WO2018108011A1

WO2018108011A1 - Method of manufacturing flexible transparent electrically conductive thin film, and product thereof

Info

Publication number: WO2018108011A1
Application number: PCT/CN2017/114832
Authority: WO
Inventors: 张莹莹; 王琪
Original assignee: 清华大学
Priority date: 2016-12-15
Filing date: 2017-12-06
Publication date: 2018-06-21
Also published as: CN106592108A; CN106592108B

Abstract

A method of manufacturing a flexible transparent electrically conductive thin film comprises the following steps: (1) preparing a macromolecular solution, and utilizing an electrostatic spinning method to prepare a non-conductive nano-fiber flexible transparent thin film; and (2) and performing a high-temperature carbonization treatment on the thin film to obtain a flexible electrically conductive nano-fiber thin film. The flexible transparent electrically conductive thin film and the manufacturing method thereof are applicable to the field of optoelectronic devices including a wearable electronic device attached to a skin surface of a human body, a flexible display, and a solar cell. The flexible transparent conductive film is simple to manufacture, low in costs, and has a favorable application prospect.

Description

Preparation method of flexible transparent conductive film and obtained product

cross reference

The present application is hereby incorporated by reference in its entirety in its entirety in its entirety in its entirety in the the the the the the the the the the the the

Technical field

The invention belongs to the field of conductive materials, and in particular relates to a flexible transparent conductive film and a preparation method thereof.

Background technique

Flexible transparent conductive films have been widely used in flexible displays, solar cells, wearable electronic devices, optoelectronic devices, etc. due to their high transmittance, high electrical conductivity, and flexibility. At present, the most commonly used material for preparing a flexible transparent conductive film is indium tin oxide (ITO), but its cost is high due to its limited stock of raw material indium. Moreover, the ITO transparent conductive film is inferior in flexibility and is not suitable for use in flexible electronic devices. Therefore, the development of other bulk-preparable, low-cost flexible transparent conductive films that can replace ITO has received extensive attention in recent years.

At present, a mature transparent electrospinning technology is used to blend an inorganic conductive material with a polymer, and a flexible transparent conductive film having a uniform morphology and a high specific surface area is obtained by high-temperature calcination, but the flexibility is poor, and the bending radius is only 2 mm (Wu H, Hu L, Carney T, et al. Journal of the American Chemical Society, 2010, 133(1): 27). There is also a method of preparing a flexible transparent conductive film by a combination of electrospinning and other post-treatment techniques. For example, the Chinese invention patent No. 201210015627.5 uses electrospinning technology to prepare a non-conductive transparent film, and then uses in-situ polymerization, electrochemical method, electroplating method, physical deposition method, thermal evaporation method, magnetron sputtering method. One or more of the transparent conductive layers are formed on the non-conductive film. However, these post-treatment methods require toxic organic solvents, expensive vacuum equipment, and high-precision targets, which are not conducive to industrial mass production. Therefore, it is of great significance to develop a flexible transparent conductive film technology with simple technology, low cost, abundant raw materials and excellent performance.

Summary of the invention

In view of the deficiencies of the prior art, an object of the present invention is to provide a method for preparing a flexible transparent conductive film.

Another object of the present invention is to provide a flexible transparent conductive film produced by the preparation method.

The technical solution for achieving the object of the present invention is:

A method for preparing a flexible transparent conductive film, comprising the steps of:

(1) preparing a polymer solution, preparing a non-conductive nanofiber flexible transparent film by electrospinning; the solute in the polymer solution is silk protein, cellulose, chitin, chitosan, polyvinyl alcohol, One or more of polyvinylpyrrolidone, polystyrene, polylactic acid, polyvinyl butyral;

(2) The film obtained in the step (1) is subjected to high-temperature carbonization treatment to obtain a flexible conductive nanofiber film.

Step (1) The nanofiber obtained by electrospinning has a diameter of 0.01 to 1 μm. Step (2) The thickness of the conductive silk nanofiber membrane after carbonization is between 0.1 and 10 micrometers.

In the step (1), the solvent of the polymer solution is one or more of polyvinylpyrrolidone, phenol, formic acid, water, phosphoric acid, methanesulfonic acid, and p-toluenesulfonic acid. The concentration of the solute in the polymer solution is 1 to 30% by weight.

