AU2021100456A4 - Cross-ordered silver nanowire film and patterning method thereof - Google Patents

Abstract

The present disclosure provides a cross-ordered silver nanowire transparent conductive film (AgNW TCF) and a patterning method thereof, including: step (1): preparing a silver nanowire (AgNW) stock solution with a polyol reduction method, and purifying; step (2): dispersing purified AgNWs in absolute ethanol to obtain an AgNW dispersion with a concentration of 0.4 wt% or more; step (3): subjecting a polyethylene terephthalate (PET) substrate to ultrasonic cleaning, surface hydrophilization treatment, and spin coating with poly-L-lysine (PLL) aqueous solution for modification; step (4): using a Meyer bar coating method to obtain a cross-ordered AgNW TCF; step (5): coating a positive photoresist on the cross-ordered AgNW TCF, precuring, exposing to UV light, developing, etching, washing and drying to obtain a conductive channel of a certain shape. The present disclosure can greatly improve an ordering level of AgNW TCF prepared by a bar coating method, where the patterning method can improve pattern accuracy without affecting optical performance of the conductive film. DRAWINGS 50 p 0 pm 100000 40000 (d) ' 75000 -,30000 50000 20000 c325000 010000 0 0_ -90 -45 0 45 90 -90 -45 0 45 90 DeviationI/ Deviation/ FIG. 1 CO.(c FIG. 2 Page 1 of5

Description

DRAWINGS

50 p 0 pm 100000 40000 (d) ' 75000 -,30000

50000 20000

c325000 010000

0 0_ -90 0 -45 DeviationI/ 45 90 -90 -45 0 45 90 Deviation/

FIG. 1

CO.(c

FIG. 2

Page 1 of5

CROSS-ORDERED SILVER NANOWIRE FILM AND PATTERNING METHOD THEREOF TECHNICAL FIELD The present disclosure belongs to the technical field of preparation and application of nano materials, and specifically relates to a method for ordering and patterning silver nanowires (AgNWs). BACKGROUND Transparent conductive electrodes are widely used in optoelectronic devices, for example, flexible solar cells, flexible touch screens and display screens. At present, the transparent conductive electrodes are mostly prepared with indium tin oxide (ITO). Since ITO materials are cost-ineffective, hard and brittle, their applications are very limited. As a most promising new material to replace ITO, AgNWs have better light transmittance and conductivity than graphene, carbon nanotubes, conductive polymers and the like. Moreover, an AgNW network can be directly prepared by methods such as bar coating, spin coating or spray coating, with a low cost and a simple process. However, a general AgNW network has randomly distributed AgNWs, which results in problems such as uneven distribution, large surface roughness, easy entanglement of AgNWs, and large junction resistance between AgNWs. In view of the above problems, researchers have adopted methods such as adding trace amount of organic matter to AgNW ink, applying a high molecular polymer coating on the surface, mechanical pressing and thermal annealing. However, these methods have complex process flows and unsatisfactory effects. In this regard, Ko et al. proposed a new method where AgNWs were adjusted so that they were arranged in the same direction to obtain an ordered AgNW network whose nodes were also uniformly arranged and ordered. A transparent conductive film (TCF) prepared by the method had small and uniform sheet resistance, smooth surface and small roughness. Although a highly ordered AgNW network can be obtained by spray coating, it has very poor uniformity and low ordering level in a sprayed area except the center, resulting in poor uniformity of transmittance and sheet resistance. Therefore, this method is not suitable for practical promotion. Many research teams have used bar coating to prepare ordered AgNW TCFs. Resulted AgNW networks had excellent uniformity but generally low ordering levels. Ordered AgNW TCFs have limited applications in display devices since most displays require both conductive and non-conductive areas. Therefore, patterning is needed to solve this problem, where accuracy of patterning directly determines performance of the device. There are many patterning methods, such as screen printing and chemical etching through a mask reticle. However, these methods have shortcomings such as low resolution and visual difference in optical performance between etched and non-etched areas.

SUMMARY A first objective of the present disclosure is to provide a method for preparing a cross-ordered silver nanowire transparent conductive film (AgNW TCF) by bar coating, which greatly improves an ordering level. A second objective of the present disclosure is to provide a method for AgNW TCF patterning to improve pattern accuracy without affecting optical performance of the conductive film. In order to achieve the above objectives, the present disclosure adopts the following specific technical solutions: In a first aspect, the present disclosure provides a method for preparing a cross-ordered AgNW TCF, including the following steps: step (1): preparing an AgNW stock solution with a polyol reduction method, and purifying with absolute ethanol as a solvent in a dynamic stirring and washing method to remove organic matter, Ag nanoparticle and short rod in the AgNW stock solution while retaining a polyvinyl pyrrolidone (PVP) layer on a surface of AgNW to obtain purified AgNWs; step (2): dispersing the purified AgNWs obtained in step (1) in absolute ethanol to obtain an AgNW dispersion with a concentration of 0.4 wt% or more; step (3): subjecting a polyethylene terephthalate (PET) substrate to ultrasonic cleaning, surface hydrophilization treatment, and spin coating with poly-L-lysine (PLL) aqueous solution for modification to obtain a pretreated PET substrate; step (4): coating the AgNW dispersion obtained in step (2) on the pretreated PET substrate in step (2) by a coating rod having a groove width less than a length of AgNW in a Meyer bar coating method where a coating speed is 60-120 mm-s, drying a solvent completely, immediately coating again with the same method in a direction perpendicular to a pre-aligned direction on unidirectionally ordered AgNW/PET substrate and drying to obtain a cross-ordered AgNW TCF. In step (1) of the present disclosure, the AgNW stock solution is prepared by a polyol reduction method which usually uses PVP as a growth directing agent. It is specifically recommended to use an AgNW prepared by a polyol reduction method with silver nitrate as an Ag source, ethylene glycol as a reducing agent and solvent, PVP as a growth directing agent, sodium chloride and sodium bromide as crystal form inducers. Preferably, the AgNW may have a diameter of 15-200 nm and a length of 20-200 m. More Preferably, the AgNW may have a diameter of 13-30 nm. The dynamic stirring and washing method described in step (1) of the present disclosure can be carried out with reference to steps reported in the existing literatures, for example, the literature

