FR2669122A1 - Electrochromic window - Google Patents

Abstract

The invention relates to an electrochromic window which includes, in succession, a glass sheet (1), a first electrode (2) constituted by a transparent electrically conductive layer whose surface resistance is less than 5 ohms per square, a layer (4) of a cathodic electrochromic material, an electrolyte (5), a layer (6) of an anodic electrochromic material and a second transparent electrically conductive electrode (8), characterised by barrier layers (3,7) which are inserted between the said electrodes and the said layers of electrochromic materials, the surface resistance of the assembly formed by one electrode and its barrier layer being less than 5 ohms per square.

Description

ELECTROCHROME GLAZING
The present invention relates to glazing with electrocontrolled transmission or in other words electrochromic glazing, the state of coloring of which can be modified by passing an electric current. The invention applies more particularly to the control of the solar contribution in the buildings or the interiors of motor vehicles.

 The electrochromic glazings which are the subject of the invention are glazings comprising a layer of a material capable of reversibly inserting cations, in general protons or lithium ions, and whose oxidation states corresponding to both inserted or uninserted states have different coloring states.

In the case of tungsten trioxide, one thus passes from a colorless oxidized state to a reduced state of dark blue color, according to the chemical reaction
WO3 + x M + + xe- <-----> MXWO3-
For this reaction to occur, it is therefore necessary to have, next to the layer of electrochromic material, a source of cations and a source of electrons, respectively constituted by a layer of an electrolyte with ionic conductivity and by an electroconductive layer serving as an electrode. To this first system comprising an electrochromic cathodic material is added by symmetry a system with an anodic electrochromic material, such as iridium oxide, capable of likewise inserting and deinserting cations in a reversible manner, the iridium oxide layer being inserted between the electrolyte layer and a second transparent electrically conductive layer.

In European patent applications EP-A-253,713 and
EP-A-338876, it has been shown the relation existing between the size of an electrochromic system and the electrical conductivity required for the electrode. The larger the dimensions of the glazing, the more the transparent electroconductive layer must have a low resistivity, otherwise the switching times become longer. For glazing larger than 200 cm2, a square resistance of less than 5 Ohms is therefore recommended.

 Such a level of performance can certainly not be obtained with all types of thin layers, especially since the other fundamental requirement is transparency, a light transmission as high as possible being sought for the discolored state which implies with number of materials of relatively small thicknesses.

 Furthermore, the transparent electroconductive layer must be stable in the medium used, including under difficult conditions, in particular at high temperature. However, this medium is very corrosive due to the presence of the electrolyte which may be acidic or basic.

In patent application EP-A-253,713, a certain number of criteria for the selection of an electrolyte suitable for producing electrochromic glazings have been defined and the choice is more particularly focused on mixtures, in particular of the complex type. solid acid-organic polymer, this type of electrolyte being advantageously less aggressive than others such as for example acid solutions in liquid phase, with regard to the other layers of the system and leading obviously to a proton conduction. In the rest of this thesis, we will limit ourselves to electrochromic systems using a proton-conducting electrolyte, preferably of the polymer type. It should be noted that even slightly aggressive, by definition even the electrolyte is a source of protons therefore very reactive elements.

 It is true that the transparent electroconductive layer is not directly in contact with the electrolyte but is separated from it by a layer of an electrochromic material. However, this intermediate layer cannot fully play a protective role because it must offer as many reactive sites for the protons as possible, therefore with a distribution over the entire thickness of the layer of electrochromic material which under means a relatively porous layer into which protons will penetrate and possibly reach the transparent electrically conductive layer.

 It should be noted that this corrosion phenomenon is relatively slow and that the system operates normally for a certain time. But after a long period of use or a simulation thereof by accelerated aging tests at high temperature, there is a significant degradation for example after 5 hours at 100 ° C. or more. This corrosion is therefore a handicap to the development of these systems, particularly in building applications facing the problem of the ten-year warranty and in automotive applications where the operating temperatures are sometimes very high.

 The attempts made to date to replace the acid polymer forming the electrolyte by other materials such as dielectrics are hardly convincing for large systems, in particular because of the risks of short circuits due to the extreme thinness of the dielectric layers for discolored state.

