FLEXIBLE TRANSPARENT ELECTRODE AND METHOD FOR MANUFACTURING SAME

Abstract

A method for manufacturing a flexible transparent electrode includes: preparing a substrate made of a flexible and transparent material, a metal nanocolloidal solution and an electrohydrodynamic jet printing device; fixing the substrate at a position spaced apart from an injection nozzle of the electrohydrodynamic jet printing device at a predetermined interval in order to print a metal pattern on the substrate using the electrohydrodynamic jet printing device; applying AC voltage of a predetermined power to the substrate and the injection nozzle of the electrohydrodynamic jet printing device; printing the metal pattern on an upper side of the substrate by the metal nanocolloidal solution using the electrohydrodynamic jet printing device in a state where the AC voltage of the predetermined power is applied to the substrate and the injection nozzle; and sintering the metal pattern formed on the substrate.

Claims

1. A transparent electrode manufacturing method comprising: a) a preparation step (S110) of preparing a substrate made of a flexible and transparent material, a metal nanocolloidal solution and an electrohydrodynamic jet printing device; b) a substrate fixing step (S120) of fixing the substrate at a position spaced apart from an injection nozzle of the electrohydrodynamic jet printing device at a predetermined interval in order to print a metal pattern on the substrate using the electrohydrodynamic jet printing device; c) an AC voltage applying step (S130) of applying AC voltage of a predetermined power to the substrate and the injection nozzle of the electrohydrodynamic jet printing device; d) a pattern forming step (S140) of printing the metal pattern on an upper side of the substrate by the metal nanocolloidal solution using the electrohydrodynamic jet printing device in a state where the AC voltage of the predetermined power is applied to the substrate and the injection nozzle; and e) a pattern sintering step (S150) of sintering the metal pattern formed on the substrate, wherein in the pattern forming step (S140), an injection cycle of the injection nozzle of the electrohydrodynamic jet printing device and an AC cycle are in integer multiple relationship with each other, and the injection nozzle carries out injection at the highest voltage or the lowest voltage of AC voltage.

2. The transparent electrode manufacturing method according to claim 1, wherein the material for the metal nanoparticles forming the metal nanocolloidal solution is at least one selected from groups comprised of silver (Ag), gold (Au), copper (Cu), aluminum (Al) and iron (Fe).

3. The transparent electrode manufacturing method according to claim 1, wherein the pattern forming step (S140) comprises the steps of: d-1) controlling the power of AC voltage (S141); d-2) controlling injection pressure of the injection nozzle (S142); d-3) controlling a distance between the injection nozzle and the substrate (S143); and d-4) moving a flat position of the substrate according to the preset form of the metal pattern (S144).

4. The transparent electrode manufacturing method according to claim 1, wherein in the pattern sintering step (S150), sintering temperature is 170° C. to 190° C. and a sintering period is 15 minutes to 25 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

[0049] FIG. 1 is a perspective view of a transparent electrode according to a prior art;

[0050] FIG. 2 is a process schematic diagram of a transparent electrode manufacturing method according to a prior art;

[0051] FIG. 3 is a conceptual view showing an electrohydrodynamic jet printing device according to a prior art;

[0052] FIG. 4 is a graph and a side view of a change of DC voltage by time to show an injection state of an injection nozzle according to application of DC voltage in case that a transparent electrode is manufactured using the electrohydrodynamic jet printing device according to the prior art;

[0053] FIG. 5 is a plan view showing a transparent electrode on which a pattern is formed by the injection nozzle shown in FIG. 4;

[0054] FIG. 6 is a perspective view of a transparent electrode according to the present invention;

[0055] FIG. 7 is a plan view of the transparent electrode shown in FIG. 6;

[0056] FIG. 8 is a partially enlarged view of the part “A” of FIG. 7;

[0057] FIGS. 9 and 10 are views of a metal pattern forming the transparent electrode according to another embodiment of the present invention;

[0058] FIG. 11 is a conceptual view of a transparent electrode manufacturing apparatus according to the present invention;

