CN111489864B

CN111489864B - Cross-ordered silver nanowire thin film and patterning method thereof

Info

Publication number: CN111489864B
Application number: CN202010083076.0A
Authority: CN
Inventors: 潘军; 何晓雄; 吴泽磊; 叶萃
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2020-02-07
Filing date: 2020-02-07
Publication date: 2021-08-24
Anticipated expiration: 2040-02-07
Also published as: CN111489864A; AU2021100456A4

Abstract

The invention provides a cross-ordered silver nanowire film and a patterning method thereof, wherein the method comprises the following steps: (1) purifying AgNWs stock solution prepared by a polyol reduction method by adopting a dynamic stirring and cleaning method; (2) dispersing the purified AgNWs in absolute ethyl alcohol to prepare AgNW dispersion liquid with the concentration of more than 0.4 wt%; (3) carrying out ultrasonic cleaning, surface hydrophilization treatment and PLL aqueous solution spin-coating modification on a PET substrate; (4) obtaining a cross-ordered silver nanowire transparent conductive film by adopting a Meyer rod coating method; (5) and spin-coating a positive photoresist on the cross-ordered silver nanowire transparent conductive film, and then precuring, ultraviolet exposing, developing, etching, washing and drying to obtain a conductive channel with a certain shape. The AgNW TCF ordering method can greatly improve the ordering degree of AgNW TCF prepared by a bar coating method, and the provided patterning method can improve the pattern precision and does not influence the optical performance of the conductive film.

Description

Cross-ordered silver nanowire thin film and patterning method thereof

Technical Field

The invention belongs to the technical field of nano material preparation and application, and particularly relates to a method for ordering and patterning silver nanowires.

Background

The transparent conductive electrode is widely applied to photoelectric devices, such as flexible solar cells, flexible touch screens, display screens and the like. The most common material for preparing transparent conductive electrodes at present is Indium Tin Oxide (ITO), but the ITO material is very expensive, hard and brittle, and has very limited application. As a new material most promising as a substitute for ITO, silver nanowires (agnws) are superior in light transmittance and electrical conductivity to graphene, carbon nanotubes, conductive polymers, and the like. Moreover, the AgNW network can be directly prepared by rod coating, spin coating or spray coating, and the like, so that the cost is low and the method is simple and convenient. However, general AgNW networks are all randomly distributed, and problems of uneven distribution, large surface roughness, easy tangling of AgNWs, large junction resistance between AgNWs and the like often exist.

In order to solve the above problems, researchers have adopted methods such as adding a trace amount of organic matter to AgNW ink, adding a polymer coating to the surface, mechanical pressing, and thermal annealing. However, these methods have complicated process flows and undesirable effects. To this end, Ko et al proposed a new method for obtaining an ordered AgNW network by adjusting the direction of the AgNWs arrangement to align the AgNWs in the same direction, in which the node arrangement becomes uniformly ordered, and the resulting Transparent Conductive Film (TCF) has a small and uniform sheet resistance, a smooth surface, and a small roughness.

Although the AgNW network with a high degree of ordering can be obtained by the spray method, the uniformity is poor, except for the position in the center of the spray area, which results in poor uniformity of transmittance and sheet resistance. Therefore, in practical application, the method is not suitable for popularization. In contrast, many groups prepared the ordered AgNW tcf by the rod coating method, and the obtained AgNW network was good in uniformity but generally low in the degree of ordering.

However, the application of the ordered AgNWTCF in display devices is limited, and most displays require both conductive and non-conductive areas, so that patterning is required to solve this problem, and the accuracy of patterning directly determines the performance of the devices. There are also many patterning methods, such as screen printing, chemical etching by applying an etching mask, and the like. However, these methods have the disadvantages of low resolution, large difference in optical properties between etched and non-etched regions, and visibility to the naked eye.

Disclosure of Invention

A first object of the present invention is to provide a method for preparing a cross-ordered silver nanowire transparent conductive film (AgNW TCF) using a rod coating method, which greatly improves the degree of ordering of the AgNW TCF prepared by the rod coating method.

A second object of the present invention is to provide a patterning method of a cross-ordered silver nanowire transparent conductive film (AgNW TCF) to improve the accuracy of the pattern without affecting the optical properties of the conductive film.

In order to achieve the purpose, the specific technical scheme of the invention is as follows:

in a first aspect, the present invention provides a method for preparing a cross-ordered silver nanowire (AgNW) transparent conductive film, comprising the steps of:

(1) the method comprises the following steps of (1) purifying AgNWs stock solution prepared by a polyol reduction method by using absolute ethyl alcohol as a purification solvent and adopting a dynamic stirring and cleaning method, removing organic matters, silver nano particles and short rods contained in the AgNWs stock solution, and simultaneously keeping a PVP layer on the surface of AgNWs to obtain purified AgNWs;

(2) dispersing the purified AgNWs obtained in the step (1) in absolute ethyl alcohol to prepare AgNWs dispersion liquid with the concentration of more than 0.4 wt%;

(3) carrying out ultrasonic cleaning, surface hydrophilization treatment and PLL (phase locked loop) aqueous solution spin-coating modification on a PET substrate to obtain a pretreated PET substrate;

(4) coating the AgNW dispersion liquid obtained in the step (2) on the PET substrate pretreated in the step (3) by adopting a Meyer bar coating method and using a coating bar with the groove width smaller than the AgNWs length, wherein the coating speed is 60-120 mm & s^-1Drying after coating is finished; and after the solvent is completely dried, immediately coating the single-direction ordered AgNWs/PET substrate in the direction perpendicular to the prealignment direction again according to the same method, and drying after coating to obtain the cross-ordered silver nanowire transparent conductive film.

