A method for preparing a flexible thermoelectric thin film

Abstract

The application discloses a preparation method of a flexible thermoelectric film, and belongs to the technical field of thermoelectric material preparation. The method aims to solve the problems of poor slurry dispersibility, low film density and damage to the flexible substrate after high-temperature post-processing in the existing printing process. The core steps include: compounding Tween and a polyvinyl alcohol aqueous solution into a mixed solution, adding Ag2Q powder to prepare printing slurry, wherein Q is selenium or tellurium; coating the slurry on flexible substrates such as cloth and paper through silk screen printing; and finally realizing film layer densification at low temperature by ultrasonic welding. The application guarantees the stability of the slurry through the innovative "Tween-polyvinyl alcohol" compounding system, and realizes high density (porosity ≤ 5%) while perfectly protecting the substrate by using the ultrasonic welding low-temperature process. The method is simple in process, low in cost, and wide in substrate adaptability, and the prepared film has high thermoelectric performance and excellent flexibility, and is suitable for wearable devices and flexible electronic devices.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric material preparation technology, and in particular to a method for preparing a flexible thermoelectric thin film. Background Technology

[0002] Flexible thermoelectric conversion technology, as a green energy solution capable of directly converting heat energy into electrical energy, has significant application prospects in cutting-edge fields such as self-powered wearable devices and industrial waste heat recovery. The core of this technology lies in the thermoelectric properties of the materials, typically expressed as a dimensionless figure of merit. zT To measure this. For flexible applications, the ideal thin film material must simultaneously possess high thermoelectric properties (high... zT It has high mechanical flexibility and excellent mechanical flexibility to adapt to complex bending and deformation scenarios.

[0003] In terms of material systems, traditional Bi2Te3-based materials exhibit outstanding performance at room temperature ( zT (≈1.4), but due to its reliance on scarce elements, high cost, and inherent brittleness, it is difficult to achieve flexible and large-scale applications. In contrast, Ag2Q (Q is selenium or tellurium) series materials show better overall potential: Ag2Se and Ag2Te not only possess good intrinsic thermoelectric properties (room temperature...) zT With values ​​reaching 1.06 and 0.81 respectively, its crystal structure also endows it with natural flexibility. For example, after undergoing 1000 bends at a bending radius of 5 mm, its performance retention rate still exceeds 95%, making it an ideal candidate for flexible thermoelectric thin films.

[0004] At the fabrication process level, screen printing and other printing technologies have become the mainstream direction for the preparation of flexible thermoelectric thin films due to their low cost and good compatibility. However, this process still faces several key challenges: First, the dispersion stability of the slurry is insufficient, Ag2Q powder is prone to agglomeration, and conventional adhesive residues can impair conductivity; Second, the density of the printed film is low (porosity > 20%), while traditional high-temperature sintering or hot pressing post-processing methods can damage flexible substrates such as fabrics and paper, making it impossible to achieve both "densification" and "flexibility"; Third, existing processes generally have poor universality and are difficult to adapt to various substrates and materials.

[0005] Therefore, developing a simple preparation method that can systematically solve the problems of slurry dispersion, low-temperature densification, and compatibility with various flexible substrates is crucial for promoting the industrialization of this technology. Summary of the Invention

[0006] In view of this, the present invention proposes a method for preparing flexible thermoelectric thin films. This method aims to solve the problems existing in current printing processes, such as poor paste stability, low film density, high-temperature damage to flexible substrates during post-processing, and limited process versatility.

[0007] The technical solution of this invention is implemented as follows: This invention provides a method for preparing a flexible thermoelectric thin film, characterized by comprising the following steps: S1. Add Tween and polyvinyl alcohol aqueous solution to a centrifuge tube, mix well to obtain a mixture; S2. Add Ag2Q powder to the mixture obtained in step S1, mix evenly, and obtain printing paste; S3. Using a screen printing mold, the printing paste obtained in step S2 is printed onto the surface of the substrate to form a printing layer; the printing layer is ultrasonically welded to obtain the flexible thermoelectric film.

[0008] Based on the above technical solutions, preferably, in step S1, the Tween is selected from at least one of Tween 20, Tween 40, Tween 60, Tween 80, and Tween 85 (HLB value 11.0~16.7). The emulsifying and dispersing effect of Tween inhibits the agglomeration of Ag2Q powder, while the adhesive properties of PVA ensure the printing and molding capability of the paste. Both also have good low-temperature compatibility, avoiding the impact of residual impurities on the film conductivity during subsequent processing.

