A flexible polyimide / silver ultrafine nanofiber transparent electrode and its preparation method

Abstract

This invention relates to a flexible polyimide / silver ultrafine nanofiber transparent electrode and its preparation method. The method includes the following steps: First, a silver precursor is added to a polyamic acid solution to obtain a spinning solution; a pre-defined nanofiber network is deposited on the surface of a transparent substrate by electrospinning; subsequently, in-situ metallization of the nanofiber surface is performed to transform the non-conductive network into a conductive network; finally, high-temperature treatment is carried out to obtain the flexible polyimide / silver ultrafine nanofiber transparent electrode. The transparent electrode formed by this method has the unique advantage of integrated molding, as well as the characteristics of good flexibility, uniform resistance, and low cost, and can be realized on transparent substrates of various shapes. In addition, the entire process is highly operable, adjustable, and controllable, providing a highly promising innovative solution for the development of metal nanomaterials.

Description

Technical Field

[0001] This invention belongs to the field of nanofiber technology, specifically relating to a flexible polyimide / silver ultrafine conductive nanofiber transparent electrode and its preparation method. Background Technology

[0002] Transparent electrodes (TCEs) are a unique class of materials that combine optical transparency and conductivity, and are key components of many modern devices, including solar cells, organic light-emitting diodes (OLEDs), liquid crystal displays (LCDs), and touchscreens. In recent years, metallic nanomaterials have been considered strong candidates to replace traditional transparent conductive materials due to their enormous potential. The high conductivity of metals endows them with extremely low resistance, and by constructing nanostructures smaller than the wavelength of visible light, high transparency is achieved, while also possessing excellent surface interface effects. Currently, significant progress has been made in the preparation technology of silver nanowires (AgNWs). Silver nanowires with diameters of approximately 80 nm are formed by controlling the slow growth of silver ions in solution through aldolothermic, hydrothermal, and photoreduction methods, and AgNWs transparent conductive films are prepared using spin-coating, roll-to-roll coating, and spray coating methods. However, the application of silver nanowires still faces many challenges. For example, during synthesis, the quality is inconsistent, purity is low, and stability is poor; during coating, uniform distribution is difficult to achieve; in addition, the flexibility and adhesion of silver nanowires themselves are poor, and their reliability decreases with frequent bending and use. Therefore, optimizing the quality and purity of silver nanowires, improving their distribution uniformity, and enhancing their flexibility and adhesion have become key issues that urgently need to be addressed in the current research field. Exploring new technologies and methods to overcome these bottlenecks is currently a hot research topic.

[0003] Polymer nanofibers have become a promising solution due to their ability to fabricate uniformly distributed flexible network structures on substrates of various shapes via electrospinning, coupled with ease of operation and high yield. Metallization of the surface of interlocking nanofiber network structures constructed using electrospinning technology creates metal nanofiber webs with high aspect ratios, endowing them with excellent conductivity and flexibility. This is gradually becoming a trend in optimizing metal nanowires and holds promise for significant applications in flexible TCEs (Transformed Chemical Electronics). Currently, the relatively large diameter of polymer nanofibers and their weak adhesion to metal layers are the main factors limiting their widespread application.

[0004] Therefore, developing a highly conductive flexible nanofiber material with adjustable diameter and a tight bond between the metal layer and the nanofiber can not only provide new possibilities for future electronic devices, but also offer new ideas for high-performance and sustainable flexible electronic devices. Summary of the Invention

[0005] This invention first loads silver into the polyamic acid spinning solution by adding a silver precursor. Then, nanofibers are fabricated on a transparent substrate using electrospinning technology, and the nanofiber diameter is controlled by parameter adjustment, allowing for direct pre-setting of nanofiber templates on the transparent substrate. Following chemical reduction, silver is reduced and grown, achieving the first silver loading on the nanofiber surface and forming a seed layer. Subsequently, multiple silver loading processes are performed on the nanofiber surface using ion exchange-reduction metallization in a silver salt aqueous solution, transforming the nanofibers from a non-conductive to a conductive mesh. Finally, high-temperature treatment converts the polyamic acid nanofibers into high-temperature resistant, flexible polyimide nanofibers, while simultaneously densifying and increasing the conductivity of the surface silver layer, effectively improving the conductivity of the polyimide / silver nanofibers and forming a uniform conductive mesh. The integrated polyimide / silver ultrafine nanofiber transparent electrode prepared by this invention possesses advantages such as high conductivity, good flexibility, uniform resistance distribution, and applicability to substrates of various shapes, showing broad application prospects in transparent electrodes.