In step (1) of the present invention, the AgNWs stock solution is prepared by a polyol reduction method, which is generally obtained by using polyvinylpyrrolidone (PVP) as a growth guide agent. Specifically, silver nitrate is used as a silver source, ethylene glycol is used as a reducing agent and a solvent, polyvinylpyrrolidone (PVP) is used as a growth guiding agent, sodium chloride and sodium bromide are used as crystal form inducers, and a polyol reduction method is adopted to prepare the silver nanowire. Preferably, the silver nanowires have a diameter of 15-200nm and a length of 20-200 μm. More preferably, the silver nanowires have a diameter of 13-30 nm.

The dynamic stirring cleaning method described in step (1) of the present invention can be operated by referring to the steps reported in the prior art documents, such as the documents [ Chen G, Bi L, Yang Z, et al, Water-based pure fi location of ultrasonic minor nano-device conductive filters with a transmission high which is 99%. ACS Applied Materials & Interfaces,2019,11: 22648-. It should be noted that the present invention does not require absolute ethanol as the purification solvent, because after coating with a bar, a wet film is obtained, the pre-ordered AgNWs is still dispersed in the solvent, and if the solvent evaporation rate is too slow or the drying temperature is too high, the thermal motion of the AgNWs is excessive, which causes the pre-ordered AgNWs to return to a disordered state again, thereby affecting the degree of ordering of the AgNWs on the final TCF. The ethanol has lower boiling point and high drying speed, does not need operations such as heating and drying, and is the most ideal solvent. The invention specifically recommends that the step (1) is carried out as follows: pouring AgNWs stock solution into a purification device with a filter membrane and a stirring paddle, wherein the aperture of the filter membrane is smaller than the length of a silver nanowire, diluting the AgNWs stock solution with absolute ethyl alcohol, rotating the stirring paddle, slowly dropping the absolute ethyl alcohol into the purification device in a cleaning process to keep the constant volume of the solution, cleaning for a certain time, performing positive pressure filtration, adding PVP (polyvinyl pyrrolidone) aqueous solution, shaking uniformly, performing positive pressure filtration again, and collecting the purified AgNWs. Preferably, the filter membrane pore size is 8 μm, the stirring speed is 900rpm, and the washing time is 40 min. Preferably, the relative molecular mass of the PVP is 55000 and the concentration of the aqueous solution of PVP is 0.5 wt%.

In step (2) of the present invention, the concentration of the AgNWs dispersion is set to 0.4 wt% or more, because as the concentration of the AgNWs dispersion increases, the density of AgNWs on the coated TCF also increases, and the degree of ordering first increases with increasing concentration, and when the AgNWs concentration reaches 0.4 wt%, the degree of ordering of the AgNWs network tends to be stable, and it is no longer meaningful to increase the concentration, so the concentration of the AgNWs dispersion is preferably 0.4 wt%.

In step (3) of the present invention, ultrasonic cleaning, surface hydrophilization treatment, and PLL aqueous solution spin-coating modification of the PET substrate can be performed by the literature methods. The surface hydrophilization treatment can be performed by ultraviolet ozone treatment, plasma treatment or coating with a hydrophilic substance, thereby changing the surface tension of the substrate. Among them, the ultraviolet ozone treatment is most convenient and has good effect, so the ultraviolet ozone treatment is preferably adopted, and the ultraviolet ozone treatment is more preferably adopted for 30 min. Preferably, the ultrasonic cleaning is to put the PET substrate in deionized water and ethanol in sequence for ultrasonic cleaning for 5-10 min. Preferably, the self-ozone treatment time is 10-30 min. Preferably, the operating parameters of the PLL aqueous solution spin-coating modification are as follows: the concentration of the aqueous PLL solution was 0.1%, the revolution speed of the spin coater was 8000rpm, and the spin coating time was 90 s.