[0059] FIG. 12 is a perspective view showing a metal pattern formed by an electrohydrodynamic jet printing device shown in FIG. 11;

[0060] FIG. 13 is a partially enlarged view of the part “B” of FIG. 12;

[0061] FIG. 14 is a flow chart showing a transparent electrode manufacturing method according to the present invention;

[0062] FIG. 15 is a flow chart showing a pattern forming steps of FIG. 14;

[0063] FIG. 16 is a graph and a side view of a change of AC voltage by time to show an injection state of an injection nozzle according to application of AC voltage in case that a transparent electrode is manufactured using the transparent electrode manufacturing apparatus according to the present invention;

[0064] FIG. 17 is a plan view showing a transparent electrode on which a pattern is formed by the injection nozzle shown in FIG. 16;

[0065] FIG. 18 is a photograph showing an image that a light-emitting diode emits light using the flexible transparent electrode according to the present invention;

[0066] FIG. 19 is a graph showing a transmittance ratio changed according to the wavelengths of transmitted light sources by filling factor values;

[0067] FIG. 20 is a graph showing a resistance value of the transparent electrode changed according to the filling factor values by sintering temperature; and

[0068] FIG. 21 is a graph showing a resistance value of the transparent electrode changed according to repeated bending cycles by materials of metal patterns.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0069] Hereinafter, reference will be now made in detail to the preferred embodiments of the present invention with reference to the attached drawings, but the scope of the present invention is not limited by the attached drawings and embodiments. In addition, in the description of the present invention, when it is judged that detailed descriptions of known functions or structures related with the present invention may make the essential points vague, the detailed descriptions of the known functions or structures will be omitted.

[0070] FIG. 6 is a perspective view of a transparent electrode according to the present invention.

[0071] Referring to FIG. 6, the transparent electrode 100 according to an embodiment of the present invention is a flexible transparent electrode, and includes a substrate 110 made of a flexible and transparent material and a metal pattern 120 which is formed on the substrate 110 in a mesh form and has an electroconductive metal material.

[0072] In this instance, the metal pattern 120 formed on the upper side of the substrate 110 may be manufactured by being sintered after being patterned on the upper side of the substrate 110 using the electrohydrodynamic jet printing method. Here, the electrohydrodynamic jet printing method will be described in detail later.

[0073] The material which is applicable to the substrate 110 according to the present invention is not limited if it is a transparent and flexible material. For instance, the material may be polyethylene terephthalate (PET). Additionally, the material which is applicable to the substrate 110 may be at least one selected from groups comprised of polyethylene naphthalate (EN), polycarbonate (PC), polyethersulfone (PES), polyarylate (PAR), polysulfone (PSF), cyclic-olefin copolymer (COC), polyimide (PI), PI-fluoro-based high molecular compound, polyetherimide (PEI) and epoxy resin.

[0074] In addition, the electroconductive metal material which forms the metal pattern 120 formed on the upper side of the substrate 110 may be silver (Ag). The electroconductive metal material is prepared in a colloidal solution state, and then, is formed on the upper side of the substrate 110 by the electrohydrodynamic jet printing method. Preferably, the electroconductive metal material is silver (Ag), but may be formed on the upper side of the substrate 110 by the electrohydrodynamic jet printing method and may be substituted with any electroconductive material. For instance, the electroconductive metal material may be at least one selected from groups comprised of silver (Ag), gold (Au), copper (Cu), aluminum (Al) and iron (Fe). Here, the electrohydrodynamic jet printing method will be described in detail later.

[0075] FIG. 7 is a plan view of the transparent electrode shown in FIG. 6, FIG. 8 is a partially enlarged view of the part “A” of FIG. 7, and FIGS. 9 and 10 are views of a metal pattern forming the transparent electrode according to another embodiment of the present invention.

