Flexible polyimide / silver superfine nanofiber transparent electrode and preparation method thereof

Abstract

The invention relates to a flexible polyimide / silver superfine nanofiber transparent electrode and a preparation method thereof. The method comprises the following steps: firstly, adding a silver precursor into a polyamide acid solution to obtain a spinning solution; depositing on the surface of the transparent substrate through electrostatic spinning to form a preset nanofiber network; then, the conversion from a non-conductive grid to a conductive grid is realized through in-situ metallization on the surface of the nanofiber; and finally, performing high-temperature treatment to obtain the flexible polyimide / silver superfine nanofiber transparent electrode. The transparent electrode formed by the method has the unique advantage of integrated forming, also has the characteristics of good flexibility, uniform resistance and low cost, and can be realized on transparent substrates in various shapes. In addition, the whole implementation process is high in operability and high in adjustability and controllability, and an innovative scheme with great potential is provided for development of metal nano materials.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofibers, and in particular relates to a flexible polyimide / silver ultrafine conductive nanofiber transparent electrode and a preparation method thereof. Background Art

[0002] Transparent electrodes (TCEs) are a class of unique materials that have both optical transparency and electrical conductivity. They are key components of many modern devices, including solar cells, organic light-emitting diodes (OLEDs), liquid crystal displays (LCDs), touch screens, etc. In recent years, metal nanomaterials have been regarded as a strong candidate to replace traditional transparent conductive materials due to their great potential. The high electrical conductivity of metals gives them extremely low resistance. By constructing nanostructures smaller than the wavelength of visible light, high transparency is achieved, and they also have excellent surface interface effects. At present, the preparation technology of silver nanowires (AgNWs) has made significant progress. Silver ions are controlled to grow slowly in solution to form silver nanowires with a diameter of about 80nm through alcohol thermal method, hydrothermal method, photoreduction method, etc., and AgNWs transparent conductive films are prepared by spin coating, roll coating, spray coating and other methods. However, the application of silver nanowires still faces many challenges. For example, during the synthesis process, the quality is uneven, the purity is not high, and the stability is low; during the coating process, it is difficult to achieve uniform distribution; in addition, the flexibility and adhesion of the silver nanowires themselves are poor, and their reliability is reduced when they are frequently bent and used. Therefore, optimizing the quality and purity of silver nanowires, improving their uniformity, and enhancing their flexibility and adhesion have become key issues that need to be addressed in the current research field. Exploring new technologies and methods to break through these bottlenecks is a hot topic in current research.

[0003] Polymer nanofibers are a promising solution because they can be electrospun to produce a uniformly distributed flexible network structure on substrates of different shapes, and are easy to operate and have a high yield rate. The surface of the overlapping nanofiber network structure constructed by electrospinning technology is metallized to form a metal nanofiber network with a high aspect ratio, which gives it excellent conductivity and flexibility. This has gradually become a trend in optimizing metal nanowires and is expected to be used in flexible TCEs. At present, the large diameter of polymer nanofibers and their weak adhesion to the metal layer are the main factors limiting their widespread application.

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

[0005] The present invention first adds a silver precursor to a polyamic acid spinning solution to achieve the loading of a silver source, then prepares nanofibers on a transparent substrate by an electrostatic spinning technique, and achieves the regulation of the diameter of the nanofibers by parameter adjustment, thereby directly presetting a nanofiber template on a transparent substrate, and then based on chemical reduction, realizes the reduction growth of silver to achieve the first silver loading on the surface of the nanofibers, forming a seed layer, and then by an ion exchange-reduction metallization method in a silver salt aqueous solution, multiple loadings of silver on the surface of the nanofibers are performed, so that the nanofibers achieve the transformation from a non-conductive grid to a conductive grid, and finally convert the polyamic acid nanofibers into high-temperature resistant and flexible polyimide nanofibers by high-temperature treatment, while further densifying and highly conductive the surface silver layer, effectively improving the conductivity of the polyimide / silver nanofibers, and forming a uniform conductive grid. The integrated polyimide / silver ultrafine nanofiber transparent electrode prepared by the present invention has the advantages of high conductivity, good flexibility, uniform resistance distribution, and being applicable to substrates of various shapes, and has broad application prospects in transparent electrodes.

