ELECTROCHROMIC DEVICE AND A METHOD TO MANUFACTURE THE SAME

Abstract: Electrochromic optical device and method to produce the same. The device includes first substrate (1) on the one side of the substrate a first transparent conductor (2) on the conductor a first electrochromic layer (3), a second substrate (4), on the one side of the second substrate a second transparent conductor (5), on the second transparent conductor, a second electrochromic layer (6), the two substrates are laminated to each other by means of a solid state polymer with their sides carrying the respective transparent conductor and electrochromic layer facing each other. The polymer works as an ion conductor and is based on methylacrylate and poly(propyleneglycol) doped with a metal salt.

Description: Electrochromic device and a method to manufacture the same Background of the Invention The invention relates to an electrochromic optical device and method to manufacture the same. The invention may be used i optical devices such as windows, mirrors and high-contrast non emissive display elements. Electrochromism is known in oxides based on W, V, Ni, Mo, Ir etc, and in numerous organic substances. Change in optical pro perties is caused by the injection or extraction of mobile ions A material colouring, i.e. lowering its transparency, under in jection or extraction is referred to, respectively, as cathodi or anodic material. Absorptance modulation as well as reflectanc modulation are possible. A practical coating in a device, for example having the form of window, could comprise an electrochromic thin film integrated i an all-solid-state multilayer configuration. It is known that one can form an optical device of this kind wit two outer transparent conductors, required for applying th electric field, an electrochromic layer, an ion conductor in th following also mentioned as electrolyte, and an ion storage. Thi configuration is backed by a transparent substrate such as glass pane; alternatively the configuration can be interpose between two transparent substrates. Coloration and bleaching ar accomplished when ions are moved from the ion storage, via th ion conductor into the electrochromic layer or when the proces is run in reverse. The ion storage can have the form of anothe electrochromic layer, preferably anodic if the base electrochro mic layer is cathodic, or vice versa. By use of a purely ioni conductor, one can obtain an open circuit memory, i.e. th electric field has to be applied only when the optical propertie are to be altered. From French Patent No. 2 568 574 is known a solid state polymeri conductor usable in optical devices of the type described. As th polymer is suggested poly(ethylene glycol) . It is also known tha poly(propylene glycol) (PPG) also known as poly(propylene oxide ... diol, doped with metal salts (e.g. lithium, sodium or potas sium) are relatively good ionic conductors. It is also known tha poly(ethylene oxide) (PEO) and its diol poly(ethylene glycol (PEG) are even better ion conductors at temperatures greater tha 60°C. Ratios of ether oxygen to metal in the range 9:1 to 25: produce the best conductivities in these series - some conductiv ties (for doped PPG) reaching as high as 5 x 10 -5S cm-l at 25oC. These prior known electrolytes are hygroscopic. In addition doped PPG is fairly fluid in the range of good ionic conducti vity, and doped PEO is crystalline below about 60 C. In a com mercial product not only properties relating to the basic func tions have to be considered, but also demands relating to th production and handling have to be fulfilled. A hygroscopi electrolyte will in practical use give a product with limite applicability or at least the necessity to build the device as hermetically sealed casset. If, on the other hand, the electro lyte has a low solidity, i.e. it is fluid or gelatinous, or has low adherence to pertinent surfaces it can not be integrated i the device as a carrying part of the same. Summary of the Invention The object of the present invention is to obtain an electrochro mic optical device with an electrolyte which is not hygroscopi and which has sufficient solidity that it could be integrated i the electrochromic device as a carrying part of the same, thi ability being secured by the adherence of the electrolyte to th substrate of the device. The invention thus offers the possi bility to form the device as a rigid laminate without the n cessity of any framing or the like. Another object is to adapt the active layers of the device each other, including an electrolyte of the mentioned type, order to form a device with a high functional quality. These and other objects of the present invention are achieved means of a co-polymer of a polyether (polypropyleneglycol-PP poly(methylmetacrylate) (PMMA) doped with a metal salt such a Lithium salt. PMMA provides in a loose network. The polymer ha physical properties making it suitable as a lamination member o the device. Brief description of the drawings On the accompanying drawings Fig. 1 is showing a crossection o an electrochromic device according to an embodiment of the in vention; and Figs. 2 and 3 are