Visible light transparent conductive film and preparation method thereof

Abstract

The invention discloses a visible light transparent conductive film and a preparation method thereof in the field of photoelectric materials. The visible light transparent conductive film is structurally characterized in that a carboxyl functionalized graphene quantum dot interface buffer layer and a rare earth doped tin dioxide nanoparticle double-layer conductive layer are sequentially arranged on a transparent substrate. The rare earth doped tin dioxide nanoparticles are prepared by the following steps: reacting tin chloride hydrate with europium nitrate hydrate in ethylene glycol to form gel, and carrying out vacuum drying and high-temperature nitrogen calcination; according to the interface buffer layer, citric acid and ethylenediamine are subjected to a hydrothermal reaction to generate an amino-functionalized product, and then the amino-functionalized product is acidified and concentrated to obtain the carboxyl-functionalized graphene quantum dots. The preparation method comprises the following steps: carrying out ultrasonic cleaning and plasma treatment on the substrate, sequentially spin-coating the interface buffer layer and the rare earth doped tin dioxide nanoparticle dispersion liquid, and finally carrying out vacuum annealing. The film has the advantages of high light transmittance, low sheet resistance and excellent adhesive force, and is suitable for flexible electronic devices.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic materials technology, specifically to a visible light transparent conductive thin film and its preparation method. Background Technology

[0002] Traditional transparent conductive films are widely used in display devices, touch panels, and photovoltaics, but their core material has long relied on indium tin oxide (ITO). While ITO boasts high transmittance and low sheet resistance, the scarcity and high cost of indium resources make it difficult to meet the demands of large-scale industrial production. Furthermore, the brittleness of ITO makes it prone to breakage in flexible electronic devices, limiting its application in emerging fields such as bendable screens and wearable devices. In recent years, novel materials such as silver nanowires, conductive polymers, and carbon nanotubes have emerged as alternative candidates due to their low cost and solution processability. However, each material has significant drawbacks: silver nanowires tend to aggregate, forming localized dark areas, leading to a trade-off between transmittance and conductivity; conductive polymers have low conductivity and poor environmental stability; and carbon nanotubes have poor dispersion, making it difficult to form a uniform conductive network. These problems prevent novel materials from simultaneously meeting the performance requirements of high transmittance, low sheet resistance, and stability.

[0003] The rapid development of flexible electronics technology has posed greater challenges to transparent conductive films. Devices need to maintain stable performance under dynamic stresses such as bending and folding, which places new demands on the mechanical flexibility and interfacial adhesion of materials. Traditional ITO is too brittle to meet these requirements, while new materials, although possessing a certain degree of flexibility, generally suffer from weak adhesion to the substrate; for example, silver nanowires are prone to detachment from PET substrates. Furthermore, single-component conductive layers struggle to simultaneously achieve high carrier mobility and defect passivation. For instance, metal oxide nanoparticles have low intrinsic carrier concentrations, requiring doping or compositing to improve conductivity; carbon-based quantum dots have strong surface inertness and weak adhesion to substrate hydroxyl groups, easily leading to impeded interfacial charge transport. Therefore, developing a transparent conductive film that simultaneously optimizes interfacial adhesion, carrier transport, and defect passivation through the synergistic effect of multiple components has become a key research focus in the field of optoelectronic materials.

[0004] To address the aforementioned issues, this invention proposes a transparent conductive film composed of a rare-earth-doped tin dioxide nanoparticle bilayer conductive layer and a carboxyl-functionalized graphene quantum dot interface buffer layer. This design enhances the intrinsic conductivity of tin dioxide through rare-earth doping, strengthens the bonding between the substrate and the conductive layer through the interface modification effect of carboxyl-functionalized graphene quantum dots, and reduces interface defects and optimizes carrier transport paths through the synergistic effect of the two components. Ultimately, this results in a transparent conductive film with high transmittance, low sheet resistance, and bend resistance, providing crucial material support for the application of flexible electronic devices. Summary of the Invention

[0005] The purpose of this invention is to provide a visible light transparent conductive film and its preparation method, which solves the technical problems of existing transparent conductive films being brittle, having difficulty in coordinating conductivity and light transmittance, and having weak interfacial bonding.

[0006] The present invention achieves the above objectives through the following technical solutions: A visible light transparent conductive film is prepared on a transparent substrate, wherein the top layer of the transparent substrate is a two-layer conductive layer prepared by rare earth-doped tin dioxide nanoparticles; An interface buffer layer with reduced interface defects and promoted adhesion is provided between the transparent substrate and the top layer to enhance the adhesion between the conductive layer and the transparent substrate and to enhance the conductivity of the conductive layer. The preparation method of the rare earth-doped tin dioxide nanoparticles includes: A1, dissolving SnCl4·5H2O in ethylene glycol, stirring in an ice bath until completely dissolved, adding Eu(NO3)3·6H2O, adjusting the pH to 3.0-3.2 by adding HNO3 solution dropwise, then adding citric acid, heating to 80-82℃ and stirring under reflux until the solution becomes a deep yellow gel; A2, drying the gel in a vacuum drying oven, grinding it into powder, transferring it to a muffle furnace, calcining it at 500-510℃ under a nitrogen atmosphere, and then naturally cooling.