In step (4) of the present inventionOther operating parameters of the Meyer bar coating process can be found in the literature. Among these, the choice of the coating stick has a great influence on the degree of ordering of the AgNW network of the present invention, since the coating stick can pre-order the AgNWs. When the groove width on the coating rod is greater than the AgNWs length, a large amount of disorganized AgNWs passes directly through the coating rod, resulting in a random orientation distribution of the AgNWs on the TCF for the most part. Therefore, a coating bar with a groove width less than the AgNWs length should be selected. Meanwhile, different coating speeds have great influence on the ordering degree of the AgNWs network. The experimental results show that the degree of AgNWs ordering on TCF increases sharply with decreasing coating speed, and then increases sharply at 60mm s^-1And slightly lowered again. Therefore, the optimum coating speed is 60mm s^-1. The invention particularly preferably adopts the operating parameters of the Meyer bar coating method in the step (4) as follows: placing the pretreated PET substrate on an operation table of an automatic coating machine, opening a vacuum system to form contact coating, fixing a coating film bar on the PET, and carrying out blade coating at a speed of 60mm s^-1And (3) setting the length of a film scraping of the system to be 200mm, then taking 0.4mL of AgNWs dispersion liquid obtained in the step (2) by using a suction pipe, stretching the AgNWs dispersion liquid at a constant speed for a fixed length of 10cm, clicking a coating button, and finishing film coating.

In a second aspect, the present invention provides a method for patterning a cross-ordered silver nanowire (AgNWs) transparent conductive film, comprising the steps of:

(4) coating the Ag obtained in the step (2) by using a Meyer bar coating method and a coating bar with the groove width smaller than the length of AgNWsCoating the PET substrate pretreated in the step (2) with NWs dispersion liquid, wherein the coating speed is 60-120 mm & s^-1Drying after coating is finished; after the solvent is completely dried, immediately coating the single-direction ordered AgNWs/PET substrate in the direction perpendicular to the pre-alignment direction again according to the same method, and drying after coating to obtain the cross-ordered silver nanowire transparent conductive film;

(5) spin-coating a positive photoresist on the cross-ordered silver nanowire transparent conductive film obtained in the step (4), pre-baking the photoresist for 30-120s at the temperature of 100 ℃ and 120 ℃ to pre-cure the photoresist, exposing the photoresist to ultraviolet rays by using a mask plate for exposure, and controlling the exposure dose of the ultraviolet rays to be 200-250mJ cm^-2Then, the film is placed in a developer for developing for 3-5s, the film is soaked in deionized water to remove the redundant developer on the surface of the film and then is soaked in a neutral sodium hypochlorite etching agent for etching, the neutral sodium hypochlorite etching agent is a neutral aqueous solution prepared from sodium hypochlorite and acetic acid, the concentration of active chlorine is 0.05-0.30 wt%, then the film is soaked in the deionized water to remove the redundant etching agent on the surface of the film, then the redundant photoresist is removed by absolute ethyl alcohol, and finally the conductive channel with a certain shape is obtained by drying.

The operation and the limitation conditions of the steps (1) to (4) are the same as above, and are not described again here.

In step (5) of the present invention, conventional positive photoresist is suitable for the present invention, and the thickness of the photoresist layer can be controlled by rotating speed and diluting with a suitable solvent (e.g., ethanol, methyl 3-methoxypropionate, etc.). At the same time, different photoresists all have corresponding optimum developers (alkaline solutions, e.g. Na)₂CO₃Aqueous NaOH, etc.). The kind and concentration of the developing solution can be determined by those skilled in the art according to the kind of the selected positive photoresist. Preferably, the positive photoresist is AZ4620 using methyl 3-methoxypropionate (MMP) as a solvent, and AZ4620 and MMP are mixed in a volume ratio of 1: 1; the developer is AZ400K aqueous solution and is according to V_{Display device}:V_{Water (W)}Mixing at a ratio of 1: 3. Preferably, the spin coating process parameters are as follows: 500rpm low speed spin coating for 3s, 7000rpm high speed spin coatingCoating for 1 min.

In step (5) of the present invention, the choice of etchant is crucial to ensure the accuracy of the pattern. The inventors have found that neutral sodium hypochlorite etchants can achieve higher pattern accuracy than acidic or basic etchants. The neutral sodium hypochlorite etchant is an aqueous solution prepared from sodium hypochlorite and acetic acid, wherein the concentration of active chlorine has an influence on the accuracy of the pattern, and the inventor finds that the active chlorine concentration is in the range of 0.05-0.30 wt% to obtain high pattern accuracy, and the optimal concentration is 0.28 wt%. In addition, the pre-baking conditions, the uv exposure dose, and the development time in step (5) all affect the accuracy of the conductive path. The prebaking is to remove the excess solvent in the photoresist layer and prevent it from affecting the solubility of the photoresist in the developing solution, and the prebaking will affect the activity of the sensitizer in the photoresist and thus the degradation reaction under the ultraviolet light, both of which will affect the precision of the final pattern. The experimental result shows that when the pre-baking time is 60s, the precision of the pattern is basically over 99%, and the pattern precision is reduced when the pre-baking time is prolonged or reduced. The photoresist AZ4620 contains azidoquinones, and can generate photolysis reaction under the irradiation of ultraviolet light to generate carboxyl, so that the water solubility is greatly improved, and the photoresist can be finally dissolved in an alkaline developing solution. Therefore, a mask can be used for shielding partial ultraviolet light, the water solubility of partial areas is improved, and various patterns are prepared by utilizing the solubility difference between different areas. Excessive uv exposure can cause a significant reduction in pattern accuracy due to reflection and refraction of light and transmission of photoelectrons during photolytic reactions. Insufficient ultraviolet exposure means insufficient photolysis reaction, which can cause the photoresist to be unclear and finally affect the etching effect of AgNWs. Therefore, the UV exposure dose needs to be strictly controlled, and the optimal exposure dose is 224mJ cm^-2. After the photolytic reaction, a strong alkaline developer is needed to dissolve the photoresist in the exposed area. The photoresist residue can be caused by too short developing time, so that the etching effect of AgNWs is influenced; too long time may cause the pattern edge (photoelectron transfer region) to be dissolved by the developer, thereby affecting the pattern precision. Although for large width channels the edges areThe fringe effect is weak but has a large effect on the accuracy of channels with widths less than 100 μm. The experimental result shows that the optimal development time is 5s, and the pattern precision is more than 99%. The prepared glue layer channel can protect AgNWs below from being etched, and AgNWs at the rest positions except the AgNWs below the glue layer are etched into particles after the AgNWs are soaked by NaClO, so that an unprotected area becomes non-conductive. The optical performance of the TCF can change along with the change of the etching time, the optimal etching time is 10s, the change of the optical performance of the TCF etched by the NaClO is very small, the TCF can not be distinguished by naked eyes at all, and the later use of a device can not be influenced.

