2 Sputter deposition for 5 minutes under the specified conditions.

[0062] (iii) After deposition, the sample is annealed in situ at 180°C for 20 minutes while maintaining an oxygen atmosphere, followed by furnace cooling. Finally, an interface optimization layer with a thickness of approximately 8 nm is formed on the transparent core layer, thus obtaining the multilayer composite transparent electrode.

[0063] Example 2

[0064] This embodiment provides a multilayer composite transparent electrode for flexible substrates, the preparation method of which includes the following steps:

[0065] (1) Flexible substrate pretreatment: A 125 μm thick polyethylene terephthalate (PET) film was selected as the flexible substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 15 minutes each, followed by drying with nitrogen. The cleaned PET substrate was placed in an oxygen plasma treatment instrument and treated at 100 W power for 2 minutes.

[0066] (2) Preparation and formation of stress buffer layer:

[0067] (i) Dissolve 0.878 g zinc acetate (Zn(CH3COO)2·2H2O) and 1.410 g tin chloride (SnCl4·5H2O) together in 50 mL ethylene glycol methyl ether and stir at 70 °C until completely dissolved to obtain a mixed salt solution.

[0068] (ii) Under stirring, 20 mL of ethylene glycol methyl ether solution containing 1.26 g of oxalic acid (H2C2O4·2H2O) was slowly added dropwise to the above mixed salt solution. After the addition was complete, the reaction was continued at 70 °C for 3 hours to obtain the composite nanoparticle precursor sol.

[0069] (iii) 70 mL of anhydrous ethanol and 2.21 mL of 3-aminopropyltriethoxysilane (APTES) were added to the precursor sol, and the mixture was refluxed at 80 °C for 8 hours under nitrogen protection. After the reaction was completed, the product was separated by centrifugation, washed three times with anhydrous ethanol, and finally redispersed in 50 mL of anhydrous ethanol to obtain a dispersion of zinc oxide-tin oxide composite nanoparticles grafted with APTES.

[0070] The above dispersion was spin-coated onto the PET substrate treated in step (1) at a speed of 3000 rpm for 30 seconds. It was then dried and cured on a hot plate at 100°C for 10 minutes to form a stress buffer layer with a thickness of about 20 nm.

[0071] (3) Preparation and formation of the transparent core layer:

[0072] (i) 40 mL of 0.15 mol / L silver nitrate (AgNO3) ethylene glycol solution was mixed with 100 mL of 0.3 mol / L polyvinylpyrrolidone (PVP) ethylene glycol solution, and the mixture was stirred in an oil bath at 130 °C for 2 hours. After the reaction was completed, the mixture was allowed to cool naturally, centrifuged, and washed three times with anhydrous ethanol to obtain silver nanowire powder.

[0073] 0.85 mmol of indium trichloride (InCl3) and 0.15 mmol of tin tetrachloride (SnCl4) were dissolved together in 10 mL of isopropanol to prepare a precursor solution with a total metal ion concentration of 0.1 mol / L.

[0074] (ii) Take 10 mg of the above silver nanowires and disperse them in 10 mL of isopropanol. While stirring, slowly add 1.5 mL of the precursor solution to the silver nanowire dispersion. Transfer the mixture to a hydrothermal reactor lined with polytetrafluoroethylene and react at 135 °C for 6 hours.

[0075] (iii) After the reaction is completed, the mixture is centrifuged, washed with isopropanol and deionized water in sequence, and finally dried in a vacuum drying oven at 70°C to obtain silver nanowire powder with a tin-doped indium oxide shell on the surface.

[0076] The aforementioned silver nanowire powder was dispersed in ethanol to prepare a conductive ink with a concentration of 2 mg / mL. This ink was spin-coated onto the surface of a stress buffer layer at 2000 rpm for 30 seconds. Subsequently, it was heat-treated on a hot plate at 120°C for 15 minutes to form a transparent core layer with a thickness of approximately 120 nm.