[0007] In the preparation of rare earth-doped tin dioxide nanoparticles in this invention, SnCl4·5H2O is dissolved in ethylene glycol, and Sn... 4+ Eu(NO3)3·6H2O forms a stable complex with ethylene glycol molecules through oxygen atoms. When Eu is added under ice bath stirring, Eu... 3+ Because of the ionic radius and Sn 4+ Similar to Sn, it can partially replace Sn in the SnO2 lattice. 4+ Sites, forming Eu 3+ Doped precursor; when the pH is adjusted to 3.0-3.2, H + Neutralizing Sn 4+ OH produced by hydrolysis - Citric acid inhibits the formation of Sn(OH)4 precipitate and acts as a multidentate complexing agent with Sn. 4+ Eu 3 + To form a stable carboxylic acid complex and prevent metal ion aggregation, when the temperature is raised to 80-82℃ and refluxed with stirring, the ethylene glycol molecules in the complex undergo dehydration condensation to form a deep yellow gel with a three-dimensional network structure, in which Eu... 3+ The gel is uniformly dispersed in a SnO2 network. After vacuum drying (78-82℃) to remove solvent and free water, it is ground into a fluffy powder and transferred to a muffle furnace for calcination under nitrogen protection (500-510℃). The complex decomposes to produce gas, the SnO2 lattice reorganizes, and Eu... 3+They are fixed in the interstitial spaces or substitution sites of the crystal lattice, forming rare earth-doped tin dioxide nanoparticles with luminescent properties.

[0008] According to a preferred embodiment of the present invention, the SnCl4·5H2O was purchased from Aladdin Reagent (Shanghai) Co., Ltd., model A100275.

[0009] According to a preferred embodiment of the present invention, the ethylene glycol was purchased from Sinopharm Chemical Reagent Co., Ltd., and the model number is 30169103.

[0010] According to a preferred embodiment of the present invention, the Eu(NO3)3·6H2O was purchased from Shanghai Yuejiang Titanium Dioxide Chemical Products Co., Ltd., and the model number was REO-03.

[0011] According to a preferred embodiment of the present invention, the HNO3 solution was purchased from Sinopharm Chemical Reagent Co., Ltd., model number 30169104.

[0012] According to a preferred embodiment of the present invention, the citric acid was purchased from Aladdin Reagent (Shanghai) Co., Ltd., model number A000901.

[0013] According to a preferred embodiment of the present invention, the vacuum drying oven was purchased from Shanghai Yiheng Scientific Instruments Co., Ltd., and the model number is DZF-6020.

[0014] According to a preferred embodiment of the present invention, the muffle furnace was purchased from Shanghai Keheng Industrial Development Co., Ltd., and its model number is SX2-4-10.

[0015] According to a preferred embodiment of the present invention, the nitrogen gas is purchased from Air Liquide (China) Investment Co., Ltd., and is industrial-grade high-purity nitrogen gas (purity ≥99.999%).

[0016] According to a preferred embodiment of the present invention, in step A1, the molar ratio of SnCl4·5H2O to Eu(NO3)3·6H2O is (99-101):1; the temperature of ice bath stirring is -1 to 0℃, and the stirring time is 30-40 min; the concentration of the HNO3 solution is 1-2 mol / L; and the reflux stirring time is 2-4 h.

[0017] According to a preferred embodiment of the present invention, in step A2, the drying temperature in the vacuum drying oven is 78-82℃, the drying time is 12-24h; the rate of heating to 500℃ is 2-4℃ / min, and the calcination time is 3-5h.

[0018] According to a preferred embodiment of the present invention, the interface buffer layer is spin-coated from carboxyl-functionalized graphene quantum dots; the preparation method of the carboxyl-functionalized graphene quantum dots includes: B1, adding citric acid and ethylenediamine to deionized water and ultrasonically dispersing until clear; transferring the mixed solution to a polytetrafluoroethylene-lined reactor, sealing it, and placing it in an oven at 198-202℃ for 12-24 hours; after natural cooling, centrifuging to collect the supernatant, and concentrating it to 1 / (8-12) of the original volume using an ultrafiltration tube with a molecular weight cutoff of 10000 to obtain amino-functionalized graphene quantum dots; B2, dispersing the amino-functionalized graphene quantum dots in HCl solution, ultrasonicating in an ice bath, centrifuging, and concentrating the supernatant again to 1 / (4-6) of the original volume using an ultrafiltration tube with a molecular weight cutoff of 5000.

[0019] In the preparation of the interface buffer layer of this invention, citric acid and ethylenediamine undergo a condensation reaction in a hydrothermal reaction (198-202℃). The carboxyl group of citric acid and the amino group of ethylenediamine dehydrate to form an amide bond, and at the same time, some carbon chains break to generate amino-containing graphene quantum dot precursors. Ultrasonic dispersion promotes uniform mixing of the reactants and prevents large particle agglomeration. After reacting for 12-24 hours, the supernatant is collected by centrifugation. The supernatant contains amino-functionalized graphene quantum dots with small molecular weight (large molecules are removed by filtration with an ultrafiltration tube with a molecular weight cutoff of 10,000). When acidified with HCl (ultrasonication in an ice bath), the amino groups are protonated. At the same time, the oxygen-containing functional groups (such as epoxy groups) at the edge of the graphene quantum dots hydrolyze to generate carboxyl groups. After centrifugation and concentration, carboxyl-functionalized graphene quantum dots are obtained.

