VAN NEER, Martin Karolus Petrus (Steenstraat 2, AS Limbricht, NL-6141, NL)
SPEE, Carolus Ida Maria Antonius (Windmolenstraat 95, AS Helmond, NL-4706, NL)
HOVESTAD, Arjan (Laagakkerstraat 12, PK 's-Hertogenbosch, NL-5231, NL)
VAN NEER, Martin Karolus Petrus (Steenstraat 2, AS Limbricht, NL-6141, NL)
SPEE, Carolus Ida Maria Antonius (Windmolenstraat 95, AS Helmond, NL-4706, NL)
Claims
1. A process for preparing a flexible substrate onto which a film of a transparent conductive oxide has been applied, which process comprises the steps of:
(a) providing a metal carrier; (b) chemically and/or thermally passivating the metal carrier;
(c) depositing a metal film on the passivated metal carrier;
(d) depositing a film of a transparent conductive oxide onto the metal film;
(e) adhering a flexible substrate onto the film of the transparent conductive oxide; (f) removing the metal carrier from the film of the transparent conductive oxide; and
(g) removing the metal film from the film of the transparent conductive oxide.
2. The process according to claim 1, wherein the metal carrier is a foil of copper, nickel, steel, stainless steel, aluminium, gold, molybdenum, tungsten, tin, titanium, zinc, or any alloy thereof.
3. The process according to claim 2, wherein the metal carrier is a foil of copper or nickel.
4. The process according to any one of claims 1-3, wherein the metal carrier is chemically passivated by means of chromic acid or nitric acid.
5. The process according to any one of claims 1-4, wherein the metal film is deposited onto the metal carrier by means of a wet chemical deposition process.
6. The process according to any one of claims 1-5, wherein the metal film is a film of copper, nickel, cobalt, tin, silver, manganese, indium or zinc.
7. The process according to claim 6, wherein the metal film is a film of copper or silver.
8. The process according to any one of claims 1-7, wherein the transparent conductive oxide is selected from the group consisting of ZnO, In 2 O 3 , SnO 2 , CdO, PbO, NiO, Co 2 O 3 , Cu 2 O, Ag 2 O, Al 2 O 3 , Ga 2 O 3 , and doped or mixed oxides thereof.
9. The process according to claim 8, wherein the transparent conductive oxide comprises ZnO or SnO 2 .
10. The process according to claim any one of claims 1-9, wherein the transparent conductive oxide is doped with a fluorine-containing compound.
11. The process according to any one of claims 1-10, wherein in step (d) the film of the transparent conductive oxide is deposited onto the metal film by means of a gas-phase deposition process or a wet chemical deposition process.
12. The process according to claim 11, wherein in step (d) the film of the transparent conductive oxide is deposited onto the metal film by means of a wet chemical deposition process, such as electrodeposition.
13. The process according to any one of claims 1-12, wherein the flexible substrate is adhered to the film of the transparent conductive oxide by means of an adhesive.
14. The process according to any one of claims 1-13, wherein the flexible substrate comprises a polymer or a textile.
15. The process according to claim 14, wherein the polymer comprises polyethylene terephthalate, polyethylene naphthalate, polyvinylchloride, polystyrene, polyethylene, polyamide, poly(tetrafluoroethene) or polyimide.
16. The process according to claim 15, wherein the polymer is polyethylene naphthalate.
17. The process according to any one of claims 1-16, wherein in step (f) the metal carrier is mechanically removed from the film of the transparent conductive oxide.
18 The process according to any one of claims 1-17, wherein the metal film is removed from the film of the transparent conductive oxide by selectively dissolving the metal film in a solution.
19. The process according to claim 18, wherein the solution comprises an oxidiser and a complex forming agent to dissolve the metal, and the solution has a pH in the range of 7-11.
20. The process according to claim 19, wherein the oxidiser is selected from the group consisting of persulphates, peroxides, dissolved oxygen, ferricyanides, and chlorates, preferably from the group consisting of ammonium persulphate, hydrogen peroxide, dissolved oxygen, potassium ferricyanide, and potassium chlorate.
21. An electronic device comprising a flexible substrate as obtained in any one of claims 1-20. |
Title: PROCESS FOR PREPARING A FLEXIBLE SUBSTRATE
CARRYING A FILM OF A TRANSPARENT CONDUCTIVE OXIDE
The present invention relates to a process for preparing a flexible substrate onto which a film of a transparent conductive oxide has been applied, and an electronic device comprising a flexible substrate as obtained with such a process. Films of transparent conductive oxides (TCOs) are used in many applications such as, for instance, windows, solar cells, displays, light emitting diodes (LEDs). The attractiveness of TCOs resides in their very good optical and electrical properties. TCOs are typically directly deposited on substrates that have a high thermal resistance, like glass. However, there is an increasing demand to use substrates that are cheap, flexible and lightweight. Substrates that meet these requirements are, for instance, polymer foils. A disadvantage of applying TCOs onto such flexible substrates is that one is restricted to relatively low deposition temperatures because of the fact that at conventional high deposition temperatures the flexible substrate melts. Object of the present invention is therefore to provide an improved process in which onto a flexible substrate a film of a transparent conductive oxide is applied.
