WO2003038511A1

WO2003038511A1 - Method of dyeing en electrode consisting of a porous film which is applied to a substrate, and method of manufacturing an electrochemical system

Info

Publication number: WO2003038511A1
Application number: PCT/SE2002/001952
Authority: WO
Inventors: Henrik Pettersson; Tadeusz Gruszecki
Original assignee: Ivf Industriforskning Och Utveckling Ab
Priority date: 2001-10-29
Filing date: 2002-10-28
Publication date: 2003-05-08

Abstract

Method of dyeing an electrode consisting of a porous film which is applied to a substrate, where said substrate is, together with said film, immersed in a dyeing bath, and method of manufacturing an electrochemical system comprising the following method steps: application of a porous film to a first substrate; dyeing of said porous film in a dyeing bath; application of a counterelectrode to a second substrate; application of a sealing material to the first or second substrate in a position which is intended to surround said working electrode and counterelectrode after said first and second substrates have been pressed together; pressing together of said first and second substrates, sealing being made possible by said sealing material joining the first substrate together with the second substrate.

Description

TITLE

Method of dyeing an electrode consisting of a porous film which is applied to a substrate, and method of manufacturing an electrochemical system.

TECHNICAL FIELD

The following invention relates to a method of dyeing an electrode according to the preamble of Patent Claim 1 , and a method of manufacturing an electrochemical system according to the preamble of Patent Claims 13 and 18. The invention relates in particular to a method of dyeing an electrode which is intended for use as a working electrode and, where appropriate, a counterelectrode in an electrochemical system. The electrochemical system is preferably used as a solar cell or an electrochemical display, or alternatively as a combination of both solar cell and display.

BACKGROUND ART

In previously described methods of manufacturing electrochemical systems with porous electrodes, electrodes are dyed by being immersed one by one in a dyeing bath in order to adsorb dye molecules. Examples of electrochemical systems where electrodes are dyed are given in EP 333641 , which describes a solar cell, and WO 98/35267 and WO 01/27690, which describe displays. Providing sufficient dyeing for the purpose is relatively time-consuming. An example of displays which are dyed is described in

"Nanostructured Ti0₂ Semiconductor Electrodes Modified with Surface

Attached Viologens: Applications for Displays and Smart Windows", Hagfeldt et al, SPIE vol. 2531. Another method of manufacturing electrochromic displays with porous electrodes is described in WO 98/35267. According to this reference, the dyeing goes on for 6 hours. According to the manufactuπng method described in "Ultra fast electrochromic windows 511

based on redox-chromophore modified nanostructured semiconducting and conducting films", D. Cummins, J. Phys. Chem. B, 2000, 104, pp 11449- 11459, the dyeing lasts 6 hours; according to the manufacturing method described in "Electric-paint displays with carbon counter electrodes", M.O.M. Edwards et al, Electrochimica Acta 2001 , 46 p 2187, the dyeing lasts 24 hours, and according to Bonhόte et al's Thin Solid Films 350 (1999) 269- 275, the dyeing continues for 12-15 hours. The dyeing time has been found to be a critical problem in the conversion of manufacturing methodology from experimental trials to industrial scale.

Other known art for dyeing electrochemical systems is disclosed in WO 96/29716. According to the method described, the electrodes are dyed using a colloidal solution by a mixture of electrolyte and colloidal colouring particles being pumped into a partly sealed electrochemical system. However, the method has the disadvantage that the dyeing procedure is complicated and there is a risk of inhomogeneous dyeing of the electrode.

DISCLOSURE OF INVENTION

The object of the invention is to provide a method of dyeing by immersing electrodes in a bath, which method considerably reduces dyeing time while maintaining or improving the degree of dyeing and also permits a homogeneous dyeing result. This object is achieved by a dyeing method according to the characterizing part of Patent Claim 1. By exposing the porous film located on the substrate to a pulsating flow in the dyeing bath, rapid uniform dyeing of the electrode is achieved. The method makes it possible to obtain a dyeing time for porous displays of down to less than 30 minutes, where appropriate less than 10 minutes. The dyeing of porous solar cells is usually quicker than the dyeing of displays, the method providing a corresponding reduction in dyeing time. The porous film consists of, for example, a nanostructured film of the type described in A. Hagfeldt, M. 8511

Gratzel, Ace. Chem. Res. 33, 269 (2000). According to a preferred embodiment of the invention, the pulsating flow is brought about by said substrate being vibrated in said dyeing bath. The vibration is suitably brought about by a set of substrates being mounted on a rack which is immersed in the bath and vibrated. Testing has shown that vibration carried out with an amplitude in excess of 0.05 mm, preferably roughly 0.3 mm, and a frequency in excess of 40 Hz, preferably between 50 and 60 Hz, results in rapid uniform dyeing.

In an especially preferred embodiment of the invention, one or more substrates are attached to a rack which is immersed in a dyeing bath. In this case, said rack is inert with regard to said dyeing bath. In a particularly preferred embodiment, the rack is used in a preceding process step in which said nanostructured film is sintered. In this case, the rack is suitably temperature-resistant to roughly 450°C. This affords a possibility for rapid processing of a great many substrates at the same time as the risk of contamination of the nanostructured film or the substrates is reduced.

In an especially preferred embodiment, the film is structured before said sintering takes place. Structuring means that the film is divided into a number of mutually separate regions.

The invention also relates to a method of manufacturing an electrochemical system comprising the following method steps: application of a porous film to a first substrate; dyeing of said porous film in a dyeing bath; application of a counterelectrode to a second substrate; application of a sealing material to the first or second substrate in a position which is intended to surround said working electrode and counterelectrode after said first and second substrates have been pressed together; heating and pressing together of said first and second substrates, sealing being made possible by a plastic layer forming part of said sealing material joining the first substrate together with the second substrate, use being made of the dyeing method according to the invention.

The porous film consists of, for example, a nanostructured film of the type described in A. Hagfeldt, M. Gratzel, Ace. Chem. Res. 33, 269 (2000).