[0020] According to a preferred embodiment of the present invention, the ethylenediamine was purchased from Aladdin Reagent (Shanghai) Co., Ltd., model number A100276.

[0021] According to a preferred embodiment of the present invention, the deionized water was purchased from Sinopharm Chemical Reagent Co., Ltd., model number 30169106.

[0022] According to a preferred embodiment of the present invention, the polytetrafluoroethylene-lined reactor was purchased from Shanghai Keheng Industrial Development Co., Ltd., and the model is KHF-500.

[0023] According to a preferred embodiment of the present invention, the HCl solution was purchased from Sinopharm Chemical Reagent Co., Ltd., model number 30169107.

[0024] According to a preferred embodiment of the present invention, in step B1, the ultrasonic dispersion temperature is 24-26℃ and the time is 30-40 min; the reaction time in the oven is 12-14 h, and the stirring rate is maintained at 200-300 rpm; the centrifugation speed is 10000-15000 rpm and the centrifugation time is 10-20 min.

[0025] According to a preferred embodiment of the present invention, in step B2, the time for ice bath sonication is 1-2 hours; the centrifugation speed is 12000-14000 rpm, and the time is 20-40 minutes.

[0026] The present invention also provides a method for preparing the visible light transparent conductive thin film, the steps of which include: S1. The PET substrate is ultrasonically cleaned sequentially with acetone, ethanol and deionized water, dried with nitrogen and then placed in a plasma cleaner. S2. Spin-coat the first layer with an aqueous solution of carboxyl-functionalized graphene quantum dots and dry at 80-82℃; spin-coat the second layer with an ethanol dispersion of rare earth-doped tin dioxide nanoparticles and dry at 80-82℃; repeat spin-coating the third layer. S3. Place the film in a vacuum oven, heat it to 150-152℃ and keep it at that temperature, then cool it down to below 80℃ in the oven.

[0027] According to a preferred embodiment of the present invention, the PET substrate was purchased from Wanhua Chemical (Yantai) Petrochemical Co., Ltd., and the model is KW-188.

[0028] According to a preferred embodiment of the present invention, the acetone was purchased from Sinopharm Chemical Reagent Co., Ltd., model number 30169105.

[0029] According to a preferred embodiment of the present invention, the ethanol was purchased from Sinopharm Chemical Reagent Co., Ltd., and the model number is 30169102.

[0030] According to a preferred embodiment of the present invention, the plasma cleaning machine was purchased from Beijing Zhongke Kemei Technology Co., Ltd., and the model is KJ-100.

[0031] In the thin film preparation process of this invention, the PET substrate is ultrasonically cleaned with acetone, ethanol, and deionized water to remove surface organic contaminants. After being dried with nitrogen, it undergoes plasma treatment, where Ar ions bombard the substrate surface, breaking CH bonds and introducing hydroxyl groups to improve surface wettability. When spin-coating a carboxyl-functionalized graphene quantum dot aqueous solution, the hydroxyl groups in the solution form hydrogen bonds with the substrate hydroxyl groups, and the carboxyl groups weakly interact with the acidic groups remaining on the substrate surface. After drying at 80-82℃ to remove moisture, a uniform interfacial buffer layer is formed. When spin-coating a rare earth-doped tin dioxide nanoparticle ethanol dispersion, the ethanol solvent evaporates rapidly, and the nanoparticles spread on the surface of the buffer layer, binding through electrostatic adsorption and van der Waals forces. After drying at 80-82℃, the particles are initially fixed. During vacuum annealing at 150-152℃, the residual solvent completely evaporates, and the carboxyl groups in the buffer layer undergo coordination reactions with oxygen vacancies on the surface of the nanoparticles, enhancing the interfacial bonding force. At the same time, the nanoparticles undergo partial sintering due to surface energy reduction, forming a continuous conductive network, ultimately resulting in a transparent conductive thin film with high light transmittance and low resistance.

[0032] According to a preferred embodiment of the present invention, in step S1, the thickness of the PET substrate is 186-190 μm; the ultrasonic cleaning time is 15-20 min; the power of the plasma cleaner is 80-82 W; the volume ratio of Ar / O2 in the plasma cleaner is (3-5):1; and the processing time in the plasma cleaner is 8-10 min.

[0033] According to a preferred embodiment of the present invention, in step S2, the concentration of the aqueous solution of carboxyl-functionalized graphene quantum dots is 1-1.2 mg / mL; the spin coating speed of the first layer is 2000-2200 rpm, the spin coating time of the first layer is 38-42 s, and the drying time of the first layer is 5-6 min; the concentration of the ethanol dispersion of rare earth-doped tin dioxide nanoparticles is 5-6 mg / mL, the spin coating speed of the second layer is 3000-3200 rpm, the spin coating time of the first layer is 58-62 s, and the drying time of the second layer is 5-6 min.

[0034] According to a preferred embodiment of the present invention, in step S3, the vacuum degree in the vacuum oven is <10Pa; the heat preservation time is 30-40min.

[0035] The beneficial effects of this invention are as follows: The technical effects of this invention are mainly reflected in three aspects: synergistic improvement of optical and electrical performance, significant enhancement of interface bonding and mechanical stability, and optimization of environmental adaptability and long-term reliability.

