Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K9/00—Tenebrescent materials, i.e. materials for which the range of wavelengths for energy absorption is changed as a result of excitation by some form of energy
  • C09K9/02—Organic tenebrescent materials
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/15—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on an electrochromic effect
  • G02F1/1514—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on an electrochromic effect characterised by the electrochromic material, e.g. by the electrodeposited material
  • G02F1/1516—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on an electrochromic effect characterised by the electrochromic material, e.g. by the electrodeposited material comprising organic material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249978—Voids specified as micro
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]

Definitions

• the present invention relates to improvements in or relating to electrochromic systems.
• EC technology is not limited to the applications described above. Others include privacy glass, angle-independent high-contrast large-area displays, glare-guards in electronic devices, electronic scratch pads.
• a nanoporous-nanocrystalline film comprising a semiconducting metallic oxide having a redox chromophore adsorbed thereto.
• a “nanocrystalline film” is constituted from fused nanometer-scale crystallites.
• the morphology of the fused nanocrystallites is such that it is porous on the nanometer-scale.
• Such films which may hereinafter be referred to as nanostructured films, typically possess a surface roughness of about 1000 assuming a thickness of about 10 ⁇ m.
• the nanostructured films used in the present invention colour on application of a potential sufficiently negative to accumulate electrons in the available trap and conduction band states .
• ions are readily adsorbed/intercalated at the oxide surface permitting efficient charge compensation and rapid switching, i.e. the need for bulk intercalation is eliminated.
• the associated change in transmittance is not sufficient for a commercial device.
• a redox chromophore is adsorbed at the surface of the transparent nanostructured film which, when reduced, increases the extinction coefficient of an accumulated trapped or conduction band electron by more than an order of magnitude.
• the redox chromophore is effectively stacked as in a polymer film, while at the same time maintaining the intimate contact with the metal oxide substrate necessary to ensure rapid switching times.
• the redox chromophore may be any suitable redox chromophore and preferably comprises a compound of the general formula I
• X is a charge balancing ion such as a halide
• R* ⁇ is any one of the following:
• R2 is any one of the following: (a) (b) -CH2CH3
• R ⁇ is as defined above
• R3 is any of the formulae (a) to (f) given above under R2
• m is an integer of from 1 to 6, preferably 1 or 2
• n is an integer of from 1 to 10, conveniently 1 to 5.
• a particularly preferred redox chromophore is a compound of formula II, viz . bis- (2-phosphonoethyl ) -4 , 4 r -bipyridinium dichloride
• the semiconducting metallic oxide may be an oxide of any suitable metal, such as, for example, titanium, zirconium, hafnium, chromium, molybdenum, tungsten, vanadium, niobium, tantalum, silver, zinc, strontium, iron (Fe ⁇ + or Fe ⁇ + ) or nickel or a perovskite thereof.
• Ti ⁇ 2, O3, M0O3, ZnO and Sn ⁇ 2 are particularly preferred.
• the invention also provides an electrochromic system comprising: a first electrode disposed on a transparent or translucent substrate; a second electrode; an electrolyte; an electron donor; and an electrochromic layer comprising a nanoporous-nanocrystalline film according to the invention intermediate the first and second electrodes.
• the substrate is suitably formed from a glass or a plastics material. Glass coated with a conducting layer of fluorine doped tin oxide or indium tin oxide is conveniently used in the EC system of the present invention.
• the electrolyte is preferably in liquid form and preferably comprises at least one electrochemically inert salt optionally in molten form in solution in a solvent.
• suitable salts include hexafluorophosphate, bis-trifluoromethanesulfonate, bis-trifluoromethylsulfonylamidure , tetraalkylammonium, dialkyl-1 , 3-imidazolium and lithium perchlorate.
• Suitable molten salts include trifluoromethanesulfonate, 1 -ethyl, 3-methyl imidazolium bis-trifluoromethylsulfonylamidure and 1 -propyl- dimethyl imidazolium bis-trifluoromethylsulfonyl- amidure.
• Lithium perchlorate is particularly preferred.
• the solvent may be any suitable solvent and is preferably selected from acetonitrile, butyronitrile, glutaronitrile, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methyloxazolidinone, dimethyl-tetrahydropyrimidinone, ⁇ -butyrolactone and mixtures thereof.