[Chen G, Bi L, Yang Z, et al. Water-based purification of ultrathin silver nanowires toward transparent conductive films with a transmittance higher than 99%. ACS Applied Materials &

Interfaces, 2019, 11: 22648-22654]. It should be pointed out that, the present disclosure needs to use absolute ethanol as the solvent for purification. This is because a wet film is obtained after scraping with the coating rod, where pre-ordered AgNWs are still dispersed in the solvent. If the solvent evaporates too slowly or a drying temperature is too high, AgNWs will have excessive thermal movement, causing the pre-ordered AgNWs to return to a chaotic state and affecting final ordering level of AgNW on TCF. Ethanol is the most ideal solvent since it has a low boiling point and a fast drying speed and requires no heat drying or other additional operations. The present disclosure specifically recommends that the step (1) is carried out as follows: pouring an AgNW stock solution into a purification device which includes a filter membrane with a pore size smaller than a length of AgNW and a stirring paddle, diluting with absolute ethanol, rotating the stirring paddle, slowly dripping absolute ethanol into the purification device to maintain a constant volume of solution during washing, after washing for a certain period of time, carrying out a positive pressure filtration, adding a PVP aqueous solution, shaking uniformly, and carrying out a positive pressure filtration to collect purify AgNWs. Preferably, the pore size of the filter membrane may be 8 m, a stirring speed may be 900 rpm, and washing time may be 40 min. Preferably, relative molecular mass of the PVP may be 55,000, and concentration of the PVP aqueous solution may be 0.5 wt%. In step (2) of the present disclosure, concentration of the AgNW dispersion is set to be 0.4 wt% or more. This is because density of AgNW on the coated TCF increases with the concentration of the AgNW dispersion, and an ordering level also increases as the AgNW concentration increases. When the AgNW concentration reaches 0.4 wt%, the ordering level of AgNW network tends to be stable, and a higher concentration no longer results in meaningful increase in ordering level. Therefore, the AgNW dispersion preferably has a concentration of 0.4 wt%. In step (3) of the present disclosure, the ultrasonic cleaning, the surface hydrophilization treatment, and the spin coating with PLL aqueous solution for modification of the PET substrate can all be carried out with reference to literature methods. The surface hydrophilization treatment can be ultraviolet (UV) ozone treatment, plasma treatment or application of a coating of hydrophilic substances for changing surface tension of the substrate. As the most convenient and effective method, the UV ozone treatment is preferred, and treatment time thereof may be preferably 30 min. Preferably, the ultrasonic cleaning may be carried out by ultrasonically cleaning the PET substrate in deionized water and ethanol in sequence for 5-10 min. Preferably, the UV ozone treatment may be carried out for 10-30 min. Preferably, the spin coating with PLL aqueous solution for modification may be carried out with the following operating parameters: concentration of the PLL aqueous solution of 0.1 % , speed of spin coater of 8,000 rpm, and spin coating time of 90 s. In step (4) of the present disclosure, other operating parameters of the Meyer bar coating method can refer to existing literature. The coating rod greatly affects the ordering level of the AgNW network of the present disclosure, since it can pre-order the AgNWs. When a groove width of the coating rod is greater than an AgNW length, a large number of AgNWs will pass through the coating rod directly and disorderly, so that most AgNWs are randomly oriented on the TCF.