A preferred technical solution of the present invention is that the solute in the polymer solution is silk fibroin, which is obtained by boiling the silkworm cocoons in an aqueous solution to remove the sericin, and washing and drying the degummed silk fibroin fibers. Thereafter, the silk fibroin fiber is dissolved in a lithium bromide salt solution system for 2 to 8 hours, and subjected to dialysis, freezing, and drying to obtain a silk fibroin sponge, and the obtained silk fibroin sponge is dissolved in a solvent to obtain a polymer solution.

In the above method, the aqueous solution of boiled silkworm pupa may be clear water or an aqueous solution containing 1 to 10% by weight of a basic substance, which may be sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate or potassium carbonate. One or more. The concentration of lithium bromide in the lithium bromide salt solution may be 5 to 10 mol/L, and the temperature at which the silk fibroin fiber is dissolved in the lithium bromide salt solution system is preferably 50 to 90 °C.

Further, in the step (1), a single-needle electrospinning method is adopted, the electrospinning voltage is 5-50 KV, the working distance is 5-20 cm, and the injection speed of the polymer solution is 0.5-1 ml/h, and the static electricity is electrostatic. The spinning time is 10s-15min.

The preparation method has different transparency for the nanofiber flexible transparent film to be obtained, and controls the electrospinning time. The longer the spinning time, the lower the transparency, and the transmittance is 90% to 30% for the transparency at a wavelength of 550 nm. Nanofiber flexible transparent film, electrospinning time is 10s-120s.

Wherein, in the step (2), the high-temperature carbonization treatment is performed in a protective atmosphere or a vacuum, and the protective atmosphere is one or more of nitrogen, argon, helium, and hydrogen.

Preferably, the protective atmosphere is a mixed gas of argon gas and hydrogen gas, and the volume ratio of argon gas to hydrogen gas is 1 to 20:1.

Wherein, in the step (2), the high temperature carbonization treatment comprises: a temperature rising phase, a temperature maintaining phase and a temperature decreasing phase, wherein the temperature in the temperature maintaining phase is 500 ° C to 3000 ° C.

In the preparation method, the step (1) prepares a nanofiber flexible transparent film by using an electrospinning method on a high temperature resistant substrate, wherein the high temperature resistant substrate is a silicon wafer, a silicon dioxide sheet, a quartz sheet, a sapphire sheet, and a copper sheet. Or one of the glass sheets, after the high temperature carbonization treatment in the step (2), dissolving the high temperature resistant substrate in the oxidizing solution, and then transferring the film to the flexible substrate, the flexible substrate is rubber, silica gel, plastic, One of polydimethylsiloxane (PDMS), polyvinyl alcohol (PVA), polyimide (PD), polyester (PET), and Ecoflex material.

The flexible transparent conductive film prepared by the preparation method of the invention.

The beneficial effects of the invention are:

The invention provides a flexible transparent conductive film and a preparation method thereof, which can be applied to the field of optoelectronic devices, such as wearable electronic devices, flexible displays, solar cells, etc., which are attached to the surface of human skin, and the preparation process of the flexible transparent conductive film is simple. Low cost and good application prospects.

in particular:

(1) The flexible transparent conductive film is mainly composed of a polymer spun material other than polyacrylonitrile, and has the advantages of wide source and low cost;

(2) By adjusting the parameters such as working voltage, working distance and spinning solution concentration in the electrospinning process, the parameters such as the diameter distribution, thickness and porosity of the polymer nanofiber membrane can be controlled, thereby realizing the macroscopic of the nanofiber material. Performance, such as controllable modulation of parameters such as conductivity, transparency, and thickness.

(3) The preparation method of the invention is simple and easy, low in cost, and suitable for large-scale production.

DRAWINGS

1 is a process flow diagram of a flexible transparent conductive film of the present invention.

2 is an optical micrograph (left of FIG. 2) of the silk nanofiber membrane prepared by the electrospinning technique of Example 1 and an electron micrograph of the carbonized silk nanofiber membrane (FIG. 2 right).

3 is a light transmittance test result of a flexible transparent conductive film of electrospinning at different times at a light wavelength of 550 nm.

4 is a microscopic electron micrograph (a, b, c, d) and a white light interferometer (e, f, g, h) of silk nanofiber membranes of different thicknesses prepared by using different electrospinning times.

Figure 5 is a transmission electron micrograph of the material obtained by the high temperature carbonization treatment of the present invention.

Fig. 6 is a view showing the transparency of the flexible transparent conductive film of the present invention.