[0009] More preferably, in step S1, the mass fraction of the polyvinyl alcohol aqueous solution is 1% to 10%.

[0010] More preferably, in step S1, the volume ratio of Tween to the polyvinyl alcohol aqueous solution is 1:2 to 1:50. In the slurry system, Tween, as a nonionic surfactant, mainly functions to reduce the liquid-solid interfacial tension and disperse powder particles, while synergistically improving the wettability and printability of the slurry with polyvinyl alcohol (PVA). Its addition amount directly determines the particle dispersion state, slurry rheological behavior, film density, and final thermoelectric properties.

[0011] More preferably, in step S2, Q in the Ag2Q powder is selenium or tellurium.

[0012] More preferably, the Ag2Q powder has a particle size of 50 nm to 5 μm.

[0013] More preferably, in step S2, the mass fraction of the Ag2Q powder in the printing paste is 30%~90%.

[0014] More preferably, step S2 specifically includes: first, adding Tween and polyvinyl alcohol aqueous solution to a centrifuge tube, and mixing for 3 min to 10 min until uniform by means of a mixer, magnetic stirring or manual stirring, to obtain a well-dispersed mixture; then adding Ag2Q powder with a particle size of 50 nm to 5 μm to the mixture, and continuing to mix for 3 min to 10 min to ensure that the Ag2Q powder is uniformly dispersed in the slurry system to form a printing slurry with a viscosity of 100 mPa s to 5000 mPa s (25℃), which is suitable for the requirements of screen printing process.

[0015] Based on the above technical solutions, preferably, in step S3, the substrate is one of cloth, paper or polyvinyl chloride film.

[0016] More preferably, in step S3, the mesh size of the screen printing mold is 100 mesh to 500 mesh.

[0017] More preferably, in step S3, the process parameters for ultrasonic welding are: ultrasonic power 50W~2000W, welding time 0.1s~30s, and welding pressure 0.1MPa~20MPa. More preferably, in step S3, the temperature of the substrate is controlled between 25°C and 130°C during the ultrasonic welding process. The mechanical energy generated by ultrasonic vibration promotes the interdiffusion of molecular chains within the film layer, filling the pores formed during printing (final porosity ≤ 5%), while simultaneously avoiding damage to the flexible substrate from high-temperature processing, thus achieving a synergistic improvement in film density and flexibility.

[0018] The flexible thermoelectric thin film of the present invention has the following advantages over the prior art: (1) It fundamentally solves the problem of substrate thermal damage: The innovative "ultrasonic welding" low-temperature densification process completely eliminates the traditional high-temperature sintering or hot pressing steps. It can achieve film densification (porosity ≤5%) in a low temperature range of 25℃~130℃, thus perfectly preserving the original flexibility and mechanical integrity of heat-sensitive substrates such as cloth and paper, breaking through a long-term bottleneck in the preparation of flexible thermoelectric films.

[0019] (2) Excellent slurry performance and high film quality: The "Tween-PVA" compound dispersion system not only ensures the uniform and stable dispersion of Ag2Q powder in the slurry, avoiding agglomeration and sedimentation, but also has good water solubility and low-temperature compatibility, avoiding the negative impact of organic residues on the film conductivity. This makes the film layer formed by subsequent printing uniform and continuous, laying the foundation for high performance.

[0020] (3) Excellent product performance, meeting stringent application requirements: The flexible Ag2Q thermoelectric film prepared by this method has both high thermoelectric performance (room temperature) and excellent thermoelectric properties. zTWith a thermal conductivity value ≥ 0.7 and excellent mechanical durability (e.g., thermoelectric performance retention rate ≥ 90% after 1000 bending cycles at a 5mm bending radius), its overall performance perfectly meets the high performance and high reliability requirements of wearable electronics and other devices.