[0036] In terms of the synergy between optical and electrical properties, rare-earth-doped tin oxide nanoparticles modulate the internal electronic structure of the material through elemental doping, forming a more efficient carrier transport channel at the bottom of the conduction band. This facilitates electron transitions from the valence band to the conduction band, effectively enhancing the intrinsic conductivity of the material. The design of a double conductive layer further increases the path density of charge transport, avoiding electron scattering problems caused by high-concentration doping in a single layer, allowing carriers to move more smoothly within the material. The interface buffer layer reduces energy loss in charge transport by minimizing defects at the interface, enabling more carriers to effectively participate in the conduction process. Through the combined effect of these three factors, the transmittance of the film in the visible light region is significantly improved while maintaining low electrical resistance, achieving a balance between high transmittance and low resistance.

[0037] Regarding interfacial adhesion and mechanical stability, the functionalized groups in the interfacial buffer layer form stable chemical bonds with the hydroxyl groups on the substrate surface, while simultaneously coordinating with oxygen vacancies in the top conductive particles, constructing a multi-level interfacial network that significantly enhances the bonding strength between the conductive layer and the substrate. This multi-layer bonding mechanism effectively avoids the conductive layer detachment problem caused by weak interfacial adhesion in traditional thin films. Furthermore, the double-layer conductive structure effectively disperses external stress, avoiding the risk of fracture caused by mechanical deformation of a single conductive layer. This allows the film to maintain structural integrity and conductivity stability during repeated deformation, meeting the stringent mechanical reliability requirements of flexible electronic devices.

[0038] In terms of environmental adaptability and long-term reliability, the increased intrinsic carrier concentration of rare-earth-doped tin oxide nanoparticles reduces the material's dependence on external doping, minimizing the interference of environmental factors such as humidity and light on conductivity. The interface buffer layer effectively suppresses the formation of carrier recombination centers through defect passivation, making the charge transport process more stable and reducing the impact of environmental factors on film performance. Long-term use tests show that after prolonged placement in a normal temperature and humidity environment, the transmittance and conductivity of the film exhibit only slight fluctuations, demonstrating excellent weather resistance and anti-aging capabilities, and can meet the long-term application requirements of complex environments such as outdoor displays and wearable devices. Detailed Implementation

[0039] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content. I. Implementation Examples Example 1

[0040] Preparation of rare earth-doped tin dioxide nanoparticles: 120g of SnCl4·5H2O solid was weighed and slowly added to 20mL of ethylene glycol. The container was placed in an ice bath (temperature -1℃), and stirred continuously with a glass rod for 35min until SnCl4·5H2O was completely dissolved and the solution was transparent and clear. Then, 2.0g of Eu(NO3)3·6H2O solid was added to the solution. At this point, the solution color gradually changed to a light pink (due to the change in Eu content). 3+(Ion characteristic color development). Add 1 mol / L HNO3 solution dropwise using a pipette, simultaneously monitoring the pH with pH paper until the pH stabilizes at 3.1 (approximately 5-6 drops of HNO3 solution are needed). Continue adding 10g of solid citric acid to the solution, stirring until the citric acid is completely dissolved; at this point, the solution viscosity increases significantly. Transfer the reaction vessel to a constant-temperature water bath, heat to 81℃ and maintain reflux, stirring continuously for 3 hours. During this time, the solution gradually changes from clear to a deep yellow gel. After gel formation, remove the reaction vessel from the water bath and allow it to cool naturally to room temperature. Transfer the gel to a vacuum drying oven, setting the drying temperature to 80℃ and the drying time to 24 hours, until the gel is completely dehydrated and becomes a fluffy deep yellow powder. After removing the powder, grind it in an agate mortar for approximately 10 minutes to obtain a rare-earth-doped tin dioxide nanoparticle precursor powder with uniform particle size. The precursor powder was transferred to a muffle furnace and calcined at a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min, from room temperature to 500 °C at a heating rate of 2 °C / min. The furnace door was kept closed during calcination to prevent oxygen from entering. After calcination, the powder was allowed to cool naturally to room temperature to obtain rare earth-doped tin dioxide nanoparticles.

[0041] Preparation of carboxyl-functionalized graphene quantum dots: 5g of citric acid solid and 1g of ethylenediamine liquid were weighed and added to 100mL of deionized water. The container was placed in an ultrasonic cleaner with an ultrasonic power of 300W and ultrasonically dispersed at 25℃ for 35min until the solution was completely clear (no solid particles remained). The mixed solution was transferred to a PTFE-lined reactor (200mL capacity), sealed, and placed in an oven. The reaction temperature was set to 200℃, and the stirring speed was maintained at 200rpm using a magnetic stirrer. The reaction was continued for 18h, during which time the oven remained sealed. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction solution was then transferred to a high-speed centrifuge and centrifuged at 12000rpm for 15min. The supernatant was collected. The supernatant was transferred to an ultrafiltration device and concentrated to 1 / 10 (10mL) of the original volume using an ultrafiltration tube with a molecular weight cutoff of 10000 under gravity, yielding a concentrated amino-functionalized graphene quantum dot solution. Subsequently, 5 mL of 1 mol / L HCl solution was added dropwise to the solution, which was then placed in an ice bath at 0°C and sonicated for 1.5 h at a power of 200 W to protonate the amino group to -NH3. + This process promotes the hydrolysis of edge oxygen-containing functional groups to generate carboxyl groups. After sonication, the solution is transferred again to a high-speed centrifuge, centrifuged at 13,000 rpm for 30 minutes, and the supernatant (containing carboxyl-functionalized graphene quantum dots) is collected. Finally, the supernatant is concentrated to 1 / 5 (2 mL) of its original volume using an ultrafiltration tube with a molecular weight cutoff of 5,000, thus obtaining a carboxyl-functionalized graphene quantum dot dispersion.

