Electrochromic window.

The invention relates to an electrochromic system especially glazing transmission of the electrochromic type or more specifically a laminated glazing whose light transmission is modified by applying to the terminals of the glazing of an electrical potential. The glazing according to the invention are used to control the solar lighting in a building or in the housing of a motor vehicle, including a vehicle equipped with a glass roof.

Applications EP-A-253713 and EP-89400814, there is known a laminated electrochromic pane which consists of two glass sheets coated with transparent electronic conductor layers - for example, layers of indium oxide doped with tin (ITO) - separated successively by a layer of a cathodic electrochromic material like tungsten oxide (WO₃), a protonic conduction electrolyte - for example, a polymeric complex between polyethylene oxide (PEO) and the orthophosphoric acid (H₃PO₄) and a layer of an anodic electrochromic material such as iridium oxide. The two layers in contact with the electrolyte are capable of reversibly inserting protons if applied at two opposite ends of the glazing of a suitable potential difference, the insertion reaction in the tungsten oxide layer corresponding to a disinsertion reaction in the iridium oxide layer which thus plays the role of an electrode against symmetrical to the tungsten oxide electrode. The thermodynamic equilibrium can be written as follows: WO₃ xH⁺ + + xe⁻ <---> HxWO₃ and HxIr0y <---> Ir0y xH⁺ + + xe⁻. The instantaneous measurement of the current I which passes through the glazing is thus a direct measure of the number of reactions sites of insertions / ejections which occur at the same instant.

The applied potential difference must be greater in absolute value to the difference of thermodynamic potentials of the insertion reaction or disinsertion protons. Over the applied potential difference, the greater the coloring - or fading - will be. However, beyond a certain voltage, noise may occur including molecular hydrogen proton reduction or oxidation of oxygen in the water present in the residual state in some layers.

Taking into account the voltages at the interfaces, the limits of electrochemical stability of the system features described above are between 0.6 and 1.5 volts coloring stage (insertion of protons in WO₃, disinsertion in HxIr0y) and between -0 and 6 or 0 Volt in decolouration phase. These limits are subsequently referred to as memory of this "range of electrochemical stability of the reaction of coloration and discoloration."

The second problem is the time required for obtaining a desired coloration or discoloration, that is to say in the case of coloring / bleaching maximum, the time required for the passage of the amount load corresponding to all potential reaction-tional websites, or in other words the time required for the current intensity I is reduced to zero - or at least to a value close to zero.

When the cell size increases, the amount of charge passing correspondingly increases; or the current intensity can grow parallel because the theoretical relationship between how the potential difference V and the current I I needed less than V / R, where R is the resistance of the current leads and can be confused with a good approximation with the resistance of the transparent electrically conductive layers. Very low for cells of smaller sizes, the term IR increases rapidly with the cell size so that the ohmic drops become a factor limiting the current and therefore the speed of coloring / bleaching.

In a cell operating in transmission - which assumes transparent electroconductive layers - it is not possible to select a material whose sheet resistance is for example less than 1 ohm; materials and deposition techniques to the most successful day allowing only achieving 2 layers than 5 ohms of resistance square. However, it is possible to dispense partly this limit using current brought nonpoint but consist of strips or electrically son along two opposite sides of the cell, hidden by a sealing bead forming a frame around the glass . These bands or son can be selected from a highly conductive material such as copper, so that all points of the same band are equipotential. Accordingly, if we identify the glass surface in a Cartesian coordinate system (x, y), where the x axis is parallel to the bands of current leads, all points having the same equipotential ordered therein. By against two points of the same x-coordinate (ordinate and different) are at different potentials, except to be equidistant from the central axis which is an axis of symmetry of the cell. In practice, if the distance between the two electroconductive strips exceeds for example 10 cm, the switching time of a cell is greater than the minute.

fictitiously can certainly divide that distance by multiplying the number of electrically conductive strips. So for a wide glazing 1, is provided as previously an electrically band y = 0 and a second band at y = 1, which are added to the strips y = y = 1/3 and 21/3 - alternating the contact faces. The so formed cell is equivalent to a set of 3 small identical cells connected in parallel, each small cell with three times lower resistance. But such an arrangement leaves exposed a network of bands electrically which harms the general appearance of the glazing.

