WO2018125015A1

WO2018125015A1 - A technique for the production of a transparent conductive oxide film by a roller coating technique

Info

Publication number: WO2018125015A1
Application number: PCT/TR2017/050704
Authority: WO
Inventors: Refika BUDAKOGLU; Ferhat ASLAN; Ibrahim BOZ
Original assignee: Turkiye Sise Ve Cam Fabrikalari Anonim Sirketi
Priority date: 2016-12-30
Filing date: 2017-12-27
Publication date: 2018-07-05

Abstract

The invention is related to a technique (100) for the production of transparent oxide thin films (F), which forms the basis of electronic device technology with high transparency and electric conductivity, without requiring vacuum systems, at atmospheric pressure on surfaces with large area when necessary, with a roller (R) coating techniques.

Description

A TECHNIQUE FOR THE PRODUCTION OF A TRANSPARENT CONDUCTIVE OXIDE FILM BY A ROLLER COATING TECHNIQUE

Technical Field

This invention, relates to the production of transparent conductive oxide thin films that form the basis of electronic device technology by a roller coating technique which allows them to deposit on glass surfaces with large areas having high transparency and electric conductivity under atmospheric pressure, without requiring a vacuum environment.

Prior art

Thin film is the name given to the materials of various layers with thicknesses ranging from a size of nanometres to micrometers. Thin films, gaining popularity among research-development studies carried out in recent years form the basis of electronic device technology.

Differences in production techniques and production conditions reveal many features not found in bulk materials in thin films. These properties give superior properties to thin film materials compared to bulky materials and open up new possibilities. With the development of technology, new production technologies have emerged and developed which can be alternative to each other in the production of thin films.

Major field of the use of transparent conductive oxide thin films include examples such as flat panel screen electrodes, polymer electronics, gas sensors, varistors, solar cells and low emission (low-E) surface coating applications which reduce the emission value of glass surfaces in heat thermal insulation, respectively. Particularly, in solar cells, in order to allow photons to reach the p-n junction range without being absorbed, films with high optical transparency are used on the front surface. In addition, the transparent material used on the front surface must be as conductive as metal in order to collect current carriers. This is only possible with transparent conductive oxide films.

Examples of techniques used for obtaining transparent conductive oxide films, ITO (indium tin oxide), FTO (flor doped tin oxide), AZO (antimony doped zinc oxide) and GZO (gallium doped zinc oxide) are spray pyrolysis, magnetron sputtering, pulsed laser deposition (PLD), chemical vapour deposition, molecular beam epitaxy (MBE) and sol-gel techniques.

ITO, which is the most commonly-used among transparent conductive oxide films, is a highly disordered n-type wideband gap semiconductor obtained by doping tin (Sn) to indium oxide (ImCb). ITO films with a commercial value need to have a visible range light transparency of over 80% and surface resistance below a value of 20 ohm/square; in other words, transparency and electric conductivity of a film is desired to be high. The most commonly used technique for the production of ITO films in today's technology is magnetron sputtering technique. In this technique, large volume vacuum systems are required for large scale implementations. Moreover, more than one sputtering source is required for the coating to deposit homogeneously on the whole surface. Since, technique magnetron sputtering technique is based on high cost and complicated systems, it is of great importance that alternative techniques which do not require a vacuum environment be developed and be introduced into the field of technology.

U.S. document no US2016024640 (Al) in the state of the art discloses a transparent and conductive film and the production technique for this film. The invention mentioned in the document relates to a transparent oxide film with high transparency in the visible light range and an organic polymer film base. A transparent conductive oxide coating is applied on the substrate. The invention which is a transparent conductive oxide film comprises a thin conductive coating which has low resistivity and surface tension. The coating is indium tin oxide (ITO). The coating applied on the polymer substrate is applied by RF superimposed DC spraying. However, in the invention of the application, glass is used as substrate and ITO is coated on the glass by roller coating technique. The RF superimposed DC sputtering technique mentioned in the invention in the state of the art is a completely different process than the roller coating technique.

In the present technique, there is not a technique for the production of an ITO thin film obtained without a need for a vacuum environment, at atmospheric conditions, with a visible range light transparency of over 80% and by applying on large surfaces with a roller coating technique.

Objects of the invention

The object of the present invention is to realize a transparent conductive oxide film production method by means of a roll coating technique which enables coating on wide surface materials at atmospheric pressure. Another object of this invention is to realize a technique for the production of a transparent conductive oxide film by a roller coating technique which allows high quality production with high optical transparency at room conditions.

Yet another object of this invention is to realize a technique for the production of a transparent conductive oxide film by a roller coating technique which allows the production of a film with high optical transparency at the visible range directly on the line by using suitable solvents.