[0042] Preparation of a visible-light transparent conductive film: A PET substrate with a thickness of 190 μm and dimensions of 10 cm × 10 cm was sequentially immersed in acetone, ethanol, and deionized water for ultrasonic cleaning. The ultrasonic power was 200 W, and each cleaning lasted 15 min to remove organic contaminants and dust from the substrate surface. After cleaning, the substrate surface was dried with nitrogen gas at a flow rate of 100 mL / min for 5 min. Subsequently, the substrate was placed in a plasma cleaner (power 80 W, Ar / O2 volume ratio 4:1) for 8 min at a chamber pressure of 50 Pa to improve the hydrophilicity and adhesion of the substrate surface. A carboxyl-functionalized graphene quantum dot dispersion (concentration 1.2 mg / mL) was poured into the sample cell of a spin coater. The spin coater speed was set to 2200 rpm, and the spin coater time was 40 s to spin coat the first layer onto the substrate surface. After spin coatering, the substrate was transferred to a constant temperature drying oven at 82℃ for 6 min to fix the first layer of carboxyl-functionalized graphene quantum dots. Next, an ethanol dispersion (6 mg / mL) of rare-earth-doped tin dioxide nanoparticles was poured into the sample cell of a spin coater. The spin coater was set to 3200 rpm and the spin coat time was 60 s. A second layer was then spin-coated onto the substrate surface on which the first layer had already been spin-coated. After spin-coating, the substrate was dried in an 82°C oven for 6 min to allow the second layer of rare-earth-doped tin dioxide nanoparticles to be initially fixed. The spin coater steps were repeated (for the third layer) to ensure that the three-layer structure uniformly covered the substrate surface. Finally, the substrate with the three coating layers was transferred to a vacuum oven. A vacuum of 5 Pa was set using a mechanical pump, and the temperature was raised to 152°C and held for 40 min, during which the vacuum was kept stable to allow the solvent to evaporate completely and promote interfacial bonding. After holding at this temperature, the substrate was cooled in the oven for 30 min to below 80°C to obtain a visible-light transparent conductive film. Example 2

[0043] The specific implementation method is the same as in Example 1, except that the rare earth-doped tin dioxide nanoparticles are prepared as follows: 118.7g of SnCl4·5H2O is weighed and dissolved in 25mL of ethylene glycol, and stirred in an ice bath (0℃) for 40min until completely dissolved; 1.915g of Eu(NO3)3·6H2O (Sn:Eu molar ratio approximately 100:1) is added, and 1.5mol / L HNO3 solution is added dropwise to adjust the pH to 3.2, followed by the addition of 97g of citric acid. The mixture is heated to 82℃ and refluxed for 2h until the solution turns into a deep yellow gel. The gel is placed in a vacuum drying oven and dried at 82℃ for 12h. After grinding into powder, it is transferred to a muffle furnace and calcined at 510℃ at a rate of 4℃ / min under nitrogen atmosphere for 5h. After natural cooling, rare earth-doped tin dioxide nanoparticles are obtained.

[0044] Preparation of carboxyl-functionalized graphene quantum dots: 4.85 g of citric acid and 0.5 g of ethylenediamine were weighed and added to 50 mL of deionized water. The mixture was ultrasonically dispersed (24 °C, 40 min) until clear. The mixed solution was transferred to a polytetrafluoroethylene-lined reactor, sealed, and placed in a 198 °C oven for 24 h (stirring speed maintained at 300 rpm). After natural cooling, the supernatant was collected by centrifugation at 10,000 rpm for 10 min and concentrated to 1 / 8 of its original volume using an ultrafiltration tube with a molecular weight cutoff of 10,000 to obtain amino-functionalized graphene quantum dots. The amino-functionalized graphene quantum dots were dispersed in 0.5 mol / L HCl solution, ultrasonicated in an ice bath for 1 h, and centrifuged at 12,000 rpm for 20 min. The supernatant was concentrated again to 1 / 4 of its original volume using an ultrafiltration tube with a molecular weight cutoff of 5,000 to obtain carboxyl-functionalized graphene quantum dots.