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

[0007] A: condensing and polymerizing a diamine monomer and a dianhydride monomer to obtain a polyamic acid solution, and after the reaction is completed, adding a certain amount of a silver precursor solution to obtain a polyamic acid spinning stock solution containing a silver source;

[0008] B: depositing the spinning solution 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: immersing the nanofibers prepared in step B together with the substrate into 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 silverization of the polyamic acid nanofibers to form a seed layer, and then cleaning with deionized water;

[0010] D: immersing the nanofibers obtained in step C together with the substrate into a water-soluble silver salt solution of a certain concentration for a certain period of time to carry out an ion exchange reaction between the polyamic acid and the silver ions to achieve the loading of the silver ions, and then washing with deionized water and reducing in a reducing agent solution to achieve secondary surface silvering of the nanofibers; and then repeating the ion exchange and reduction reaction 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 in a nitrogen atmosphere to convert the polyamic acid into polyimide by imidization reaction, and at the same time, the surface silver layer is densified and highly conductive, and finally a polyimide / silver ultrafine nanofiber transparent electrode is obtained.

[0012] Wherein, the diamine described 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-diaminobenzyloxy trifluoride (TFBDA); the dibasic acid anhydride is selected from hexafluoroisopropylphthalic acid One or more of 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), 4,4'-(3,4-dicarboxyphenoxy) diphenylsulfide dianhydride (BDSDA); the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0013] Furthermore, the silver precursor in step A is one or more of 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, and the concentration is 0.01g / ml to 1g / ml; 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 transparent polyimide film, quartz glass, transparent ceramic, single crystal alumina, and special silicate glass; and the spinning deposition time is 0.5h to 6h.

[0015] Furthermore, the reducing solution in step C is dimethylamine borane, glucose or ascorbic acid aqueous solution, the concentration is 0.005-0.050 mol / L, and the reducing time is 1-10 min.

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

[0017] Furthermore, the imidization treatment conditions described in step E are: under a nitrogen atmosphere, the room temperature is raised to 135° C. over 1 hour, kept at 135° C. for 1 hour, then raised to 250-300° C. over 2 hours, and kept for 0.5-3 hours, then raised to 420-480° C. over 1 hour and kept 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 characteristics of integrated molding. By directly anchoring a preset high aspect ratio nanofiber as a template on a transparent substrate and in-situ metallizing the nanofiber, the transformation from a non-conductive to a conductive grid is achieved without the need for secondary processing. Complex shapes and fine structure designs can be achieved, thus broadening the possibilities of product design.

[0020] 2. The method of the present invention regulates the diameter of the nanofibers by introducing a silver precursor during the electrospinning process, thereby regulating the specifications of the metal nanomesh and forming a metal nanomesh with uniform structure. The method does not require complicated reaction conditions and is simple to operate and easy to implement. The silver precursor introduced into the spinning solution is reduced during the reduction process, so that the silver grows from the inside out. The bonding force between the silver layer and the substrate is greatly improved due to the mechanical interlocking effect, and the adhesion force is greatly improved, which solves the problem that the silver layer is easy to fall off due to the heterogeneous interface. At the same time, the preparation method of introducing silver by ion exchange-reduction external secondary load greatly improves the silver loading efficiency and the problem of high conductivity of the silver layer, thereby improving the preparation efficiency.

[0021] 3. The method of the present invention further performs high-temperature treatment after the thermal imidization of polyamic acid, and the silver on the surface of the nanofiber can move by diffusion to fill the gaps between the particles, so that the silver layer is coated more tightly and evenly, giving it higher stability and effectively improving the conductivity of polyimide / silver nanofibers, forming a transparent electrode with a higher quality factor;

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

[0023] Figure 1 This is a scanning electron microscope image of the polyimide / silver ultrafine nanofiber transparent electrode prepared according to Example 1, with a magnification of 50,000 times for the left image and 200,000 times for the right image.

[0024] Figure 2 This is a bending resistance test of the polyimide / silver ultrafine nanofibers prepared according to Example 1.

[0025] Figure 3 This is a physical picture of the polyimide / silver ultrafine nanofiber prepared according to Example 1

[0026] Table 1 shows the metal nanomesh diameter, transmittance and square resistance of the samples obtained in different embodiments and comparative examples. DETAILED DESCRIPTION

[0027] The following examples are combined to further illustrate the content of the invention. It should be noted that the following examples are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification describes the present invention in detail with reference to the following examples, it should be understood by those skilled in the art that any technical solutions and improvements that can be modified or equivalently replaced with the present invention and that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

[0028] Example 1

[0029] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0030] (2) The 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 spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. The receiving distance was 20 cm, and the spinning deposition time was 3 h.

[0031] (3) The nanofibers prepared above and the substrate are immersed in dimethylaminoborane with a concentration of 0.01 mol / L.