Therefore, a coating rod with a groove width less than an AgNW length should be selected. At the same time, coating speed also has a great influence on the ordering level of the AgNW network. Experimental results show that, as the coating speed decreases, the ordering level of AgNW on TCF increases sharply and then decreases slightly at 60 mm s-1. Therefore, the best coating speed may be mm s-1. In the present disclosure, it is particularly preferable that, the Meyer bar coating method in step (4) may be carried out by placing the pretreated PET substrate on an operating table of an automatic coating machine, turning on a vacuum system to form contact coating, fixing a coating rod on PET, setting a scraping speed of 60 mm s-1 and a systemic scraping film length of 200 mm, taking 0.4 mL of the AgNW dispersion in step (2), forming a fixed length of 10 cm at a constant speed and clicking a coating button to complete film coating. In a second aspect, the present disclosure provides a method for patterning a cross-ordered AgNW TCF, including the following steps: step (1): preparing an AgNW stock solution with a polyol reduction method, and purifying with absolute ethanol as a solvent in a dynamic stirring and washing method to remove organic matter, Ag nanoparticle and short rod in the AgNW stock solution while retaining a PVP layer on a surface of AgNW to obtain purified AgNWs; step (2): dispersing the purified AgNWs obtained in step (1) in absolute ethanol to obtain an AgNW dispersion with a concentration of 0.4 wt% or more; step (3): subjecting a PET substrate to ultrasonic cleaning, surface hydrophilization treatment, and spin coating with PLL aqueous solution for modification to obtain a pretreated PET substrate; step (4): coating the AgNW dispersion obtained in step (2) on the pretreated PET substrate in step (2) by a coating rod having a groove width less than a length of AgNW in a Meyer bar coating method where a coating speed is 60-120 mm-s-1, drying a solvent completely, immediately coating again with the same method in a direction perpendicular to a pre-aligned direction on unidirectionally ordered AgNW/PET substrate and drying to obtain a cross-ordered AgNW TCF; step (5): spin coating a positive photoresist on the cross-ordered AgNW TCF obtained in step (4), prebaking at 100-120°C for 30-120 s to precure the photoresist, exposing to UV light at a dose of 200-250 mJ cm-2 with a mask reticle, developing in a developer for 3-5 s, immersing in deionized water to remove excess developer on a film surface, etching by immersing in a neutral NaClO solution as an etchant which is a neutral aqueous solution prepared by NaClO and acetic acid where an active chlorine concentration is 0.05-0.30 wt%, then immersing in deionized water to remove excess etchant on a film surface, removing excess photoresist with absolute ethanol, and finally drying to obtain a conductive channel of a certain shape. Operation conditions and limitation of the above steps (1)-(4) are the same as those described above, and not repeated herein. In step (5) of the present disclosure, conventional positive photoresists are all suitable for the present disclosure, where thickness of a layer thereof can be controlled by rotating speed and dilution with appropriate solvents (for example, ethanol, and methyl 3-methoxypropionate (MMP)). At the same time, different photoresists correspond to different optimal developers (alkaline solutions such as Na2CO3 or NaOH aqueous solution). Therefore, those skilled in the art can determine type and concentration of the developer based on a selected type of positive photoresist. Preferably, the positive photoresist may be AZ4620, which is mixed with MMP as a solvent in a volume ratio of 1:1 in use and corresponds to an aqueous solution of AZ400K as a developer. The aqueous solution of AZ400K may be obtained by mixing in a ratio of Veveloper: Vwater = 1:3. Preferably, the spin coating may be carried out by low-speed spin coating at 500 rpm for 3 s, and high-speed spin coating at 7,000 rpm for 1 min. In step (5) of the present disclosure, type of etchant is very important for pattern accuracy. The disclosure finds that, a neutral NaClO solution as an etchant can achieve higher pattern accuracy compared to an acidic or alkaline etchant. The neutral solution of NaClO as an etchant is an aqueous solution prepared from NaClO and acetic acid where concentration of active chlorine has an impact on the pattern accuracy. The disclosure finds that, the concentration of active chlorine in a range of 0.05-0.30 wt% can achieve high pattern accuracy, and an optimal concentration is 0.28 wt%. Moreover, prebaking conditions, UV exposure dose, and development time in step (5) all affect accuracy of the conductive channel. The prebaking is carried out to remove excess solvent in a photoresist layer, preventing the solvent from affecting solubility of the photoresist in the developer. Excessive prebaking will affect activity of sensitizer in the photoresist, thereby affecting a degradation reaction thereof under UV light. Both the activity of sensitizer and the degradation reaction will affect accuracy of a final pattern. Experimental results show that, when the prebaking is carried out for 60 s, the pattern accuracy is basically 99% or more. Extended or reduced prebaking time causes decreased pattern accuracy. The photoresist AZ4620 contains a quinone azide compound which generates a carboxyl group in a photolysis reaction under UV light irradiation, greatly improving solubility in water and finally dissolving in an alkaline developer. Therefore, a mask reticle can be used to block part of the UV light and improve water solubility of a certain area, thereby preparing various patterns based on difference in solubility of different areas. Due to reflection and refraction of light and photoelectron transmission in a photolysis reaction, excessive UV exposure will result in greatly reduced pattern accuracy. Insufficient UV exposure means incomplete photolysis reaction in which the photoresist cannot be cleared completely, and ultimately affects an AgNW etching effect. Therefore, the UV exposure dose needs to be strictly controlled, and the best exposure dose may be 224 mJ cm-2. After the photolysis reaction, a strong alkaline developer is needed to dissolve the photoresist in an exposed area. If development time is too short, there will be residual photoresist, which affects an AgNW etching effect. If the development time is too long, a pattern edge (photoelectron transferring area) may be dissolved by the developer, thereby affecting the pattern accuracy. Although an edge effect is very small for large-width channels, it has a great impact on accuracy of channels with a width less than 100 [m. Experimental results show that, the best development time is 5 s when the pattern accuracy is 99% or more. The prepared photoresist layer channel can protect underlying AgNWs from being etched. After being immersed in NaClO, all the AgNWs except those under the photoresist layer are etched into particles, so that unprotected areas become non-conductive. Optical performance of TCF changes with etching time and is best when the etching time is 10 s. At this point, the optical performance of TCF changes so little after etching with NaClO that no difference can be detected visually, and the change does not affect future use of a device. Compared with the prior art, the present disclosure has the following beneficial technical effects: (1) The present disclosure adopts an improved dynamic stirring and washing method, which can perfectly retain the PVP layer on the AgNW surface while removing the organic matter, Ag nanoparticle and short rod in the stock solution completely, thereby ensuring density and ordering level of AgNWs on the TCF. Moreover, the present disclosure uses an improved Meyer bar coating method to greatly increase fluid driving force that promotes the ordering of AgNWs, further improving the ordering level of AgNW TCF. Finally, an AgNW TCF is obtained with significantly improved ordering level. (2) The present disclosure uses conventional photolithography and wet etching to pattern the cross-ordered AgNW TCF. By optimizing the etchant and various process conditions, the pattern accuracy is significantly improved, where the accuracy of conductive channel having a width of -500 m is higher than 99%. Moreover, the optical performance of the TCF after patterning changes little, which does not affect subsequent use of a device. BRIEF DESCRIPTION OF DRAWINGS In order to make the objectives, technical solutions and beneficial effects of the present disclosure clearer, the present disclosure provides the following drawings: FIG. 1 shows optical microscope (OM) photos (a, b) and ordering parameters (c, d) of the unidirectionally ordered (a) and cross-ordered AgNW networks (b) in Example 1; FIG. 2 are transmission electron microscope (TEM) images showing morphology of AgNWs obtained with different washing methods (a, b, d, e, g, h) and OM photos (c, f, i) of unidirectionally ordered AgNW TCFs, where: (a-c) Comparative Example 1: centrifugal method, (d-f) Comparative Example 2: positive pressure filtration method, (g-i) Example 1: dynamic stirring method. FIG. 3 shows SEM images (low magnification) of unidirectionally ordered TCFs prepared by dynamic stirring and washing with different solvents: (a) Comparative Example 3: water, (b) Comparative Example 4: water and ethanol (volume ratio of 1:1), (c) Example 1: ethanol. FIG. 4 shows SEM images (low magnification) of unidirectionally ordered TCFs prepared by different types of coating rods: (a) Comparative Example 5: OSP-25, (b) Comparative Example 6: OSP-08, (c) Example 1: OSP-03. FIG. 5 shows OM photos of unidirectionally ordered TCFs prepared at different coating speeds and changes in ordering level: (a) 50 mm/s, (b) 60 mm/s, (c) 90 mm /s, (d) 120 mm/s, (e) 150 mm/s, (f) 180 mm/s, (g, h) changes in ordering parameters. FIG. 6 shows OM photos of unidirectionally ordered TCFs prepared with different concentrations of AgNW dispersion and changes in ordering level: (a) 0.1 wt%, (b) 0.2 wt%, (c) 0.3 wt%, (d) 0.4 wt%, (e) 0.5 wt%, (f) 0.6 wt%, (g, h) changes in ordering parameters. Fig. 7 shows changes in accuracy of AgNW conductive channels obtained with different prebaking time. Fig. 8 shows changes in accuracy of AgNW conductive channels obtained at different UV exposure doses. Fig. 9 shows changes in accuracy of AgNW conductive channels obtained with different development time. Fig. 10 shows SEM images (a, b) before and after etching, and diagrams (c, d) of changes in optical performance of TCFs obtained with different etching time. FIG. 11 shows a schematic diagram of conductive channels and OM photos of photoresist channels having different widths: (a) schematic diagram of conductive channels, (b) 20 m, (c) 50

