GB2177516A - Electrochromic device - Google Patents

Description

1 GB 2 177 516 A 1

SPECIFICATION

Electrochromic device This invention relates to an electrochromic device.

The present invention providesan electrochromic device comprising a conductive layer, bearing an electrochromic layercomprising a metal phthalocyanine capable of the colour changes red<->green<->biue,->purple, itself bearing an electrolytic medium (e.g. liquid orsolid) contactingthe electrochromic layer, and a conductive layer overlying the electrolytic medium, at leastoneof theconductive layers being translucent, and preferably one or both conductive layers being electronically conductive, and a 10 controllerwhich applies a potential between thetwo conductive layers sandwiching the other layers,the potential being limited to within the range red.(->green<->biue<->, said rangetypically being from +2Vto -1.OV, more preferably from +2V to -0.8V, the device being characterised in that the electrochromic layer is a duplex or mixed layer of APC2 with at least one of MPc, SnPCC12 and anotherAPC2, where M= Ru, Fe, Zn or Co or mixtures thereof, and A= any rare earth (including forthis purpose Sc, La and Y) or mixtures thereof, and Pc= 15 phthalocyanine. A bright opaque ion conductorsuch as hydrogen uranyl phosphate, conducting protons, would sufficefor at leastthe red<-green colourchange. The disproportionately damaging effect of forcing such a material into its purple colour (at about - 1.5V) had not hitherto been appreciated.

Thetranslucent electronically conductive layer may be a doped tin-oxidecoated glass or a thin metal film.

The mixed layer maythus comprise a mixture of rare earth diphthalocyanines in which mixture at leastthree 20 rare earth elements accountfor at least 10 weight percent each of thetotal rare earths; the mixture maycontain rare earth elements in substantiallythe proportions occurring in a natural deposit, such asthe proportions occurring naturally in monazite, bastnaesite orxenotime or mixtures thereof. Examples of such mixtures are (i)'iightfraction'and (ii)'heavy fraction', which are composed asfollows, byweight:

25 (i) lanthanumoxide 37% ceriumoxide 3% praseodymium oxide 15% neodymium oxide 25% samarium oxide 4% 30 others 16% (ii) dysprosium oxide 30% holmiumoxide 10% erbiumoxide 25% 35 thulium oxide 4% ytterbium oxide 15% lutetium oxide 4% yttrium oxide 5% others 7% 40 It has been customary to use single rare earths, which have been laboriously and expensively purified, in order to ensure sharp spectral absorption peaks. This need has never been questioned, and we have found thatthe peaks forthe various rare earth or lanthanide diphthalocyanines, though different, are sufficiently close that mixtures give not only adequately clear but even more pleasing colours, especially mixtures of only'light' 45 (atomic number up to gadolinium) or (slightly more preferably) of only'heavy'(atomic number of terbium or greater) rare earths. This finding,that mixtures are perfectly satisfactory, can lead to a cost reduction, as regardsthe rare earth content, of two orthree orders of magnitude. Moreover, the colour intensity shows less declinewith use of the devicewhen mixedrare earth diphthalocya nines are used. A mixture of'heavy'APC2 further comprising either SnPCC12 or MPc is especially preferred, for strong and unusual colours.

In the manufacture of the electrochromic layer, it is useful to preheatthe subliming material first, to drive off impurities e.g. 1300C for 1-2 days; the conditions depend on the vacuum used, for example at 10-4 torra period of 1-2 minutes is suitable, as maybe checked by trial and error. It appears that such heating, in driving off impurities (such as polymers formed by non-metal-bearing phthalocyanine molecules), ensures less incorporation of such impurities in the layer, so improving the performance. Thus, after such heating, devices 55 can be laid down by sub] i mation, forming layers which need no subsequent treatment.

2 GB 2 177 516 A The inventionwill nowbedescribed bywayof example.

Asalready mentioned, mixturesof rare-earth diphthalocyanines are advantageous, and maybe synthesised asfollows:

One equivalent of a mixed rare-earth acetate (prepared by double decomposition from the starting mixed rare-earth material) is ground up with a slight excess of eight equivalents or phthalonitrile (1,2-d icya no benzene). This mixture isthen heated in an openvessel Q-4 hours at30WC) until averydarkmelt, appearing almost purple-black, is produced.The meltisthen allowedto coolto room temperature and ground to a fine powder. The powder is refluxed with acetic anhydride, filtered and the remaining powder washed with cold acetone.The required productremains undissolved atthisstage. It is extracted with dimethylformamide 1() solvent(DMF) andappliedto ashortcolumn (slurryin DMF) after first reducing the volume ofthe DMFextracts 10 by rotary evaporation (90-100'C). The column packing is70-230 B.S. meshsilica gel or activated neutral alumina (such as Brockman (Trade Mark) Grade 1).