• the electron donor is preferably a metallocene or a derivative thereof.
• the electron donor is preferably soluble in the electrolyte solvent. Ferrocene is particularly preferred.
• the invention is illustrated in the following Example.
• a 2.5 cm x 2.5 cm transparent nanostructured film consisting of a 4 ⁇ m thick layer of fused Ti ⁇ 2 nanocrystallites, was deposited on a 3.3 cm x 3.3 cm fluorine doped tin oxide on glass substrate (Glastron, Trade Mark) .
• a colloidal Ti ⁇ 2 dispersion was prepared by hydrolysis of titanium tetraisopropoxide .
• the average diameter of the initially formed crystallites (7 nm) was increased by autoclaving at 200 °C for 12 hours to 12 nm. Concentrating the autoclaved dispersion to 160 g/l and adding Carbowax (Trade Mark) 20000 (40% wt. equiv.
• a redox chromophore, bis- ( 2-phosphonoethyl )- 4, 4* -bipyridinium dichloride was prepared by adding 4, 4 1 -bipyridine (4.4 g) and diethyl-2-ethylbromo- phosphonate (15.0 g) to water (75 ml). The reaction mixture was refluxed for 72 h and allowed to cool.
• Figure 1 is a schematic view of the prepared film disposed on a substrate
• Figure 2 is a schematic view of the prepared electrochromic system including the film shown in Figure 1 ;
• Figure 3 is an exploded view of the electrochromic system of Figure 2.
• a first glass substrate 11 having a conductive layer 13 of fluorine doped tin oxide coated thereon.
• the exposed surface of the layer 13 is coated with a transparent nanostructured film 14 of Ti ⁇ 2 having a redox chromophore 15 adsorbed thereon.
• the redox chromophore 15 is bis- ( 2-phosphonoethyl ) -4, 4- bipyridinium dichloride prepared as described in the Example.
• Figs. 2 and 3 illustrate an EC system 10 according to the invention comprising the first glass substrate 11 with the layer 13 and the modified Ti ⁇ 2 film 14 shown in Fig.
• the second glass substrate 22 has a 0.25 cm border 24 of epoxy resin deposited thereon with a small gap 25, which is sealed after addition of the electrolyte/electron donor solution 16 described above.
• construction of the EC system 10 according to the invention is simple and utilises low-cost and non-toxic materials. These are particularly attractive features in the context of the large-scale manufacture of the EC system 10.
• a dielectric spacer In prior art electrochromic systems, a dielectric spacer must be included to isolate the electrodes electrically from each other. In the present invention, no such spacer is required because the solid particle nature of the nanocrystalline film provides for sufficient electrical isolation between the electrodes. In a commercial version of the EC system according to the invention, the absence of a spacer will have a positive impact on the manufacturing costs of the system.
• Figs. 4a and 4b A typical set of test results is shown in Figs. 4a and 4b. Specifically, shown in Fig. 4a are the absorption spectra in the low transmittance (LT) state, after 1 and 10 000 cycles. It will be observed that this spectrum, as expected, corresponds to that of the radical cation of the viologen moiety of the redox chromophore. It will also be noted that, in practice, this corresponds to an intense blue coloration of the EC system and that the extent of this coloration is not diminished after 10 000 cycles.
• LT low transmittance
• Figs. 5a and 5b are plots of the switching times (as defined above) for the same EC system. These are consistently between 0.9 s and 1.1 s.
• Nanostructured Ti ⁇ 2 films were deposited on the following conducting glass substrates : Indium tin oxide glass and fluorine doped tin oxide glass. No significant difference in the performance in the resulting EC system was detected.
• the time for which a film is fired is important for the following reason: If a film is fired for 1 h its porosity, and consequently its surface roughness, will be optimal. However, under the same conditions, film conductivity will be less than optimal due to incomplete sintering of the constituent nanocrystallites. Conversely, if a film is fired for 168 h, its connectivity, and consequently its conductivity, will be optimal.