The invention also relates to a method of manufacturing a sealed monolithic electrochemical system, which method comprises the following method steps: application of electrolyte to a pattern comprising a porous structure and located on a substrate, which structure constitutes at least one monolithic electrochemical cell and comprises a working electrode, an insulating layer and a counterelectrode; application of a sealing material surrounding said porous structure to form at least one sealed monolithic electrochemical system comprising a front plane consisting of said substrate and the porous structure and a rear plane consisting of the sealing material; - adsorption of an active substance to the porous structure; sealing of the monolithic electrochemical system, where said adsorption of the active substance to the porous structure is effected by the porous structure being exposed to a pulsating flow in a bath containing the active substance.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will be described in greater detail below with reference to accompanying drawing figures, in which

Fig. 1 shows diagrammatically a display in cross section; Fig. 2 shows diagrammatically a display in cross section according to an alternative embodiment of the invention; Fig. 3 shows diagrammatically a display in cross section according to a second alternative embodiment of the invention;

Fig. 4 shows a plan view from above of a display;

Fig. 5 shows a cross section along the section line I-l in Figure 4;

Fig. 6 shows an embodiment of conducting tracks which have the same resistance;

Fig. 7 shows a flow diagram of a method of manufacturing a display;

Fig. 8 shows in cross section a sealed monolithic electrochemical system in the form of solar cells comprising a plurality of cells;

Fig. 9 shows a second embodiment of a monolithic electrochemical system in the form of solar cells, where series connection between a number of cells is effected by alternate interconnection of end walls;

Fig. 10 shows a set of cells applied to a substrate;

Fig. 11 shows a flow diagram of the sealing process of the monolithic electrochemical system;

Fig. 11 A shows a flow diagram of a set of part processes in the sealing process shown in Figure 4; Fig. 12 shows the pressing-together of an electrochemical system by means of a flexible membrane;

Fig. 13 shows a soft pressing head; Fig. 14 shows a two-chamber system for pressing an electrochemical system together;

Fig. 15 shows an electrochemical system with a two-part sealing material, and

Fig. 16 shows an electrochemical system with the outer edges pressed together hard.

MODE(S) FOR CARRYING OUT THE INVENTION

According to the above, the invention relates to a method of dyeing an electrode consisting of a nanostructured film which is applied to a substrate, where said substrate is, together with said film, immersed in a dyeing bath, the nanostructured film located on said substrate being exposed to a pulsating flow in the dyeing bath.

In a preferred embodiment, a pulsating flow is brought about by said substrate being vibrated in said dyeing bath.

In another preferred embodiment of the invention, the pulsating flow is turbulent.

In a first embodiment of the invention, the dyeing method is used in connection with manufacturing an electrochemical system where the following process steps are carried out: application of a nanostructured film to a first substrate; 8511

dyeing of said nanostructured film in a dyeing bath; application of a counterelectrode to a second substrate; application of a sealing material to the first or second substrate in a position which is intended to surround said working electrode and counterelectrode after said first and second substrates have been pressed together; pressing together of said first and second substrates, sealing being made possible by the sealing material joining the first substrate together with the second substrate.

In a second embodiment of the invention, the dyeing method is used in connection with manufacturing an electrochemical system where the following process steps are carried out: application of electrolyte to a pattern comprising a porous structure and located on a substrate, which structure constitutes at least one monolithic electrochemical cell and comprises a working electrode, an insulating layer and a counterelectrode; application of a sealing material surrounding said porous structure to form at least one sealed monolithic electrochemical system comprising a front plane consisting of said substrate and the porous structure and a rear plane consisting of the sealing material; adsorption of an active substance to the porous structure; sealing of the monolithic electrochemical system.

A number of illustrative embodiments of electrochemical systems constituting displays which have been manufactured using the method according to the invention are given in connection with Figures 1-7.

A number of further illustrative embodiments where the electrode is included in a monolithic structure intended to be used as a solar cell are given in connection with Figures 8-16. Figure 1 shows an electrochromic display 1 in cross section. The display comprises a first substrate 2 bearing a conductive pattern 3. The substrate 2 usually consists of a relatively rigid non-conductive material, for example glass, but it is possible to make the substrate 2 from a non-conductive flexible material, for example a plastic material. The conductive pattern 3 is preferably made from a layer of conductive or semiconductive material which is borne by the substrate 2, material being machined away to form a conductive pattern 3. According to an embodiment, use is made of glass plates coated with a thin layer of doped SnO₂.

The conductive pattern 3 bears a working electrode 4. The working electrode 4 consists of an electrically conductive or semiconductive porously nanostructured film. Porously nanostructured films as electrodes in electrochromic displays are described by A. Hagfeldt, L. Waldner and M. Gratzel in Proc. Soc. Photo-Opt. Instrum. Engn. 2531 , 60 (1995) and by P. Bonhόte, E. Gogniat, F. Campus, L. Waldner and M. Gratzel in Displays 20 (1999) 137-144.

The working electrode and/or the counterelectrode preferably consist(s) of an electrically conductive or semiconductive porously nanostructured film which is manufactured from a semiconductive metal oxide, preferably an oxide or peroxide of one or some of the following metals: titanium, zirconium, hafnium, chromium, molybdenum, tungsten, vanadium, tantalum, silver, zinc, tin, strontium, iron, cobalt, wolfram, ruthenium, niobium or nickel.

In the porously nanostructured film, electrochromic dye molecules, for example viologens, are adsorbed. Electrochromic dye molecules are adapted so as to assume an oxidized and a non-oxidized state depending on the voltage applied between the working electrode and the counterelectrode, the appearance of the electrochromically active molecules in the oxidized state differing from the appearance in the non-oxidized state. A fuller description of electrochromic materials is given in Cummins, D. et al, J. Phys. Chem. B104, 11449-11459.

The display 1 also comprises a second substrate 5 bearing a layer 6 of conductive or semiconductive material. The substrate 5 usually consists of a relatively rigid non-conductive material, for example glass, but it is possible to make the substrate 5 from a non-conductive flexible material, for example a plastic material. According to an embodiment, use is made of glass plates coated with a thin layer of doped SnO₂. The second substrate 5 bears a counterelectrode 7. The counterelectrode is preferably coated with a contrast layer 8. The contrast layer 8 has an appearance which forms a contrast to the appearance of said working electrode when said electrochromically active molecules are in one of said oxidation states. According to one embodiment of the invention, the contrast layer has a visual appearance which corresponds closely to the appearance of the working electrode when said electrochromically active molecules, which have been adsorbed on the working electrode, are in their other oxidation state. According to one embodiment of the invention, use is made of a white contrast layer and electrochromically active molecules which are blue in their one state and transparent in their other state. In the transparent state, the working electrode, which in this case is essentially the same colour as the contrast layer, is visible. When the electrochromically active molecules are blue, the working electrode contrasts with the contrast layer.