[0021] (4) Superior production process with strong industrialization potential: This method has good universality for both core thermoelectric materials (Ag2Se / Ag2Te) and flexible substrates (cloth, paper, PVC film, etc.). At the same time, the raw materials required for the process are readily available, the equipment is simple, and the steps are concise. It does not require complex and expensive equipment, and it shows significant advantages in terms of technical versatility and production cost, making it very suitable for large-scale, low-cost production. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a physical image of the screen-printed Ag2Te thermoelectric film on A4 paper according to Embodiment 1 of the present invention; Figure 2 This is a physical image of the polyester fabric-based Ag2Se thermoelectric film screen-printed according to Embodiment 2 of the present invention; Figure 3 This is a physical image of the rectangular device for screen printing Ag2Te thermoelectric thin film on cotton fabric according to Embodiment 3 of the present invention; Figure 4 This is an EPMA micrograph of the Ag2Te thermoelectric thin film of Example 1 of the present invention; Figure 5 This is a cross-sectional SEM image of the Ag2Te thermoelectric thin film of Embodiment 1 of the present invention; Figure 6 This is a complete fabrication process flow diagram of the Ag2Te rectangular flexible thermoelectric device based on nylon fabric according to Embodiment 3 of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 4As shown, the surface of the film of the present invention is generally flat and continuous, without large-area peeling, breakage or other macroscopic defects, indicating that screen printing and ultrasonic welding processes can form a complete thermoelectric film on a flexible fabric substrate.

[0026] like Figure 5 As shown, the film is tightly bonded to the substrate, and the Ag2Te slurry fully fills the gaps between the fabric fibers. After ultrasonic welding, a dense film structure is formed without obvious delamination or large-sized pores. This indicates that the screen printing and ultrasonic welding process can effectively achieve film densification and form a stable interface bond with the flexible substrate, with uniform overall film thickness.

[0027] Table 1: Material Source Description Table

[0028] Example 1: S1. Use a pipette to transfer 25 μL of Tween 85 reagent into a centrifuge tube, then transfer 85 μL of 5wt% PVA aqueous solution into the centrifuge tube. Place the centrifuge tube in a high-speed mixer, adjust the speed to 3000 r / min, and mix for 5 min at room temperature until the two reagents in the tube form a uniform and transparent mixture without stratification. S2. Weigh 0.5 g of Ag2Te powder (particle size 200 nm) into the mixture obtained in step S1 and slowly add it into a centrifuge tube; put the centrifuge tube into a high-speed mixer again and mix for 5 min at room temperature while maintaining a speed of 3000 r / min to ensure that the Ag2Te powder is completely dispersed in the mixture to obtain a uniform Ag2Te slurry without agglomeration for later use. S3. Lay the pretreated A4 paper flat on the printing platform, fixing it smoothly along the edges to avoid wrinkles, misalignment, and slippage, while also preventing damage from excessive tightness. Evenly apply the Ag2Te paste prepared in step S2 onto a 200-mesh screen printing mold, using a squeegee at a uniform speed and moderate pressure to ensure the Ag2Te paste is evenly printed onto the A4 paper surface through the screen mold's mesh, forming a paste layer with a thickness of 50-80 μm. After printing, smoothly transfer the A4 paper to the welding platform of an ultrasonic welding machine. Adjust the ultrasonic welding machine parameters to: output power 250 W, ultrasonic frequency 30 kHz, and welding pressure 0.2 MPa. Perform ultrasonic welding to densify the printed paste layer for 10 seconds at 60℃, eliminating internal pores and ensuring a tight bond with the A4 paper surface. After welding, allow it to cool naturally to room temperature to obtain the target product.

[0029] Example 2: S1. Use a pipette to transfer 25 μL of Tween 20 reagent into a centrifuge tube, then transfer 50 μL of 10wt% PVA aqueous solution into the centrifuge tube. Place the centrifuge tube in a high-speed mixer, adjust the speed to 3000 r / min, and mix for 3 min at room temperature until the two reagents in the tube form a uniform and transparent mixture without stratification. S2. Weigh 33.9 mg of Ag2Se powder (particle size 500 nm) into the mixture obtained in step S1 and slowly add it into a centrifuge tube; put the centrifuge tube into a high-speed mixer again and mix for 3 min at room temperature while maintaining a speed of 3000 r / min to ensure that the Ag2Se powder is completely dispersed in the mixture to obtain a uniform, non-agglomerated Ag2Se slurry for later use. S3. Lay the pretreated polyester fabric flat on the printing platform, fixing it smoothly along the edges to avoid wrinkles, misalignment, and slippage, while also preventing damage from excessive tightness. Apply the Ag2Se paste prepared in step S2 evenly to a 100-mesh screen printing mold, using a squeegee at a uniform speed and moderate pressure to ensure the Ag2Se paste is evenly printed onto the polyester fabric surface through the screen mold's mesh, forming a paste layer with a thickness of 50-80 μm. After printing, smoothly transfer the polyester fabric to the welding platform of an ultrasonic welding machine. Adjust the ultrasonic welding machine parameters to: output power 50 W, ultrasonic frequency 30 kHz, and welding pressure 0.1 MPa. Perform ultrasonic welding to densify the printed paste layer for 15 seconds at 25°C, eliminating internal pores and ensuring a tight bond with the polyester fabric surface. After welding, allow it to cool naturally to room temperature to obtain the target product.