Fig. 7 is a test result of transparency of the flexible transparent conductive film of the present invention.

Fig. 8 is a test result of electrical conductivity of a flexible transparent conductive film of the present invention at different high temperature carbonization heat treatment temperatures.

detailed description

The invention is illustrated by the following examples, which are not intended to limit the scope of the invention. The means used in the examples, unless otherwise specified, are conventionally used in the art.

The technical solutions in the embodiments of the present invention will be clearly and completely described in the following with reference to the accompanying drawings.

Example 1: Preparation of silk nanofiber membrane by single needle electrospinning technique using silk as raw material

First, the silkworm cocoons are boiled in a 0.5% by weight aqueous solution of sodium bicarbonate for 30 minutes to remove the sericin, and then the degummed silk fibroin fibers are washed three times with deionized water, after the silk fibroin fibers are completely dried. 2 g of silk fibroin fibers were dissolved in 8 ml of a 9.3 mol/L lithium bromide salt solution solution at 70 ° C for 4 hours, and then dialyzed in deionized water for three days to obtain an aqueous silk fibroin solution, which was then freeze-dried to obtain silk. Protein sponge.

The obtained silk fibroin sponge was dissolved in 98-100% anhydrous formic acid to obtain a 15 wt% silk fibroin formic acid solution. Then use single needle electrospinning technology, working voltage 20KV, working distance 20cm, silk fibroin formic acid solution injection speed 0.5ml / hour, electrospinning for 30 seconds, silk nanofibers deposited on high temperature resistant base copper foil Nanofiber membrane.

Optical photographs and electron micrographs of the electrospun protein nanofibers are shown in Fig. 2. The silk nanofibers obtained under the electrospinning conditions have a diameter ranging from 0.3 to 0.7 micrometers and an average diameter of about 0.35 micrometers.

Example 2: Electrospinning technology to prepare nanofiber membranes of different thicknesses

By controlling the electrospinning deposition time, the thickness and transparency of the resulting nanofiber film can be controlled.

Using the silk fibroin formic acid solution prepared in Example 1, the electrospinning working voltage was 20 kV, the working distance was 20 cm, and the silk fibroin formic acid solution injection rate was 0.5 ml/hr, respectively, and electrospinning was performed for 60 seconds, 90 seconds, and 120 seconds, respectively. second. The other operations are the same as in the first embodiment. Silk nanofiber membranes with different thicknesses of transparency were obtained, and electrospun silk nanofiber membranes of different thicknesses were different in transparency (see Fig. 3). The longer the electrospinning time, the lower the transparency. For the nanofiber flexible transparent film with a transmittance of 90% at a wavelength of 550 nm, the electrospinning time is preferably 20s-40s (Fig. 3 and Fig. 7 are both carbonized). Transmittance. Fig. 3 is a fixed wavelength of 550 nm, and Fig. 7 is a visible light band). Fig. 7 shows the transparency of the silk nanofiber membrane at different electrospinning times at a wavelength of 300 to 800 nm.

The morphology and thickness of silk nanofiber membranes with different thicknesses were characterized by scanning electron microscopy and white light interferometer (Fig. 4). By changing the electrospinning time, silk nanofiber membranes with different fiber densities, different film thicknesses and different transparency can be obtained. It can be seen from the graphs of e, f, g, and h in Fig. 4 that the thickness of the conductive silk nanofiber membrane is between 0.5 and 5 micrometers under the operating conditions of electrospinning for 30 seconds to 120 seconds, and the longer the spinning time, the thickness The bigger.

Example 3: Preparation method of flexible transparent conductive film based on silk fibroin material

Under the electrospinning conditions described in Example 1 and Example 2, a high temperature resistant metal copper foil was selected as the receiving substrate, and the electrospun silk nanofibers were deposited at different times to obtain nanofiber films of different thicknesses.

The silk nanofiber membranes having an electrospinning time of 30 seconds to 120 seconds were subjected to high-temperature heat treatment at 800 ° C for 1 hour in an inert atmosphere of argon:hydrogen=10:1 to obtain a conductive silk nanofiber membrane having the original nanofiber structure. The silk fibroin polypeptide chain structure is converted into a graphite microcrystalline carbon structure during high temperature treatment, and its transmission electron microscope image is shown in FIG. 5.