Brief Description of the Invention In the technique for the production of a transparent conductive oxide film defined in the preamble claim and the other claims depending on this claim, provided to fulfil the objects of this invention, a solution of the film which is to be formed on the glass is prepared firstly. This solution is a solution which comprises tin and indium as starting materials, preferably at different proportions. After the coating solution is prepared, wet films are obtained by applying them on the glass surface by a roller coating technique. In order to obtain a high quality thin film, a glass substrate whereon the coating is to be applied is cleaned by using chemicals in an ultrasonic bath. For the coating application, the coating solution is poured into an application vessel of a roller device, and the glass substrate is coated after the solution passes through the rollers. After the coating process is completed, the coated glass is subjected to heat treatment to remove the organic components to produce a thin film. The obtained film is annealed and oxide layers are formed. Detailed Description of the Invention

The technique for the production of a transparent conductive oxide film by a roller coating technique applied in order to fulfil the objects of this invention is shown in the enclosed figures, wherein:

Figure 1. is a schematic view of the steps of the technique for the production of a transparent conductive oxide film by roller coating technique.

Figure 2. is a schematic view of the technique for the production of a transparent conductive oxide film by roller coating technique.

Figure 3. is a graph of the optical transparency (%, y axis) - wavelength (nm, x axis) of a glass 5 times ITO coated by roller coating technique and an uncoated glass

Parts in the figures are individually numbered, and the meanings of these numbers are given below. 100. A technique for the production of a transparent conductive oxide film

R. Roller

B. Band

A. Glass substrate

F. Film

V. Solution vessel

S. Solution

G. Glass

I/G. ITO coated glass

A technique for the production (100) of a transparent oxide thin film (F), wherein transparent conductive oxide thin films which form the basis of electronic device technology are produced by a roller coating technique which allows them to deposit on glass surfaces with large areas with high transparency and electric conductivity without requiring vacuum systems, comprises the steps of:

preparing a transparent conductive oxide solution (S) belonging to the film which is to be formed on a glass substrate (A) with a sol-gel technique (101), during which

· an indium oxide solution (S) comprising indium (III) nitratehydrate and tin 2-ethyl ethanoate as starting materials and triethanolamine as a stabilizer at different ratios is produced (1011),

obtaining (102) a thin film (F) with a rotating roller (R), during which

• a glass substrate (A) whereon the coating is to be applied is cleaned (1021),

• solutions (S) prepared with the sol -gel technique are transferred (1022) onto the glass substrate (A) with the help of rollers (R),

• organic components within the coating are removed away from the surface by a heat treatment of the glass substrate (A) whereon wet coating is applied and the thin film (F) on the glass substrate (A) is obtained (1023), • the conductive oxide layers are deposited (1024) by annealing amorphous films (F) at high temperature in air or inert gas environment,

• the process is terminated if the initially determined quality (q) parameter is reached, the process is returned to step of 1022 (1025) if the quality parameter q is not reached.

A q quality parameter is determined according to the field of utilization of the film (F) to be formed on the glass substrate (A) before starting the coating process, q quality parameter of the film (F) varies according to the field of the utilization of the product to be obtained at the end of the process. Q, quality parameter can be the thickness, optical transparency, resistivity, mobility or carrier intensity of the film (F). According to the determined q quality parameter value, the glass substrate (A) is subjected to coating processes successively. In the technique for the production (100) of a transparent conductive oxide film (F), the solution (S) to be used is prepared (101) first. The solution (S) is prepared by sol-gel technique. In this step, a homogeneous mixture is obtained by dissolving suitable salts or alkoxides of the elements in the chemical composition of the film (F) in a suitable solvent. In this embodiment of the invention, in the step of preparing solution (S) (101), it comprises starting materials of tin and indium preferably at different proportions.

Indium (III) nitratehydrate or indium acetate or tin (II) chloride or 2-ethyl ethanoate as starting materials is used in the step of producing (1011) an indium oxide solution (S) comprising tin. In this embodiment of the invention, indium (III) nitratehydrate and tin 2-ethyl ethanoate are chosen as starting materials. Triethanolamine is preferably used as a stabilizer. Preferably ethanol as a solvent and preferably acetic acid as a catalyst are used. In the step of producing (1011) indium oxide solution (S) comprising tin, the amounts of indium (III) pentahydrate and acetic acid are determined first. 2.0-6.0 grams of indium (III) pentahydrate and 10-20 ml of acetic acid are used in the solution. The stirring process continues until a homogeneous solvent (S) is obtained. After the homogeneous solution (S) is obtained, 0.5-3.0 gr triethanolamine is added. In this embodiment of the invention, 0.5-2.0 gr triethanolamine is used. The addition of triethanolamine into the homogeneous solvent (S) is performed dropwise. 30-50 ml ethanol is added to the solvent (S) first. After this process, the amounts of tin 2-ethyl ethanoate and ethanol are determined. In another beaker 1.0-3.0 gr tin 2-ethyl ethanoate and 20-30 ml ethanol are mixed. The solution (S) formed by indium (III) pentahydrate and glacial acetic acid and the solution (S) formed by tin 2-ethyl ethanoate and ethanol are stirred separately at room temperature for 1-2 hours. After the stirring is completed separately, the stirring process is repeated after combining the two solutions (S). While preparing (101) the coating solution (S), the molar ratio of Sn/In in the solution is adjusted so as to be in a range of % 10-20. The said Sn/In ratio is determined by indium and tin starting materials. The stirring process of the two solutions (S) continues at room temperature for 12-24 hours. The stirring process is preferably performed with a magnetic mixer.

