DE102018126263A1 - interference film - Google Patents

Abstract

The present invention relates to an electrochromic device 1, which is constructed as an electrochemical element of at least two transparent films 2, 3, wherein one of the films with a transparent coating 4 is coated conductive and provided as an electrode. Between the two films 2, 3, an electrically conductive electrolyte layer 5 is arranged, which is in contact with a likewise disposed between the films counter electrode 7.

Description

The present invention relates to an electrochromic device, which is constructed as an electrochemical element of at least two transparent films, wherein one of the films is coated with a transparent conductive coating and is provided in the electrochemical element as an electrode. Between the two films, an electrically conductive electrolyte layer is arranged, which is in contact with a likewise disposed between the films counter electrode.

Electrochromic devices are currently being used in particular for vehicle and building glazings to color transparent systems as desired and thus absorb incident visible light. A typical example of the use of electrochromic systems are dimmable rearview mirrors, wherein a film is arranged behind the mirror glass and reflects brighter or darker depending on the applied voltage. The electrochromic device usually consists of two electrodes each applied to a separate carrier and an electrolyte arranged between the electrodes. At least one of the carriers and the electrode applied thereon are transparent. In addition, conventional electrochromic devices include an electrochromic material deposited on the transparent electrode and in intimate contact with the electrolyte. Examples of electrochromic materials are the oxides of the transition metals, such as tungsten, niobium, vanadium, titanium, tantalum and nickel, or electrically conductive polymers, such as polyaniline or polythiophene. The electrochromic mechanism is based on the fact that, after applying a voltage, ions on interstitial sites penetrate into the electrochromic material, resulting in discrete color centers with a material-specific absorption band, which causes the desired color change.

In the DE 196 22 600 A1 describes an electrochromic unit with an electrochemical cell having at least two electrodes applied to a support, in which an electrochromic polymer is used as the electrochromic material and a proton-conducting membrane as a solid electrolyte and support for the electrodes applied on both sides.

The DE 101 48 438 B4 describes an electrochromic device containing at least a few glass or plastic plates or plastic films, wherein at least one plate or film is conductively coated and transparent together with the conductive coating. One of the two plates or foils is coated with an electrochromic organic oligo- or polymer and the volume formed from the two plates or foils and a sealing ring is filled with an electrochromic medium.

The DE 1 218 794 B1 describes an electrochromic element which comprises an electrode, an electrochromic functional layer, an ion-conducting electrolyte, a layer with high electrical charge capacity and a counterelectrode, the electrochromic functional layer consisting of a nanoporous, doped semiconductor layer which forms a coherent, electrically conductive network the ion-conducting electrolyte fills the nanopores of the electrochromic functional layer.

The US 5,903,382 A. relates to an electrochromic device having two spaced-apart transparent substrates, wherein the inner surface of one of the substrates is provided with a conductive layer and in a region of the inner surface of the other substrate, a counter electrode is arranged which does not make direct electrical contact with the conductive Layer of a substrate s has. Furthermore, an electrolyte with a metal salt contained therein and corresponding to the counter electrode and a lateral seal for connecting the cell volume are arranged between the two substrates. When a voltage is applied to the two electrodes, a metal layer is deposited on the conductive layer of the substrate.

The object of the present invention is to provide an electrochromic device that differs from the known electrochromic devices by the particular shape of the color and the associated color effects. The object of the invention is to technically reproduce and selectively adjust the interference colors occurring in the case of oil stains or soap bubbles.

The object is achieved by an electrochromic device comprising a first transparent film, which is coated areally with a conductive layer and thus provided as an electrode. Compared to the first film, a second transparent film is also arranged areally. Between the first and the second film is a metal counter electrode, wherein the counter electrode has no direct contact with the conductive layer of the first film. The electrochromic device further comprises an electrolyte for completing the electrochemical cell, wherein the electrolyte is also disposed between the first and second foils. The two films are connected via a lateral seal with each other to form an electrochemical cell. The electrolyte comprises a metal salt corresponding to the counterelectrode, so that on the conductive layer of the first transparent film when depositing a current, a metal layer can be deposited.