The carbonized silk nanofiber membrane was placed in a 5% ammonium persulfate solution together with a metal substrate to dissolve the copper foil metal substrate. Transferring carbonized electrospun silk nanofiber membrane to polydimethylsiloxane (An elastic polymer, the degree of flexibility determines the flexibility of the flexible film after transfer) on the substrate to form a flexible transparent conductive film, the assembly flow chart is shown in Figure 1. The flexible transparent conductive film has good light transmittance and flexibility, as shown in FIG. Its transparency is as high as 90.75% (Figure 7) for wearable electronics.

The silk nanofiber membrane of the same thickness increases in electrical conductivity as the temperature of the high temperature heat treatment increases. The silk nanofiber membrane with electrospinning time of 30 seconds was subjected to high temperature heat treatment at 700 ° C, 800 ° C, 900 ° C and 1000 ° C for 1 hour, and the electrical conductivity was 28, 68, 130, 202 s / cm, respectively, as shown in FIG.

The above embodiments are merely illustrative of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention. And improvements are intended to fall within the scope of the protection as defined by the appended claims.

Claims

A method for preparing a flexible transparent conductive film, comprising the steps of:

(1) preparing a polymer solution, preparing a non-conductive nanofiber flexible transparent film by electrospinning; the solute in the polymer solution is silk protein, cellulose, chitin, chitosan, polyvinyl alcohol, One or more of polyvinylpyrrolidone, polystyrene, polylactic acid, polyvinyl butyral;

(2) The film obtained in the step (1) is subjected to high-temperature carbonization treatment to obtain a flexible conductive nanofiber film.
The preparation method according to claim 1, wherein in the step (1), the solvent of the polymer solution is polyvinylpyrrolidone, phenol, formic acid, water, phosphoric acid, methanesulfonic acid or p-toluenesulfonic acid. The concentration of the solute in the polymer solution is 1 to 30% by weight.
The preparation method according to claim 1, wherein the solute in the polymer solution is silk fibroin, and the polymer solution is obtained by boiling the silkworm cocoons in an aqueous solution to remove the sericin, and degumming After the silk fibroin fiber is washed and dried, the silk fibroin fiber is dissolved in a lithium bromide solution solution for 2 to 8 hours, and the silk fibroin sponge is obtained by dialysis, freezing and drying to dissolve the obtained silk fibroin sponge. In the solvent.
The preparation method according to any one of claims 1 to 3, wherein in the step (1), a single-needle electrospinning method is employed, the voltage of the electrospinning is 5 to 50 kV, and the working distance is 5 to 20 cm, the injection rate of the polymer solution is 0.5 to 1 ml/h, and the electrospinning time is 10 s to 15 min.
The preparation method according to claim 4, wherein the time for electrospinning is controlled for the transparency of the nanofiber flexible transparent film to be obtained, the longer the spinning time is, the lower the transparency is, and the transparency is 550 nm. The nanofiber flexible transparent film with a light rate of 90% to 30% has an electrospinning time of 10 s to 120 s.
The preparation method according to any one of claims 1 to 3, wherein in the step (2), the high-temperature carbonization treatment is performed in a protective atmosphere or a vacuum, and the protective atmosphere is nitrogen gas. One or more of argon, helium, and hydrogen.
The preparation method according to claim 6, wherein the protective atmosphere is a mixed gas of argon gas and hydrogen gas, and the volume ratio of argon gas to hydrogen gas is 1 to 20:1.
The preparation method according to any one of claims 1 to 3, wherein the step In the step (2), the high-temperature carbonization treatment includes: a temperature rising phase, a temperature maintaining phase, and a temperature decreasing phase, wherein the temperature maintaining phase has a temperature of 500 ° C to 3000 ° C.
The preparation method according to any one of claims 1 to 3, wherein the step (1) is to prepare a nanofiber flexible transparent film by using an electrospinning method on a high temperature resistant substrate, wherein the high temperature resistant substrate is a silicon wafer, two a silicon oxide sheet, a quartz sheet, a sapphire sheet, a copper sheet or a glass sheet, after the high temperature carbonization treatment in the step (2), dissolving the high temperature resistant substrate in an oxidizing solution, and then transferring the film onto the flexible substrate. The flexible substrate is one of rubber, silica gel, plastic, polydimethylsiloxane, polyvinyl alcohol, polyimide, polyester, and Ecoflex material.
The flexible transparent conductive film prepared by the preparation method according to any one of claims 1 to 9.