It has now been found that this object can be realised when a film of a transparent conductive oxide is first deposited on a metal carrier, a flexible substrate is then adhered to the film obtained, and subsequently the metal carrier is removed from the film.
Accordingly, the present invention relates to a process for preparing a flexible substrate onto which a film of a transparent conductive oxide has been applied, which process comprises the steps of: (a) providing a metal carrier;
(b) chemically and/or thermally passivating the metal carrier;
(c) depositing a metal film on the passivated metal carrier;
(d) depositing a film of a transparent conductive oxide onto the metal film;
(e) adhering a flexible substrate onto the film of the transparent conductive oxide;
(f) removing the metal carrier from the film of the transparent conductive oxide; and (g) removing the metal film from the film of the transparent conductive oxide.
The process in accordance with the present invention has the advantages that it is cheaper and provides less chemical waste when compared to similar processes wherein TCOs are applied onto flexible substrates by chemical dissolution of the metallic carrier as described for example in
WO-A-01/78156 or WO-A-2006/053889. In addition, the present process has the advantage that it allows for a much wider choice of TCOs that can be used, which is due to the fact that no or non-aggressive chemical dissolution is used. Furthermore, the metal film can be selected to match with a specific type of TCO. In addition, the material of the metal film can be selected such that a metal film is obtained which is easy to remove.
The metal carrier to be used in accordance with the present invention can suitable be a foil of copper, nickel, steel, stainless steel, aluminium, gold, molybdenum, tungsten, tin, titanium, zinc, or any alloy thereof.
Preferably, the metal carrier comprises copper or nickel. The metal carrier can for instance be a copper or nickel foil.
In the process according to the present invention the transparent conductive oxide can suitably be selected from the group consisting of ZnO, In 2 O 3 , SnO 2 , CdO, PbO, NiO, Co 2 O 3 , Cu 2 O, Ag 2 O, Al 2 O 3 , Ga 2 O 3 or mixtures thereof. The transparent conductive oxide may optionally be doped, such as with fluorine. The dopant depends on the type of TCO. For instance, in case the TCO is ZnO suitable dopants are F, Cl, Al, B, P, N, In, and Ga. In case the TCO is SnO 2 suitable dopants are F, Mo, and Sb. In case the TCO is In 2 O 3 suitable dopants are Sn, Sb and Mo.
Preferably, the transparent conductive oxide comprises ZnO or
SnO 2 .
In a preferred embodiment of the present invention the transparent conductive oxide is doped with fluorine. Suitably, in step (d) the film of the transparent conductive oxide is deposited onto the metal film by means of a gas-phase deposition process or a wet chemical deposition process. The most commonly used deposition technique for transparent conductive oxides is sputtering. For this technique targets of the material itself can suitable be used for depositing the transparent conductive oxide. For chemical vapour deposition a wide range of precursors is available. Also for wet chemical processes it is possible to use suitable precursors of the transparent conductive oxide. Suitable precursors depend on the transparent conductive oxide to be deposited and can be readily determined by the person skilled in the art. Suitable examples of such gas-phase deposition processes include sputtering (DC (direct current), RF (radiofrequency) or magnetron), pulsed layer deposition, chemical vapour deposition, and evaporation (reactive, electron-beam or thermal).
Suitable examples of such a wet chemical deposition process include electrodeposition, chemical bath deposition, sol- gel deposition and spray pyrolysis.
Preferably, in step (d) the film of the transparent conductive oxide is deposited onto the metal carrier by means of a wet chemical deposition process. In the process according to the present invention the flexible substrate can suitably be adhered to the film of the transparent conductive oxide by means of an adhesive.
Adhesives capable of adhering a flexible substrate to a transparent conductive oxide film are widely available in the art. The choice of adhesive is not of particular importance. The person skilled in the art will be able to
determine suitable adhesives to be used in accordance with the invention. For instance standard epoxy-based adhesives may be applied.
The flexible substrate to be used in accordance with the present invention can suitably be a polymer and/or a textile. The term "flexible substrate" as used herein means a free-standing substrate comprising a flexible material which readily adapts its shape and in particular refers to a substrate which is able to easily flex and/or bend without breaking. Such substrates are well-known to the person skilled in the art.