[0077] (4) Formation of the interface optimization layer:

[0078] (i) Weigh, mix and grind molybdenum trioxide (MoO3) and tungsten trioxide (WO3) powders at a molar ratio of 1:3, cold press them into shape, and sinter them at 900°C for 2 hours in an argon atmosphere to obtain a composite ceramic target.

[0079] (ii) Place the PET substrate, after being processed in steps (1) to (3) and having its surface sequentially coated with a stress buffer layer and a transparent core layer, onto the sample stage of the magnetron sputtering equipment. Evacuate the substrate until the base vacuum is below 5.0 × 10⁻⁶. -4 After Pa, a mixture of argon and oxygen is introduced, with the oxygen volume partial pressure controlled at 25% and the working pressure at 0.5 Pa. The sample stage is heated to 110℃, using a composite ceramic target as the cathode, at a target power density of 3 W / cm². 2 Sputter deposition for 5 minutes under the specified conditions.

[0080] (iii) After deposition, the sample is annealed in situ at 160°C for 20 minutes while maintaining an oxygen atmosphere, followed by furnace cooling. Finally, an interface optimization layer with a thickness of about 10 nm is formed on the transparent core layer, thus obtaining the multilayer composite transparent electrode.

[0081] Comparative Example 1

[0082] This comparative example provides a multilayer composite transparent electrode for flexible substrates. The difference from Example 1 is that step (2) (i) is replaced by: weighing 2.196 g of zinc acetate (Zn(CH3COO)2·2H2O) and dissolving it in 50 mL of ethylene glycol methyl ether, stirring at 70°C until completely dissolved to obtain a mixed salt solution.

[0083] Comparative Example 2

[0084] This comparative example provides a multilayer composite transparent electrode for flexible substrates. The difference from Example 1 is that step (2) (iii) is replaced by: adding 70 mL of anhydrous ethanol to the precursor sol for dilution, then adding 5 wt% (relative to the mass of nanoparticles) of polyvinyl alcohol as a physical binder, stirring and mixing evenly to obtain a zinc oxide-tin oxide composite nanoparticle dispersion containing PVA binder. The above dispersion is spin-coated onto the PET substrate treated in step (1) at a speed of 3000 rpm for 30 seconds. Subsequently, it is dried and cured on a hot plate at 80°C for 10 minutes to form a stress buffer layer with a thickness of approximately 15 nm.

[0085] Comparative Example 3

[0086] This comparative example provides a multilayer composite transparent electrode for flexible substrates. The difference from Example 1 is that the precursor solution in step (3) (i) is replaced by dissolving 1.0 mmol of zinc acetate (Zn(CH3COO)2) and 0.04 mmol of aluminum chloride (AlCl3) together in 10 mL of isopropanol to prepare a precursor solution with a total metal ion concentration of 0.104 mol / L.

[0087] Comparative Example 4

[0088] This comparative example provides a multilayer composite transparent electrode for a flexible substrate, which differs from Example 1 in that the transparent core layer in step (3) is replaced with a conventional flexible transparent conductive material in the art: conductive polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)) film.

[0089] The preparation method is as follows: A commercially available PEDOT:PSS aqueous dispersion (solid content 1.0-1.3 wt%, conductivity ≥100 S / cm) was used. 5 vol% dimethyl sulfoxide was added as a conductivity enhancer, and 0.1 wt% Tween20 was added as a wetting agent. After thorough mixing, the mixture was filtered through a 0.45 μm filter. This solution was then spin-coated onto the surface of a stress buffer layer at 1500 rpm for 30 seconds, followed by heat treatment on a hot plate at 120°C for 15 minutes to form a transparent conductive film with a thickness of approximately 100 nm as the core layer.

[0090] Comparative Example 5

[0091] This comparative example provides a multilayer composite transparent electrode for flexible substrates, which differs from Example 1 in that the composite ceramic target in step (4)(i) is replaced with a single-component molybdenum trioxide (MoO3) ceramic target.