Compared with the prior art, the invention has the following beneficial technical effects:

(1) the invention utilizes an improved dynamic stirring cleaning method, which can perfectly keep a PVP layer on the AgNWs surface, and can also clean organic matters, silver nano particles and short bars in stock solution, thereby ensuring the density and the ordering degree of AgNWs on TCF; the improved Meyer bar coating method is utilized to greatly increase the fluid power for promoting the AgNWs to be ordered, and the ordering degree of the AgNW TCF is further improved; finally, the silver nanowire transparent conductive film with the obviously improved ordering degree is obtained.

(2) The method utilizes the conventional photoetching method and wet etching to pattern the cross-ordered AgNW TCF, obviously improves the pattern precision by optimizing the etching agent and the working conditions, and the precision of the conductive channel with the width of 20-500 mu m is higher than 99 percent; moreover, the optical property of the patterned TCF is slightly changed, and the subsequent use of the device is not influenced.

Drawings

In order to make the purpose, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings:

fig. 1 is OM photographs (a, b) of the AgNW network for unidirectional ordering and cross-ordering of example 1 and their degree of ordering parameters (c, d): a unidirectional ordered AgNW network (a); cross-ordering AgNW networks (b).

Fig. 2 is a TEM topography of AgNWs obtained under different cleaning methods (a, b, d, e, g, h) and (c, f, i) OM photographs of unidirectionally ordered AgNW TCFs: (a-c) comparative example 1: centrifuging; (d-f) comparative example 2: positive pressure filtration; (g-i) example 1: dynamic stirring method.

FIG. 3 is a low-magnification SEM photograph of unidirectionally ordered TCFs prepared by dynamic agitation washing with different solvents: (a) comparative example 3: water; (b) comparative example 4: water and ethanol (volume ratio 1: 1); (c) example 1: and (3) ethanol.

FIG. 4 is a low-magnification SEM photograph of unidirectionally ordered TCFs prepared from different types of coated rods: (a) comparative example 5: OSP-25; (b) comparative example 6: OSP-08; (c) example 1: OSP-03.

Fig. 5 is OM photographs of unidirectionally ordered TCFs prepared at different coating speeds and the change in the degree of ordering thereof: (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) variation of the degree of ordering parameter.

Fig. 6 is OM photographs of unidirectionally ordered TCFs prepared from dispersions of different AgNWs concentrations and the change in their degree of ordering: (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) variation of the degree of ordering parameter.

Fig. 7 is a graph of the variation in AgNW conduction channel accuracy obtained at different pre-bake times.

Fig. 8 is a graph of the variation in AgNW conduction channel accuracy obtained at different uv exposure doses.

Fig. 9 is a graph of the variation in AgNW conduction channel accuracy obtained at different development times.

FIG. 10 shows SEM pictures (a) and (b) before and after etching, and graphs (c) and (d) showing changes in optical properties of TCFs at different etching times.

FIG. 11 is a schematic view of a conductive via and OM photos of a photoresist via at different widths: (a) a schematic diagram of a conductive channel; (b)20 μm; (c)50 μm; (d)100 μm; (e)200 mu m; (f)300 mu m; (g)500 μm.

Detailed Description

The following detailed description of the preferred embodiments of the invention is intended to be illustrative of the invention and is not to be construed as limiting the invention. The experimental procedures, in which specific conditions are not specified in the examples, are generally carried out under conventional conditions or under conditions recommended by the manufacturers.

Example 1:

the AgNWs stock solution is prepared according to the literature [ Chen G, Bi L, Yang Z, et al, Water-based purification of ultra-thin silver nanowiware driven delivery films with a transmission high which is 99%. ACS Applied Materials & Interfaces,2019,11:22648-22654 ], and the silver nanowires have a diameter of 15-30nm and a length of 20-40 μm.