[tm, (d) 100 [m, (e) 200 [m, (f) 300 m, (g) 500 [m. DETAILED DESCRIPTION Preferred embodiments of the present disclosure are described in detail below, which is an explanation rather than a limitation of the present disclosure. Experimental methods in the following embodiments which are not specified with specific conditions are generally carried out according to conventional conditions or conditions recommended by manufacturers. Example 1: An AgNW stock solution was prepared with reference to the literature [Chen G, Bi L, Yang Z, et al. Water-based purification of ultrathin silver nanowires toward transparent conductive films with a transmittance higher than 99%. ACS Applied Materials & Interfaces, 2019, 11: 22648-22654], where AgNWs had a diameter of 15-30 nm and a length of 20-40 m. Step (1): the AgNW stock solution was dynamically stirred and washed with ethanol as a solvent. Specific operations were as follows: 60 mL of AgNW stock solution was poured into a purification device provided with a filter membrane (pore size of 8 m) and a six-hole stirring paddle, and diluted to 300 mL with absolute ethanol. A stirring speed of the six-hole stirring paddle was set to 900 rpm. During washing, the absolute ethanol was slowly dripped into the purification device to maintain a constant volume of solution. The washing was carried out for a total of 40 min. After washing, a positive pressure filtration was carried out, and then 36 mL of PVP solution (0.5 wt%, molecular weight of 55,000) was added and shaken uniformly. A positive pressure filtration was carried out again to collect purified AgNW for later use. Step (2): the purified AgNW in step (1) was dispersed in ethanol to prepare an AgNW dispersion with a concentration of 4.0 mg mL- 1