Suitable examples of polymers to be used as flexible substrate include polyethylene terephthalate, polyethylene naphthalate, polyvinylchloride, polystyrene, polyethylene, polyamide, poly(tetrafluoroethene) and polyimide.
Suitable examples of textiles to be used as flexible substrate are textiles comprising cotton, nylon, polyester, aramid, and/or polyacrylonitrile. Preferably, the flexible substrate comprises a polymer.
In step (f) of the process of the present invention the metal carrier is preferably mechanically removed from the film of the transparent conductive oxide. This can for instance be performed in a roll-to-roll production unit in which the metal carrier and the flexible substrate are transferred from a joint roll to two distinct rolls.
Suitably, steps e) and f) are carried out in a roll-to-roll process, for instance by unwinding a roll of metal carrier with a transparent conductive oxide film and simultaneously unwinding a roll of flexible substrate having a higher adherence to the transparent conductive oxide film than the metal carrier. Thereafter the metal carrier with the transparent conductive oxide film can be pressed against the flexible substrate on a joint roll. Subsequently, the flexible plastic foil and the metal carrier can be wound on different rolls, while the transparent conductive oxide is removed from the metal carrier and adheres to the flexible plastic foil.
In the process according to the invention the metal carrier is chemically, electrochemically and/or thermally passivated in step (b) (i.e. the reactivity of the metal foil is reduced) and a metal film is deposited on the passivated metal carrier in step c), and the metal film is removed from the film of the transparent conductive oxide in step (g).
The metal carrier can suitably be chemically or electrochemically passivated by means of chromic acid or nitric acid, whereas the metal film can suitably be deposited onto the metal carrier by means of electrodeposition.
Suitably, the metal film to be used comprises copper, nickel, cobalt, tin, silver, manganese, indium, and/or zinc. Preferably, the metal film is a film of copper or silver.
Suitably, in step (g) the metal film is removed from the film of the transparent conductive oxide by selectively dissolving the metal film in a solution. Suitably, such a solution comprises an oxidiser and a complex forming agent to dissolve the metal. It is preferred that the solution has a pH in the range of 7-11, more preferably in the range of 8-10.
The oxidiser to be used in such a solution can suitably be selected from the group consisting of persulphates, peroxides, dissolved oxygen, ferricyanides, and chlorates.
The method of the invention can suitably be used in a roll-to-roll process.
The present invention also relates to an electronic device comprising a flexible substrate onto which a film of a transparent conductive oxide has been applied in accordance with the present invention.
Suitable examples of such electronic devices include OLEDs (organic light emitting diodes), thin film photovoltaic cells, displays and touch screens.
Examples
Example 1
High quality electrodeposited sulphamate nickel foil was degreased with ethanol rinsed with demineralised water and hot air dried. The nickel foil was passivated in 10 g/1 sodium chromate for 4 minutes. A 2 micron thick copper film was deposited on the passivated nickel foil using a standard acid copper plating bath. A zinc oxide film was electrodeposited on the nickel foil at a voltage of -0.9 V vs Ag/AgCl in a solution of 0.1 M zinc nitrate, 0.1 M sodium nitrate at 70 °C for 15 minutes. Polyvinyl chloride (PVC) foil with adhesive was applied to the ZnO film. The nickel foil was mechanically separated from the Cu film leaving a ZnO and copper coated PVC foil. The PVC foil with ZnO and Cu film was dipped in a solution of 100 g/1 sodium persulphate and 100 g/1 sodium gluconate at pH 9. After 15 minutes the copper film was completely dissolved in the solution leaving ZnO coated PVC foil.
Example 2
As 3, but after separation from the nickel foil the PVC foil with ZnO and Cu film was dipped in a solution of 100 g/1 potassium ferricyanide and 100 g/1 sodium gluconate at pH 9. After 15 minutes the copper film was completely dissolved in the solution leaving ZnO coated PVC foil.
Example 3
As 3, but after separation from the nickel foil the PVC foil with ZnO and Cu film was dipped in a solution of 100 g/1 potassium ferricyanide and 100 g/1 glycolic acid and at pH 11 and 60 °C. After 15 minutes the copper film was completely dissolved in the solution leaving ZnO coated PVC foil.
Example 4
As 3, but after separation from the nickel foil the PVC foil with ZnO and Cu film was dipped in a solution of 100 g/1 sodium persulphate and 100 g/1 citric
acid and at pH 9 and 40 °C. After 15 minutes the copper film was completely dissolved in the solution leaving ZnO coated PVC foil.