 On the other hand, we indicated above that the level of performance required for the electrically conductive layer is particularly high in terms of conductivity and transparency. For automotive applications, there is also the requirement of compatibility with a heat treatment of the bending type of the glass sheet and / or thermal toughening. This compatibility can be obtained with a so-called bendable layer, that is to say capable of withstanding a treatment at 6000C without degradation or with a layer which can be deposited on a cold substrate, the reheating of the glass being liable to make it lose its shape and the effects beneficial from possible thermal quenching.

Finally, the technology used must be adapted to the dimensions of the glazing and to industrial production, in particular in terms of cost and yield.

 The confrontation of these requirements has led the inventors, in the current state of knowledge in the field of electrically conductive layers to choose either indium oxide doped with tin or tin oxide doped with fluorine which can provide layers having a very low square resistance provided, for example, using deposition techniques of the vapor phase pyrolysis type and relatively large thicknesses of the order of 800 to 900 nanometers. Such a layer is inert towards an acid electrolyte.

This problem of preserving the electrically conductive layer can also be solved by means of a barrier layer and according to claim 1 the invention also relates to an electrochromic glazing successively comprising a sheet of glass, a first electrode constituted by a transparent electroconductive layer whose square resistance is less than 5 Ohms, a layer of cathodic electrochromic material, an electrolyte, a layer d of an anodic electrochromic material and a second transparent electroconductive electrode, this glazing comprising further according to the invention barrier layers inserted between said electrodes and said layers of electrochromic materials, the square resistance of the assembly formed by an electrode and its barrier layer being less than 5
Ohms.

The barrier layer according to the invention therefore constitutes the assembly forming the electrode and in this way opposes the system described by M. Stuart F Cogan and R David
Rauth in the article entitled "The a-WO3 / IrO2 electrochromic system" published by the SPIE Institutes for advanced
Optical Technologies (volume IS4), a system in which it is recommended at the electrolyte-electrochromic material interface, the presence of a barrier layer of the dielectric type, which amounts to framing the most corrosive electrolyte (the acid polymer) with a other electrolyte. The barrier layer described in the aforementioned article cannot protect the transparent electrode against the action of protons because the latter must reach the layer of electrochromic material for the phenomenon of electrochromism to occur. At the rear of the layers of electrochromic materials, the barrier layer according to the invention can be "waterproof" to the protons, or at least be as waterproof as possible.

 A given layer can be used as a barrier layer according to the invention when the ratio between its thickness and its porosity is large. In practice, however, it is not desirable to increase its thickness too much because then the optical absorption linked to the barrier layer becomes annoying and moreover the mechanical strength of the system is degraded with a greater propensity for delamination.

Therefore, it is preferable to work with layers of less than 600 nanometers. On the other hand, it is advantageous to operate under deposition conditions which lead to high densities, that is to say within the meaning of the invention relatively close to the theoretical density of the corresponding crystal lattice.

 Even if the barrier layer is part of the assembly forming the electrode, it does not need to be very electrically conductive. This point, which appears at first sight quite paradoxical given the qualities required for electro-des, is due to the fact that the barrier layer is preferably deposited in a very thin layer, for example less than 600 nanometers, and that in the thickness, its insulating nature will always be insufficient under these conditions to effectively limit the electronic conduction, this of course provided that the electronic density behind the barrier layer is as homogeneous as possible which supposes a transparent electrically conductive layer of very conductive base.

 The barrier layer must be as stable as possible with respect to the electrolytes, which in particular implies good resistance to acid attacks. We indicated previously that its thickness must remain low, in particular so as not to harm the transparency of the electrode, but nevertheless it must be sufficient for obtaining a sufficient impermeability to protons.

 It has been found that the tin dioxide SnO2, possibly slightly doped with antimony, deposited without special precautions is very particularly suitable for the production of such barrier layers, thicknesses of 100 to 500 nanometers giving any satisfaction.

 Very satisfactory results have also been obtained with a barrier layer formed of dense tungsten oxide, having a density greater than or equal to 95% of the theoretical maximum density. It should be noted that such a layer of tungsten oxide can practically no longer exhibit an electrochromism phenomenon because the protons cannot reach the reactive sites.

 Other details and advantageous characteristics of the invention are given below with reference to the single appended sheet in which there is an electrochromic glazing according to the invention, seen in a schematic representation where, for the sake of maximum clarity, we has ruled out any objective of respecting the proportionality of the different layers.

 The electrochromic system consists of a glass sheet 1 coated with a transparent electroconductive layer 2 forming the first electrode. The glass sheet 1 faces a second glass sheet which is likewise coated with a transparent electroconductive layer 8. These two electrodes are connected to a voltage generator not shown here.