What is true electrochromic glazing operating in transmission, the other is also electrochromic systems of the type display or mirror which must include at least one transparent electrically conducting layer whose conductivity is relatively low compared, for example, a layer thick metal.

Moreover, whatever the mode of operation of the electrochromic system - insertion of protons or other cations or another, for example, reduction / dissolution of a metal salt -, we find the same problems with these ohmic drops.

The invention relates to an electrochromic system large whose switching time from a colored state to a colored state and vice versa is less than 30 seconds even if the width of the glass is for example of the order of 50 cm, this corresponds to building glazing or dimensions of motor vehicles.

This technical problem is solved according to the invention by a system consisting of two sheets of glass coated with electrically conductive layers separated by a layer of an electrochromic material, an electrolyte and an against-electrode, said electrically conducting films being each provided with a electroconductive strip made of a material whose electrical conductivity is large compared to that of the electrically conducting films, the electrically conductive strips being arranged along opposite edges of the glazing and connected to a voltage generator which applies color phase (or respectively in decolouration phase), between two points a and B adjacent electroconductive strips, a potential difference U₁ = (V_AT-V_B) (T) such that between the point A and the point R of the other electrically conductive layer, directly facing the point A, there is a potential difference U₂ = (V_AT-V_R) (T) = U₀, where U₀ is constant and is chosen in the stability range of the staining reaction (or discoloration respectively).

The ohmic drops are directly linked to the distance between the electrodes, it is generally operated with electrically conducting strips parallel to the length of the glazing.

In traditional operation, it is required the potential difference between the two strips A and B, in other words between two points of extreme ordinates; according to the invention, the potential is imposed between two points of the same abscissa, on the same side of the glazing but on different electroconductive layers. In this way, the effective voltage is maximum at time t = 0 and therefore the appearance of the color - or rather his disappearance - is quickly responsive to an observer. It may be noted that the proposed type of food does not really compensate for the ohmic drops; and if a potential difference is imposed U₀ one side of the glazing, except at the ends of the glazing (y = 0 or y = 1) two points facing each other always have between them a difference of potential V (y) lower than the imposed pressure. However, it is found experimentally that this value V (y) is always greater than the value V '(y) obtained when imposes Vo between two extreme bands glazing U₁ = U₀; accordingly, the maximum color is reached much more quickly and can be achieved for example by glazing (40 x 80) cm overall response times of the order of 30 seconds.

Compared to known electrochromic glazings in the art actually observed with a glazing according to the invention a much greater difference between the transient states of the marginal regions of staining and the transitional states of the central region of the glazing coloring; the value of the difference in effective potential between two points of the glazing facing depends much more than previously of the position of these points. However, whatever the position difference actual potential is higher than with a pane according to art. This results in a virtually non uniform coloration but with a very strong contrast, the edges of the glass very quickly appearing midnight blue while the color of the central part appears only at the end of the switching time. But of course, from that moment the color of the glazing is perfectly uniform.

According to a first embodiment of the invention, is determined by preliminary voltammetric recordings what should be the potential difference U₁ to be applied at time t for obtaining a difference of potential U₂ constant over time. These determined values, simply set accordingly the voltage generator.

To simplify this programming, we can approximate the curve U₁ = f (t) by an exponential function, which simplifies the electronics associated with the voltage generator but does not remove the need for full-scale tests, repeated for each model glazing, to determine the parameters of the exponential function.

To overcome this last difficulty, it is best to use an assembly with 3 electrodes, the type potentiostat using for example an operational amplifier. then placed a reference electrode at point A. As a matter of balance of electric charges, regardless of the position of the reference electrode on the line y = 0, all the points of this line are equipotential. Consequently, the reference electrode may be indifferently formed by an electrically conductive strip covering the whole length of the window (and thus identical to the strip forming the electrode A) or only a part thereof.