[0076] Referring to the drawings, the metal pattern 120 formed on the upper side of the substrate 110 may have a mesh structure. As shown in FIG. 7, the mesh structure has a plurality of vertical lines and a plurality of horizontal lines which are spaced apart from each other at regular intervals. That is, as shown in FIGS. 7, 9 and 10, the mesh structure may be a structure that at least two squares, equilateral triangles or polygons are arranged to adjoin each other. The mesh structure of the metal pattern 120 is not restricted to the above, and of course, may be properly varied according to a designer's intention.

[0077] In the meantime, referring to FIG. 8, the linewidth (w) of the metal pattern 120 is not limited if it does not considerably reduce transmittance and electroconductivity of the transparent electrode, but, preferably, is in a range of 1 μm to 30 μm. Moreover, a distance between lines of the metal pattern 120 is not limited if it does not considerably reduce transmittance and electroconductivity of the transparent electrode, but, preferably, is in a range of 200 μm to 1,000 μm.

[0078] In order to quantifiably indicate an area ratio of the metal pattern 120 formed on the upper side of the substrate 110, the filling factor (FF) may be defined as follows:

[00001]$\begin{array}{cc}\mathrm{FF}=\frac{\left(\mathrm{pSw}\right)+\left[\left(p-w\right).Math.\mathrm{Sw}\right]}{p^2}& \left(\mathrm{Equation}.Math..Math.1\right)\end{array}$

[0079] In the equation 1, the filling factor (FF) is a value showing the area ratio to form the metal pattern 120 contrast to the area of the substrate 110, p is a linewidth of the metal pattern 120, and w is a distance between the lines of the metal pattern 120.

[0080] As shown in the equation 1, the area of the metal pattern 120 formed on the upper side of the substrate 110 is increased as the FF value increases. Of course, the FF value is not limited if it does not considerably reduce transmittance and electroconductivity of the transparent electrode, but, preferably, is less than 0.3, and more preferably, less than 0.07.

[0081] FIG. 11 is a conceptual view of a transparent electrode manufacturing apparatus according to the present invention, FIG. 12 is a perspective view showing a metal pattern formed by an electrohydrodynamic jet printing device shown in FIG. 11, and FIG. 13 is a partially enlarged view of the part “B” of FIG. 12.

[0082] Referring to FIG. 11, the transparent electrode manufacturing apparatus 200 according to the embodiment of the present invention includes an electrohydrodynamic jet printing device 210, an AC voltage supplier 220, a driving unit 230 and a control unit 240.

[0083] In detail, the electrohydrodynamic jet printing device 210 is a device applying an electrohydrodynamic spray technology to ultra-atomize a solution having charges after providing charges by applying high voltage. The electrohydrodynamic jet printing can electrically carry out the preconditioning process before printing after conveying lots of ink toward an object to be sprayed, remarkably enhance resolution of nano-scale compared with the conventional inkjet printing method because it is capable of applying a flow of an electrically induced fluid to a nano-scale nozzle, and control a printed state in a new way to control electrically.

[0084] In general, as shown in FIG. 11, the electrohydrodynamic jet printing device 210 may include a driving unit 230 and a fixing unit 211 moved by the control unit 240, and an injection nozzle 212 which is spaced apart from the fixing unit 211 at a predetermined interval. Moreover, as shown in FIGS. 12 and 13, a metal nanocolloidal droplet 1 injected through the injection nozzle 212 is attached onto the upper side of the substrate 110 to print the pattern 120 while moving.

[0085] Furthermore, the AC voltage supplier 220 can apply AC voltage of a predetermined size to the fixing part 211 and the injection nozzle 212, and the control unit 240 controls the electrohydrodynamic jet printing device 210, the AC voltage supplier 220 and the driving unit 230.

[0086] According to circumstances, as shown in FIG. 11, the transparent electrode manufacturing apparatus 200 according to the embodiment of the present invention may further include a camera 250 which monitors the state of the metal pattern 120 printed on the substrate 110 by the electrohydrodynamic jet printing device 210.

[0087] Additionally, it is preferable that the transparent electrode manufacturing apparatus 200 according to the embodiment of the present invention be installed and managed inside a class-100 clean room 201.