[0092] Performance testing

[0093] The following performance tests were performed on the electrode samples prepared in Examples 1-2 and Comparative Examples 1-5:

[0094] 1. Surface sheet resistance: Measured using a four-probe tester, unit Ω / sq.

[0095] 2. Visible light transmittance: The transmittance at a wavelength of 550 nm was measured using a UV-Vis spectrophotometer, in units of %.

[0096] 3. Bending resistance: The electrode sample was continuously bent around a cylinder with a diameter of 3 mm. The change rate of sheet resistance (ΔR / R0) after 10,000 bends was recorded.

[0097] 4. Interfacial adhesion: Tested using the cross-cut adhesion test (according to ASTM D3359), with ratings from 0B (worst) to 5B (best).

[0098] 5. Work function: The work function value is calculated by measuring the initial kinetic energy of the interface optimization layer using ultraviolet photoelectron spectroscopy (UPS), with the unit being eV.

[0099] The test results are shown in Table 1.

[0100] Table 1 Performance Test Results

[0101]

[0102] The performance test results above show that all embodiments achieved a balanced overall performance of high transmittance, low sheet resistance, excellent bending resistance, strong interfacial adhesion, and high work function. This demonstrates that the multilayer composite structure and the specially designed materials of each layer of this invention effectively and synergistically solve the key problems of flexible electrodes in terms of conductivity, transmittance, flexibility, interfacial bonding, and efficient charge injection.

[0103] Comparative Example 1 shows a significant decrease in bending stability and a slight reduction in adhesion. The reason for this may be that replacing the zinc oxide-tin oxide composite nanoparticles with single zinc oxide weakens the synergistic effect of the stress buffer layer in terms of matching thermal expansion coefficients and stress dissipation, leading to a decrease in flexible reliability. Comparative Example 2 shows a sharp decrease in interfacial adhesion, with direct film detachment failure during bending. This demonstrates that using physical adhesive PVA instead of chemically grafted APTES cannot form a strong chemical bond interface between the nanoparticles and the flexible substrate, resulting in a complete loss of mechanical reliability. Comparative Example 3 shows a significant increase in surface sheet resistance and a deterioration in bending stability. This indicates that the AZO shell's protective effect on the silver nanowires and its ohmic contact performance with surrounding materials are inferior to the ITO shell of this invention, leading to deterioration in conductivity and electrical stability under bending. Comparative Example 4 shows extremely high surface sheet resistance, a large change in resistance after bending, and a low work function. This demonstrates that the PEDOT:PSS material system cannot achieve the performance levels of this invention in terms of intrinsic conductivity, mechanical tolerance, and energy level characteristics. Comparative Example 5 uses a single-component MoO3 target deposition, and its electrical and mechanical properties are similar to those of Example 1, but its work function is significantly lower. This indicates that a single component is insufficient to achieve the same high efficiency in work function control, thus affecting hole injection efficiency and overall device performance.

[0104] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multilayer composite transparent electrode for flexible substrates, characterized in that, The electrode is attached to a flexible substrate and, starting from the surface of the flexible substrate, includes, in sequence: a stress buffer layer, a transparent core layer, and an interface optimization layer. The stress buffer layer is made of zinc oxide-tin oxide composite nanoparticles grafted with 3-aminopropyltriethoxysilane. The transparent core layer is a conductive network composed of silver nanowires with a tin-doped indium oxide shell on the surface. The interface optimization layer is made of a thin film formed by blending molybdenum oxide and tungsten oxide.

2. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The thickness of the stress buffer layer is 10~25 nm; the thickness of the transparent core layer is 80~150 nm; and the thickness of the interface optimization layer is 5~12 nm.

3. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The molar ratio of zinc to tin in the composite nanoparticles is (0.8~1.2):

1.

4. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The material of the stress buffer layer is prepared by the following method: (1) Weigh zinc acetate and tin chloride at a zinc-tin molar ratio of (0.8~1.2):1, dissolve them together in ethylene glycol methyl ether, stir, and obtain a mixed salt solution; (2) Add oxalic acid solution dropwise to the mixed salt solution to obtain composite nanoparticle precursor sol; (3) Add anhydrous ethanol to the precursor sol, and add an amount equivalent to 1.0 molar of the total metal salt. 1.5 times 3 aminopropyltriethoxysilane, reaction 6 Grafting was completed in 10 hours; the resulting product was centrifuged, washed, and 3 grafts were obtained. Zinc oxide of aminopropyltriethoxysilane Tin oxide composite nanoparticles are the material for stress buffer layers.

5. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The thickness of the tin-doped indium oxide shell is 2-5 nm, wherein the tin doping amount is 8-12 at.%.

6. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The material of the transparent core layer is prepared by the following method: (1) Mix 0.1-0.3 mol / L silver nitrate in ethylene glycol solution with 0.2-0.5 mol / L polyvinylpyrrolidone in ethylene glycol solution and react to obtain silver nanowires; dissolve indium trichloride and tin tetrachloride together in isopropanol at an indium-tin molar ratio of (88-92):(8-12) to prepare a precursor solution with a total metal ion concentration of 0.05-0.15 mol / L; (2) Disperse silver nanowires in isopropanol to form a dispersion with a concentration of 1-5 mg / mL; add the precursor solution dropwise to the dispersion, and control the mass ratio of total metal ions to silver nanowires in the precursor solution to be (1:15)-(1:25); after the addition is complete, react at 120-150℃ for 4-8 hours. (3) After the reaction is complete, the product is centrifuged, washed and dried to obtain silver nanowires with a tin-doped indium oxide shell, which is the core layer material.

7. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The molar ratio of molybdenum to tungsten in the interface optimization layer is (1:3) to (3:1).

8. The multilayer composite transparent electrode for flexible substrates according to claim 1, characterized in that, The material of the interface optimization layer is prepared by the following method: (1) Molybdenum trioxide powder and tungsten trioxide powder are mixed at a molar ratio of molybdenum to tungsten of (1:3) to (3:1), ground, pressed into shape, and sintered to obtain composite ceramic target material; (2) Using a composite ceramic target as the sputtering source, magnetron sputtering deposition is performed in a mixed atmosphere containing argon and oxygen at a substrate temperature of 80-120℃. During the deposition process, the volume partial pressure of oxygen in the mixed gas is adjusted to 10%-30% to form a blended thin film of molybdenum oxide and tungsten oxide. (3) After deposition, the film is annealed to obtain the material of the interface optimization layer.

9. The method for preparing a multilayer composite transparent electrode for a flexible substrate according to any one of claims 1-8, characterized in that, Includes the following steps: (1) The flexible substrate is cleaned and then subjected to oxygen plasma treatment; (2) A dispersion of zinc oxide-tin oxide composite nanoparticles grafted with 3-aminopropyltriethoxysilane was prepared and coated on the surface of the treated flexible substrate. Then, it was dried and cured at 80-120℃ to form a stress buffer layer. (3) Disperse silver nanowires with tin-doped indium oxide shells on their surface in an organic solvent to obtain conductive ink. Coat the conductive ink onto the surface of the stress buffer layer and heat-treat it at 100-150℃ to form a transparent core layer. (4) Using magnetron sputtering, a composite ceramic target material of molybdenum oxide and tungsten oxide is deposited on the surface of the transparent core layer to form an interface optimization layer, thus obtaining the multilayer composite transparent electrode.

10. The preparation method according to claim 9, characterized in that, In step (4), the substrate temperature is 80-120℃ during deposition, and the working gas is a mixture of argon and oxygen, with the oxygen volume partial pressure being 10%-30%. After deposition, the substrate is annealed at 150-200℃ in an oxygen-containing atmosphere to form an interface optimization layer.

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