After the solution (S) is prepared (101), a thin film (F) is obtained (102). For this end, glass substrate whereon the coating is to be applied are cleaned (1021). Glass substrate (A) are cleaned by using chemicals in an ultrasonic bath. Glass substrate (A) used in a preferred embodiment of the invention preferably have a size of 200 mm x 300 mm. After the cleaning (1021) of the glass substrate is finished, a coating is applied (1022) on the glass substrate (A). For this end, the prepared solution (S) is first poured into a solution vessel (V) of a roller (R). The coating process is started after the solution (S) and the glass substrate (A) are put in a roller (R) device. During the coating process, the glass substrate (A) is coated with the solution (S) by means of a cylindrical roller (R) (Figure 2, in the arrow direction). By changing the roller's (R) distance to the glass substrate (A), the type of the roller (R) and the rotational speed of it, thinner or thicker films (F) are obtained. After the glass substrate (A) is coated (1022), the glass substrate (A) is heat treated (1023) at a low temperature. In this step, organic components of the solution (S) used in coating are removed from the surface of the glass substrate (A). The removing process is preferably performed in an incubator by carrying out a heat treatment. Upon removing the organic components present on the glass substrate (A), a thin film (F) layer is formed on the glass substrate (A). After the heat treatment, films (F) still have an amorphous form. Thus, films (F) with an amorphous form are annealed (1024) at a high temperature, in open air or in an inert gas environment. After the annealing process (1024), the film (F) obtained on the glass substrate (A) is measured for the pre-determined quality parameter q. If the value obtained as a result of the measurement is concordant with the pre-determined q value, the process is ended. If the quality parameter q of the film (F) obtained as a result of the measurement hasn't reached the pre-determined value, the process is repeated (1025) by returning to step (1022). The processes of (1022), (1023) and (1024) are repeated (1025) successively until the pre-determined q quality parameter is achieved and transparent oxide layers are formed.

For instance, the quality parameter q of the film (F) which is desired to be obtained on the glass substrate (A) by the technique for production (100) of a transparent conductive oxide film is the thickness of the obtained film (F) and the targeted q value is determined as 400 nm. The thickness of the coating formed on the glass substrate (A) as a result of the first cycle is measured as 100 nm. In such case, a film (F) with a thickness of 400 nm on the glass substrate (A) is formed by performing three more cycles. In an embodiment of the invention, according to measurements performed by an ellipsometer, the thickness of ITO films (F) coated five times is measured about 350 nm. According to the results of hall effect measurements, the resistivity, mobility and carrier intensity of an ITO sample are measured respectively as 4.49xl0^"3 Ωαη, 5.73 cm²/Vs and 2.42 x 10²⁰ cm^"3. In Figure 3, a graph of the optical transparency of a 5 times ITO coated glass (I/G) with a roller (R) device and an uncoated glass is given. In the graph, the vertical axis (y axis) represents transparency (%) and the horizontal axis (x axis) represents wavelength. According to Figure 3, the transparency of ITO films (F) in the visible range is over 84%. Results of hall effect measurements and results of UV-VIS spectrometry shows that transparent conductive oxide films produced with a roller (R) technique can be used in optoelectronic applications.

With the technique for the production (100) of a transparent conductive oxide film (F) of the present invention, a transparent conductive oxide film (F) is produced on a glass substrate (A) under atmospheric pressure without using high-cost and complex systems such as vacuum systems. The technique of the invention allows operation under atmospheric pressure and the coating of glass substrate (A) with a large surface area. Therefore, the technique of the invention can be used in industrial applications. The absence of any vacuum devices in the system reduces the cost of the system and coating. By using solutions (S) consistent with the technique (100) for the production of a transparent conductive oxide film (F), high quality films (F) with a high transparency can be produced.