According to an alternative embodiment, the working electrode is transparent when said electrochromically active molecules are in one of their oxidation states and visible in the other oxidation state. This is brought about by making the working electrode sufficiently thin, preferably with a thickness of less than 5 μm. The particles which form the nanostructured film should also be sufficiently small, that is to say preferably smaller than 5 nm. In a case where the electrode itself has the necessary contrast, the contrast layer 8 consists of the surface layer of the counterelectrode. The statement that the counterelectrode comprises a contrast layer thus means on the one hand, according to a first embodiment, that a contrast layer is applied to the counterelectrode, and on the other hand, according to a second embodiment, that the contrast layer is integrated in the counterelectrode, or alternatively that the counterelectrode itself has essentially the same visual appearance as the working electrode when the electrochromically active molecules are in one of their oxidized states.

The contrast layer 8 is designed to have essentially the same visual appearance as the working electrode when the electrochromically active molecules are in one of their oxidized states. In order to achieve this, according to one embodiment of the invention, the working electrode and the contrast layer have essentially the same particle composition. This means that the contrast layer has a particle composition which corresponds closely to the working electrode. According to an embodiment, however, the contrast layer is treated in order to ensure that the electrochromic material cannot be adsorbed on the contrast layer.

The purpose of the counterelectrode 7 is to provide a voltage field when a change in colour of electrochromically active molecules adsorbed on the working electrode 4 takes place. This means that the counterelectrode can be made in a number of alternative ways. According to one embodiment, use is made of a counterelectrode made of metal, for example zinc. If use is made of a counterelectrode made of metal, it is necessary to use an electrolyte which contains a redox pair which precipitates the metal on charging of the electrochromically active molecules, which are located on the working electrode, and metallizes on discharging. Electrochromic displays where use is made of a counterelectrode made of zinc are described in the patent US 6067184. According to a preferred embodiment of the invention, use is made of a capacitively chargeable electrode as the counterelectrode 7. Capacitively chargeable counterelectrode means a counterelectrode which is charged without chemical processes. These electrodes use an electrolyte consisting of, for example, an organic solvent with a salt, for example a lithium salt. An alternative to using a solvent is to use an electrolyte consisting of a molten salt. The electrolyte is inert in the respect that no charge transfer process takes place in the form of redox chemistry between the electrodes and the salt. The charge transfer in the inert electrolyte occurs instead by ions moving towards the films and compensating for the charges which the counterelectrode and the viologen molecules take up. This means that, when the viologen molecules are charged, they are charge-compensated with the ions, for example lithium ions. In the same way, the counterelectrode is charge-compensated with Li ions when it is charged.

In a case where use is made of a capacitively chargeable counterelectrode, it preferably consists of an electrically conductive or semiconductive porously nanostructured film. According to a preferred embodiment, this film is made from a semiconductive metal oxide, preferably an oxide or peroxide of one or some of the following metals: titanium, zirconium, hafnium, chromium, molybdenum, tungsten, vanadium, tantalum, silver, zinc, tin, strontium, iron, cobalt, wolfram, ruthenium, niobium or nickel. A carbon electrode can also be used as a capacitively chargeable electrode.

The display also comprises a sealing material 9 which connects the first substrate 2 to the second substrate 5 and comprises an inner edge 10 which defines an inner space 11. The inner space 11 contains an electrochemically inert electrolyte which separates the working electrode from the counterelectrode. In a case where use is made of a counterelectrode made of metal, the inner space 11 can preferably, as shown in Figure 2, be divided into a first part 12 which adjoins the working electrode 4 and contains a chemically inert electrolyte, and a second part 13 which adjoins the counterelectrode 7 and contains an electrolyte with a redox pair. The first part 12 is separated from the second part 13 via a barrier layer 14.

The chemically inert electrolyte is preferably liquid and preferably comprises an electrochemically inert salt which is either present in molten form or dissolved in a solvent.

Suitable molten salts are, for example, dialkylimidazolinium trifluoromethanesulphonate and dialkylimidazolinium bis(trifluoromethylsulphonyl)amide.

Suitable salts are composed of cations such as ions of lithium, sodium, potassium, magnesium, tetraalkylammonium and dialkylimidazolinium, and anions such as ions of chloride, perchlorate, trifluoromethanesulphonate, bis(trifluoromethylsulphonyl)amide, tetrafluoroborate and hexafluorophosphate.

Suitable solvents are, for example, water, acetonitrile, methoxyacetonitrile, butyronitrile, propionitrile, 3-methoxypropionitrile, glutaronitrile, gamma- butyrolactone, propylene carbonate, ethylene carbonate, dimethyl sulphoxide, dimethylformamide, dimethylacetamide and N- methyloxazolidinone and mixtures thereof.

The sealing material 9 preferably consists of a plastic layer which is joined together with the first substrate 2 and the second substrate 5. If use is made of a thermoplastic, the plastic is heated to a temperature exceeding the transition temperature of the plastic. The substrates are pressed against one another while being heated. In a preferred embodiment, the substrates are subjected to a vacuum pressure during the joining-together process, the substrates being placed in a mobile pressure chamber and the pressure difference between the vacuum pressure in the pressure chamber and the surrounding atmosphere pressing the substrates together. The substrates are preferably placed under a flexible membrane which forms an air pocket which is subjected to vacuum pressure. In a preferred embodiment, the sealing material is also used as a spacing element for the first substrate 2 and the second substrate 5 and ensures that the working electrode 4 and the counterelectrode 7 with its contrast layer 8 do not touch one another. Preferably, only the sealing material is used as a spacing element without separate spacing elements having to be added, which makes the manufacturing process considerably easier. In preferred embodiments of the invention, use is made of a working electrode which has a thickness of between 1 and 20 μm, a contrast layer with a thickness of between 0 and 30 μm and a counterelectrode with a thickness of between 5 and 50 μm. The contrast layer can be omitted if the counterelectrode has a visual appearance which corresponds sufficiently closely to one of the oxidation states of the working electrode. Visual appearance means colour, degree of saturation and transparency. This means that, altogether, the electrodes have a thickness of between 6 and 100 μm. The distance between the substrates after closing should thus be between 10 and 200 μm. To this end, use is then made of a plastic film with a thickness before compression of between 25 and 300 μm. In a preferred example, the combined layer thickness is 40 μm, and a 100 μm thick plastic film is fused and compressed to a thickness of roughly 60 μm. This means that use is preferably made of a plastic film which has a thickness in excess of twice the thickness of the counterelectrode, contrast layer and working electrode, the film being compressed, during joining together, to a thickness of between 50 and 80% of the original thickness of the plastic film. The thickness of the plastic film is preferably between 2.2 and 3.0 times the thickness of the counterelectrode, contrast layer and working electrode.