. Step (3): a PET substrate was treated with specific operations as follows: A PET substrate was ultrasonically cleaned in deionized water and ethanol respectively for 5 min, and then treated with UV ozone for 30 min. A KW-4A desktop spin coater (Beijing Setcas Electronics Co., Ltd.) was turned on, and a film was placed in it. A suction button was clicked, so that the film was tightly adhered to the spin coater. A speed was adjusted to 8,000 rpm, and time was adjusted to 90 s. A pipette was used to drip 5 L of 0.1% PLL aqueous solution (Wuhan Qianrui Biological Co., Ltd.) at the center of the film. A coating button was clicked to complete coating. The film was dried with a hair dryer for later use. Step (4): the substrate in step (3) was placed on the operating table of an automatic coating machine symmetrically, and a vacuum system was turned on to form contact coating. An OSP-03 scraping rod was fixed on the PET, a scraping speed was 60 mm s-, and a systemic scraping film length was set to be 200 mm. Then a pipette was used to take 0.4 mL of the AgNW dispersion in step (2) and form a fixed length of 10 cm. A coating button was clicked to complete coating. A wet film was immediately taken out and dried with a hair dryer to obtain a unidirectionally ordered AgNW TCF. In order to prepare a cross-ordered AgNW array, right after the solvent was completely dried, coating was carried out again in a direction perpendicular to a pre-aligned direction on a unidirectional ordered AgNW/PET substrate. That is, the unidirectionally ordered AgNW TCF was rotated 90° and placed symmetrically on the operation table of the automatic coating machine, then the vacuum system was turned on to form a contact coating. An OSP-03 scraping rod was fixed on the PET, a scraping speed was 60 mm s-1, and a systemic scraping film length was set to be 200 mm. Then a pipette was used to take 0.4 mL of AgNW ink in step (2) and form a fixed length of 10 cm. A coating button was clicked to complete coating. A wet film was immediately taken out and dried with a hair dryer to obtain a cross-ordered AgNW TCF for later use. Step (5): patterning: 0.5 mL of AZ4620 (photoresist, Suzhou Wenhao Microfluidic Technology Co., Ltd.)/ MMP (Shanghai Aladdin Biochemical Technology Co., Ltd.) solution (mixed in a volume ratio of 1:1) was dripped at the center of the cross-ordered AgNW TCF obtained in step (4). A KW-4A desktop spin coater for low-speed spin coating at 500 rpm for 3 s, and high-speed spin coating at 7,000 rpm for 1 min. After the spin coating was completed, the TCF was placed on a hot plate at 100°C to prebake for 60 s to precure the photoresist. When the TCF cooled to room temperature, it was placed in a UV curing oven with a mask reticle placed on its surface and exposed to UV light for 4 s with relative intensity of 50%. The TCF was allowed to stand still and immersed in AZ400K (developer, Suzhou Wenhao Microfluidic Technology Co., Ltd.) aqueous solution (Vdeveloper: Vwater = 1:3) for 5 s, then immersed in deionized water for 5 s to remove excess developer on a film surface. The TCP was immersed in a prepared neutral NaCO-based etchant (a mixture of NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL-1, 1 M acetic acid and deionized water in a volume ratio of NaClO : CH 3 COOH : deionized water =5:3:92, pH=7.01, produced by Shanghai Aladdin Biochemical Technology Co., Ltd.) for 10 s, and then immersed in deionized water for 5 s to remove excess etchant on the film surface. The film was immersed in absolute ethanol for 1 min to remove excess photoresist under shaking, and then placed in a 60 °C blast drying oven for 10 min for later use. An OM (Axio Lab.A1) was used to characterize morphology of unidirectionally ordered AgNW TCF and cross-ordered AgNW TCF obtained in step (4), and results were shown in FIG. 2 (a) and (b). A four-point probe method (RST-9) was used to measure sheet resistance of the cross-ordered AgNW TCF obtained in step (4) and the cross-ordered AgNW TCF after patterning in step (5). A blank reference was used or a UV-treated PET was used as a reference to measure the cross-ordered AgNW TCF obtained in step (4) and the cross-ordered AgNW TCF after patterning in step (5) with a UV-visible-near infrared spectrometer (Lambda 7500) at room temperature for transmittance and haze. Results were shown in Table 1: Table 1 Sheet resistance after Transmittance before and after Haze before and after PH of Sheet resistance before etching /% etching /% PtHof Shetresisncebefore Shetreigstaneate etchant etching /[sq' etching /Gsq 1 Tbefore Tater AT Hbefore Hafter AH 7.01 41.6 Not conductive 90.71 90.75 0.04 2.19 2.31 -0.12

The ordering level parameter S2D of the unidirectionally ordered AgNW TCF obtained in step (4) can be obtained by the following formula: &Sm=< 2cos2 , - 1>= NYN(2 1=1 cos2 cs 6j --11) In the formula, O1 was an angle between an average vector of AgNW arrangement and a vector of the i-th AgNW arrangement. The value of S2D was between 0 and 1 where a value closer to 1 represented higher level of alignment of the AgNWs. S2D=1 meant that the AgNWs were arranged in the same direction. S2D=O meant that the AgNWs were oriented completely randomly. In the present disclosure, orientation of AgNW was detected with the ImageJ software. From calculation by the above formula, it can be obtained that, the ordering level S2D of the unidirectionally ordered AgNW TCF prepared in this example was 0.82 (FIG. 2 (c) and (d)), meaning that 84% of AgNWs had deflection angles within 300, and 81% of AgNWs had deflection angles within 15°. The full width at half maxima (FWHM) was only 18.2. Another calculation formula was also used: 1 S= -(3<cos 2 0>_