When the reference electrode R is formed by an electrically conductive strip of the length of the glazing, one of the two glass sheets is advantageously provided with two electrodes mounted on two parallel edges. This assembly can then be further exploited to address other disabilities electrochromic glazing, that the reaction kinetics can be very low at low temperatures and in particular to temperatures below 10 ° C. In this case, the transparent electroconductive layer between these two electrodes may be used as a heating layer, through the exotherm - due to the resistance of said layer - which occurs when applying a potential difference between these two electrodes. Preferably, the potential difference applied to this pre-heating is greater than 20 volts and about 24 volts, which generally corresponds to a voltage of about 0.5 volt per centimeter of distance between the electrodes. This preheating phase may precede any such coloration and have a duration of about 2 mm. Given the proximity of the second glass sheet, it has a tendency to load during the coloring phase, which in the long run causes a blue stain which may advantageously be avoided by using an AC voltage.

Further details of advantageous features of the invention emerge from the description given below with reference to the accompanying drawings, wherein:<ul><li><b>. <u>figure 1</u></b> : A block diagram of an electrochromic cell of the invention,</li><li><b>. <u>2</u></b> : A sectional view of a glass roof for motor vehicles.</li></ul>

In Figure 1 is shown schematically an electrochromic cell; for clarity, the thickness ratios between the different elements of the system have not been respected. This cell is constituted by a glass sheet 1 coated with a transparent electroconductive layer 2, provided with a current input strip 3. This strip 3 is preferably parallel to the length L of the glazing which is otherwise of a width 1. the glass sheet 1 faces a second glass sheet 4 which is itself coated with a transparent electroconductive layer 5 provided with a current input strip 6. Between the two transparent electrodes 2, 5 , are successively provided a layer 7 of an anodic electrochromic material (preferably iridium oxide), an electrolyte layer protonic conduction 8 (preferably a polymeric complex between polyethylene oxide and orthophosphoric acid rigorously anhydrous) and a layer 9 of a cathodic electrochromic material (preferably detungstène trioxde).

For information, you can use layers having specifically the following: <b>- <u>Substrates (1 and 4)</u> :</b> . sheet of float glass of 3 mm thickness,<b>- <u>Transparent electroconductive layers (2 and 5)</u> :</b> . indium oxide layer doped with tin, deposited by magnetron cathode sputtering, . thickness 400 nm, . sheet resistance of 5 ohms.<b>- <u>cathodic electrochromic layer (9</u>):</b> . layer of tungsten oxide deposited by thermal evaporation in a molybdenum crucible under an air pressure of 5 x 10⁻⁵ Torr, . thickness 260 nm.<b>- <u>Electrolyte (organic polymer 8)</u> :</b> . solid solution of anhydrous phosphoric acid in ethylene oxide,

. <u>preparation</u> :

. Under strictly anhydrous conditions are dissolved per liter of phosphoric acid solvent (17.5g) NORMAPUR and polyethylene oxide of molecular weight equal to 5 000 000 (1.21 density, glass transition temperature -40 ° C, O / H ratio of the number of oxygen atoms of the polymer to the number of hydrogen atoms of the acid equal to 0.66).

. The common solvent is for example a 50:50 mixture of acetonitrile and of tetrahydro-furan.

. The solution was cast on a glass plate coated with a tungsten oxide layer deposited as described above. The uniform thickness is obtained by the method of film drawer. The casting is carried out under an atmosphere of controlled humidity. After evaporation of the solvent yields a film of 50 microns having a conductivity at 20 ° C is from 9.10⁻⁵ Ohm.⁻¹.cm⁻¹ and whose light transmission is greater than 85%. The moisture content at the time of casting should preferably be between 40 and 100 ppm thereby subsequently optimal contrast.<b>- <u>anodic electrochromic layer</u> :</b> . iridium oxide layer deposited by sputtering assisted by a magnetic field under a pressure of 6 millitorr an oxygen / hydrogen (in a 80:20 ratio), . 55 nanometers thickness.

Preferably, the electrolytic layer is deposited on the tungsten oxide layer within a short time after the filing thereof. The assembly of the glazing is carried out in an autoclave at a temperature of 90 ° C under a pressure of 15 kg / cm².

The data above are given only as examples and should not be considered as limiting the scope of the present invention applies to all electrochromic cells of large dimensions.