The majority of remaining impurity is removed by eluting the column with methanol. The required product isthen obtained by unpacking the column and extracting with DIVIF or run through with trichloromethane, which dissolvesthe material. The extracts are rotary evaporated to dryness immediately and finally dried in an 15 oven (120'C, 4 hours) to give,with DIVIF, a dark blue solid micro-crystal line material, orwith CHC13 a green material. Atthis stage, the sample is now pure enough to make reasonable electrochromic devices. Yields are 10-15%.

Use of acetonitrile in place of DM17throughout can be more economical in terms of solvent, and moreover much of it can be recovered. In particular, the purification can be performed in one column using methanol as 20 the eluant. First a green band is eluted (waste). Then an azure blue band, the required product, is eluted, and is thus collected quantitatively.

Such mixtures can be dissolved in dimethylformamide and the solutions sprayed onto preheated tin-oxide-coated glass, butthis has not proved the best method of deposition. Sublimation of the solid mixture undervacuum onto tin-oxide-coated glass orgold-coated glass (asthe electronically conductive transparent 25 substrate) proved successful. Forthis purpose, itwas mixed with dichlorophthalocyaninato tine (IV) (PcSnC12).

The latter material acted both as a carrierto aid sublimation of the lutetium phthalocyanine and as a spacerin the crystal lattice of the deposited lutetium phthalocyanine, allowing thetwo rings of the latterto moveduring the activity of the device. The PcSriCI2 is itself electrochromic and undergoes a colour change from blueto purple at about 2.5 V. The sublimation sourceltarget spacing is adjusted by trial and error for best results. 30 Other rare-earth diphthalocyanines can also be produced as even films by vacuum sublimation. Asuitable film of area 64 CM2, pale blue, required 15 mg of compound.

This film, mounted on its glass substrate, is placed in a transparent containerwhich can befillewith a liquid electrolyte, which electrolyte however cannot contact the conductive layer on the glass. The electrolyte may be a polyhydric alcohol (e.g. ethylene glycol) or, more preferably, propylene carbonate/tetraethylammonium 35 fluoride; other suitable electrolytes are (i) 25% water, balance ethylene glycol and tetraethylammonium fluoride and (5) (less preferable) 25% water, balance ethylene glycol and lithium chloride, the ionic salt being present in about 5 weight%. The electrolyte does not have to be anhydrous, as has been recommended previously.

These electrolytes maybe applied instead to the film in gel form, e.g. stiffened with agar. Current may befed 40 to the electrolyte by a platinum wire probe. Colour change is localised to that part of the f i 1 m close to the probe; thus it is possible to'write'across the film by moving the probe across the gel.

The diphthalocyanine ring maybe substituted by sterically bulky groups (i. e. at leastthe size of chloro-). This gives inner parts of the molecule, in a crystal, more room to flex (on colour change) withough disturbing the crystal structure, and hence aids durability of adhesion of a sublimed film or a conductive glass substrate. 45 In a different embodiment, made as a curiosity, the following structure operated satisfactorilywhen the membrane was slightly damp.

GlassiRare Earth DPC1Membrane Electrolyte 1 Rare Earth 13PC1Glass The glass in both cases is conductively coated, with tin-oxide, between which coatings a potential can be applied. The membrane is of perfluorosulphonic acid, which is a solid- state electrolyte acting as an ion-exchanging medium, being "Nafion", a trademark of du Pont. The Nafion is prepared by boiling it successivelyfor 1 hour in a saturated aqueous solution of barium nitrate and in dilute sulphuric acid,to precipitate barium sulphate within the membrane to opacify it, otherwise the colours of the two Rare Earth DPC layers will conflict.

In a further embodiment, glass coated with a translucently thin interference layer of aluminium is steeped in electrolyte, the said electrochromic layer being applied into the steeped aluminium, and tin-oxide-coated glass being fixed overthe layer. The aluminium-coated glass may itself by replaced by (likewise steeped) tin-oxide-coated glass. The latter may be made by evaporating indium and stannous chloride in aqueous solution on the glass under an oxygen atmosphere.