In the formula, <0 was the angle between an arrangement direction of AgNWs and an initial direction. Through this formula and data obtained by ImageJ, the ordering level of the prepared unidirectionally ordered AgNW network S=0.87. Comparative Example 1 Step (1): 60 mL of AgNW stock solution was prepared by a polyol reduction method and centrifuged to remove impurities. Specifically: step a): two batches of 12 mL of AgNW stock solution prepared by a polyol reduction method were respectively dissolved in 24 mL of deionized water, and shaken with a shaker at 110 rpm for 10 min. Step b): centrifuging was carried out in a centrifuge at 4,500 rpm for 10 min. Step c): a supernatant was poured out and a precipitate was ready for later use. Steps (2)-(4) were the same as those in Example 1 and a unidirectionally ordered AgNW TCF was obtained. Comparative Example 2 Step (1): 60 mL of AgNW stock solution prepared by a polyol reduction method was subjected to positive pressure filtration. Specifically: step a): two batches of 16 mL of AgNW stock solution prepared by a polyol reduction method were taken and dissolved in 30 mL of deionized water and shaken with a shaker at 110 rpm for 10 min. Step b): positive pressure filtration was carried out. AgNWs on a filter membrane were dissolved in 48 mL of deionized water, and shaken with a shaker at 110 rpm for 10 min. Step c): positive pressure filtration was carried out, and a precipitate was dissolved in 48 mL of PVP (relative molecular weight of 55,000), shaken with a shaker at 110 rpm for 2 h. Step d): positive pressure filtration was carried out and a precipitate was ready for later use. Steps (2)-(4) were the same as those in Example 1 and a unidirectionally ordered AgNW TCF was obtained. From results of Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that, the centrifugal method can successfully retain the PVP layer on the surface of AgNW (FIG. 2, (a) and (b)). The coated TCF had denser AgNWs, but the Ag particles were not washed away completely, which greatly affected the optical performance of TCF (FIG. 2, (c)). For the positive pressure filtration method, as shown in FIG. 2, (d)-(f), although the Ag particles and short rods were washed away completely, the PVP layer on the surface of AgNWs was also washed away completely, which greatly reduced the electrostatic force between the surface and PLL, causing significantly decreased density of AgNWs on TCF. The dynamic stirring and washing method of the present disclosure successfully retained the PVP layer on the AgNW surface (FIG. 2, (g) and (h)), while the Ag particles and short rods in the ink were washed away completely. The resulted TCF had a high density of AgNWs with a high ordering level (FIG. 2, (i)). Comparative Example 3

A dispersing agent in step (2) of Example 1 was replaced by water, and other operations were the same as those in Example 1. A unidirectionally ordered AgNW TCF was obtained. Comparative Example 4 A dispersing agent in step (2) of Example 1 was replaced by a mixed solution of water and ethanol in a volume ratio of 1:1, and other operations were the same as those in Example 1. A unidirectionally ordered AgNW TCF was obtained. From Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that when AgNWs dynamically stirred and washed were dispersed in ethanol, the coated AgNW TCF had higher nanowire ordering level than those prepared by dispersing in water and a mixture of water and ethanol (as shown in FIG. 3, (a)-(c)). After scrape coating with the OSP-03 coating rod, a wet film was obtained, where pre-ordered AgNWs were still dispersed in a solvent. If the solvent evaporated too slowly or a drying temperature was too high, AgNWs would have excessive thermal movement, causing the pre-ordered AgNWs to return to a chaotic state and affecting final ordering level of AgNW on TCF. Ethanol was the most ideal solvent since it had a low boiling point and a fast drying speed and required no heat drying or other additional operations. Comparative Example 5 A coating rod was replaced by OSP-25, and other operations were the same as those in Example 1. A unidirectionally ordered AgNW TCF was obtained. The AgNWs on the obtained film were all randomly oriented. Comparative Example 6 A coating rod was replaced by OSP-08, and other operations were the same as those in Example 1. A unidirectionally ordered AgNW TCF was obtained. The AgNWs on the obtained film were all randomly oriented. Examples 2-6 A coating speed was changed (see Table 2 for details) and other operations were the same as those in Example 1. A unidirectionally ordered AgNW TCF was obtained. OM photos of obtained TCFs and changes of ordering level thereof were shown in FIG. 5. Table 2 Example Coating speed

Example 2 50 mm-s-1

Example 1 60 mm-s-1

Example 3 90 mm-s-1

Example 4 120 mm-s-1

Example 5 150 mm-s-1

Example 6 180 mm-s-1

It can be seen from FIG. 5 (a)-(h) that, as the coating speed decreased, the ordering level of

AgNW on TCF increased sharply and then decreased slightly at 60 mm s-1 Example 7-11 A concentration of dispersion in step (2) was changed (see Table 3 for details) and other operations were the same as those in Example 1. A unidirectionally ordered AgNW TCF was obtained. OM photos of obtained TCFs and changes of ordering level thereof were shown in FIG. 6. Table 3 Example Concentration