In one embodiment of the invention, use is made of a contrast layer which is designed as an electrical insulator. In this case, the display can be designed in accordance with Figure 3. Figure 3 shows a display 1 , a first substrate 2 bearing a conductive pattern 3 forming a set of separate regions 20 coated with a porously nanostructured film constituting the working electrode 4. Above the working electrode 4 is a layer 8 of electrically insulating material which at the same time constitutes an applied contrast layer. The counterelectrode 7 is then located on the contrast layer 8. A monolithic structure is preferably built up on one of the substrates, which comprises the counterelectrode, the contrast layer and the working electrode. The display 1 also comprises a conductive layer 15 which is arranged so as to afford a good electrical connection for the counterelectrode. The conductive layer can consist of a conductive or semiconductive film which is applied to the counterelectrode but can also comprise conductors in the form of, for example, a thin metal mesh. Finally, the display is encapsulated by a sealing material 16. In this case, the sealing material preferably consists of a plastic film which is applied to the substrate in the presence of heat and pressure. In this case, the electrolyte can be applied before sealing.

Figure 4 shows an embodiment of a display 1 in a plan view from above. The display comprises a set of separate regions 20 coated with said electrically conductive or semiconductive porously nanostructured film constituting the working electrode 4. In the case shown, the working electrode 4 comprises a matrix of 7x5 separate regions. The separate regions are located inside an inner edge 10 of a sealing material 9. Each region 20 is also connected via conducting tracks 21 to a contact device 22 which has ports for voltage connection. Also shown is the duct 23 which connects the inner space 11 in the display to the surrounding environment. The duct is preferably formed by the plastic film which forms the sealing material 9 having a slit. The slit suitably has a width of less than 2 mm. The duct 23 is closed by a closure 24, which can preferably consist of adhesive, after the electrolyte has been supplied to the display.

Figure 5 shows a display in cross section along the section line I-l in Figure 4. The figure shows a first substrate 2 bearing a conductive pattern comprising a set of separate regions 20 which are coated with a working electrode 4. The conductive pattern also comprises conducting tracks 21 which connect said regions 20 to a contact device (not shown). The display also comprises a second substrate 5 which has a conductive layer 6 and bears a counterelectrode 7. A contrast layer 8 is also arranged on said counterelectrode 7.

Figure 6 shows an embodiment of conducting tracks within a region which corresponds to the region II in Figure 4. This figure shows a conductive pattern 20 with conductive tracks 21 which are designed so as, when the conductive pattern has a given voltage level applied to it, to allow a homogeneous charge transfer per unit area to said set of separate regions of the working electrode. Homogeneous charge transfer per unit area means that the charge transfer per unit area deviates by less than 20% between that region within said set of regions which has the highest charge transfer per unit area and that region within said set of regions which has the lowest charge transfer per unit area. The relevant unit area consists of the surface area of the regions which are coated with porous structure. This is due to the fact that a certain quantity of charge per unit area has to be supplied or dissipated in order to bring about a potential which is sufficient for change. This means that regions of the same size should be connected to voltage ports at the same potential via conducting tracks which have the same resistance. For regions of larger area, the resistance should be lower. Generally, for the resistance R of a conducting track of a region with an area 8511

16

A, R^*A is ideally invariant for all the different regions of the display. The conducting tracks for one and the same display are preferably designed so that (R^*A)min/(R*A)max>0.8.

According to a preferred embodiment, this homogeneous level is brought about by the selection of the length and/or thickness of the conducting tracks. Figure 6 shows this by the conducting tracks 211-219 having been designed with the same length between the region and a voltage port (not shown).

According to an alternative embodiment, said homogeneous charge transfer is brought about by resistance means being applied between a voltage source for addressing the separate regions 20 and the separate regions 20. The resistance means are preferably integrated on said first substrate.

Figure 7 shows a flow diagram of a method of manufacturing an electrochromic display of the type referred to above. In a first set of method steps 30-33, the working electrode is formed on a first substrate. In a second set of method steps 40-43, the counterelectrode is formed on a second substrate. The working electrode and the counterelectrode are assembled in a common set of method steps 50-51. Filling with electrolyte is then performed in a method step 60, after which sealing is finally carried out in a method step 70.

According to a preferred embodiment, the manufacture of the working electrode takes place as follows: in a first method step 30, a number of separate regions 20 are screen-printed on a substrate with a paste which, after sintering, forms an electrically conductive or semiconductive porously nanostructured film constituting the working electrode 4. The paste is then sintered in a second method step 31. Sintering is carried out by heating the substrate and the paste to 450°C for 30 minutes. Then, in a third method step 32, a conductive pattern is formed, with conducting tracks 21 and separate regions 20 which can be addressed separately via said conducting tracks, by a thin conductive layer 3 formed on the substrate being machined away in regions which surround the conductive pattern. This machining away is preferably Uarried out by means of a laser. In a fourth method step 33, the electrically conductive or semiconductive porously nanostructured film is dyed in a bath containing electrochromically active molecules.

According to the invention, dyeing is effected by the substrate bearing the porous film being exposed to a pulsating flow in a dyeing bath. In a preferred embodiment, the pulsating flow is brought about by said substrate being vibrated in said dyeing bath. In an alternative embodiment, the pulsating flow is brought about by the liquid in said dyeing bath being pulsated. In another alternative embodiment, the pulsating flow is brought about by the vessel which accommodates said dyeing bath being vibrated.