[0032] The sample was placed in a DMAB reducing agent solution for 5 min and then rinsed with deionized water. Subsequently, the sample was placed in a 0.1 mol / L AgNO3 solution for 5 min, then rinsed with deionized water and placed 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.

[0033] (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 kept at this temperature for 1 h to carry out imidization reaction, and then the temperature is raised to 480° C. and kept at this temperature for 10 min to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0034] Example 2

[0035] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.03 g / ml, and continuing to stir to obtain a spinning solution;

[0036] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0037] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0038] (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 kept at the temperature for 1 hour to carry out an imidization reaction, and then the temperature is raised to 480° C. and kept at the temperature for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0039] Example 3

[0040] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver borofluoride (AgBF4) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0041] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0042] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0043] (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 kept at the temperature for 1 hour to carry out an imidization reaction, and then the temperature is raised to 480° C. and kept at the temperature for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0044] Example 4

[0045] (1) synthesizing a BPDA / TFMB system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0046] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0047] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0048] (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 for 1 h to carry out imidization reaction, and then the temperature is raised to 480° C. for 10 min to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0049] Example 5

[0050] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0051] (2) The spinning solution is 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 are spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time is 3 h.

[0052] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0053] (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 for 1 h to carry out imidization reaction, and then the temperature is raised to 480° C. for 10 min to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0054] Example 6

[0055] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0056] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0057] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L ascorbic acid reducing agent solution for 5 min and washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L silver fluoride (AgF) solution for ion exchange for 5 min, washed with deionized water, and placed in a 0.01 mol / L ascorbic acid reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0058] (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 kept at the temperature for 1 hour to carry out an imidization reaction, and then the temperature is raised to 480° C. and kept at the temperature for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0059] Example 7

[0060] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0061] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0062] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0063] (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 kept at the temperature for 1 hour to carry out an imidization reaction, and then the temperature is raised to 420° C. and kept at the temperature for 10 minutes to obtain a polyimide / silver ultrafine nanofiber transparent electrode.

[0064] Comparative Example 1

[0065] ((1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding only 5 ml of DMF solvent and continuing to stir to obtain a spinning solution;

[0066] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0067] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for ion exchange for 5 min, and then washed with deionized water, and then placed in a 0.01 mol / L DMAB reducing agent solution for 1 min, and then washed with deionized water. The above ion exchange and reduction steps were repeated 20 times.

[0068] (4) The polyamic acid / silver transparent electrode obtained in step (3) was heated to 300° C. in nitrogen at a heating rate of 3° C. / min and kept at the temperature for 1 h to carry out imidization reaction, and then the temperature was raised to 480° C. and kept at the temperature for 10 min.

[0069] Comparative Example 2

[0070] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding 5 ml of a silver nitrate (AgNO3) solution with a concentration of 0.78 g / ml, and continuing to stir to obtain a spinning solution;

[0071] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0072] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0073] (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 for 1 h to carry out imidization reaction without subsequent heating.

[0074] Comparative Example 3

[0075] (1) synthesizing a PMDA / ODA system polyamic acid solution with a solid content of 12% in a DMF solvent by condensation polymerization, and after the reaction is completed, adding only 5 ml of DMF solvent and continuing to stir to obtain a spinning solution;

[0076] (2) The spinning solution is deposited on the surface of a transparent polyimide film by an electrospinning method to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface. The specific parameters of the electrospinning machine are as follows: spinning voltage: 25 kV; spinning temperature: room temperature; spinning humidity: 20%; syringe needle diameter: No. 12; propulsion speed: 0.002 ml / min. Receiving distance: 20 cm, and spinning deposition time: 3 h.

[0077] (3) The nanofibers prepared above with the substrate were immersed in a 0.01 mol / L dimethylamine borane (DMAB) reducing agent solution for 5 min, and then washed with deionized water. Subsequently, the nanofibers were placed in a 0.1 mol / L AgNO3 solution for 5 min, washed with deionized water, and placed in a 0.01 mol / L DMAB reducing agent solution again for 1 min, washed with deionized water, and the above ion exchange and reduction steps were repeated 20 times.

[0078] (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 for 1 h to carry out imidization reaction without subsequent heating.