In contrast to conventional electrochromic elements, in the case of the present invention, no oxide of the transition metals or an electrically conductive polymer effects the color change, but the formation of a metal layer on the electrically conductive layer of the first transparent film. As long as the metal layer does not exceed a certain thickness, interference occurs when light falls on the layer, and colored iridescent interference patterns occur, similar to bubbles, dragonflies, or a thin layer of oil on water. This effect is due to some of the incident light being reflected at the surface of the layer, while another part of the light refracts to the solder as it enters the layer, reflects back to the bottom of the layer, and refracts as it exits the layer becomes. Both partial beams then coincide again and interfere. The occurring interference color is dependent on the path difference of the reflected light beams and thus on the strength of the metal layer. In this case, the layer thickness of the metal layer deposited according to the invention is preferably in the range from 100 nm to 1 μm. From a certain thickness of the metal layer, the path difference is greater than the coherence length of the incident light and there is no fixed phase relationship between the two partial beams, so that then a stable interference pattern can no longer arise.

klein zu halten, wobei die Metallschicht als Metallinterferenzschicht in einer derartigen Schichtdicke d ausgebildet ist, dass bestimmte Interferenzmuster auftreten und entsprechende Interferenzfarben gebildet werden.Due to the high refractive index of the metal layer, the dependence of the color on the viewing angle is small in the electrochromic device according to the invention. In this case, the refractive index n of the metal layer should preferably be greater than 2 in order to determine the dependence of the color on the viewing angle α according to the equation for the optical path difference $\Delta s=2d\sqrt{n^2-si{n}^2}\alpha$

small, wherein the metal layer is formed as a metal interference layer in such a layer thickness d that certain interference patterns occur and corresponding interference colors are formed.

Because of these particular optical properties and effects, the present electrochromic device is also referred to as interference foil and is particularly intended for use in the design field, where, for example, bodies of cars, cases of smartphones, furniture or electrical appliances are to be pasted with the film to appropriate to realize optical effects. Other areas of application include the darkening of car windows, windows, rear-view mirrors, partitions made of glass, mirrors and glasses.

A preferred embodiment of the present invention provides that the first transparent film is conductively coated with a transparent graphite layer. The graphite layer must not exceed a certain thickness to ensure transparency. Preferably, the thickness of the graphite layer is 10 to 30 nm, particularly preferably 20 nm. Such layers can advantageously be obtained via a physical vapor deposition (PVD).

Depending on the application, the counter electrode can be designed differently. An advantageous embodiment of the present invention provides as a counter electrode before a metal grid, which is arranged in the electrolyte layer between the two films and thereby lies directly on the second transparent film. At the same time, this metal grid can serve as a spacer between the films, whereby it is very important to ensure that there is no direct contact between the conductive coating of the first film and the metal grid, since in this case a short circuit would occur. One can prevent the direct contact by an insulating layer on the side facing the conductive layer of the first film side of the metal grid. A suitable insulation is, for example, the coating with polyethylene. The embodiment described above is particularly suitable for the design field, because in this way the interference foil is sufficiently stabilized even without a carrier and at the same time flexible enough to be glued to, for example, an automobile body.

Further possibilities for configuring the counterelectrode are that the counterelectrode is arranged in the form of metal strips in the electrolyte layer or is applied directly as a coating on the second film. It goes without saying that, even in these cases, there must be no direct contact between the conductive layer of the first film and the counterelectrode. The above-described geometrical arrangements of the counterelectrode are intended as explanatory examples and should by no means be regarded as limiting.

As already mentioned, the electrolyte arranged between the two foils comprises a metal salt corresponding to the metallic counterelectrode. Examples of particularly well-suited systems are zinc (Zn) - zinc iodide (ZnJ ₂ ) or iron (Fe) - iron bromide (FeBr ₃ ), in which the metal ion present in the solution is reduced and when a current is applied as a metal layer at the cathode connected conductive layer of the first film is deposited, while the halogen deposited at the anode reacts with the metal again to the metal salt.

The voltage required for this process is about 2 to about 20 V and the current is depending on the desired deposition rate at 100 cm ^{2 film} surface 1 mA to 1 A. If the current is reversed, so on the conductive layer of the first film deposited metal layer dissolved again until the interference film is completely transparent again. Thus, taking the example of the automobile body again, the original paint under the film becomes visible again. By reversing polarity, you can then set the desired interference colors in a targeted manner via the current intensity and the duration of the current flow.

A particularly suitable material for the transparent films is polyethylene terephthalate (PET). But it can also be used any other thermoplastic materials in the form of transparent films.

In some applications, such as darkening car windows, windowpanes, glass walls, mirrors or goggles, the interference foil is bonded to a transparent support of glass or plastic. As an example of such an application, glasses or a visor can be mentioned, which can be adapted to the light conditions via such an interference layer. For example, a visor of a motorcycle helmet can be covered with an interference foil. The electricity receives the interference foil from a battery, which is housed in the helmet body. A light sensor on the front of the helmet detects the current lighting conditions and passes the value to a controller, which is also integrated in the helmet body. From the brightness value and a characteristic curve of the interference foil, the controller determines the required amount of current in order to darken or lighten the visor. In this way, the light transmission of the visor can be automatically adapted to the lighting conditions, which increases the safety and ride comfort of the driver.