Claims

A technique for the production (100) of a transparent conductive oxide thin film (F), which forms the basis of electronic device technology, with high transparency and electric conductivity, without requiring vacuum systems, at atmospheric pressure, on surfaces with a large area when it is necessary, with a roller (R) coating technique, characterized by process steps of

preparing a permeable conductive oxide solution (S) belonging to the film which is to be formed on a glass substrate (A) with a sol-gel technique (101), during which

• an indium oxide solution (S) comprising tin at different ratios is produced (1011) by using indium (III) nitratehydrate, tin 2-ethyl ethanoate as starting materials and triethanolamine as a stabilizer, obtaining (102) a thin film (F) with a rotating roller (R), during which

• solutions (S) prepared with the sol-gel technique are transferred (1022) onto the glass substrate (A) with the help of rollers (R)

• the organic components within the coating are removed away from the surface with a heat treatment of the glass substrate (A) whereon wet coating is made at low temperatures and the thin film (F) on the glass substrate (A) is obtained (1023),

• the conductive oxide layers are deposited (1024) by annealing amorphous films (F) at high temperature in air or inert gas environment,

A technique for the production (100) of a transparent conductive oxide film (F) with a roller technique according to claim 1, characterized in that a homogeneous mixture is obtained by dissolving suitable salts or alkoxides of the elements in the chemical composition of the film (F) with suitable solvents in the step of preparing (101) a solvent (S) belonging the film (F) to be formed on the glass substrate (A).

A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 2, characterized in that 2.0-6.0 gr indium (III) pentahydrate is stirred in 10-20 ml glacial acid with a mixer until a solution (S) is obtained, in the step of producing (1011) an indium oxide solution (S) with tin.

A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 3, characterized in that 0.5-3.0 gr triethanolamine is added into the solution (S) dropwise after a homogeneous solution (S) is obtained, in the step of producing (1011) an indium oxide solution (S) with tin.

A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 4, characterized in that between 40-50 ml, preferably 45 ml ethanol is added into the solution (S) to which triethanol is added, in the step of producing (1011) an indium oxide solution (S) with tin.

A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 5, characterized in that 1-3 gr tin 2-ethyl ethanoate and 20-30 ml ethanol are blended in another beaker, in the step of producing (1011) an indium oxide solution (S) with tin.

A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 6, characterized in that the solution formed by indium (III) pentahydrate and glacial acetic acid and the solution formed by tin 2-ethyl ethanoate and ethanol are stirred separately at room temperature and for 1-2 hours, in the step of producing (1011) an indium oxide solution (S) with tin.

8. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 7, characterized in that separately stirred solution (S) formed by indium (III) pentahydrate and glacial acetic acid and solution (S) formed by tin 2-ethyl ethanoate and ethanol are combined and stirred at room temperature for 12-24 hours preferably with a magnetic mixer, in the step of producing (1011) an indium oxide solution (S) with tin.

9. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 1, characterized in that Sn/In molar ratio is adjusted to be in a range of 10-20%, in the step of producing (1011) an indium oxide solution (S) with tin.

10. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 8, characterized in that triton which is chosen as a surface agent is added after the solution (S) formed by indium (III) pentahydrate and glacial acetic acid and the solution (S) formed by tin 2-ethyl ethanoate and ethanol are combined, in the step of producing (1011) an indium oxide solution (S) with tin.

11. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 1, characterized in that glass substrate (A) to be coated preferably of glass and preferably with a size of 200 mm x 300 mm is cleaned (1021) by an ultrasonic bathing technique or a chemical cleaning technique, in the step of obtaining (102) a thin film (F).

12. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 1, characterized in that the coating process starts after the prepared solutions (S) are poured into a solution vessel (V) of the roller (R) device, and the solution (S) and the glass substrate (A) are placed into the roller (R) device, in the step of coating (1022) on the glass substrate (A).

13. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 12, characterized in that the surface of the glass substrate (A) is coated with the solution (S) by means of a cylindrical roller (R) rotating throughout the coating process, in the step of coating (1022) on the glass substrate (A).

14. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 13, characterized in that the quality and the thickness of the coating is adjusted by changing the distance of the rubber to the glass substrate (A), and the groove type and the rotational speed of the roller (R), in the step of coating (1022) on the glass substrate (A).

15. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 1, characterized in that the glass substrate (A) is heat treated (1023) after the glass substrate (A) is coated (1022), in the step of obtaining (102) a thin film (F).

16. A technique for the production (100) of a transparent conductive oxide film (F) with a roller (R) coating technique according to claim 13, characterized in that the organic components of the solvent (S) used in coating the glass substrate

(A) are removed from the surface of the glass substrate (A) preferably by performing a heat treatment in an incubator and forming a thin film (F) layer on the glass substrate (A), in the step of heat treating (1023) the glass substrate (A).