According to a preferred embodiment, the dyeing is effected by a set of finished substrates being mounted in a rack made of a material which is inert with regard to said bath, for example titanium or Teflon. According to the invention, dyeing is then carried out while vibration takes place. According to a suitable method, the vibration is carried out with an amplitude in excess of 0.3 mm and a frequency in excess of 40 Hz. In a preferred manufacturing method, the rack is attached to a vibrator. This procedural step reduces the process time and produces more homogeneously dyed substrates. Moreover, substrates with a greater degree of purity are obtained. After dyeing, the substrates are rinsed and dried.

In a fifth method step 40, the counterelectrode is screen-printed on a substrate. In a sixth method step 41 , the substrate is dried, suitably at 125°C for 10-30 minutes, after which a contrast layer is screen-printed on the counterelectrode in a seventh method step 42. The seventh method step 8511

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does not have to be included if the counterelectrode has a visual appearance which corresponds sufficiently closely to the visual appearance of the working electrode in one of the oxidation states of the electrochromically active molecules. In an eighth method step, the counterelectrode is sintered by the substrate being heated to 450°C for 30 minutes.

In a common set of method steps 50-51 , the substrates are assembled to form a display unit. In a ninth method step 50, a sealing material 9 is positioned, which, with an inner edge 10, surrounds a set of separate regions 20 coated with an electrically conductive or semiconductive porously nanostructured film constituting the working electrode 4. The sealing material preferably has a duct which connects the inner space 11 to the surrounding environment, in which case filling with electrolyte can be performed after sealing. The sealing material, which preferably consists of a plastic film, is preferably located on the substrate bearing the working electrode as this allows easier centring of the inner edge of the sealing material around said set of separate regions. In a tenth method step 51 , the substrates are pressed against one another while being heated, the first and the second substrate being joined together to form a unit. In a preferred embodiment, the substrates are subjected to a vacuum pressure during the joining-together process, the substrates being placed in a mobile pressure chamber and the pressure difference between the vacuum pressure in the pressure chamber and the surrounding atmosphere pressing the substrates together. The substrates are preferably placed under a flexible membrane which forms an air pocket which is subjected to vacuum pressure. In a preferred embodiment, the sealing material is also used as a spacing element for the first substrate 2 and the second substrate 5 and ensures that the working electrode 4 and the counterelectrode 7 with its contrast layer 8 do not touch one another. Preferably, only the sealing mateπal is used as a spacing element without separate spacing elements having to be added, which makes the manufacturing process considerably easier. In preferred embodiments of the invention, use is made of a working electrode which has a thickness of between 1 and 20 μm, a contrast layer with a thickness of between 0 and 30 μm and a counterelectrode with a thickness of between 5 and 50 μm. The contrast layer can be omitted if the counterelectrode has a visual appearance which corresponds sufficiently closely to one of the oxidation states of the working electrode. This means that, altogether, the electrodes have a thickness of between 6 and 100 μm. In order that the working electrode and the counterelectrode with its contrast layer do not touch one another, the distance between the substrates after closing should be between 10 and 200 μm. To this end, use is then made of a plastic film with a thickness before compression of between 25 and 300 μm. In a preferred example, the combined layer thickness is 40 μm, and a 100 μm thick plastic film is fused and compressed to a thickness of roughly 60 μm. This means that use is preferably made of a plastic film which has a thickness in excess of twice the thickness of the counterelectrode, contrast layer and working electrode, the film being compressed, during joining together, to a thickness of between 50 and 80% of the original thickness of the plastic film. The thickness of the plastic film is preferably between 2.2 and 3.0 times the thickness of the counterelectrode, contrast layer and working electrode.

In an eleventh method step 60, the inner space 11 is filled with electrolyte by electrolyte being allowed to pass through the duct 23 which connects the inner space 11 in the display to the surrounding environment. The display is preferably filled by utilizing vacuum pressure where the display is subjected to vacuum pressure, after which the duct 23 is exposed to electrolyte which is subjected to a higher pressure, preferably atmospheric pressure. The positive pressure of the surrounding environment will then ensure that the display is filled with electrolyte. In a preferred embodiment, use is made of the vacuum pressure which is used in the joining-together process, which reduces the risk of contamination of the interior of the display.

In a twelfth method step 70, the display is then closed by the duct 23 being closed. In one embodiment, this is effected by a drop of adhesive being applied at the opening of the duct, a closure 24 being formed.

An electrochemical system in the form of a solar cell arranged as a monolithic structure is described below.

In Figure 8, a sealed monolithic electrochemical system 1 comprising a number of cells 2A, 2B, 2C is shown in cross section. Each cell 2A, 2B, 2C constitutes a porous structure and comprises a working electrode or photoelectrode 6, an insulating layer 7 and a counterelectrode 8. The cells 2A, 2B, 2C or the porous structures are applied to a substrate in a pattern. The pattern is surrounded by an edge which consists of an inner edge which separates the individual cells from one another and an outer edge which surrounds a group of cells which constitute said pattern. An example of such a system is described in WO 97/16838, the description of which is incorporated in its entirety in this description.

The monolithic electrochemical system 1 comprises working electrodes in the form of nanoporous photoelectrodes 6 constructed on a substrate. The substrate comprises a supporting layer 3 of completely or partly transparent material and also a thin conductive layer 4 which is applied to the supporting layer 3. The supporting layer 3 can be made of glass or plastic, in which case the photoelectric system can be designed somewhat flexibly. Each photoelectrode 6 is positioned on the thin conductive layer. The conductive layer is divided into a pattern of thin dividing lines 5 where the conductive layer has been removed, a set of mutually insulated cells thus being formed. The pattern preferably consists of a set of elongate rectangles, but can of 511

21

course be designed in an arbitrary manner, although preferably in a surface- covering pattern. An example of a suitable pattern is shown in Figure 9, which shows an electrochemical system 2 seen from above.