The structure of the interference foil according to the invention is explained in detail below with reference to drawings. The show 1 to 3 schematic sectional views of some selected embodiments.

The 1 shows a section through a sandwiched electrochromic device 1 (Interference film 1 ) passing through a first transparent film 2 and a second transparent film 3 is limited. The first transparent foil 2 is with a conductive layer 4 coated, which is provided as an electrode, which is preferably a thin graphite layer, which is also transparent due to their low strength. On the graphite layer is a metal interference layer 6 deposited, by which the desired interference colors are generated. Between the two transparent films 2 and 3 is an electrolyte solution comprising a metal salt 5 arranged. In addition, located between the two transparent films 2 and 3 the counter electrode 7 that in the case of 1 directly as a flat layer on the second transparent film 3 is arranged. Side seals 9 stabilize the sandwich-type interference foil and prevent leakage of the electrolyte solution from the composite.

The 2 shows a further embodiment of the electrochromic device 1 , in particular by the shape of the counter electrode 7 from the interference film described above 1 different. In this case, the counter electrode is located 7 in the form of strips, between the two transparent films 2 and 3 on the second transparent foil 3 are arranged and in the electrolyte solution 5 protrude.

In the 3 is a further embodiment of the interference film according to the invention 1 shown, wherein the counter electrode 7 designed as a network. This network also serves as a spacer between the two transparent films 2 and 3 and thus stabilizes the entire film composite. The metal grid 7 lies directly on the second transparent foil 3 , So that no short circuit occurs during operation of the electrochemical cell is between the conductive layer 4 and the counter electrode 7 an insulation 8th arranged, for example, in the present grid 7 as a surface coating of the upper, the conductive layer facing region of the counter electrode 7 can be made with polyethylene. Otherwise corresponds to the structure of the interference foil 1 the two previous examples.

LIST OF REFERENCE NUMBERS

1

Electrochromic device (interference foil)

2

First transparent foil

3

Second transparent film

4

Conductive layer

5

Electrolyte (solution)

6

Metal interference layer

7

counter electrode

8th

insulation

9

poetry

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19622600 A1 [0003]
• DE 10148438 B4 [0004]
• DE 1218794 B1 [0005]
• US 5903382 A [0006]

Claims (9)

Electrochromic device (1), comprising - a first transparent film (2) which is coated with a conductive layer (4) and thus provided as an electrode, - a second transparent film (3) lying flat opposite the first film (2), a counterelectrode (7) made of metal, which is arranged between the first and the second film (2, 3), wherein the counterelectrode (7) has no direct contact with the conductive layer (4) of the first film (2), Electrolytes (5) for completing the electrochemical cell, wherein the electrolyte (5) is likewise arranged between the first and the second film (2, 3), and - a lateral seal (9), over which the two films (2, 3 ) are connected to one another to form an electrochemical cell, characterized in that the electrolyte (5) comprises a metal salt corresponding to the counterelectrode (7), so that on the conductive layer (4) of the first transparent film (2) during application a metal layer (6) can be deposited, wherein the metal layer (6) is designed as a metal interference layer in such a layer thickness that interference patterns occur. Electrochromic device (1) according to Claim 1 , characterized in that the layer thickness of the metal layer (6) is in the range of 100 nm to 1 micron. Electrochromic device (1) according to Claim 1 or 2 , characterized in that the first transparent film (2) is coated in a conductive manner with a transparent graphite layer (4). Electrochromic device (1) according to one of the Claims 1 to 3 , characterized in that the layer thickness of the graphite layer (4) is between 10 nm and 30 nm, preferably 20 nm. Electrochromic device (1) according to one of the Claims 1 to 4 , characterized in that the counter electrode (7) is arranged in the form of a metal grid on or above the second transparent film (3) Electrochromic device (1) according to one of the Claims 1 to 4 , characterized in that the counter electrode (7) is arranged in the form of metal strips on or above the second transparent film (3). Electrochromic device (1) according to one of the Claims 1 to 4 , characterized in that the counter electrode (7) is arranged as a flat layer on the second transparent film. Electrochromic device (1) according to one of the Claims 1 to 7 , characterized in that the transparent films (2, 3) consist of PET (polyethylene terephthalate). Electrochromic device (1) according to one of the Claims 1 to 8th , characterized in that the electrochromic device (1) is connected to a carrier.

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