[0006] A method for preparing a transparent electrode based on ultrafine polyimide / silver nanofibers, the specific steps of which are as follows:

[0007] A: The polyamic acid solution is obtained by condensing and polymerizing diamine monomer and dianhydride monomer. After the reaction is complete, a certain amount of silver precursor solution is added to obtain polyamic acid spinning solution containing silver source.

[0008] B: The above spinning solution is deposited on the surface of a transparent substrate by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface.

[0009] C: The nanofibers and substrates obtained in step B are immersed in a reducing agent solution to reduce the silver ions in the nanofibers to silver and load them on the surface of the nanofibers, thereby achieving the first surface silvering of the polyamic acid nanofibers and forming a seed layer. Then, they are cleaned with deionized water.

[0010] D: The nanofibers and substrate obtained in step C are immersed in a water-soluble silver salt solution of a certain concentration for a certain period of time to carry out the ion exchange reaction between polyamic acid and silver ions, thereby loading silver ions. After washing with deionized water, the nanofibers are reduced in a reducing agent solution to achieve secondary surface silvering. The ion exchange and reduction reaction is repeated multiple times to complete the surface silvering of the nanofibers.

[0011] E: The polyamic acid / silver transparent electrode obtained in step D is subjected to high temperature treatment under a nitrogen atmosphere to cause the polyamic acid to undergo an imidization reaction to transform into polyimide, while simultaneously densifying and increasing the conductivity of the surface silver layer, ultimately yielding a polyimide / silver ultrafine nanofiber transparent electrode.

[0012] The diamine mentioned in step A is one or more of 4,4'-diaminodiphenyl ether (ODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 4,4'-diaminodiphenylmethane (MDA), 1,4-phenylenediamine (PDA), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), and 3,4-diaminobenzyloxytrifluoride (TFBDA); the diacid anhydride is selected from hexafluoroisopropylphthalic acid. Formic anhydride (6FDA), pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4-diphenyl ether dianhydride (ODPA), 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride (DSDA), and 4,4'-(3,4-dicarboxyphenoxy)diphenylthionine dianhydride (BDSDA); the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0013] Further, in step A, the silver precursor is one or more of the following: silver trifluoroacetylacetonate (AgTFA), silver hexafluoroacetylacetonate (AgHFA), silver nitrate (AgNO3), silver fluoroborate (AgBF4), and silver trifluoromethanesulfonate (AgOTf); the solvent of the solution is the corresponding solvent in step A, with a concentration of 0.01 g / ml to 1 g / ml; and the silver content is controlled at 5% to 60% of the total solid mass.

[0014] Furthermore, in step B, the substrate material is preferably one of the following: transparent polyimide film, quartz glass, transparent ceramic, single crystal alumina, or special silicate glass; the spinning deposition time is 0.5h to 6h.

[0015] Further, the reducing solution in step C is an aqueous solution of dimethylamine borane, glucose, or ascorbic acid, with a concentration of 0.005–0.050 mol / L, and the reduction time is 1–10 min.

[0016] Furthermore, in step D, the silver salt solution is an aqueous solution of one or more of silver nitrate, silver fluoride, or silver tetrafluoroborate, with a concentration of 0.05–0.2 mol / L and an ion exchange time of 5–30 min.