[0088] FIG. 14 is a flow chart showing a transparent electrode manufacturing method according to an embodiment of the present invention, and FIG. 15 is a flow chart showing a pattern forming steps of FIG. 14.

[0089] Referring the drawings together with FIG. 11, the transparent electrode manufacturing method (S100) according to the embodiment of the present invention includes a preparation step (S110) of preparing a substrate 110 made of a flexible and transparent material, a metal nanocolloidal solution and an electrohydrodynamic jet printing device 210.

[0090] In this instance, the substrate 110 made of the flexible and transparent material may be at least one selected from groups comprised of polyethylene naphthalate (EN), polycarbonate (PC), polyethersulfone (PES), polyarylate (PAR), polysulfone (PSF), cyclic-olefin copolymer (COC), polyimide (PI), PI-fluoro-based high molecular compound, polyetherimide (PEI) and epoxy resin. In addition, the material for the metal nanoparticles forming the metal nanocolloidal solution may be at least one selected from groups comprised of silver (Ag), gold (Au), copper (Cu), aluminum (Al) and iron (Fe).

[0091] Moreover, as shown in FIG. 8, the electrohydrodynamic jet printing device 210 is a device applying the electrohydrodynamic spray technology, and a detailed description of the device will be omitted because it is described above.

[0092] The transparent electrode manufacturing method (S100) according to the embodiment of the present invention includes a substrate fixing step (S120) of fixing the substrate 211 at a position spaced apart from the injection nozzle 212 of the electrohydrodynamic jet printing device 210 at a predetermined interval in order to print the metal pattern 120 on the substrate 110 using the electrohydrodynamic jet printing device 210.

[0093] Furthermore, the transparent electrode manufacturing method (S100) according to the embodiment of the present invention includes an AC voltage applying step (S130) of applying AC voltage of a predetermined power to the substrate 211 and the injection nozzle 212 of the electrohydrodynamic jet printing device 210; and a pattern forming step (S140) of printing the metal pattern 120 on the upper side of the substrate 110 by the metal nanocolloidal solution using the electrohydrodynamic jet printing device 210 in a state where the AC voltage of the predetermined power is applied to the substrate 110 and the injection nozzle 212.

[0094] In detail, the injection nozzle 212 to which AC voltage is applied induces a sprayed flow of the metal nanocolloidal solution electrically so as to stably print the pattern on the upper side of the substrate 110.

[0095] Additionally, as shown in FIG. 12, the pattern forming step (S140) includes: the steps of controlling the power of AC voltage (S141); controlling injection pressure of the injection nozzle 212 (S142); controlling a distance between the injection nozzle 212 and the substrate 110 (S143); and moving a flat position of the substrate 110 according to the preset form of the metal pattern (S144). The order of the steps of the pattern forming step (S140) may be changed and at least two steps may be carried out at the same time. In addition, of course, one or more steps of the steps may be omitted according to a user's intention.

[0096] FIG. 16 is a graph and a side view of a change of AC voltage by time to show an injection state of an injection nozzle according to application of AC voltage in case that a transparent electrode is manufactured using the transparent electrode manufacturing apparatus according to the present invention, and FIG. 17 is a plan view showing a transparent electrode on which a pattern is formed by the injection nozzle shown in FIG. 16.

[0097] Referring to the drawings, the transparent electrode manufacturing method (S100) will be described continuously.

[0098] The transparent electrode manufacturing method (S100) according to the embodiment of the present invention applies AC voltage of a predetermined power to the substrate 211 and the injection nozzle 212 of the electrohydrodynamic jet printing device 210.

[0099] In case that AC voltage of the predetermined power is applied to the substrate 211 and the injection nozzle 212 of the electrohydrodynamic jet printing device 210 in order to print a pattern, as shown in FIG. 17, the pattern aligned in a row as a user intended can be obtained. Because the metal nanocolloidal droplets charged into positive or negative polarity are cyclically repeat to be attached onto the upper side of the substrate 110 when AC voltage is applied, charges of the metal nanocolloidal droplets accumulated on the substrate 110 are neutralized, and hence, it makes stable printing of the pattern 120 possible.