 These electrodes are for example formed by layers of indium oxide doped with tin deposited by magnetron sputtering, according to a thickness of 400 nm and have a square resistance of the order of 5 Ohms.

Between these electrodes, there is the electrolyte 5 formed by a solid solution of anhydrous phosphoric acid in polyethylene oxide, prepared in the following manner under strictly anhydrous conditions, 20 g of phosphoric acid are dissolved per liter of solvent normapur and 20 g of polyethylene oxide with a molecular mass equal to 5,000,000 (density 1.21, glass transition temperature -40 C, O / H ratio of the number of oxygen atoms in the polymer to the number of atoms d hydrogen of the acid equal to 0.66).
The solvent used is a 50-50 mixture of acetonitrile and tetrahydro-furan. The solution is poured onto a glass plate after depositing a layer of electrochromic material (see below). The uniform thickness is obtained by the film puller method. The casting is carried out under an atmosphere with controlled humidity. After evaporation of the solvent, a film of 50 micrometers is obtained whose conductivity at 20 "C is 2 10-5 Ohms cm-1 and whose light transmission is higher 85% The moisture content at the time of casting should preferably be between 40 and 100 ppm, which allows optimal contrast to be obtained later.

 The electrolyte 5 is surrounded by two layers of electrochromic materials, a cathode material, tungsten oxide 4, deposited by magnetron sputtering over a thickness of 260 nm and an anode material, iridium oxide 6 deposited in the same way. by magnetron sputtering (with an oxygen-hydrogen gas mixture in an 80/20 ratio during deposition in accordance with the teachings of EP-A-338876), over a thickness of 55 nanometers.

 After assembly in an autoclave of the system described below without barrier layer, after 5 hours at 1000C we begin to observe a drop in system performance, in particular due to optical degradation of the layers, the indium oxide layers doped with l tin dissolve in the polymer which ultimately leads to the complete loss of system functionality.

 If we now interpose between the electrodes 2 and 8 and the layers of electrochromic material 4 and 6 two barrier layers 5 and 7, constituted by tin oxide deposited by magnetron sputtering at a thickness of for example 300 nanometers, we no more degradation of the resistivity of the electrodes is observed after 100 hours at 100 ° C. which clearly indicates that the ITO electrodes have been completely protected.

Claims (10)

 1. Electrochromic glazing successively comprising a glass sheet (1), a first electrode (2) constituted by a transparent electroconductive layer whose square resistance is less than 5 Ohms, a layer (4) of a cathodic electrochromic material, an electrolyte (5), a layer (6) of an anodic electrochromic material and a second transparent electroconductive electrode (8) characterized by barrier layers (3,7) inserted between said electrodes and said layers of electrochromic materials, the square resistance of the assembly formed by an electrode and its barrier layer being less than 5 Ohms.  2. Electrochromic glazing according to claim 1, characterized in that said barrier layer has a square resistance greater than 20 Ohms.  3. Electrochromic glazing according to claim 1, or 2 characterized in that said barrier layer has a thickness less than 600 nanometers.  4. Electrochromic glazing according to one of claims 1 to 3, characterized in that said layer has a high density.  5. Electrochromic glazing according to one of the preceding claims, characterized in that said barrier layer consists of a layer of tin oxide.  6. Electrochromic glazing according to claim 5, characterized in that said layer of tin is doped with antimony.  7. Electrochromic glazing according to one of claims 5 or 6 characterized in that the thickness of said barrier layer is between 100 and 500 nanometers.  8. Electrochromic glazing according to one of claims 1 to 4, characterized in that said barrier layer is constituted by a layer of tungsten oxide whose density is greater than or equal to 95% of the density of a pure crystal d tungsten oxide.  9. Electrochromic glazing comprising successively a sheet of glass (1), a first electrode (2) constituted by a transparent electroconductive layer whose square resistance is less than 5 Ohms, a layer (4) of a cathodic electrochromic material, an electrolyte (5), a layer (6) of an anodic electrochromic material and a second transparent electroconductive electrode (8), characterized in that said transparent electroconductive layers (2, 8) consist of layers of doped tin oxide fluorine.  10. Electrochromic glazing according to claim 9, characterized in that said layer of tin oxide is deposited by a technique of pyrolysis from vapors and has a thickness of between 800 and 900 nanometers.