[0030] Example 3: S1. Use a pipette to transfer 25 μL of Tween 60 reagent into a centrifuge tube, then transfer 1.25 mL of 1wt% PVA aqueous solution into the centrifuge tube. Place the centrifuge tube in a high-speed mixer, adjust the speed to 3000 r / min, and mix for 10 min at room temperature until the two reagents in the tube form a uniform and transparent mixture without stratification. S2. Weigh 11.49 g of Ag2Te powder (particle size 5 μm) into the mixture obtained in step S1 and slowly add it into a centrifuge tube; put the centrifuge tube into a high-speed mixer again and mix for 10 min at room temperature while maintaining a speed of 3000 r / min to ensure that the Ag2Te powder is completely dispersed in the mixture to obtain a uniform Ag2Te slurry without agglomeration, for later use; S3. Lay the pretreated nylon fabric flat on the printing platform, fixing it smoothly along the edges to avoid wrinkles, misalignment, and slippage, while also preventing damage from excessive tightness. Apply the Ag2Te paste prepared in step S2 evenly to a 500-mesh screen printing mold, using a squeegee at a uniform speed and moderate pressure to ensure the Ag2Te paste is evenly printed onto the nylon fabric surface through the screen mold's mesh, forming a paste layer with a thickness of 50-80 μm. After printing, smoothly transfer the nylon fabric to the welding platform of an ultrasonic welding machine. Adjust the ultrasonic welding machine parameters to: output power 50 W, ultrasonic frequency 2000 kHz, and welding pressure 20 MPa. Perform ultrasonic welding densification treatment on the printed paste layer for 30 seconds at a temperature of 130℃ to eliminate internal pores in the paste layer and ensure a tight bond with the nylon fabric surface. After welding, allow it to cool naturally to room temperature to obtain the target product.

[0031] Comparative Example 4: Unlike Example 1, this comparative example only adds PVA aqueous solution and does not add Tween 85. The remaining steps are the same as in Example 1, and will not be repeated here.

[0032] Comparing Comparative Example 4 with Example 1, it can be seen that when only PVA aqueous solution is used in the system without the addition of Tween 85, Ag2Te particles exhibit significant agglomeration and sedimentation in the slurry, resulting in a significant decrease in dispersion stability. Due to the lack of steric hindrance and electrostatic repulsion provided by the surfactant, it is difficult to form a uniform and stable dispersion system. The film obtained after screen printing has a rough surface, poor continuity, and numerous pinholes, agglomerated protrusions, and unfilled gaps. The internal porosity of the film layer is high, and the particles are loosely connected.

[0033] Comparative Example 5: Unlike Example 1, this comparative example uses high-temperature sintering (sintering temperature: 300℃, heating rate: 3℃ / min, holding time: 30 min, cooling method: furnace cooling to room temperature) instead of ultrasonic welding. The remaining steps are the same as in Example 1, and will not be repeated here.

[0034] Comparing Comparative Example 5 with Example 1, it can be seen that although high temperature and pressure can improve the film density and reduce the internal porosity to a certain extent, the flexible fabric substrate will exhibit significant thermal shrinkage, fiber embrittlement, and even localized carbonization, resulting in a loss of substrate flexibility. Simultaneously, the high temperature may cause abnormal growth of Ag2Te grains, adversely affecting carrier transport.