Example 7 10 mg mL-1

Example 8 20 mg mL-1

Example 9 30 mg mL-1

Example 1 40 mg mL-1

Example 10 50 mg mL-1

Example 11 60 mg mL-1

As shown in FIG. 6 (a)-(f), as the concentration of AgNW in the dispersion increased, the density of AgNW on the coated TCF also increased. The ordering level increased with increased AgNW concentration initially. When the AgNW concentration was greater than 0.4 wt%, the ordering level of the AgNW network tended to be stable (FIG. 6, (g) and (h)). Example 8 The prebaking time was 30 s, 90 s and 120 s, and other operations were the same as those in Example 1. A patterned AgNW TCF was obtained. Change of AgNW conductive channel accuracy with different prebaking time was shown in FIG. 7. Example 9 The UV exposure dose and width of mask reticle were changed, and other operations were the same as those in Example 1. A patterned AgNW TCF was obtained. Accuracy changes of AgNW conductive channels obtained at different UV exposure doses were shown in FIG. 8. Example 10 The development time was changed, and other operations were the same as those in Example 1. A patterned AgNW TCF was obtained. Accuracy changes of AgNW conductive channels obtained with different development time were shown in FIG. 9. Example 11 The etching time was changed, and other operations were the same as those in Example 1. A patterned AgNW TCF was obtained. The optical performance of TCF changed with the etching time. As shown in FIG. 10 (c) and (d), the best etching time was 10 s. FIG. 10 (a) and (b) were SEM images of TCF before and after etching for 10 s respectively. Example 12 The width of mask reticle was changed, and other operations were the same as those in

Example 1. A patterned AgNW TCF was obtained. FIG. 11 (a) was a schematic diagram of conductive channels, and (b-f) in FIG. 11 were OM photos of the conductive channels having a width of 20-500 tm prepared by mask reticles with different width. By measuring the width of the channels, it can be seen that, accuracy of the conductive channels was higher than 99%. Example 13 The etchant was changed and other operations were the same as those in Example 1. Results were as shown in Table 4. In Table 4, the etchant with pH=3.98 was prepared from NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL- 1, 1 M acetic acid and deionized water in a volume ratio of NaClO : CH 3COOH : deionized water =5:8.8:86.2. The etchant with pH=7.01 was prepared from NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL- 1, 1 M acetic acid and deionized water in a volume ratio of NaClO : CH 3COOH : deionized water =5:3:92; The etchant with pH=10.05 was prepared from NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL- 1, 1 M acetic acid and deionized water in a volume ratio of NaClO : CH3COOH (IM): deionized water =5: 0.37:94.63. Table 4 PH of Sheet resistance before Sheet resistance after Transmittance before and after Haze before and after 1 1 etchant etching /Q sq- etching /Q sq- etching /% etching /%

Tbefore Tafter AT Hbefore Hafter AH

1 3.98 152.1 Not conductive 90.21 90.72 0.51 2.87 2.39 0.48

2 7.01 41.6 Not conductive 90.71 90.75 0.04 2.19 2.31 -0.12

3 10.05 152.1 Not conductive 90.21 91.12 0.91 2.87 2.21 0.66

Example 14 An AgNW stock solution was prepared with reference to the literature [Korte K E, Skrabalak S E, Xia Y. Rapid synthesis of silver nanowires through a CuCl- or CuCl2-mediated polyol process. Journal of Materials Chemistry, 2008, 18(4): 437-441] where AgNWs had a diameter of 80-120 nm and a length of 20-50 [m, etchant preparation was the same as that of Example 13, and other experimental steps were the same as those of Example 1. Results were shown in Table 5: Table 5 Transmittance before and after etching PH of Sheet resistance before etching /Q Sheet resistance after etching /Q /00 sq-I 1 etchant sq- Tbefore Tafter AT

1 3.98 8.4 Not conductive 83.57 88.10 4.53

2 7.01 8.4 Not conductive 83.57 84.26 0.69

3 10.05 8.4 Not conductive 83.57 89.98 6.41

Example 15 The concentration of active chlorine in neutral etchant was changed and other operations were the same as those in Example 1. Results were as shown in Table 6. In Table 6, the etchant with an active chlorine content of 0.28 wt% was prepared from NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL- 1, 1 M acetic acid and deionized water in a volume ratio of NaClO : HAc : deionized water =5:3:92. The etchant with an active chlorine content of 0.14 wt% was prepared from NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL-1, 1 M acetic acid and deionized water in a volume ratio of NaClO : HAc : deionized water =2.5: 1.5:96. The etchant with an active chlorine content of 0.07 wt% was prepared from NaClO aqueous solution having an active chlorine concentration of 0.056 mg mL-1, 1 M acetic acid and deionized water in a volume ratio of NaClO : HAc : deionized water =1.25:0.75:98.

