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roller-induced bundling of long silver nanowire networks for strong interfacial adhesion, highly flexible, transparent conductive electrodes

by:Top-In     2020-02-07
Silver Line (AgNWs)
Thanks to its excellent electrical performance, cost-effectiveness, synthetic scalability and suitability for mass production, it has always been the most promising electrode material for the manufacture of flexible transparent touch screens, displays and many other electronic products.
Although some literature reports describe the use of short Ag NWs in random directional Ag Northwest Network manufacturing
Its conductivity is still far lower than that of Ag film.
So far, no literature report has been able to provide any simple solution to manufacture largearea and mass-
Manufacturing capability to solve problems such as conductivity, transparency, current resistance, bending stability, and interface adhesion.
In the current work, we provide a simple solution to overcome the above problems.
The challenges mentioned and reported developments in the rapid and simple use of steel roller coated, aligned and bundled long Ag northwest beam network electrodes on large-area PET Films.
AgNWs we developed-
The bundled network has excellent performance in photoelectric performance (
Block resistance 5. 8 Ω sq−1;
Optical transmission ratio at 5 nm wavelength is 89%)
, The current can withstand a current of up to 500 µma, maintain bending stability during 5000 bending cycles, and have strong interface adhesion.
Transparent conductive electrode (TCEs)
Devices with high conductivity and optical transmission ratio are widely used in many optoelectronic devices such as organic LEDs, touch screens, solar cells and wearable electronics.
The traditional TCEs are based on the oxidation of indium tin (ITO).
Therefore, the equipment made with ITO cannot be flexible, stretchable or wearable.
Several new materials that can produce flexible TCEs have been studied, including graphene, carbon nanotubes, gels, and metal nanoparticles.
In these materials, silver nanoparticles (AgNWs)
Thanks to its excellent electrical performance, cost-effectiveness, synthetic scalability and suitability for mass production, it has always been the most promising alternative.
Some AgNWs issues have been partially improved in recent years.
For example, because the processing temperature must be kept below 30 °c in order to achieve TCEs on a flexible polymer substrate (PET)
In addition to hot sintering, some sintering techniques, such as high
Pressing and pressing process (up to 25 Mpa), a light-
Welding Technology or welding technology.
Although the square resistance of 8.
After the above sintering process, 6 Ω sq was obtained, and the optical transmission ratio was 80%. it is difficult to apply the above sintering process to large-scale-
Extend the TCEs process.
Other key issues, such as poor adhesion to the substrate, low bending stability (
3 for 1000 cycles. 1-
Bending radius mm)
Low current withstand (200u2009mA)
, Poor corrosion resistance, mainly due to random orientation-and-
Distributed AgNWs structure.
Recently, efforts have been made to draw patterns of the ag northwest grid using neutral steam etching, inkjet printing and screen printing.
However, these methods produce AgNWs in each of the randomly oriented conductive traces, and therefore do not run in the best way.
In past studies, these methods lead to AgNWs on randomly oriented electrodes, and therefore perform poorly in Photoelectric Applications.
Alignment of AgNWs is one of the ways to improve the efficiency of electrical transmission.
A variety of techniques have been employed to align the nano-wires, including the Langum-bloggit technique, shape memory polymer shrinkage, capillary printing of nano-channels, water-
Bath auxiliary convection assembly and curved moon surface-
Drag deposition.
Recently, 2x2mm silver nano-wire ordered arrays have been developed using nano-template stamping technology
Exposure technology.
Although these technologies have successfully aligned the NM line to 92, reaching a 20Ω sq.
9% optical transmission ratio, they require certain preparations, such as additional transfer processing, Substrate pretreatment, or nano-pre-mapping, which limit the mass production capacity of large equipment using them.
In addition, well-
Alignment NWs of parallel deposits significantly reduces the intersection of the ag Northwest Network.
Therefore, the highly arranged short ag Northwest Network loses some conductivity.
In general, due to the increase in contact area between parallel wires, metal bundles are widely used in electronic products, such as wires, to provide excellent electrical transmission.
So far, most of the metal nano-wire harnesses have beenof-
Plane structure.
Due to the difficulty of manipulation and assembly of metal wire harnesses at nano-scale, only a few metal wires have successfully realized in-
Plane bundles, such as gold nano-wire harnesses made using templates
Auxiliary technology.