A controller is connected to the conductive layers so as to apply a potential between them and thus to the 60 electrochromic material. This potential is limited to the range +2V to - 1V in this example, to avoid forcing the material into its purple colour. The controller acts also as a source of current,which flows corresponding tothe potential, providing a source of electrons.

f- 0 3 v 10 The actual colours obtained at the specified voltages on the specified materials areas follows:

bis(p htha locya n in ato) 1 uteti u m (111):

red green blue (purple bis(phtha 1 ocya n in ato)eu ro p i u m(] 11):

red +2V green + 1/2V blue -1V (purple -2V; GB 2 177 516 A 3 +2V + 1/2V -1V -2V; purple is not available in devices according to the invention, the controller being limited to a less negative potential).

purple is not available in devices according to the invention, the controller being limited to a less negative potential).

is The device according to the invention maybe used as an optical filter. One use of this filter would be in front 20 of a monochromatic television receiving successively frames in the three primary colours which add up to form a colour image; the filter would be showing those three colours synchronised with the respective images, to buildup the ful I colour image. Colours of various bandwidths are available in each of the colours red, green and blue. Where SnP'CC12 is present, a rich red tending to purple is obtainable, this colour not being otherwise available at voltages within the permitted range according to the invention. Where CoPc is a predominant 25 component, the colour sequence becomes red/magenta-grey-->green/blue blue This grey is effectively clear or neutral if the illu m ination level is sufficient.

The device may also be used for electrochromic data storage, for mounting on or incorporation in electrochromic credit cards (which will be scanned in a low-voltageverifier at the point of sale) and for other 35 security applications.

A device according to the invention in translucent form could have a colour image electrochromically written onto it, such device then being capable of projection in the same way as a photographic slide.

Another application for devices according to the invention is as su nglass lenses or fitters, which maybe altered in colour at the wearer's whim as often as desired, More general applications as optical wavelength 40 filters are of course possible.

Claims (11)

1. An electrochromic device comprising a conductive layer, bearing an electrochromic layer comprising a metal phthalocyanine capable of the colour changes red<->green<-->biue<-> purple, itself bearing an electrolytic 45 medium contacting the electrochromic layer, and a conductive layer overlying the electrolytic medium, at least one of the conductive layers being translucent, and a controller which applies a potential between thetwo conductive layers sandwiching the other layers, characterised in thatthe controller limits the potential between the conductive layers to within the range red<-->green<->blue, the device being characterised in thatthe electrochrom ic layer is a duplex or mixed layer of APC2 with at least one of M Pc, SnPCC12 and another APC2, 50 where A= any rare earth (including Sc, La and Y) or mixtures thereof, M= Ru, Fe, Zn or Co or mixturesthereof, and Pc = phthalocyanine.

2. An electrochromic device according to Claim 1, wherein the electrolytic medium is liquid orsolid.

3. An electrochromic device according to Claim 1 or 2, wherein one or both of the conductive layers are electronically conductive.

4. An electrochromic device according to Claim3, wherein the electronically conductive layer(s) is (are) hydrogen uranyl phosphate.

5. An electrochromic device according to any preceding claim, wherein the controller limits the potential to within the range +2Vto -1.OV.

6. An electrochromic device according to Claim 5, wherein the controller limits the potential to within the 60 range +2Vto -0.8V.

7. An electrochromic device according to any preceding claim, wherein thetranslucent electronically conductive layer is a doped tin-oxide-coated glass or a thin metal film.

8. An electrochromic device according to any preceding claim, in the electrochromic layer of which at least three rare earth elements accountfor at least 10 weight percent each of the total rare earths.

4 GB 2 177 516 A 4

9. An electrochromic device according to Claim 8, in which the electrochromic layer contains rare earth elements in substantially the p roportionsoccurring in a natural depositor mixtures of natural deposits.

10. An electrochromic device according to any preceding claim, before the manufacture of which the electrochromic material is preheated to drive off impurities, said material then being sublimed into position in 5 the device being manufactured.

11. An electrochromic device substantially as hereinbefore described.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (L1 K) Ltd, 11186, D8817356. Published by The Patent Office, 25 Southampton Buildings, London WC2A 'I AY, from which copies maybe obtained.