(1) And dynamically stirring and cleaning the AgNWs stock solution by using an ethanol solvent. The specific operation is as follows:

the 60mL of stock solution of LAgNWs was poured into a purification apparatus equipped with a filter (8 μm pore size) and a six-well stirring paddle and diluted to 300mL with absolute ethanol. The stirring speed of the six-hole stirring paddle was set to 900 rpm. During the cleaning process, the absolute ethyl alcohol is slowly dropped into the purification device to keep the solution constant in volume, and the cleaning is carried out for 40 min. After washing, firstly carrying out positive pressure filtration, then adding 36ml of VP solution (0.5 wt%, molecular weight of 55000), shaking uniformly, then carrying out positive pressure filtration, and collecting purified AgNWs for later use.

(2) Dispersing the AgNWs purified in the step (1) in ethanol to prepare the AgNWs with the concentration of 4.0mg mL^-1The AgNWs dispersion of (1).

(3) The treatment of the PET substrate was carried out as follows:

the PET substrate is ultrasonically cleaned in deionized water and ethanol for 5min respectively, and then treated with ultraviolet ozone for 30 min. Opening a KW-4A type desk type spin coater (Beijing Saidekais electronic Limited responsibility company), placing the film in the spin coater, and clicking a suction button to tightly attach the film to the spin coater; regulating the rotating speed to 8000rpm and the time to 90 s; dripping 5 μ L of 0.1% PLL aqueous solution (Wuhan Qianrui biological Co., Ltd.) to the center of the film with a pipette, clicking a coating button, and finishing the coating; and (5) drying the film by using a blower for later use.

(4) And (4) symmetrically placing the substrate in the step (3) on an automatic coating machine operating platform, and opening a vacuum system to form contact coating. An OSP-03 bar was fixed to PET at a speed of 60mm s^-1The length of the scraping film of the system is set to be 200mm, and then the straw is used0.4mL of AgNWs dispersion liquid obtained in the step (2) is stretched at a constant speed for a fixed length of 10cm, a coating button is clicked, and coating is completed; immediately taking out the wet film, and drying the wet film by using a blower to obtain the unidirectional ordered AgNW TCF; to prepare a cross-ordered AgNW array, immediately after the solvent was completely dried, a film was coated again on a unidirectionally ordered AgNWs/PET substrate perpendicular to the pre-alignment direction. Namely, the AgNW TCF with the unidirectional ordering is rotated by 90 degrees and symmetrically placed on an automatic coating machine operation platform, and a vacuum system is opened to form contact coating. An OSP-03 bar was fixed to PET at a speed of 60mm s^-1Setting the length of a system film scraping to be 200mm, then drawing 0.4mL of AgNWs ink obtained in the step (2) by using a suction pipe at a constant speed for a fixed length of 10cm, clicking a coating button, and finishing film coating; the wet film was immediately removed and blown dry with a blower to obtain cross-ordered AgNW TCF for use.

(5) Patterning: 0.5ml of solution of LAZ4620 (photoresist, produced by Wensun technologies, Inc.)/MMP (methyl 3-methoxypropionate, Shanghai Alatin Biochemical technologies, Inc.) (volume ratio 1:1 mixed) was dropped on the cross-ordered AgNW TCF center in step (4), and spin-coated at 500rpm for 3s and 7000rpm for 1min by a KW-4A type desk spin coater; after the spin coating is finished, placing the photoresist on a heating plate at 100 ℃ and baking for 60s to pre-cure the photoresist; after the mixture is cooled to room temperature, the mixture is placed in an ultraviolet curing box, a mask is placed on the surface of the ultraviolet curing box, the ultraviolet is carried out for 4s, and the relative strength is 50%; then, it was left to stand and immersed in an aqueous solution of AZ400K (developer, Mass. micro fluid technology Co., Ltd.) (V)_{Display device}:V_{Water (W)}1:3)5s, and soaking in deionized water for 5s to remove the redundant developer on the surface of the film; then, the substrate was immersed in a prepared neutral NaClO-based etchant (active chlorine concentration 0.056mg mL, manufactured by Shanghai Aladdin Biochemical technology Ltd.)^-1The sodium hypochlorite aqueous solution, 1M acetic acid and deionized water according to the volume ratio of NaClO to CH₃COOH, deionized water 5:3:92, pH 7.01) for 10 s; soaking in deionized water for 5s to remove excessive etchant on the surface of the film, soaking the film in anhydrous ethanol for 1min while removing photoresist and shaking to remove excessive photoresist, and standing at 60 deg.CDrying in air oven for 10 min.

The morphologies of the unidirectional ordered AgNW TCF and the cross-ordered AgNW TCF obtained in step (4) were characterized by an optical microscope (OM, Axio lab. a1), and the results are shown in fig. 2(a) and (b).

The sheet resistance of the cross-ordered AgNW TCF obtained in step (4) and the cross-ordered AgNW TCF patterned in step (5) was measured using a four-point probe method (RST-9). The transmittance and haze of the cross-ordered AgNW TCF obtained in step (4) and the cross-ordered AgNW TCF patterned in step (5) were measured at room temperature with an ultraviolet-visible near-infrared spectrometer (Lambda 7500) using either blank reference or uv treated PET as reference. The results are shown in Table 1.