So far, no literature has proposed any simple solutionarea and mass-
The manufacturing capacity to solve the AgNWs problem at the same time, such as high conductivity, high transparency, low current tolerance, low bending stability and poor interface adhesion.
In this paper, we report on the development of long AgNW-
Use steel rollers on PET film to quickly and simply coat, align and bundle the network electrode of the bundle.
Proposed AgNWs-
The bundled network has excellent performance in photoelectric performance (
Block resistance 5. 8 Ω sq;
Optical transmission ratio at 5 nm wavelength is 89%)
Current bearing (up to 500u2009mA)
Bending stability (
More than 1mm bending cycles with a bending radius of 5000)
Compared with ITO, it has strong interface adhesion in the same system.
In addition, they are quite efficient and greatly improve durability.
This technology can be easily applied to large scale
The scale of ag Northwest Network, in which the conductivity can be greatly improved at low temperature.
Silver follow {111}
Surface in multi-alcohol solution (
PVP, nac1 and agno3.
We synthesized AgNWs using a previously reported nitrate ion-promoted polyols process, in addition to the use of a dispersing agent PVP with a molecular weight of 1300 k, which ensures a highaspect-
Ratio of long AgNWs.
After synthesis, AgNWs is precipitated with acetone to remove ethylene glycol (EG)
In the original solution.
Then re-suspend AgNWs in acetone (IPA)
The concentration is 20 ml.
Three AgNWs of length and similar diameter were obtained in subsequent experiments.
The aspect ratio of synthetic AgNWs with a length of 82 μm and a diameter of 45 nm is the highest (up to 1800)
As shown in the figure (
Support information).
Measured to about 4 northwest of a single ag. 95 Ω/μm.
We\'re ready.
Bundle the network through the rolling process (Fig. )
, Quickly and easily coated PET film.
AgNW network in 125-
Use the μ m PET film of Meyer Rod 14 wrapped with a wire diameter of 0.
36mm and heated on hot plate at 120 °c
Rinse 30 m/s with DI water to remove PVP on the northwest surface of the ag and then dry on the hot plate.
The alignment and bundling process is dominated by the following mechanisms :(i)
Landau-Levich curved surface drag wet film to produce a pure stress gradient in the direction of the coating (Fig. ). (ii)Evaporation-
Induced convection flow brings AgNWs into a dry void formed by surface tension (Fig. ). (iii)
When the wet film of AgNWs is dry, AgNWs is squeezed between the two gaps and aligned AgNW-
A bundled network is formed.
The deposited AgNW beam is oval (Fig. ).
In the traditional roll coating, the wet film will dry before it breaks.
However, in our approach, we dry the AgNW wet film more slowly, in a time almost equal to the natural drying of the AgNW wet film. AgNW-
A beam network is formed by simultaneously controlling the drying temperature and rolling speed.
The capillary fluid in the curved moon surface near the Landau-Levich substrate produces shear stress, extending the gap of the ag northwest Wet film during drying.
The thickness of the film is calculated using the following equation: h u2009 = u2009 where the viscosity of the ag northwest suspension, U is the coating speed, is the surface tension, and r is the radius of the curved moon surface.
Because the wire diameter is small (0. 36u2009mm)
On the roller that causes the flow of the curved moon surface, the radius of the curved moon surface can be reduced to r u2009 = u2009 2, which represents the clearance height between the roller and the PET substrate.
If the coating speed increases, the adhesive suspension stretches the meniscus and increases its radius to form a thicker wet film.
The performance of AgNW slurry is listed in the table and the relationship between thickness and coating speed is calculated as shown in the figure.
The figure describes the square resistance measured when using different coating speeds. Evaporation-
Induced convection flow and surface tension induced flow are two main factors that lead to the rupture of the wet membrane and subsequent AgNWs extrusion and merging into bundles.
The void size caused by the convection flow known as the Marangoni flow is calculated, where M is the Marangoni number, h is the thickness of the wet film, and λ is half of the void size.
The fluid system is dominated by evaporation.
Induced convection flow when M is greater than 80.
As mentioned earlier, if a higher coating speed is used, the AgNW wet film will be thicker and the aligned AgNW-
Lower bundled network.