According to the embodiment shown in Figure 9, the pattern comprising the porous structure is designed as a set of rectangular cells 2A-2D. The cells are positioned long side to long side. In this case, the outer edge is formed by a rectangle 40 which surrounds the set of cells and an inner edge is formed by a set of parallel lines 41 which separate the cells from one another. A group of cells is series-connected in a known manner, for example as indicated below. Other surface-covering patterns are also conceivable, for example a set of hexagons. However, the preferred embodiment with rectangles allows simple series-connection between cells. In order to bring about series-connection between cells in a simple manner, the plies of the cell are arranged in the embodiment shown in Figure 8, where cells are interconnected side to side as follows: the photoelectrode 6 extends up to one edge of the conductive layer 4 of the cells while another edge is left free. The dividing lines 5 are designed with such a width that there is no risk of the photoelectrode coming into contact with an adjacent cell.

The photoelectrode 6 is covered by a porous ply of an insulator 7, which extends over one edge of the conductive layer and insulates the photoelectrode 6 from a porous counterelectrode 8 which is located on the insulator 7. The insulator 7 can preferably also constitute a diffuse reflector which reflects light which has passed through the photoelectrode 6 without being absorbed in it, the degree of absorption of the system being increased.

In a preferred embodiment, the counterelectrode 8 is applied in such a manner that it essentially covers the insulator 7 and extends up to that layer on an adjacent cell not covered by an insulator 7. In this manner, series- connected cells are created, contacting 11 , 12 having to be provided only for the first and the last in an interconnected group of cells.

The counterelectrodes 8 in the respective cells are separated by an interspace 9. It is important that the cells are insulated from one another so that electrolyte cannot leak out from the electrodes or the insulator and bring about contact between electrodes in different cells. In order to ensure that this does not occur, the interspace can be filled with an insulating material. In a preferred embodiment, this insulating material consists of parts of the sealing material 10 which is pressed into the interspace 9.

Before the electrochemical system 1 is sealed, an active substance, for example a light-absorbing dye or an electrochromic material, is adsorbed to the photoelectrode 6. According to the invention, said adsorption of the active substance to the porous structure is effected by the porous structure being exposed to a pulsating flow in a bath containing the active substance.

According to a preferred embodiment, the pulsating flow is brought about by said substrate being vibrated in said bath. According to an alternative embodiment, the pulsating flow is brought about by the liquid in said bath being pulsated. This pulsation is brought about by, for example, stirring or shaking. According to another alternative embodiment, the pulsating flow is brought about by a vessel which accommodates said bath being vibrated. This vibration can be brought about by the vessel being vibrated or rotated. According to another preferred embodiment, the pulsation is carried out with an amplitude exceeding 0.2 mm and a frequency exceeding 40 Hz.

Furthermore, electrolyte is supplied to the porous structure consisting of photoelectrode 6, insulator 7 and counterelectrode 8. In a preferred embodiment, the electrolyte is supplied by means of a printing process, 8511

suitably screen printing. By using this method, the correct quantity of electrolyte can be supplied, so that the porous structure in each cell is filled but does not become overfull. If too much electrolyte is supplied, there is a risk that electrolyte will run out in the interspace 9 between the cells, giving rise to a risk of short-circuiting between the cells. In another embodiment, the electrolyte is supplied by the porous structure being allowed to adsorb electrolyte during a dispensing process.

In another embodiment, which is shown in Figure 10, series-connection between a number of cells 2A, 2B and 2C is effected by end walls of the cells being connected as described below. In this embodiment, the cells are in a pattern in which each cell is rectangular and has two long sides and two end walls. The cells are formed on a substrate with a ply 4 of conductive material. The cells are insulated from one another by tracks 5 of the conductive material being etched away. Each cell comprises an anode 6 made of porous material, and where appropriate this anode consists of a light-sensitive photoelectrode. An insulator 7 made of porous material is applied to the anode 6. A counterelectrode 8 made of porous material is applied to said insulator 7. In order to bring about series-connection between the cells, the cells are connected in such a manner that the anode of one cell is connected to the counterelectrode of the next cell. In the embodiment shown in Figure 8, this is effected by the etched-away tracks 5 being designed in a zig-zag pattern, which produces an L-shaped pattern of conductive surfaces consisting of a set of Ls, having a back 13 and a foot 14, facing one another so that the protuberance from one L tends to be located directly adjacent to the next L. The photoelectrode 6 is located entirely within the back, that is to say the elongate part, of an L-shaped area. The insulator 7 is positioned so that it covers the photoelectrode and extends in slightly onto the foot 14 of the L-shaped area of an adjacent cell, that is to say the insulator 7 bridges the etched-away track 5 within an area corresponding to the width of the cell. Series-connection is effected by the counterelectrode 8 of one cell being allowed to extend into the conductive layer 4 of an adjacent cell. In the embodiment shown in Figure 10, this is brought about by virtue of the counterelectrode 8 extending into the foot 14 of an L-shaped area of an adjacent cell. Figure 10 also shows an encapsulating material 10A and a cover layer 10B which together constitute a sealing material 10. In a preferred embodiment, the encapsulating material 10A consists of an adhesion ply 19A, and the cover layer 10B consists of an adhesion layer 19B and a barrier layer 19C.

After the electrolyte has been supplied to the porous structure, the electrochemical system 1 is sealed by means of a sealing material 10 according to the invention using a method described below in connection with Figure 11.

In a first method step 20, a sealing material 12 is applied to the substrate 3 in such a manner that it completely covers the cells 2A-2C and their porous structure to form a sealed monolithic photoelectric system comprising a front plane consisting of said substrate and the porous structure, and a rear plane consisting of the sealing material. The sealing material comprises at least one ply of plastic, preferably a thermoplastic such as, for example, methacrylic acid polyethylene, which is intended, on heating, to adhere to the underlying substrate and, if appropriate, the porous structure located on the substrate. In a preferred embodiment, the sealing material consists of a laminate comprising an adhesion ply of plastic and a barrier ply with low or no air and liquid permeability, for example an aluminium foil. In another preferred embodiment, the sealing material comprises on the one hand an adhesion ply of plastic which is intended, as above, to bear against the substrate, and on the other hand a laminate consisting of a plastic layer and an aluminium layer where the plastic layer is intended to adhere to said adhesion ply. The plastic layer is bonded to the aluminium layer in a manner well-known to the person skilled in the art, for example by adhesive bonding. By using an intermediate play, a good join is brought about because the more flexible adhesion ply takes on the shape of the support more effectively then the less flexible aluminium ply.