showing the spectral transmittanc of two devices manufactured according to the invention. Descriptions of the preferred embodiments A preferred embodiment of an electrochromic-based device accor ding to the invention is illustrated in Fig. 1. The device i comprises a laminate and includes layers having the same func tions as have been described before in the general description o the electrochromic optical devices. Accordingly a first layer i formed on a substrate and is then covered by the active layers o the device. This substrate has in fig. 1 the reference numeral and consists of a transparent glass pane; a suitable thicknes would be 1 or a few mm. The substrate 1 is on its one side carry ing a first transparent conductor 2. On its surface turned awa from the substrate 1 the conductor is carrying a first electro chromic layer 3 of the device. A second substrate 4, preferably a second glass pane of a simila thickness, is also on its one side carrying a transparent con ductor 5, which in turn is carrying a second electrochrom layer 6 of another composition than the first electrochromi layer 3. The layers are very thin: For example layer 2 could be 0.2 μ layer 3 0.3 μm, layer 5 0.2 μm and layer 6 0.03 μm. These laye should be strongly adherent to the substrate or the underlyi layer respectively. The two substrates 1 and 4, with their sa layers, are joined together as shown in fig. 1 with their coat sides facing each other. As joining member is used a co-polym layer 7 forming the ion conductor of the device. This polym layer preferable has a thickness of the order 0.1 mm. Coloration and bleaching are accomplished by connecting the t conductors 2 and 5 by means of a suitable wiring to the poles electrical source and applying a voltage of the order of 1 V f a suitable time. A reversible change of the optical properties caused by reversing the polarity of the electrical source. In the manufacturing of devices according to the preferred embo ments two pieces of 1 mm thick glass were each coated on one si with 0.2 μm thick electrically conducting indium tin oxide (I i.e. In 2 0_:Sn) layers forming the conductors 2 and 5. One these was then overcoated with 0.3 μm of WO_ on top of the co ducting layer thus forming the first electrochromic layer 3. one embodiment the other was overcoated with 0.03μm of NiO al on the conducting layer and forming the second electrochrom layer 6. In NiO x is over or about 1 but lower or about (1 < x < 2) . In another embodiment the substrate 4 with its co ductor 5 was overcoated with 0.1 μm of 2 0 5 thus forming t second electrochromic layer 6. The substrate 1 with its layers 2 and 3 and the substrate 4 wi its layers 5 and 6 were joined, with their coated sides faci each other, by means of the co-polymer layer 7 being a tran parent polymeric electrolyte which served so as to glue t samples together. The co-polymer thus acts as a lamination mat rial. In the lamination process, the co-polymer at approx. 9 polymerization is smeared onto the electrochromic layer 3. Sub- strate 4, with its layers 5 and 6, is then placed on the co polymer with layer 6 making contact to the co-polymer. The assem ly is then heated to between 50 and 60°C to complete the poly merization in order to reach the solid state of the co-polymer. Further coatings can be applied on those glass surfaces which ar shown as being uncoated in Fig. 1, i.e. the outer sides of th device. These additional coatings could be used, for example, t diminish the thermal emittance, thereby improving the therma insulation, when the device in Fig. 1 is integrated in a doubl or multiply glazed window. For producing the first electrochromic layer 3 an electrochromi amorphous WO_ film was prepared by reactive electron-beam evapo ration. The thin film deposition unit was evacuated to 5.10 - Torr and was then backfilled with air to a pressure of 0.8 mTorr Evaporation of 99.8% pure WO- granules was conducted onto th substrate 1, with its electrically conducting layer 2, positione 30 cm above the hearth. The evaporation rate was kept constant a llnnmmss " feedback control until a thickness of 0.3 μm wa reached. For producing the second electrochromic layer 6 according to on of the preferred embodiments, NiO counterelectrode films wer produced by reactive dc magnetron sputtering. The despositio —6 system was evacuated to 2.5 x 10 Torr and was then backfille with oxygen to a pressure of 8 m Torr. Sputtering from a 99.5 pure nickel target, 10cm in diameter, was conducted onto th substrate 4, with its electrically conducting layer 6, positione 5 cm below the target. Presputtering was performed for 15 minute before deposition begun. The power fed into the sputter plasm was 36W, which gave a sputter rate equal to 2.5 nms " . Films wit a thickness of 0.03 μm were produced. For producing the second electrochromic layer 6 according t another preferred embodiment, -O j . counterelectrode films wer produced by reactive dc magnetrom sputtering. The depositio —fi system was evacuated to 5 x 10 Torr and was then backfille with oxygen to a pressure of 12 mTorr. Sputtering from a 99.8% pure vanadium target, 10 cm in diameter, was