[0017] Further, the imidization treatment conditions described in step E are as follows: under a nitrogen atmosphere, the temperature is raised to 135°C at room temperature for 1 hour, held at 135°C for 1 hour, then raised to 250-300°C for 2 hours and held for 0.5-3 hours, then raised to 420-480°C for 1 hour and held for 5-30 minutes.

[0018] Compared with existing materials and technologies, the present invention has the following beneficial effects:

[0019] 1. The method of the present invention has the feature of integrated molding. By anchoring a preset high aspect ratio nanofiber directly on a transparent substrate as a template and performing in-situ metallization on the nanofiber, the transformation from non-conductive to conductive mesh is achieved without secondary processing. This enables the design of complex shapes and fine structures, thus broadening the possibilities of product design.

[0020] 2. The method of this invention introduces a silver precursor during electrospinning, which regulates the diameter of nanofibers and thus controls the specifications of the metal nanomesh, forming a uniform metal nanomesh. This method requires no complex reaction conditions and is simple and easy to implement. The silver precursor introduced into the spinning solution undergoes reduction during the reduction process, enabling silver to grow from the inside out. The adhesion between the silver layer and the substrate is significantly improved due to mechanical interlocking, solving the problem of silver layer detachment from heterogeneous interfaces. Simultaneously, the method of introducing silver through ion exchange-reduction external secondary loading greatly improves the silver loading efficiency and addresses the issues of dense and highly conductive silver layers, thereby increasing the preparation efficiency.

[0021] 3. In the method of the present invention, after the polyamic acid is thermally imidized, it is further subjected to high temperature treatment. The silver on the surface of the nanofiber can diffuse and move to fill the gaps between the particles, thereby making the silver layer coating more compact and uniform, giving it higher stability and effectively improving the conductivity of polyimide / silver nanofibers, forming a transparent electrode with higher quality factor.

[0022] 4. The ultrafine nanofibers with silver as the shell and polymer as the core generated by the method of the present invention significantly reduce the amount of silver used under similar conductivity and light transmittance conditions, thereby effectively reducing costs; and providing a more economical solution for the application of metal nanomaterials. Attached Figure Description

[0023] Figure 1 The images are scanning electron microscope (SEM) images of the polyimide / silver ultrafine nanofiber transparent electrode prepared according to Example 1, with magnifications of 50,000x on the left and 200,000x on the right.

[0024] Figure 2 The bending resistance test is performed on the polyimide / silver ultrafine nanofibers prepared according to Example 1.

[0025] Figure 3 This is a photograph of the polyimide / silver ultrafine nanofibers prepared according to Example 1.

[0026] Table 1 shows the diameter, transmittance, and sheet resistance of the metal nanomesh samples obtained under different embodiments and comparative examples. Detailed Implementation

[0027] The invention will be further illustrated below with reference to the embodiments. It should be noted that the following embodiments are only used to illustrate the invention and not to limit the technical solutions described herein. Therefore, although this specification has described the invention in detail with reference to the following embodiments, those skilled in the art should understand that any modifications or equivalent substitutions to the invention, without departing from the spirit and scope of the invention, and all such technical solutions and improvements should be covered within the scope of the claims of the invention.

[0028] Example 1

[0029] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0030] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0031] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0032] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out an imidization reaction. Then the temperature is raised to 480°C and held for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0033] Example 2

[0034] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.03 g / ml was added and stirring was continued to obtain the spinning solution.

[0035] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0036] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0037] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out an imidization reaction. Then the temperature is raised to 480°C and held for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0038] Example 3

[0039] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver fluoroborate (AgBF4) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0040] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0041] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0042] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out an imidization reaction. Then the temperature is raised to 480°C and held for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0043] Example 4

[0044] (1) A polyamic acid solution with a solid content of 12% BPDA / TFMB system was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0045] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0046] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0047] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out the imidization reaction. Then, the temperature is raised to 480°C and held for 10 minutes to obtain the polyimide / silver ultrafine nanofiber transparent electrode.