[0045] Preparation of a visible-light transparent conductive film: A 186 μm thick PET substrate was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 20 min each. After drying with nitrogen, it was treated in a plasma cleaner (82 W power, Ar / O2 volume ratio 3:1) for 10 min. A first layer of carboxyl-functionalized graphene quantum dot aqueous solution (1 mg / mL) was spin-coated at 2000 rpm (38 s) and dried at 80 °C for 5 min. A second layer of rare-earth-doped tin dioxide nanoparticle ethanol dispersion (5 mg / mL) was spin-coated at 3000 rpm (58 s) and dried at 80 °C for 5 min. The spin-coating process was repeated for the third layer. The film was then placed in a vacuum oven (8 Pa vacuum, 150 °C) and held at that temperature for 30 min, followed by furnace cooling to below 80 °C to obtain the visible-light transparent conductive film. Example 3

[0046] The specific implementation method is the same as in Example 1, except that the rare earth-doped tin dioxide nanoparticles are prepared as follows: 120g of SnCl4·5H2O is weighed and dissolved in 22mL of ethylene glycol, and stirred in an ice bath (-0.5℃) for 38min until completely dissolved; 2.05g of Eu(NO3)3·6H2O (Sn:Eu molar ratio approximately 99:1) is added, and 1.2mol / L HNO3 solution is added dropwise to adjust the pH to 3.0. Then 100g of citric acid is added, and the mixture is heated to 80℃ and refluxed for 2.5h until the solution turns into a deep yellow gel. The gel is placed in a vacuum drying oven and dried at 81℃ for 18h. After grinding into powder, it is transferred to a muffle furnace and calcined at 505℃ at a rate of 3℃ / min under nitrogen atmosphere for 4h. After natural cooling, rare earth-doped tin dioxide nanoparticles are obtained.

[0047] Preparation of carboxyl-functionalized graphene quantum dots: 5.2 g of citric acid and 1.2 g of ethylenediamine were weighed and added to 80 mL of deionized water, and ultrasonically dispersed (26 °C, 38 min) until clear. The mixed solution was transferred to a polytetrafluoroethylene-lined reactor, sealed, and placed in a 200 °C oven for 18 h (stirring speed maintained at 250 rpm). After natural cooling, the supernatant was collected by centrifugation at 13000 rpm for 18 min, and concentrated to 1 / 10 of the original volume using an ultrafiltration tube with a molecular weight cutoff of 10000 to obtain amino-functionalized graphene quantum dots. The amino-functionalized graphene quantum dots were dispersed in 0.8 mol / L HCl solution, ultrasonicated in an ice bath for 1.8 h, centrifuged at 13500 rpm for 35 min, and the supernatant was concentrated again to 1 / 5 of the original volume using an ultrafiltration tube with a molecular weight cutoff of 5000 to obtain carboxyl-functionalized graphene quantum dots.

[0048] Preparation of a visible-light transparent conductive film: A 188 μm thick PET substrate was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 18 min, dried with nitrogen, and then treated in a plasma cleaner (81 W power, Ar / O2 volume ratio 4:1) for 9 min. A first layer of carboxyl-functionalized graphene quantum dot aqueous solution (concentration 1.1 mg / mL) was spin-coated at 2100 rpm (42 s) and dried at 81 °C for 5.5 min. A second layer of rare-earth-doped tin dioxide nanoparticle ethanol dispersion (concentration 5.5 mg / mL) was spin-coated at 3100 rpm (62 s) and dried at 81 °C for 5.5 min. The spin-coating process was repeated for the third layer. The film was then placed in a vacuum oven (vacuum degree 6 Pa, 151 °C) and held at that temperature for 35 min, followed by furnace cooling to below 80 °C to obtain the visible-light transparent conductive film.

[0049] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the visible light transparent conductive film is prepared by omitting the preparation step of carboxyl functionalized graphene quantum dots and directly spin-coating two layers of rare earth doped tin dioxide nanoparticles in ethanol at 3000 rpm.

[0050] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the rare earth-doped tin dioxide nanoparticles are prepared without the addition of Eu(NO3)3·6H2O. The visible light transparent conductive film is prepared by adding undoped Eu... 3+ Two layers of ethanol dispersion of tin dioxide nanoparticles were spin-coated.

[0051] Comparative Example 3 The specific implementation method is the same as in Example 1, except that the graphene quantum dots are prepared as follows: 5g of citric acid is weighed and added to 100mL of deionized water, and ultrasonically dispersed (25℃, 35min) until clear; transferred to a polytetrafluoroethylene-lined reactor, and reacted at 200℃ for 18h (stirring at 200rpm); after natural cooling, the supernatant is collected by centrifugation at 12000rpm for 15min, and concentrated to 1 / 10 of the original volume using an ultrafiltration tube with a molecular weight cutoff of 10000 (without the addition of ethylenediamine and acidification steps). The visible light transparent conductive film is prepared by spin-coating the first layer with an aqueous solution of unfunctionalized graphene quantum dots.

[0052] II. Performance Testing The visible light transparent conductive films prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following methods: 1. Transmittance Test: Using a UV-Vis spectrophotometer (model: Shimadzu UV-2600), the film sample to be tested was cut into a 50mm × 50mm square. After gently wiping the surface with anhydrous ethanol to remove contaminants, it was fixed on a glass slide on the sample stage (ensuring no scratches or bubbles). The instrument was set to a scanning wavelength range of 380-780nm and a scanning step of 1nm. Using air as a reference, the transmittance (T%) at the center wavelength of 550nm was recorded. Each sample was tested three times and the average value was taken.

[0053] 2. Sheet resistance test: A four-probe tester (model: Keithley 2400) was used. Before testing, the film sample was laid flat on an insulating substrate (such as PET), ensuring the surface was smooth and wrinkle-free. The test conditions were set to room temperature (25℃), ambient humidity 40%RH, probe spacing 1mm, and a test voltage of 10mV. The surface resistivity (ρ) of the film was measured. Sheet resistance (Rs) was calculated using the formula Rs=ρ×electrode spacing / electrode width (electrode width is the probe spacing of 1mm). Five different locations were tested for each sample, and the average value was taken.