[0079] Table 1 Diameter, transmittance and square resistance of metal nanonets of samples obtained in different embodiments and comparative examples

[0080] sample Average diameter(nm) <![CDATA[Transmittance T 550nm %]]> Square 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

[0081] As can be seen from Table 1, the diameter of the nanofibers obtained by electrospinning using the blended silver salt spinning solution in Examples 1, 2, 3 and Comparative Example 1 is significantly smaller than that of the nanofibers obtained by the unblended silver salt spinning solution, and the corresponding transmittance is significantly improved, indicating that the addition of silver salt during the electrospinning process is conducive to regulating the diameter of the nanofibers, and then regulating the diameter of the conductive metal grid. This is because the addition of silver salt greatly improves the conductivity of the spinning solution, significantly improves the spinnability, and obtains finer nanofibers. The metal grid formed after surface metallization has more advantages in the application of transparent electrodes.

[0082] The nanofiber transparent electrodes treated at high temperature in Examples 1 and 6 and Comparative Example 2 have stronger conductivity and lower square resistance, while the nanofibers treated only at 300°C have ultra-high resistance. This is because of the nano effect, the melting point of nanosilver is greatly reduced, and in the process of increasing the temperature, the silver particles on the fiber surface melt at high temperature and continuously fill the gaps between the particles, forming a more uniform conductive metal nanonetwork, which greatly improves the conductivity of the transparent electrode.

[0083] The flexibility of polyimide / silver ultrafine nanofibers is determined by 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.

[0084] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A transparent electrode based on polyimide / silver ultrafine conductive nanofibers, which is composed of polyimide / silver conductive nanofibers and a transparent substrate, with a fiber diameter of 20nm to 80nm and a surface coated with a nanosilver layer.

2. A method for preparing a transparent electrode based on ultrafine polyimide / silver nanofibers according to claim 1, characterized in that The following steps are involved: A: condensing and polymerizing a diamine monomer and a dianhydride monomer to obtain a polyamic acid solution, and after the reaction is completed, adding a certain amount of a silver precursor solution to obtain a polyamic acid spinning stock solution containing a silver source; B: depositing the spinning solution on the surface of a transparent substrate by electrospinning to obtain a transparent electrode with ultrafine polyamic acid / silver nanofibers attached to the surface; C: immersing the nanofibers prepared in step B together with the substrate into 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 silverization of the polyamic acid nanofibers to form a seed layer, and then cleaning with deionized water; D: immersing the nanofibers obtained in step C together with the substrate into a water-soluble silver salt solution of a certain concentration for a certain period of time to carry out an ion exchange reaction between the polyamic acid and the silver ions to achieve the loading of the silver ions, and then washing with deionized water and reducing in a reducing agent solution to achieve secondary surface silvering of the nanofibers; and then repeating the ion exchange and reduction reaction multiple times to complete the surface silvering of the nanofibers; E: The polyamic acid / silver transparent electrode obtained in step D is subjected to high temperature treatment in a nitrogen atmosphere to convert the polyamic acid into polyimide by imidization reaction, and at the same time, the surface silver layer is densified and highly conductive, and finally a polyimide / silver ultrafine nanofiber transparent electrode is obtained.

3. The preparation method according to claim 2, characterized in that: The diamine described 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-diaminobenzyloxy trifluoride (TFBDA); the dibasic acid anhydride is selected from hexafluoroisopropylphthalic acid The organic solvent is selected from one or more of: 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), 4,4'-(3,4-dicarboxyphenoxy) diphenylsulfide dianhydride (BDSDA); the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

4. The preparation method according to claim 2, characterized in that: The silver precursor in step A is one or more of 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, and the concentration is 0.01 g / ml to 1 g / ml; and the silver content is controlled to be 5% to 60% of the total solid mass.

5. The preparation method according to claim 2, characterized in that: In step B, the substrate material is one of transparent polyimide film, quartz glass, transparent ceramic, single crystal alumina, and special silicate glass; and the spinning deposition time is 0.5h to 6h.

6. The preparation method according to claim 2, characterized in that: The reducing solution in step C is dimethylamine borane, glucose or ascorbic acid aqueous solution, the concentration is 0.005-0.050 mol / L, and the reducing time is 1-10 min.

7. The preparation method according to claim 2, characterized in that: The silver salt solution in step D is a mixed aqueous solution of one or more of silver nitrate, silver fluoride or silver tetrafluoroborate, with a concentration of 0.05 to 0.2 mol / L, and the ion exchange time is 5 to 30 min.

8. The preparation method according to claim 2, characterized in that: The imidization treatment conditions described in step E are: under a nitrogen atmosphere, the room temperature is raised to 135°C over 1 hour, kept at 135°C for 2 hours, then raised to 250-300°C over 2 hours, and kept for 0.5-3 hours, then raised to 420-480°C over 1 hour and kept for 5-30 minutes.

9. A conductive polyimide / silver ultrafine nanofiber transparent electrode prepared by the method according to any one of claims 1 to 8.

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