Traditionally, is imposed between the point A - which can be considered as a point of the electrically conductive strip 3 - and the point B - which can be considered as a point of the electrically conductive strip 6 -a difference of fixed potential V₁ selected in the stability range of the desired electrochemical reaction. Such an arrangement has been used for three cells S1, S2 and S3 homothetic, whose current supply strips are respectively spaced 3, 4.5 and 9 cm. Figure 3 shows the variation over time of the coloring intensity of the current. For both small cell current I₀ at t = 0 is proportional to the surface and the staining time is almost identical. Also after 5 seconds, the bulk of the coloring process is completed. By cons, with the S3 cell, we find that the I₀ current is not proportional to the surface and is limited by the ohmic drops. In practice this prohibits the embodiment of a cell whose current supply strips are spaced more than 10 cm - except to experience higher switching times per minute.

Another way to analyze the problem is to examine two points M_AT and M_B that in the coordinate system (x, y, z) shown schematically in Figure 1 have coordinates respectively (x, y, a) and (x, y, b). Between these two points, it was at time t a potential difference V = VM_AT - VM_B. Moreover if band is chosen electrically 3, 6 copper or other highly conductive material, we can consider all the points M_AT - And respectively M_B - An ordered data are equipotential. Is plotted in Figure 4 the curve representing 10 different values ​​of V as a function of the ordered pairs of (M_ATM_B), This for a cell of 14 cm in width (distance AB) and a potential difference U₁ 1.4 Volt and at time t = 0. It is noted that the effective voltage V is much smaller than U₁, and that this difference is accentuated for the central zone of the cell.

If now we choose to operate according to the invention by maintaining a difference U₂ fixed potential between point A and point R facing it on conducting strip 6 ', we obtain the curve established for 11 U₂ = 1.4 Volt . Note that for any pair of points (M_ATM_B), The observed difference of potential V is always less than or equal to U₂. For the desired electrochemical reaction, and only thus imposing a U₂ value in the area said electrochemical stability of the invention. Furthermore, except around the edges, the effective voltage is not equal to the voltage imposed U₂; the invention therefore does not totally eliminate the ohmic drops. However, the comparison of curves 10 and 11 shows that the RMS voltage according to the invention is about 3 times higher for every pair of points M_ATM_B. The result is a color - or discoloration - much faster. Furthermore we find that the effect of the edges is greater than a traditional installation; this results in an almost instantaneous appearance of color near the edges of the glazing, but later in the central region. This gradual coloring appearance which "part" of the edges is characteristic of the glazing according to the invention.

For terminals A and B spaced 14 cm, the gain in staining time is 6 seconds, a time saving of 30%. For more spaced across the gain increases again. Thus one can achieve an electrochromic roof, the smallest length exceeds 30 cm and yet the switching time is less than 1 minute at 20 ° C, or in this case a division by 6 in the switching time can be typically reduced by 3 minutes 30 seconds. .

The arrangement according to the invention endows the electroconductive layer 5 of two strips current lead 6 and 6 '. Advantageously, one can use the electrical resistance of this layer 5 for heating the cell. For this, prior to staining, is applied between the point B and the point A, a potential difference U₃ of for example 24 volts, thereby raising the temperature of the electrolytic layer known that the maximum performance is obtained to a temperature between 20 and 80 ° C. The potential difference U₃ is preferably an AC voltage to avoid the polarization of layers of electrochromic materials, in this case with such an effective voltage of 24 volts. It should be noted that the heating can be used regardless of the oxidation state of the electrochromic layers.

The invention has been described with reference to a cell whose electrolyte is proton conduction but it should be understood that it applies mutatis mutandis to all electrochromic systems including cells the electrolyte is ionically conductive by eg lithium. Similarly, other materials than those mentioned may be employed for producing the electrochromic layer and the electrode against, this in particular in order to obtain other colors, the values ​​of the applied voltages to be adjusted new thermodynamic equilibria. In addition, a 3-electrode assembly can be used more generally in any system requiring at least one transparent electrically conductive layer, whether the systems operating by insertion / ion disinsertion as those discussed in this paper, the display systems systems with an electrochromic or liquid crystal gel again.