In order to ensure that adequate tightness against liquid penetration through the edge of the adhesion ply is obtained, the adhesion ply is designed, in a preferred embodiment, with a thickness of less than 50 μm and, in a further preferred embodiment, with a thickness of less than 30 μm. With said thicknesses, a ply is obtained, which is sufficiently thin that edge throughflow does not impact negatively on the long-term stability of the enclosed cells at the same time as the thickness is sufficiently great to be easy to handle.

In a second method step 21 , the sealing material is pressed together with the substrate and the cells located on the substrate. The sealing is effected by a front plane consisting of said substrate and the porous structure and a rear plane consisting of the sealing material being pressed together while subjected to heat, the adhesion ply fusing together with the front plane, and sealing along the edge of the pattern being permitted. This sealing insulates the individual cells from one another along the inner edge of the pattern and thus prevents leakage of electrolyte between the cells and also insulates the group of cells of which a pattern consists from the surrounding environment at the outer edge of the pattern and thus prevents dirt or moisture penetrating the cells. Alternative preferred embodiments of the pressing- together are indicated below.

Furthermore, certain preferred part processes during sealing 21 are shown symbolically in Figure 11A. In a first part process 22, an adhesion ply of plastic is first positioned against the front plane, above which a laminate consisting of an adhesion layer, preferably made of plastic, and a barrier layer, preferably made of aluminium, is arranged. In the event that use is made of a plastic layer and an aluminium layer, the plastic layer is bonded to the aluminium layer in a manner well-known to the person skilled in the art, for example by adhesive bonding. By using an intermediate ply, a good join is brought about because the more flexible adhesion ply adapts to the shape of the support more effectively than the less flexible aluminium ply. Figure 15 shows the front plane 19, the adhesion ply 19A and the barrier ply consisting of adhesion layer 19B and barrier layer 19C. The adhesion layer 19B has the function of joining the barrier layer 19C and the adhesion ply 19A together. The adhesion ply preferably consists of a thermoplastic.

In a second part process 23, the front plane and the sealing material are subjected to a vacuum pressure, making it possible to reduce the presence of dirt and moisture in the cells.

In a third part process 24, the front plane and the sealing material are pressed together by a flexible pressing tool, good sealing around both inner and outer edges being achieved.

In order to obtain still better sealing around the outer edge, the outer edge can moreover, a little way outside the cells, for example 2-5 mm from the edge of the cells, be pressed together by a hard pressing tool in a fourth part process 25. This pressing-together makes any adhesion ply 19A present thinner, the risk of penetration of dirt and moisture from the surrounding environment after joining together being reduced. Figure 16 shows a group of cells which are pressed together by a hard pressing tool within two areas 26A and 26B essentially surrounding a grouping of cells 2A-2D. In an area 26C, 26D around each of the contacts 11 , 12, the cell grouping is not pressed together in order to avoid the aluminium layer in the barrier ply being pressed together with the conductive ply on the substrate. In order to ensure that any flashover between the conductive ply and the aluminium layer in the areas 26A and 26B does not impact negatively on the cell grouping, these areas are separated by etched-away tracks 26E and 26F, the areas where hard pressing takes place being electrically insulated from the cell grouping as a whole.

The part processes indicated above can be combined individually to obtain different preferred embodiments of the invention.

In a preferred embodiment, the pressing-together is carried out by a flexible pressing tool. A flexible pressing tool means that the pressing tool is allowed to be deformed sufficiently to allow the pressing tool to be deformed for access into the interspaces between the cells, the sealing material being pressed in against the front plane so that the sealing material is pressed against the cells and down into the interspaces between the cells and also around the edges of the pattern. Figures 12, 13 and 14 show examples of embodiments of flexible pressing tools.

Figure 12 shows the pressing-together of a monolithic photoelectric system by means of a flexible membrane 15A. The electrochemical system 1 is placed on a support 15B, after which it is covered by the flexible membrane 15A. The flexible membrane can suitably be made of rubber. The electrochemical system is then subjected to pressure via the membrane 15A, and heat is supplied, sealing being brought about. In a preferred embodiment, the pressure on the membrane 15A is brought about by the space 16 around the electrochemical system 1 being subjected to vacuum pressure. This vacuum pressure reduces the presence of moisture and impurities in the cells before sealing takes place, the quality of the cells being improved. The support 15B can also be designed as a flexible membrane.

In a preferred embodiment, the pressing-together takes place under pressure which is obtained from flexible membranes which surround the monolithic electrochemical system. By making use of a flexible membrane, a uniform pressure is obtained over the entire monolithic electrochemical system and good sealing is obtained in the abovementioned interspaces 9 between the cells.

In a preferred embodiment, the pressure is obtained by virtue of the monolithic electrochemical system being placed in a pocket between two flexible membranes and said pocket being subjected to a vacuum pressure, the pressure of the surrounding environment pressing the monolithic electrochemical system together. This vacuum pressure also contributes to reducing the presence of moisture and dirt in the porous structure before sealing finally takes place.

Figure 13 shows an alternative embodiment where the pressing-together is effected by a pressing head 17 comprising a pressing surface 18 made of soft material, for example rubber, pressing together of the sealing material and the front plane being permitted so that the sealing material is pressed against the cells and down into the interspaces between the cells and also around the edges of the pattern. According to a preferred embodiment, this type of pressing can take place in a chamber subjected to vacuum pressure, making it possible to reduce the presence of dirt and moisture in the finished product.

In an illustrative embodiment, the monolithic electrochemical system is placed in a heating furnace which heats the monolithic electrochemical system to roughly 100°C, heating from room temperature taking place over roughly 30 minutes. The material is then cooled slowly.

According to an alternative method, the electrochemical system is sealed by the front plane and the sealing material being placed in a chamber which is subjected to a vacuum pressure. According to a preferred embodiment, in order to permit the evacuation to reduce further the presence of dirt and moisture, the front plane and the sealing material are separated by a gap for a period of time while subjected to the vacuum pressure.

When the front plane and the sealing material have reached the correct temperature, the front plane is pressed together with the sealing material.