TABLE 1

The ordering degree parameter S of the unidirectional ordering AgNW TCF obtained in the step (4)_2DCan be obtained by the following formula:

wherein, theta_iIs the angle between the average vector of the AgNWs arrangement and the vector of the ith AgNW arrangement. S_2DValues of (A) are between 0 and 1, with closer to 1 indicating more aligned AgNWs. S_2DWhen 1, it means that AgNWs is arranged in the same direction; s_2DWhen 0, it means that AgNWs is completely randomly oriented;

in the present invention, the orientation of AgNWs is determined by ImageJ software, and the degree of ordering S of the unidirectional ordered AgNW TCF prepared in this example can be calculated from the above formula_2DUp to 0.82 ((c) and (d) of FIG. 2), representing an AgNWs deflection angle of 84% within 30 °With 81% AgNWs deflection angle within 15 °. The full width at half maximum FWHM is only 18.2 °.

Using other calculation formulas:

wherein phi is an included angle between the AgNWs arrangement direction and the initial direction. From the data obtained by this formula and ImageJ, the degree of ordering S of the prepared unidirectional ordering AgNW network was 0.87.

Comparative example 1

(1) Removing impurities from 60mL of AgNWs stock solution prepared by a polyol reduction method by adopting a centrifugal method; the method comprises the following steps: a) dissolving two batches of AgNWs stock solutions prepared by a 12mL polyhydric alcohol reduction method in 24mL deionized water respectively, and shaking for 10min at 110 rpm; b) placing in a centrifuge, centrifuging at 4500rpm for 10 min; c) and pouring out the supernatant for later use.

Steps (2) to (4) obtained single-direction ordered AgNW TCF in the same manner as in example 1.

Comparative example 2

(1) 60mL of AgNWs stock solution prepared by the polyol reduction method is subjected to positive pressure filtration. The method comprises the following steps: a) dissolving two batches of AgNWs stock solution prepared by 16mL of polyalcohol reduction method in 30mL of deionized water, and shaking at 110rpm for 10 min; b) filtering under positive pressure, dissolving the silver nanowires on the filter membrane in 48mL of deionized water, and shaking at 110rpm for 10 min; c) filtering under positive pressure, dissolving in 48ml of LPVP (relative molecular weight is 55000), and shaking at 110rpm for 2 h; d) filtering under positive pressure for later use.

From the results of example 1 and comparative examples 1 and 2, it was found that the centrifugation method successfully retained the PVP layer on the AgNWs surface (fig. 2(a) and (b)), and the AgNWs density on the coated TCF was high, but the silver particles were not cleaned cleanly, and the optical properties of the TCF were greatly affected (fig. 2 (c)). The positive pressure filtration method, as shown in fig. 2(d) - (f), although the silver particles and the short rods are cleaned well, the PVP layer on the surface of the AgNWs is also cleaned, so that the electrostatic force between the AgNWs and the PLL is greatly reduced, and the AgNWs density on the TCF is greatly reduced. The dynamic agitation cleaning method of the present invention successfully retained the PVP layer on the AgNWs surface (fig. 2(g) and (h)), and cleaned the silver particles and short rods in the ink, and the prepared TCF had a high AgNWs density and a high degree of ordering (fig. 2 (i)).

Comparative example 3

The unidirectional ordered AgNW TCF was obtained in the same manner as in example 1 except that the dispersing agent in step (2) in example 1 was changed to water.

Comparative example 4

The unidirectional ordered AgNW TCF was obtained in the same manner as in example 1 except that the dispersing agent in step (2) in example 1 was changed to a mixed solution of water and ethanol (volume ratio 1: 1).

As can be seen from comparison of example 1 with comparative examples 3 and 4, when agnws washed with dynamic agitation were dispersed in ethanol, the agnws TCFs obtained by coating were more well-ordered than nanowires dispersed in an aqueous solution and a mixed solution of water and ethanol (see fig. 3(a) - (c)). Because a wet film is first obtained after bar coating with OSP-03, the pre-ordered AgNWs remain dispersed in the solvent, and if the solvent evaporation rate is too slow or the drying temperature is too high, the thermal motion of the AgNWs can be excessive, causing the pre-ordered AgNWs to return to a disordered state again, thereby affecting the degree of ordering of the AgNWs on the final TCF. The ethanol has lower boiling point and high drying speed, does not need operations such as heating and drying, and is the most ideal solvent.

Comparative example 5

The coating bar was changed to OSP-25, and the same procedure as in example 1 was repeated to obtain a one-way ordered AgNW TCF. The AgNWs on the resulting film were all randomly oriented.

Comparative example 6

The coating rod was changed to OSP-08, and the same procedure as in example 1 was repeated to obtain a unidirectional ordered AgNWTCF. The AgNWs on the resulting film were all randomly oriented.

Examples 2 to 6

The film coating speed was changed as shown in Table 2, and other examples are the same as example 1, and the one-way ordered AgNWTCF was obtained, and the OM photograph of TCFs and the results of the change of the ordering degree are shown in FIG. 5.