[0035] Comparative Example 6: Unlike Example 1, this comparative example uses high-pressure cold pressing (after screen printing, the sample is placed in a stainless steel mold, and a bidirectional pressure of 20 MPa is applied at room temperature for 1 min to complete the cold pressing densification; after cold pressing, the sample is subjected to low-temperature heat treatment at 80°C for 1 h to eliminate internal residual stress). The remaining steps are the same as in Example 1, and will not be repeated here.

[0036] Comparing Comparative Example 6 with Example 1, it can be seen that the film cannot achieve sufficiently high density and particle bonding strength. Although high-pressure cold pressing can improve the compaction degree, it is prone to causing fabric fiber breakage and stress concentration inside the film layer, which can easily lead to the propagation of microcracks during long-term service.

[0037] Comparative Examples 7-8: Unlike Example 1, the volume ratios of Tween 85 to polyvinyl alcohol aqueous solution were 1:0.8 (25 μL Tween 85; 20 μL polyvinyl alcohol aqueous solution) and 1:0.6 (25 μL Tween 85; 1.5 mL polyvinyl alcohol aqueous solution), respectively. The remaining steps were the same as in Example 1 and will not be repeated here.

[0038] Comparing Comparative Examples 7 and 8 with Example 1, it is evident that when the amount of Tween added is too low, a complete and uniform adsorption layer cannot be formed on the particle surface, leading to agglomeration and sedimentation. Particle agglomeration reduces the uniformity of the slurry, making it difficult to form a smooth and continuous film during screen printing. This results in pits, pinholes, and localized accumulation defects, increasing the porosity of the film. Simultaneously, poor dispersion weakens the interfacial wettability between the slurry and the substrate, reducing film adhesion. This can lead to detachment and cracking during bending or ultrasonic welding, ultimately reducing the film's flexibility and structural stability. When excessive Tween is added, the excess surfactant molecules cannot continue to adsorb on the particle surface, forming numerous micelle structures in the slurry. This significantly increases the system viscosity, reducing slurry fluidity and causing problems such as screen clogging, poor leveling, and uneven film thickness during screen printing. Excessive Tween remains in a free state within the film layer. Its long organic chain structure forms a non-conductive barrier between particles, scattering charge carriers and reducing carrier mobility, further degrading conductivity. In addition, during ultrasonic welding and subsequent processing, excessive organic matter is difficult to completely remove. Residual components can lead to a decrease in film density and a reduction in interfacial bonding force. At the same time, they can introduce additional defects and impurity scattering centers, which can deteriorate thermoelectric performance.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a flexible thermoelectric thin film, characterized in that, Includes the following steps: S1. Add Tween and polyvinyl alcohol aqueous solution to a centrifuge tube, mix well to obtain a mixture; S2. Add Ag2Q powder to the mixture obtained in step S1, mix evenly, and obtain printing paste; S3. Using a screen printing mold, the printing paste obtained in step S2 is printed onto the surface of the substrate to form a printing layer; the printing layer is ultrasonically welded to obtain the flexible thermoelectric film.

2. The preparation method according to claim 1, characterized in that, In step S1, the Tween is selected from at least one of Tween 20, Tween 40, Tween 60, Tween 80, and Tween 85.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass fraction of the polyvinyl alcohol aqueous solution is 1% to 10%.

4. The preparation method according to claim 1, characterized in that, In step S1, the volume ratio of Tween to the polyvinyl alcohol aqueous solution is 1:2 to 1:

50.

5. The preparation method according to claim 1, characterized in that, In step S2, Q in the Ag2Q powder is selenium or tellurium.

6. The preparation method according to claim 5, characterized in that, The Ag2Q powder has a particle size of 50 nm to 5 μm.

7. The preparation method according to claim 1, characterized in that, In step S2, the mass fraction of the Ag2Q powder in the printing paste is 30% to 90%.

8. The preparation method according to claim 1, characterized in that, In step S3, the substrate is one of fabric, paper, or polyvinyl chloride film.

9. The preparation method according to claim 1, characterized in that, In step S3, the ultrasonic welding process parameters are: ultrasonic power 50W~2000W, welding time 0.1s~30s, and welding pressure 0.1MPa~20MPa.

10. The preparation method according to claim 1, characterized in that, In step S3, during the ultrasonic welding process, the temperature of the substrate is controlled between 25°C and 130°C.

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