Table 6

Active Transmittance before and after Sheet Haze before and after etching /% chlorine Sheet resistance etching /% resistance content in after etching /Q before etching sq- etchant/ Tbefore Tafter AT Hbefore Hafter AH /Q sq wt%

1 0.28 41.6 Not conductive 90.71 90.75 0.04 2.19 2.31 -0.12

2 0.14 116.2 Not conductive 89.92 90.43 0.51 3.04 3.37 -0.33

3 0.07 116.2 Not conductive 89.92 90.70 0.78 3.04 2.79 0.25

Claims (5)

1. What is claimed is: 1. A method for preparing a cross-ordered silver nanowire transparent conductive film (AgNW TCF), comprising the following steps: step (1): preparing a silver nanowire (AgNW) stock solution with a polyol reduction method, and purifying with absolute ethanol as a solvent in a dynamic stirring and washing method to remove organic matter, silver (Ag) nanoparticle and short rod in the AgNW stock solution while retaining a polyvinyl pyrrolidone (PVP) layer on a surface of AgNW to obtain purified AgNWs; step (2): dispersing the purified AgNWs obtained in step (1) in absolute ethanol to obtain an AgNW dispersion with a concentration of 0.4 wt% or more; step (3): subjecting a polyethylene terephthalate (PET) substrate to ultrasonic cleaning, surface hydrophilization treatment, and spin coating with poly-L-lysine (PLL) aqueous solution for modification to obtain a pretreated PET substrate; step (4): coating the AgNW dispersion obtained in step (2) on the pretreated PET substrate in step (2) by a coating rod having a groove width less than an AgNW length in a Meyer bar coating method wherein a coating speed is 60-120 mm-s, drying a solvent completely, immediately coating again with the same method in a direction perpendicular to a pre-aligned direction on unidirectionally ordered AgNW/PET substrate and drying to obtain a cross-ordered AgNW TCF.
2. 2. The method for preparing a cross-ordered AgNW TCF according to claim 1, wherein the AgNW has a diameter of 15-200 nm, preferably 15-30 nm, and a length of 20-200 [m.
3. 3. The method for preparing a cross-ordered AgNW TCF according to claim 1, wherein step (1) is carried out as follows: pouring an AgNW stock solution into a purification device which comprises a filter membrane with a pore size smaller than a length of AgNW and a stirring paddle, diluting with absolute ethanol, rotating the stirring paddle, slowly dripping absolute ethanol into the purification device to maintain a constant volume of solution during washing, after washing for a certain period of time, carrying out a positive pressure filtration, adding a PVP aqueous solution, shaking uniformly, and carrying out a positive pressure filtration to collect purified AgNWs; preferably, the pore size of the filter membrane is 8 m, a stirring speed is 900 rpm, and washing time is 40 min; wherein in step (2), the AgNW dispersion has a concentration of 0.4 wt%; wherein in step (3), the surface hydrophilization treatment is carried out with ultraviolet (UV) ozone; wherein in step (4), the coating speed is 60 mm-s'.
4. 4. A method for patterning a cross-ordered AgNW TCF, comprising the following steps: step (1): preparing an AgNW stock solution with a polyol reduction method, and purifying with absolute ethanol as a solvent in a dynamic stirring and washing method to remove organic matter, Ag nanoparticle and short rod in the AgNW stock solution while retaining a PVP layer on a surface of AgNW to obtain purified AgNWs; step (2): dispersing the purified AgNWs obtained in step (1) in absolute ethanol to obtain an AgNW dispersion with a concentration of 0.4 wt% or more; step (3): subjecting a PET substrate to ultrasonic cleaning, surface hydrophilization treatment, and spin coating with PLL aqueous solution for modification to obtain a pretreated PET substrate; step (4): coating the AgNW dispersion obtained in step (2) on the pretreated PET substrate in step (2) by a coating rod having a groove width less than an AgNW length in a Meyer bar coating method wherein a coating speed is 60-120 mm-s-1, drying a solvent completely, immediately coating again with the same method in a direction perpendicular to a pre-aligned direction on a unidirectionally ordered AgNW/PET substrate and drying to obtain a cross-ordered AgNW TCF; step (5): spin coating a positive photoresist on the cross-ordered AgNW TCF obtained in step (4), prebaking at 100-120°C for 30-120 s to precure the photoresist, exposing to UV light at a dose of 200-250 mJ cm-2 with a mask reticle, developing in a developer for 3-5 s, immersing in deionized water to remove excess developer on a film surface, etching by immersing in a neutral NaClO solution as an etchant which is a neutral aqueous solution prepared by NaClO and acetic acid wherein an active chlorine concentration is 0.05-0.30 wt%, then immersing in deionized water to remove excess etchant on a film surface, removing excess photoresist with absolute ethanol, and finally drying to obtain a conductive channel of a certain shape.
5. 5. The method for patterning a cross-ordered AgNW TCF according to claim 4, wherein in step (5), the positive photoresist is AZ4620, which is mixed with methyl 3-methoxypropionate (MMP) as a solvent in a volume ratio of 1:1 in use and the developer is an aqueous solution of AZ400K which is obtained by mixing in a ratio of Veveloper: Vwater = 1:3; wherein the neutral NaClO solution as an etchant has an active chlorine concentration of 0.28 wt%; wherein in step (5), the prebaking is carried out at 100°C for 60 s, the exposing to UV light is carried out at a dose of 224 mJ cm-2 , the developing is carried out for 5 s, and the etching is carried out for 10 s.