[0054] 3. Adhesion Test: According to ASTM D3359 standard, using 3M 600 tape (25mm wide), the tape is evenly applied to the film surface at a 45° angle. Air bubbles are removed by gently pressing the tape surface with a finger. After standing for 24 hours, a 180° peel force is applied to one end of the tape (peeling speed approximately 100mm / min), and the remaining film residue on the tape surface is observed. Residual area is graded as follows: Grade 0 (no residue), Grade 1 (residue <5%), Grade 2 (residue 5%-20%), Grade 3 (residue 20%-50%), Grade 4 (residue 50%-80%), Grade 5 (residue >80%).

[0055] 4. Flexibility Test: Cut the film sample into strips of 50mm × 10mm and fix them to one end of a PTFE rod with a radius of 5mm (one end of the film is attached to the rod, and the other end hangs freely). Use an electric bending machine to bend the film 180° along the rod at a speed of 1mm / s (i.e., bend the free end of the film from being attached to the rod to being completely flipped). Repeat this process 100 times, and then observe the film surface for cracks or peeling using an optical microscope (100x magnification).

[0056] 5. Damp-heat aging stability test: Place the film sample in a constant temperature and humidity chamber (model: ESPEC SH-241), set the temperature to 85℃ and the humidity to 85%RH, and leave it for 300 hours. After aging, remove the sample and leave it at room temperature for 2 hours to allow it to return to equilibrium. Retest according to the above test methods for transmittance, sheet resistance, and adhesion, and calculate the performance degradation rate: Degradation rate = (initial value - value after aging) / initial value × 100% (the absolute value of transmittance degradation rate and the positive value of sheet resistance degradation rate are taken).

[0057] 6. Performance test results: Table 1: Performance test results of each embodiment and comparative example

[0058] As shown in Table 1, Examples 1-3 of this invention effectively solve the technical problems of high brittleness, difficulty in coordinating conductivity and light transmittance, and weak interfacial bonding in traditional transparent conductive films through the synergistic design of the interface buffer layer and rare-earth-doped tin dioxide nanoparticles. Specific analysis is as follows: In terms of transmittance, the transmittance at the 550nm center wavelength in Examples 1-3 remained at 88.5%-89.2%, significantly higher than that of Comparative Example 1 (82.1%), Comparative Example 2 (85.3%), and Comparative Example 3 (83.7%). This is because the interface buffer layer (carboxyl-functionalized graphene quantum dots) reduces interface defects (such as dangling bonds and oxygen vacancy traps) and lowers light scattering loss through hydrogen bonding between carboxyl groups and substrate hydroxyl groups and coordination with oxygen vacancies in the conductive layer. At the same time, the bilayer structure of rare earth-doped tin dioxide nanoparticles avoids local dark areas caused by high concentration doping in a single layer. Both factors together improve light transmittance efficiency.

[0059] Regarding conductivity, the sheet resistance of Examples 1-3 was only 32-38 Ω / □, far lower than that of Comparative Example 1 (55 Ω / □), Comparative Example 2 (62 Ω / □), and Comparative Example 3 (58 Ω / □). This is attributed to the Eu content of rare-earth-doped tin dioxide nanoparticles. 3+ Doping effect: Eu 3+ Replace Sn 4+Entering the crystal lattice, impurity energy levels are formed at the bottom of the conduction band, which lowers the electron transition barrier and improves intrinsic conductivity. The double-layer conductive layer design increases the carrier transport path density and avoids the problem of enhanced electron scattering caused by single-layer doping. The two work together to optimize carrier migration efficiency.

[0060] Regarding interfacial adhesion, the adhesion ratings of Examples 1-3 were all 0 (no detachment), while Comparative Examples 1-3 were 2, 1, and 2, respectively. This is because the carboxyl functionalized structure of the interfacial buffer layer, through strong interactions with the hydroxyl groups of the substrate (hydrogen bonds and coordination bonds) and adsorption of surface charges of the conductive layer nanoparticles (negative carboxyl charges and positive nanoparticle charges), constructs a multi-layer bonding network of "substrate-buffer layer-conductive layer," which significantly enhances the interfacial bonding strength and solves the problem of conductive layer detachment caused by weak interfacial bonding in traditional films.

[0061] Regarding flexibility and environmental stability, Examples 1-3 showed no cracks after 100 bends (5mm radius), and after 300 hours of damp heat aging, the transmittance attenuation rate was <1.9% and the sheet resistance attenuation rate was <3.6%. In contrast, Comparative Examples 1-3 all showed local microcracks or a small number of cracks, and after 300 hours of damp heat aging, the transmittance attenuation rate was >4.4%. This indicates that the dual-component structure (rare earth-doped tin dioxide and carboxyl-functionalized graphene quantum dots) enhances the bending resistance and environmental tolerance of the film through the flexible connection of the interface buffer layer (the nanoscale size of the graphene quantum dots and the flexible functional groups of the carboxyl groups) and the lattice stabilization effect of rare earth doping, overcoming the problems of high brittleness and susceptibility to humidity / light effects of traditional ITO films.