• Figs. 6a and 6b Shown in Fig. 6a are the transmittance changes after 10 000 cycles on switching an EC system in which the constituent nanoporous-nanocrystalline film has been fired for the indicated time. The best performance is obtained for systems containing films that have been fired for 12 h. However, as can be seen from Fig. 6b, while there is improved colouring on going from 6 to
• Film thickness was 4 ⁇ m or less.
• the film firing temperature should be above about 400°C to remove the added Carbowax, the addition of which is essential to ensure a porous film, and less than 500°C to prevent conversion of anatase to rutile, the latter being a significantly poorer conductor. For these reasons the firing temperature was fixed at approximately 450°C.
• the substituent groups of the redox chromophore are irreversibly chemisorbed at Ti 4+ sites at the surface of the i ⁇ 2 nanocrystallites that constitute the nanoporous-nanocrystalline film.
• These substituent groups referred to as linker groups, serve, therefore, to irreversibly attach the redox chromophore to the surface of the nanoporous-nanocrystalline film.
• the density of these states (about 5 x 10 ⁇ 3 -Cm -2) , and the surface roughness, (about 1000 for a 4 ⁇ m film) provide the upper limit for the number of molecular amplifiers which may be adsorbed per unit geometric area.
• the redox chromophore unlike previous linkers, there is no discoloration of the modified film due to the existence of a charge transfer interaction between the occupied molecular orbitals of the linker and the available conduction band stated of the semiconductor substrate.
• the viologen moiety is stable with a large associated change in extinction for a one electron reduction.
• the redox chromophore may be readily modified to change its electrochemical and optical properties by use of the various substituents associated with R in the general formula. Each variation possesses different formal potentials and different colours upon being switched.
• the redox chromophore may be readily prepared with high yield in a pure form and, perhaps most importantly, adsorbed onto the Ti ⁇ 2 substrate from an aqueous solution.
• redox chromophore One parameter which was studied in respect of the redox chromophore was the extent of modifier adsorption in a given period. As would be expected, the redox chromophore is adsorbed to an increasing extent from more concentrated solutions in a shorter time. In practice, for a 0.02 mol.dm- ⁇ aqueous solution of the redox chromophore, close to maximum coverage is observed after about 6 h with only a small subsequent increase in coverage during the following week, see Figs. 7a and 7b. Some variability of this process is observed.
• the electrolyte solution consists of LiCl ⁇ 4 (0.05 mol.dm ⁇ 3) and ferrocene (0.05 mol.dm ⁇ 3) in ⁇ -butyrolactone (BL) (m.p. -45°C, b.p 204°C) .
• the concentration of the LiCl ⁇ 4 and ferrocene were systematically varied and the results of these studies are summarised in Figs. 8a, 8b, 9a and 9b.
• the disadvantage of the latter is that the ferrocene attacks the epoxy resin seal on the cell and results in device failure after about 48 h.
• Figure 4 (a) Absorption spectrum of the EC system 10 in low transmittance state. (b) Test result of modified EC system 10 in (a) after 1 and 10 000 test cycles.
• Figure 5 (a) Change in transmittance at 600 nm of the EC system 10 in Fig.4 during 10 000 test cycles. (b) Change in colouring and clearing times of the EC system 10 in (a) during 10 000 test cycles.
• Figure 6 (a) Change in transmittance at 600 nm of modified EC system 10 after 10 000 test cycles as a function of the firing time of nanostructured film, (b) Test results of modified EC system 10 in (a) after 10 000 test cycles.
• Figure 7 (a) Change in transmittance at 600 nm of modified EC system 10 after 10 000 test cycles as a function of the dying time of nanostructured film, (b) Test results of modified EC system 10 in (a) after 10 000 test cycles.
• Figure 8 (a) Change in transmittance at 600 nm of modified EC system 10 containing 0.20 mol.dm- ⁇ LiCl ⁇ 4 during 10 000 test cycles, (b) Change in colouring and clearing times of modified EC system 10 in (a) during 10 000 test cycles.
• Figure 9 (a) Change in transmittance at 600 nm of modified EC system 10 containing 0.05, 0.10 and 0.20 mol.dm ⁇ 3 ferrocene during 10 000 test cycles, (b) Change in colouring and clearing times of modified EC systems 10 in (a) during 10 000 test cycles.

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• Engineering & Computer Science (AREA)
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• Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)

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• 1998
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