[0048] Example 5

[0049] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0050] (2) The above-mentioned spinning solution was deposited on the surface of quartz glass by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0051] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0052] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out the imidization reaction. Then, the temperature is raised to 480°C and held for 10 minutes to obtain the polyimide / silver ultrafine nanofiber transparent electrode.

[0053] Example 6

[0054] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0055] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0056] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L ascorbic acid reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L silver fluoride (AgF) solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L ascorbic acid reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0057] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out an imidization reaction. Then the temperature is raised to 480°C and held for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0058] Example 7

[0059] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0060] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0061] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0062] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out an imidization reaction. Then the temperature is raised to 420°C and held for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0063] Comparative Example 1

[0064] ((1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, only 5 ml of DMF solvent was added and stirring was continued to obtain the spinning solution.

[0065] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0066] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and then placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min. After rinsing with deionized water, the above ion exchange and reduction steps were repeated 20 times.

[0067] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out the imidization reaction. Then the temperature is raised to 480°C and held for 10 minutes.

[0068] Comparative Example 2

[0069] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, 5 ml of silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml was added and stirring was continued to obtain the spinning solution.

[0070] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0071] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0072] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out the imidization reaction without further heating.

[0073] Comparative Example 3

[0074] (1) A PMDA / ODA polyamic acid solution with a solid content of 12% was synthesized in DMF solvent by condensation polymerization. After the reaction was completed, only 5 ml of DMF solvent was added and stirring was continued to obtain the spinning solution.

[0075] (2) The above-mentioned spinning solution was deposited on the surface of a transparent polyimide film by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine were as follows: spinning voltage: 25kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; feed speed: 0.002ml / min; receiving distance: 20cm; and spinning deposition time: 3h.

[0076] (3) The nanofiber-linked substrate prepared above was immersed in a 0.01 mol / L dimethylaminoborane (DMAB) reducing agent solution for 5 min, and then rinsed with deionized water. Subsequently, it was placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, then rinsed with deionized water, and placed again in a 0.01 mol / L DMAB reducing agent solution for 1 min, then rinsed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0077] (4) The polyamic acid / silver transparent electrode obtained in step (3) is heated to 300°C in nitrogen at a heating rate of 3°C / min and held for 1 hour to carry out the imidization reaction without further heating.

[0078] Table 1. Diameter, transmittance, and sheet resistance of the metal nanomesh samples obtained in different embodiments and comparative examples.

[0079] sample Average diameter (nm) <![CDATA[Transmittance T 550nm %]]> Shear resistance (Ω / sq) Example 1 40.5 71.1 3.2 Example 2 52.7 66.3 4.3 Example 3 50.2 69.1 4.8 Example 4 48.8 68.2 10.1 Example 5 45.2 78.3 6.2 Example 6 56.3 70.5 22.4 Example 7 42.6 68.2 73 Comparative Example 1 203 54.5 2.2 Comparative Example 2 43.1 62.7 ＞1000 Comparative Example 3 182 57.2 ＞1000

[0080] As shown in Table 1, the nanofibers obtained by electrospinning using the silver salt blend spinning solution in Examples 1, 2, and 3, and Comparative Example 1, have significantly smaller diameters than those obtained by electrospinning using the unblended silver salt spinning solution. The corresponding light transmittance is significantly improved, indicating that the addition of silver salt during electrospinning is beneficial for controlling the diameter of the nanofibers, thereby adjusting the diameter of the conductive metal mesh. This is because the addition of silver salt greatly improves the conductivity of the spinning solution, significantly enhances spinnability, and yields finer nanofibers. The metal mesh formed after surface metallization has greater advantages in the application of transparent electrodes.

[0081] In Examples 1 and 6 and Comparative Example 2, the nanofiber transparent electrodes treated at high temperatures exhibit stronger conductivity and lower sheet resistance, while the nanofibers treated only at 300℃ with imidization possess ultra-high resistance. This is due to the nano-effect; the melting point of nano-silver is significantly reduced. As the temperature continuously increases, the silver particles on the fiber surface melt at high temperatures, continuously filling the gaps between the particles, forming a more uniform conductive metal nanonetwork, which greatly improves the conductivity of the transparent electrode.