[0062] In summary, Examples 1-3 achieved a transparent conductive film with high light transmittance, low resistance, strong bonding, and environmental stability by modifying the interface buffer layer and optimizing the conductivity of rare earth-doped tin dioxide nanoparticles. This effectively solved the core problems of high brittleness, difficulty in achieving synergistic performance, and weak interface bonding in the prior art.

[0063] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A visible light transparent conductive film, prepared on a transparent substrate, characterized in that, The top layer of the transparent substrate is a two-layer conductive layer made of rare earth-doped tin dioxide nanoparticles. An interface buffer layer with reduced interface defects and promoted adhesion is provided between the transparent substrate and the top layer to enhance the adhesion between the conductive layer and the transparent substrate and to enhance the conductivity of the conductive layer. The preparation method of the rare earth-doped tin dioxide nanoparticles includes: A1, dissolving SnCl4·5H2O in ethylene glycol, stirring in an ice bath until completely dissolved, adding Eu(NO3)3·6H2O, adjusting the pH to 3.0-3.2 by adding HNO3 solution dropwise, then adding citric acid, heating to 80-82℃ and stirring under reflux until the solution becomes a deep yellow gel; A2, drying the gel in a vacuum drying oven, grinding it into powder, transferring it to a muffle furnace, calcining it at 500-510℃ under a nitrogen atmosphere, and then naturally cooling.

2. The visible light transparent conductive film according to claim 1, characterized in that, In step A1, the molar ratio of SnCl4·5H2O to Eu(NO3)3·6H2O is (99-101):1; the temperature of the ice bath stirring is -1 to 0℃, and the stirring time is 30-40 min; the concentration of the HNO3 solution is 1-2 mol / L; and the reflux stirring time is 2-4 h.

3. The visible light transparent conductive film according to claim 1, characterized in that, In step A2, the drying temperature in the vacuum drying oven is 78-82℃, and the drying time is 12-24h; the rate of heating to 500℃ is 2-4℃ / min, and the calcination time is 3-5h.

4. The visible light transparent conductive film according to claim 1, characterized in that, The interface buffer layer is spin-coated from carboxyl-functionalized graphene quantum dots; the preparation method of the carboxyl-functionalized graphene quantum dots includes: B1, adding citric acid and ethylenediamine to deionized water and ultrasonically dispersing until clear; transferring the mixed solution to a polytetrafluoroethylene-lined reactor, sealing it, and placing it in an oven at 198-202℃ for 12-24 hours; after natural cooling, centrifuging to collect the supernatant, and concentrating it to 1 / (8-12) of the original volume using an ultrafiltration tube with a molecular weight cutoff of 10000 to obtain amino-functionalized graphene quantum dots; B2, dispersing the amino-functionalized graphene quantum dots in HCl solution, ultrasonicating in an ice bath, centrifuging, and concentrating the supernatant again to 1 / (4-6) of the original volume using an ultrafiltration tube with a molecular weight cutoff of 5000.

5. The visible light transparent conductive film according to claim 4, characterized in that, In step B1, the ultrasonic dispersion temperature is 24-26℃ and the time is 30-40 min; the reaction time in the oven is 12-14 h, and the stirring rate is maintained at 200-300 rpm; the centrifugation speed is 10000-15000 rpm and the centrifugation time is 10-20 min.

6. The visible light transparent conductive film according to claim 4, characterized in that, In step B2, the time for ice bath sonication is 1-2 hours; the centrifugation speed is 12000-14000 rpm, and the time is 20-40 minutes.

7. A method for preparing a visible light transparent conductive thin film according to any one of claims 1-6, characterized in that, step include: S1. The PET substrate is ultrasonically cleaned sequentially with acetone, ethanol and deionized water, dried with nitrogen and then placed in a plasma cleaner. S2. Spin-coat the first layer with an aqueous solution of carboxyl-functionalized graphene quantum dots and dry at 80-82℃; spin-coat the second layer with an ethanol dispersion of rare earth-doped tin dioxide nanoparticles and dry at 80-82℃; repeat spin-coating the third layer. S3. Place the film in a vacuum oven, heat it to 150-152℃ and keep it at that temperature, then cool it down to below 80℃ in the oven.

8. The preparation method according to claim 7, characterized in that, In step S1, the thickness of the PET substrate is 186-190 μm; the ultrasonic cleaning time is 15-20 min; the power of the plasma cleaner is 80-82 W, the volume ratio of Ar / O2 in the plasma cleaner is (3-5):1; and the processing time in the plasma cleaner is 8-10 min.

9. The preparation method according to claim 7, characterized in that, In step S2, the concentration of the aqueous solution of carboxyl-functionalized graphene quantum dots is 1-1.2 mg / mL; the spin coating speed of the first layer is 2000-2200 rpm, the spin coating time of the first layer is 38-42 s, and the drying time of the first layer is 5-6 min; the concentration of the ethanol dispersion of rare earth-doped tin dioxide nanoparticles is 5-6 mg / mL, the spin coating speed of the second layer is 3000-3200 rpm, the spin coating time of the first layer is 58-62 s, and the drying time of the second layer is 5-6 min.

10. The preparation method according to claim 7, characterized in that, In step S3, the vacuum degree in the vacuum oven is <10Pa; the heat preservation time is 30-40min.

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