TABLE 2

Examples	Speed of coating
		Example 2	50mm·s^-1
Example 1	60mm·s^-1
		Example 3	90mm·s^-1
Example 4	120mm·s^-1
		Example 5	150mm·s^-1
Example 6	180mm·s^-1

As can be seen from FIGS. 5(a) - (h), the degree of AgNWs ordering on TCF increases sharply with decreasing coating speed, and then increases sharply at 60mm s^-1And slightly lowered again.

Examples 7 to 11

As shown in table 3, the unidirectional ordering AgNW TCF was obtained in the same manner as in example 1 except that the concentration of the dispersion in step (2) was changed, and OM photographs of the obtained TCFs and the results of changing the ordering program thereof are shown in fig. 6.

TABLE 3

As shown in fig. 6(a) - (f), as the concentration of AgNWs in the dispersion increases, the density of AgNWs on the coated TCF increases. The degree of ordering increases with increasing AgNWs concentration, and tends to stabilize when the AgNWs concentration is greater than 0.4 wt% (fig. 6(g) and (h)).

Example 8

Patterned AgNW TCFs were obtained in the same manner as in example 1, except that the pre-baking time was changed to 30s, 90s, and 120 s. The variation in AgNW conduction channel accuracy at different pre-bake times is shown in fig. 7.

Example 9

The patterned AgNW TCF was obtained in the same manner as in example 1, except that the ultraviolet exposure dose and the mask width were changed. The variation in AgNW conduction channel accuracy for different uv exposure doses is shown in fig. 8.

Example 10

The patterned AgNW TCF was obtained in the same manner as in example 1, except that the development time was changed, and the variation in AgNW conduction channel accuracy at different development times is shown in fig. 9.

Example 11

The patterned AgNW TCF was obtained in the same manner as in example 1, except that the etching time was changed. The optical properties of the TCF changed with the etching time, as shown in fig. 10(c) and (d), the optimum etching time was 10s, and fig. 10(a) and (b) are SEM photographs of the TCF before and after etching at the etching time of 10s, respectively.

Example 12

The patterned AgNW TCF was obtained in the same manner as in example 1, except that the mask width was changed. Fig. 11(a) is a schematic view of a conductive path, and fig. 11(b-f) are OM views of conductive paths having a width of 20-500 μm, which are made by using masks having different widths, respectively, and it can be seen that the accuracy of the conductive paths is higher than 99% by measuring the widths of the paths.

Example 13

The results are shown in Table 4, which are otherwise the same as in example 1, with the etchant being changed.

In Table 4, the etchant with pH 3.98 was composed of active chlorine concentration 0.056mg mL^-1The sodium hypochlorite aqueous solution, 1M acetic acid and deionized water according to the volume ratio of NaClO to CH₃COOH (1M) deionized water (5: 8.8: 86.2);

the pH value of the etching agent is 7.01, and the concentration of active chlorine is 0.056mg mL^-1The sodium hypochlorite aqueous solution, 1M acetic acid and deionized water according to the volume ratio of NaClO to CH₃COOH (1M) deionized water (5: 3: 92);

the pH value of the etching agent is 10.05, and the concentration of active chlorine is 0.056mg mL^-1The sodium hypochlorite aqueous solution, 1M acetic acid and deionized water according to the volume ratio of NaClO to CH₃COOH (1M) deionized water 5:0.37: 94.63.

TABLE 4

Example 14

The AgNW stock solution is prepared according to the literature [ Korte K E, Skrabalak S E, Xia Y. Rapid synthesis of silver nanowires a CuCl-or CuCl2-media polyol process. journal of Materials Chemistry,2008,18(4):437-441], and the silver nanowires have a diameter of 80-120nm and a length of 20-50 μm; the etchant was prepared as in example 13, and the other experimental procedures were as in example 1. The results are shown in Table 5.

TABLE 5

Example 15

The results are shown in Table 6, which are otherwise the same as in example 1, with the concentration of active chlorine in the neutral etchant being varied.

In Table 6, the etchant having an active chlorine content of 0.28 wt.% was composed of an active chlorine concentration of 0.056mg mL^-1Aqueous sodium hypochlorite solution, 1M acetic acid and deionized water in a volume ratio of NaClO: HAc: deionized water is prepared in a ratio of 5:3: 92;

the active chlorine content of the etching agent is 0.14 wt% and the active chlorine concentration is 0.056mg mL^-1Aqueous sodium hypochlorite solution, 1M acetic acid and deionized water in a volume ratio of NaClO: HAc: deionized water 2.5:1.5: 96;

the etchant with active chlorine content of 0.07 wt% consists of active chlorine concentration of 0.056mg mL^-1Aqueous sodium hypochlorite solution, 1M acetic acid and deionized water in a volume ratio of NaClO: HAc: deionized water 1.25:0.75: 98.