Using this method, we can not only control the film resistance by adjusting the ag northwest suspension concentration, but also by adjusting the coating speed.
The DeWet speed of the Ag northwest suspension is calculated, where k is the characteristic of the fluid, for IPA-based system.
We calculated the Dewetting and drying speeds of 918 and 106 μm s, respectively.
The removal and drying duration is calculated by dividing the thickness of the wet film by the removal and drying speed.
Combined evaporation-
Induced and surface tension induced flow, the void size of the wet film during the coating process is given by the following equation: hole size.
The relevant number of the Ag northwest suspension, B is the surface tension gradient caused by the temperature gradient.
Wetting film thickness from 1. 63 to 4.
As shown in the figure, when the coating speed is increased from 2 to 10 μm, it is 78 μm.
The vertical and horizontal void sizes calculated and measured are compared in the figure.
As the coating speed increases, the thickness of the wet film increases, and the void becomes larger due to the longer drying time.
AgNWs are squeezed into a network of arranged bundles dominated by surface tension effects.
When using different coating speeds, we first checked the gap size between the alignment direction of the AgNWs beam and the AgNW beam, as shown in the figure.
If a higher coating speed is used, the resulting void will be larger and the experimental results are consistent with the calculated results. The AgNW-
The bundled network manufactured using the coating speed of 10 cms s is most aligned.
Scanning electron microscope (SEM)
Images of bundled AgNWs manufactured using various coating speeds are shown in Fig. and .
The diagram is a polar diagram of the film resistance and AgNWs ratio when the coating speed is 10 cms s is used.
From the measurement results, the average direction of AgNWs over 85% of the network at this speed is not more than 30 °.
The corresponding relationship between the vertical void size and the coating speed is shown in the figure.
The resistance of the plates parallel to and perpendicular to the coating direction is 3, respectively. 6 Ω sq and 8.
5 Ω square, respectively.
This electrical heterogeneity is due to the weak connectivity of aligned AgNWs perpendicular to the direction of the coating.
The figure shows the alignment of the localization rate in the near infrared spectrum
The vertical void size is from the bundled AgNWs network of 13. 1 μm to 6. 7u2009μm.
The spectrum from the wavelength of 1000 nm to 2500 nm is obtained at the polarization angle of 0 ° and 90 °, which represent two samples of parallel and vertical, respectively.
Polarized light source.
The polarization-transmission ratio shows a significant heterogeneity of the arrangement
AgNWs network bundle.
Transmission ratio of AgNWs network with void size 13.
The 1 μm observed at 0 ° polarization angle is 10% higher than the observed at 90 ° polarization angle (8.
2500 degree polarization at 3% nm).
For the gap size of the AgNWs network that holds down to the NIR wavelength, the degree of polarization should be enhanced according to the Saito equation.
However, alignment is also reduced as the gap size continues to shrink.
As a result, the degree of polarization decreases as the size of the void decreases.
For AgNWs networks with an average gap size of 6.
7 μm, the transmission ratio of the NIR spectrum shows a 2% difference between the polarization angles of 0 ° and 90 ° (1.
2500 degree polarization at 5% nm).
So we define
Bundle AgNWs network for Void size 6.
Randomly oriented 7 μm.
The figure describes the relationship between the calculated void size under different conditions of the roller coating process and the performance of the AgNWs/IPA suspension manufacturing alignment
AgNWs network bundle.
The suspension performance of AgNWs on the PET substrate represents the dewetting speed of the wetting film. For Fig.
, Shows and calculates the connection between the coating speed and the void size, the drying temperature is 120 °c, and the clearance height is 0. 8u2009mm.
It is worth noting that the invalid size of the AgNWs network is less than 6.
This paper defines the random orientation of 7 μm, and the gap size of 40 μm or more can be regarded as the wrapped AgNWs during the roll coating process. As for Fig.
, The connection between the drying temperature and the void size is shown as 2 cm/s coating and 0. Clearance height of 8mm.
By adjusting the roll coating conditions, we can easily align and bundle AgNWs and get alignment-
Bundled AgNWs networks of different void sizes.
The figure shows the relationship between the clearance height on the PET substrate and the suspension performance of AgNWs.
To date, the reported roll coating process is operated in close contact with the roller and the target substrate (gap heightu2009
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