[0082] The flexibility of polyimide / silver ultrafine nanofibers is due to Figure 2 The bending performance test shows that the conductivity of the transparent electrode changes by only 10% when the bending radius is 1 mm, indicating that the polyimide / silver ultrafine nanofibers have excellent flexibility.

[0083] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultrafine polyimide / silver nanofiber transparent electrode, characterized by The method comprises the following steps: A: condensation polymerization of diamine monomers and dianhydride monomers to obtain a polyamic acid solution, after the reaction is completed, a certain amount of silver precursor solution is added to obtain a polyamic acid spinning solution containing a silver source; B: the spinning solution is deposited on the surface of a transparent substrate by electrospinning to obtain a transparent electrode with superfine polyamic acid / silver nanofibers attached to the surface; C: the nanofibers obtained in step B are immersed in a reducing agent solution to reduce silver ions in the nanofibers to silver and load the silver on the surface of the nanofibers, realize the first surface silverization of the polyamic acid nanofibers, form a seed layer, and then clean with deionized water; D: the nanofibers obtained in step C are immersed in a certain concentration of water-soluble silver salt solution for a certain time to realize ion exchange reaction of polyamic acid and silver ions, load silver ions, then clean with deionized water, and reduce in a reducing agent solution to realize the second surface silverization of the nanofibers; the ion exchange and reduction reaction is repeated multiple times to complete the surface silverization of the nanofibers; E: the polyamic acid / silver transparent electrode obtained in step D is heated to 135 DEG C under nitrogen atmosphere at room temperature for 1 h, kept at 135 DEG C for 2 h, then heated to 250-300 DEG C at a rate of 2 h, and kept at 250-300 DEG C for 0.5-3 h, the polyamic acid is converted into polyimide through imidization, then heated to 420-480 DEG C at a rate of 1 h and kept at 420-480 DEG C for 5-30 min to complete the densification and high conductivity of the surface silver layer, and finally obtain a polyimide / silver superfine nanofiber transparent electrode.

2. The production method according to claim 1, characterized by, The diamine in step A is one or more of 4,4'-diamino diphenyl ether (ODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 4,4'-diaminodiphenyl methane (MDA), 1,4-phenylenediamine (PDA), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), and 3,4-diaminobenzyloxy trifluoride (TFBDA); the dianhydride is one or more of hexafluoroisopropyl phthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4-biphenyl ether dianhydride (ODPA), 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride (DSDA), and 4,4'-(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride (BDSDA); and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl pyrrolidone.

3. The preparation method according to claim 1, characterized in that, The silver precursor in step A is one or more of silver trifluoroacetylacetone (AgTFA), silver hexafluoroacetylacetone (AgHFA), silver nitrate (AgNO3), silver fluoroborate (AgBF4), and silver triflate (AgOTf), and the concentration of the silver precursor is 0.01-1 g / ml.

4. The method of claim 1, wherein, The base material in step B is one of transparent polyimide film, quartz glass, transparent ceramic, single crystal alumina, and special silicate glass; and the time for the spinning deposition is 0.5-6 hours.

5. The preparation method according to claim 1, characterized in that, The reducing agent solution in step C is one of dimethylamine borane, glucose, or ascorbic acid aqueous solution, with a concentration of 0.005-0.050 mol / L, and the reducing time is 1-10 minutes.

6. The method of claim 1, wherein, The silver salt solution in step D is one of silver nitrate, silver fluoride, or silver tetrafluoroborate, or a mixture of two or more of them, with a concentration of 0.05-0.2 mol / L, and the ion exchange time is 5-30 minutes.

7. The conductive polyimide / silver ultrafine nanofiber transparent electrode prepared according to any one of claims 1-6, which is composed of polyimide / silver conductive nanofibers and a transparent base, with a fiber diameter of 20-80 nm and a surface coated with a nanosilver layer.

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