conducted onto t substrate 4, with its electrically conducting layer 6, position 5 cm below the target. The power fed into the sputter plasma w 135 W which gave a sputter rate equal to about 0.1 nms . Fil with a thickness of 0.1 μm were produced. After removal av t substrate with its ^O- coating from the deposition system, t coated substrate was immersed into an electrolyte consisting of Molar lithium perchlorate and propanol carbonate. Lithium io were introduced into the " 2 O g layer by use of electrochemic treatment. A platinum foil served as counterelectrode during th process. Now will be described two alternative processes to prepare t co-polymer forming the ion conductor of the layer 7. Process I: PPG 4000 - LiClO. - methylmetacrylate (MMA) : _2 1. MMA is dried for 12-24 hours under low vacuum ( ~ 10 Tor by adding Ca 2 H 2 and stirring. The monomer-powder mixture then degassed to a pressure of 10 " Torr and vacuum distill into Pyrex ® tubes which are sealed on the vacuum line a taken to a dry laboratory with argon atmosphere. 2. PPG 4000 (polypropylene glycol) is filtered (1 μm Millipor Teflon ® filter) and dried in a vacuum oven at 120 C f 4-5 days. The material is transferred to the dry-laborato with argon atmosphere. 3. Anhydrous LiClO. is opened as received (packed in argon supplier) in the dry-laboratory argon atmosphere and stor under a low vacuum ( -10 Torr) when not being used. 4. LiClO. salt, in the weight range of 0.300 - 0.320 mg, prepared in a small beaker with stirrer. The tube of M prepared in (1) above is opened under argon and 0.3 to 0 mg is added to the LiClO. and stirred on a hot plate 50-60 C. When the LiClO. is dissolved or nearly dissolve PPG 4000 is added in the weight range of 1.6 to 1.7 mg a stirred at 50-60 C until a clear, homogeneous solution obtained. 5. The solution is heated under argon at 50°C and the MMA i allowed to polymerize, or co-polymerize, with the PP (LiClO. is a good catalyst) until one can draw a long strin of sticky substance from the surface. Some MMA has evapo rated. In this state the co-polymer has reached about 90 polymerization and can now be coated onto the substrate an thereafter cured to its fully solid state. It can also be stored in its partly polymerized state fo some time by allowing the mixture to stand at room tempera ture for one week under argon. At the end of this time an remaining MMA is pumped off in a vacuum oven. About 5% or less, by weight MMA to PPG remains in the fina product, which is a transparent, conducting, adhesive, soli elastomer. Conductivities between 5x10~ and 5x10~ S cm " have bee measured at room temperature, depending on the network ob tained. Process II: Silwet 77-LiClO. - MMA (methylmetacrylate) : "Silwet" is a trade name of Union Carbide. It is a polyalkan oxide modified dimethylpoly(siloxane) . Silwet 77 is a particula low-viscosity product with 25% EO units by weight. 1. The same procedure as for 1, 2, 3 in I above are followed, except that the Silwet 77 is dried at 80 C in a vacuum oven. (It degreades at 120°C) . 2. LiC10 4 salt, in the weight range 0.300 - 0.500 mg, is pre¬ pared in a small beaker with stirrer. 0.3 to 0.4 mg MMA is added to the LiClO., and the mixture is stirred on a ho plate at 50-60 C until the LiClO. is dissolved or nearly so. Silwet 77 in the weight range 1.6 to 1.7 mg is added and stirred at 50 until a clear homogeneous solution is ob¬ tained. 3. The solution is stirred at room temperature under argon f 2 days and then allowed to stand for 2-3 weeks under arg until the loose-sticky network mentioned is formed. The same properties as in I ar found, but with better c dduuccttivities (all in the 10 *" S cm " range at room tempe ture) In the descriptions of process I and II LiClO. has been mentio as the metal salt with which the co-polymer is doped. Howev also other metal salts are usable for doping of the polym Suitable such salts are NaCF 3 SO_, LiCF 3 S0 3 , LiSCN and NaSCN. The different components of the electrochromic-based window c tings will now be discussed. The electrochromic layer used both of the preferred embodiments is amorphous WO- which displ absoptance modulation and can yield a variation of the transm tance between wide limits. Crystalline 0 3 , which can be produ by deposition onto substrates heated to a high temperatu allows a fair degree of reflectance modulation. Electrochro W0_ shows best durability when operated in conjuction w aprotic electrolytes, preferrably containing Li ions. Fi crystalline NiO is a relatively newly discovered electrochro material permitting absorptance modulation. Its durability se to be better than for WO_. 