In one embodiment of the invention, the pressing-together is carried out by using a two-part chamber as shown in Figure 14. The chamber 30 is formed in a housing 31 and comprises a first and a second part chamber 34, 35 separated by a flexible membrane 32. The electrochemical system 33 to be joined together is placed in one of the part chambers. An air pump (not shown) is or can be connected to the chamber so as to make evacuation of both the first and the second part chamber possible. To this end, the housing 31 can be provided with a communication duct between the first and the second chamber, the communication duct comprising a check valve positioned so that evacuation of the first and the second chamber can be effected jointly, but air does not flow from the second to the first chamber when air is subsequently introduced in order to allow pressing together of the front plane and the sealing material of the electrochemical system. The invention is not limited to the embodiments described above but can be varied within the scope of the patent claims below. For example, the electrochemical system can consist of a photoelectrochemical system, that is to say a solar cell, or a display in which elements constitute, for example, letter segments. In one embodiment, it is conceivable to encapsulate a display alongside a solar cell. In this case, different electrolytes will be used for the display and the solar cell, which are encapsulated simultaneously. Furthermore, both rear plane and front plane can comprise additional plies; for example, a coloured layer can be located between the adhesion ply 19A and the adhesion layer 19B in order to give the product a desired appearance, or alternatively these or other layers forming part of the product can be coloured.

Claims

1 Method of dyeing an electrode consisting of a porous film which is applied to a substrate, where said substrate is, together with said film, immersed in a dyeing bath, characterized in that said substrate bearing said porous film is exposed to a pulsating flow in said dyeing bath.

2 Dyeing method according to Claim 1 , characterized in that said pulsating flow is brought about by said substrate being vibrated in said dyeing bath.

3 Dyeing method according to Claim 1 , characterized in that said pulsating flow is brought about by the liquid in said dyeing bath being pulsated.

Dyeing method according to Claim 1 , where a vessel accommodates said dyeing bath, characterized in that said pulsating flow is brought about by said vessel being vibrated.

5 Method according to any one of Claims 2-4, characterized in that the vibration is carried out with an amplitude in excess of 0.2 mm and a frequency in excess of 40 Hz.

Method according to any one of the preceding patent claims, characterized in that a set of substrates is mounted on a rack which is insert with regard to the dyeing bath and is immersed in said bath.

Method according to Claim 6, characterized in that said rack is connected to a vibrator. Method according to Claim 6, characterized in that said rack is used in a preceding process step in which said porous film is sintered.

Method according to Claim 5, characterized in that said film is structured before said sintering takes place.

Method according to any one of the preceding claims, characterized in that said dyeing bath contains electrochromically active molecules which are adsorbed on the porous film.

Method according to any one of Claims 1-9, characterized in that said dyeing bath contains light-absorbing molecules which are adsorbed on the porous film.

Manufacturing method according to any one of the preceding claims, characterized in that said pulsating flow is turbulent.

Method of manufacturing an electrochemical system comprising^' the following method steps: application of a porous film to a first substrate; dyeing of said porous film in a dyeing bath; application of a counterelectrode to a second substrate; application of a sealing material to the first or second substrate in a position which is intended to surround said working electrode and counterelectrode after said first and second substrates have been pressed together; pressing together of said first and second substrates, sealing being made possible by said sealing material joining the first substrate together with the second substrate, characterized in that said dyeing of said porous film is effected by the porous film being exposed to a pulsating flow in said dyeing bath. Manufacturing method according to Claim 13, characterized in that said pulsating flow is brought about by said substrate being vibrated in said dyeing bath.

Manufacturing method according to Claim 13, characterized in that said pulsating flow is brought about by the liquid in said dyeing bath being pulsated.

Manufacturing method according to Claim 13, where a vessel accommodates said dyeing bath, characterized in that said pulsating flow is brought about by said vessel being vibrated.

Manufacturing method according to any one of Claims 13-16, characterized in that the vibration is carried out with an amplitude in excess of 0.2 mm and a frequency in excess of 40 Hz.

Manufacturing method according to any one of Claims 13-17, characterized in that said pulsating flow is turbulent.

Method of manufacturing a sealed monolithic electrochemical system, which method comprises the following method steps:

application of electrolyte to a pattern comprising a porous structure and located on a substrate, which structure constitutes at least one monolithic electrochemical cell and comprises a working electrode, an insulating layer and a counterelectrode;

application of a sealing material surrounding said porous structure to form at least one sealed monolithic electrochemical system comprising a front plane consisting of said substrate and the porous structure and a rear plane consisting of the sealing material;

adsorption of an active substance to the porous structure;

sealing of the monolithic electrochemical system,

characterized in that said adsorption of the active substance to the porous structure is effected by the porous structure being exposed to a pulsating flow in a bath containing the active substance.

Manufacturing method according to Claim 19, characterized in that said pulsating flow is brought about by said substrate being vibrated in said bath.

Manufacturing method according to Claim 19, characterized in that said pulsating flow is brought about by the liquid in said bath being pulsated.

Manufacturing method according to Claim 19, where a vessel accommodates said bath, characterized in that said pulsating flow is brought about by said vessel being vibrated.

Manufacturing method according to any one of Claims 19-22, characterized in that the vibration is carried out with an amplitude in excess of 0.05 mm and a frequency in excess of 40 Hz.

Manufacturing method according to any one of Claims 19-23, where electrolyte is applied to the electrochemical system, characterized in that the following method steps are performed after said application of electrolyte: said front plane and rear plane are heated and pressed together, sealing along the edge of the pattern comprising the porous structure being permitted by virtue of a plastic layer forming part of the sealing material being heated to a temperature exceeding the transition temperature of the plastic layer and being joined together with said front plane.

Method according to any one of Claims 19-24, characterized in that the front plane and the rear plane are pressed together by a flexible pressing tool.

Method according to any one of Claims 19-25, characterized in that, in conjunction with said heating and pressing together, said front plane and rear plane are subjected to a vacuum pressure, evacuation of moisture and gases from the porous structure being permitted.

Method according to any one of Claims 19-26, characterized in that said front plane and rear plane are pressed together by means of a flexible membrane.

Manufacturing method according to any one of Claims 19-27, characterized in that said pulsating flow is turbulent.