[0100] Furthermore, in order to print the pattern more stably, as shown in FIG. 16, an injection cycle of the injection nozzle 212 and an AC cycle are in integer multiple relationship with each other, and the injection nozzle 212 may carry out injection at the highest voltage or the lowest voltage of AC voltage.

[0101] Through a series of the steps described above, the metal pattern 120 is printed on the upper side of the substrate 110, and then, manufacturing of the transparent electrode 110 is finally completed through a pattern sintering step (S150) of sintering the metal pattern 120 formed on the substrate 110. In this instance, in the pattern sintering step (S150), sintering temperature is 170° C. to 190° C. and a sintering period is 15 minutes to 25 minutes. Of course, the sintering temperature and the sintering period can be properly changed according to the design of the transparent electrode and the user's management.

[0102] Here, the sintering process is a method that metal powder particles become lumpy into one through a thermal activation process in the metallurgy. Because sintering is a well-known method in the metallurgy, its detailed description will be omitted.

[0103] As described above, the transparent electrode manufacturing method according to the embodiment of the present invention can manufacture a transparent electrode having a pattern with a thinner linewidth than that of the prior art because using the electrohydrodynamic jet printing method. Furthermore, the transparent electrode manufacturing method according to the embodiment of the present invention can manufacture a transparent electrode utilizing a high molecular compound or resin which is more inexpensive compared with the prior arts and manufacture a transparent electrode by more simplified processes compared with the prior arts, thereby reducing manufacturing costs. Additionally, the transparent electrode manufacturing method according to the embodiment of the present invention is safe and does not cause environmental pollution because not using special chemical substances which are dangerous.

[0104] FIG. 18 is a photograph showing an image that a light-emitting diode emits light using the flexible transparent electrode according to the present invention.

[0105] As shown in FIG. 18, the transparent electrode 100 according to the present invention is flexible and transparent and has electroconductivity.

[0106] FIG. 19 is a graph showing a transmittance ratio changed according to the wavelengths of transmitted light sources by filling factor (FF) values.

[0107] Referring to FIG. 19, as described above, the FF value is defined as shown in the formula 1 in order to quantifiably indicate an area ratio of the metal pattern 120 formed on the upper side of the substrate 110.

[0108] As shown in FIG. 19, if the FF value is less than 0.07, high transmittance more than 70% is shown. Moreover, if the FF value is 0.26, transmittance in the range of 40% to 50% is shown.

[0109] FIG. 20 is a graph showing a resistance value of the transparent electrode changed according to the filling factor (FF) values by sintering temperature.

[0110] Referring to FIG. 20, if the sintering temperature is set to 120° C. in the patterning sintering step, the resistance value of the transparent electrode remarkably increases compared with the case that the sintering temperature is set to 180° C. Additionally, the resistance value of the transparent electrode is decreased as the FF value increases, and a difference between the resistance value at the sintering temperature of 120° C. and the resistance value at the sintering temperature of 180° C. is gradually reduced as the FF value increases.

[0111] FIG. 21 is a graph showing a resistance value of the transparent electrode changed according to repeated bending cycles by materials of metal patterns.

[0112] Referring to FIG. 21, a graph of the transparent electrode according to the prior art to which ITO is applied as the metal pattern is marked with the dotted line, and a graph of the transparent electrode according to the present invention to which silver (Ag) is applied as the metal pattern is marked with the solid line.

[0113] As shown in FIG. 21, the transparent electrode according to the prior art shows that the resistance value of the transparent electrode was remarkably increased by just 30 flexural tests. On the contrary, the transparent electrode according to the present invention kept the resistance value of the uniform level even by 200 to 500 flexural tests.

[0114] As described above, while the present invention has been particularly shown and described with reference to the preferable embodiment thereof, it will be understood by those of ordinary skill in the art that the present invention is not limited to the above embodiment and that various changes, modifications and equivalences may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.