2 0 5 , finally, is a known elect chromic material. A particularly interesting design of the device, which is embodiment of the present invention, is to combine one anodic one cathodic electrochromic material via the transparent po meric ion conductor which also serves as a lamination materi The transparent conductors, finally, is in this embodiment of heavily doped oxide semiconductor described. Electrochromic mu layer coatings can be backed by reflecting surfaces so t variable-reflectance devices are accomplished. A solid transparent adhesive polymeric ion conductor is a cruc material for a successful large-scale electrochromics-ba device. This crucial material is developed with a new approa and can be produced as has been described. A loose network poly(methylmethacrylate) (PMMA) - normally a substance of hi glass transition temperature ( ~ 105°C) - is accordingly used a base material into which units of doped ethylene oxide (EO) doped poly(propylene glycol) (PPG) or doped Silwet are integra ed. Basically the monomer (methyl methacryalte) (MMA) is used a solvent, or partial solvent, for a metal salt, and the sol tion, or solution plus undisolved salt, is mixed with the appr priate amount of PPG or Silwet. The substance is heated a stirred in an argon atmosphere until complete dissolution of t metal salt takes place. The MMA in the mixture is then allowed polymerize, or co-polymerize, to form a loose network. Some M evaporates so that the final product contains about 10%, or les MMA to PPG or Silwet by weight. The final product is a stick transparent, adhesive solid elastomer with ionic conducting pr perties as good as, or better than , those of the correspondi pure doped PPG or doped Silwet. Further, the ability of the pu doped PPG, or doped Silwet, to pick up and incorporate water severly restricted by the network. In the PPG (molecular wig 4000) - LiC10 4 - MMA system, about 10:1 to 20:1 0:Li gives t best results. For the Silwet 77-LiClO. - MMA sytem about 2:1 5:1 0:Li gives the best results. It is possible to substitute LiClO. with some other metal sal as has been mentioned before. The indication of a certain met salt for doping do not exclude that also two or more kinds sa can be present in the polymer. Some spectral data for devices Figures 2 and 3 show spectral transmittance, in the waveleng interval pertinent to solar irradiation, for devices of the ki shown in Fig. 1 and with materials prepared as outlined abov Figure 2 refers to an embodiment with a counterelectrode of Ni and Figure 3 to an embodiment with a counterelectrode of v 2 ° The data were taken at normal incidence in a double-beam spectr photometer, with the devices mounted in the sample beam and t reference beam left free. The large range of optical modulati that can be accomplished is apparent from the figures.

Claims: CLAIMS 1. Electrochromic optical device comprising a first su strate (1) on the one side of the substrate a first transpare conductor (2) on the conductor a first electrochromic layer (3) a second substrate (4) , on the one side of the second substrate second transparent conductor (5) , on the second transparent co ductor, a second electrochromic layer (6) , the two substrat with their sides carrying the respective transparent conduct and electrochromic layer facing each other being laminated each other by means of a solid state polymer provided to work an ion conductor, i n w h i c h, the ion conductor is based methylacrylate and poly(propyleneglycol) doped with a metal sal 2. Device according to claim l, i n w h i c h, the metal sa is LiClO4.. 3. Device according to claim 1, in which, the metal salt NaCF 3 S0 3 . 4. Device according to claim 1, in which, the metal salt LiCF 3 S0 3 . 5. Device according to claim 1, in which, the metal salt LiSCN. 6. Device according to claim 1, in which, the metal salt NaSCN. 7. Device according to any of the claims 1-6, i n w h i c the one electrochromic layer (3) consists of an anodic electr chromic material and the other (6) of an cathodic electrochrom material. 8. Device according to claim 7, i n w h i c h, the one elect chromic layer substantially consists of WO- and the other su stantial consists of NiO with 1 < x < 2. 9. Device according to claim 7, i n w h i c h, the one elect chromic layer substantially consists of W0 3 and the other subst tially consists of V 2 0_. 10. Method to produce the electrochromic optical device accor ing to any of the claims 1-10, i n w h i c h, a first su strate (1) as a glass pane is coated on one side with a tran parent layer forming a first transparent conductor (2) , coati the substrate onto the conductor with an electrochromic layer ( and coating a second substrate (4) with a transparent layer for ing a second conductor (5) and coating the substrate onto t transparent conducting layer with an electrochromic layer (6 preparing a co-polymer including methylacrylate and polyethe doped with a metal salt, providing a layer of the co-polymer in highly viscous state between the two substrates with their coat sides facing each other, bringing the polymere to cure with t metal salt as a catalyst to a solid state thus laminating the t coated substrate together and forming an ion conductor (7) of t device. 11. Method according to claim 10, i n w h i c h, the polym forming the ion conductor is prepared by dissolving the met salt in the methylmethacrylate and then adding the poly(propyle glycol) , forming a layer between said two coated substrates a letting the polymer curing with the lithium salt as a catalyst.

Inventors: STEVENS JIM, STEVENS, JIM
Applicants: COAT I GOETEBORG AB
Application year: 1989
Main classification: G02F1
IPC codes: G02F1