TABLE 6

Claims

1. A preparation method of a cross-ordered silver nanowire transparent conductive film comprises the following steps:

(1) the method comprises the following steps of (1) purifying AgNWs stock solution prepared by a polyol reduction method by using absolute ethyl alcohol as a purification solvent and adopting a dynamic stirring and cleaning method, removing organic matters, silver nano particles and short rods contained in the AgNWs stock solution, and simultaneously keeping a PVP layer on the surface of AgNWs to obtain purified AgNWs; the dynamic stirring cleaning method specifically comprises the following steps: pouring AgNWs stock solution into a purification device with a filter membrane and a stirring paddle, wherein the aperture of the filter membrane is smaller than the length of a silver nanowire, diluting the AgNWs stock solution with absolute ethyl alcohol, rotating the stirring paddle, slowly dropping the absolute ethyl alcohol into the purification device in the cleaning process to keep the volume of the solution constant, cleaning for a certain time, performing positive pressure filtration, adding PVP (polyvinyl pyrrolidone) aqueous solution, shaking uniformly, performing positive pressure filtration again, and collecting purified AgNWs;

(4) coating the AgNWs dispersion liquid obtained in the step (2) on the PET substrate pretreated in the step (3) by adopting a Meyer bar coating method and using a coating bar with the groove width smaller than the AgNWs length, wherein the coating speed is 60-120 mm & s^-1Drying after coating is finished; and after the solvent is completely dried, immediately coating the single-direction ordered AgNWs/PET substrate in the direction perpendicular to the prealignment direction again according to the same method, and drying after coating to obtain the cross-ordered silver nanowire transparent conductive film.

2. The method of preparing a cross-ordered silver nanowire transparent conductive film of claim 1, wherein: the diameter of the silver nanowire is 15-200nm, and the length of the silver nanowire is 20-200 mu m.

3. The method of preparing a cross-ordered silver nanowire transparent conductive film of claim 1, wherein: the diameter of the silver nanowire is 15-30 nm.

4. The method of preparing a cross-ordered silver nanowire transparent conductive film of claim 2 or 3, wherein: in the step (1), the aperture of the filter membrane is 8 μm, the stirring speed is 900rpm, and the cleaning time is 40 min.

5. The method of preparing a cross-ordered silver nanowire transparent conductive film of claim 1, wherein: in step (2), the AgNWs dispersion was at a concentration of 0.4 wt%.

6. The method of preparing a cross-ordered silver nanowire transparent conductive film of claim 1, wherein: in the step (3), the surface hydrophilization treatment method adopts ultraviolet ozone treatment.

7. The method of preparing a cross-ordered silver nanowire transparent conductive film of claim 1, wherein: in the step (4), the coating speed is 60mm s^-1。

8. A method of patterning a cross-ordered silver nanowire transparent conductive film, comprising the steps of:

(4) coating the AgNWs dispersion liquid obtained in the step (2) on the PET substrate pretreated in the step (3) by adopting a Meyer bar coating method and using a coating bar with the groove width smaller than the AgNWs length, wherein the coating speed is 60-120 mm & s^-1Drying after coating is finished; after the solvent is completely dried, immediately coating the single-direction ordered AgNWs/PET substrate in the direction perpendicular to the pre-alignment direction again according to the same method, and drying after coating to obtain the cross-ordered silver nanowire transparent conductive film;

(5) spin coating a positive photoresist on the substrate obtained in step (4)Cross-ordering the silver nanowire transparent conductive film, pre-baking the film for 30-120s at the temperature of 100-^-2Then, the film is placed in a developer for developing for 3-5s, the film is soaked in deionized water to remove the redundant developer on the surface of the film and then is soaked in a neutral sodium hypochlorite etching agent for etching, the neutral sodium hypochlorite etching agent is a neutral aqueous solution prepared from sodium hypochlorite and acetic acid, the concentration of active chlorine is 0.05-0.30 wt%, then the film is soaked in the deionized water to remove the redundant etching agent on the surface of the film, then the redundant photoresist is removed by absolute ethyl alcohol, and finally the conductive channel with a certain shape is obtained by drying.

9. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: in the step (5), the positive photoresist is AZ4620 which uses methyl 3-methoxypropionate as a solvent, the AZ4620 and MMP are mixed in a volume ratio of 1:1, and the developer is AZ400K aqueous solution which is V_{Display device}:V_{Water (W)}Mixing at a ratio of 1: 3.

10. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: the active chlorine concentration of the neutral sodium hypochlorite etching agent is 0.28 wt%.

11. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: in the step (5), the pre-drying temperature is 100 ℃, and the pre-drying time is 60 s; the ultraviolet exposure dose is 224mJ cm^-2The developing time is 5s, and the etching time is 10 s.

12. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: the diameter of the silver nanowire is 15-200nm, and the length of the silver nanowire is 20-200 mu m.

13. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: the diameter of the silver nanowire is 15-30 nm.

14. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 12 or 13, wherein: in the step (1), the aperture of the filter membrane is 8 μm, the stirring speed is 900rpm, and the cleaning time is 40 min.

15. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: in step (2), the AgNWs dispersion was at a concentration of 0.4 wt%.

16. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: in the step (3), the surface hydrophilization treatment method adopts ultraviolet ozone treatment.

17. The method of patterning a cross-ordered silver nanowire transparent conductive film of claim 8, wherein: in the step (4), the coating speed is 60mm s^-1。