WO2002071139A1 - Electrochemical pixel device - Google Patents

Abstract

A pixel device is provided, which comprises: (A) an electrochemical transistor device with a source and a drain contact; a gate electrode; an electrochemically active element arranged between, and in direct electrical contact with, the source and drain contacts, which electrochemically active element comprises a transistor channel and is of a material comprising an organic material having the ability of electrochemically altering its conductivity through change of redox state thereof; and a solidified electrolyte in direct electrical contact with the electrochemically active element and the gate electrode and interposed between them in such a way that electron flow between the electrochemically active element and said gate electrode(s) is prevented; whereby flow of electrons between source contact and drain contact is controllable by means of a voltage applied to said gate electrode(s), and (B) an electrochromic device comprising: an electrochromic element comprising (i) a material that is electrically conducting in at least one oxidation state and (ii) an electrochromic material, wherein said materials (i) and (ii) can be the same or different; a layer of a solidified electrolyte which is in direct electrical contact with said electrochromic element; and two electrodes adapted for application of a voltage therebetween; each of said electrodes being in direct electrical contact with a component selected from said electrolyte layer(s) and said electrochromic element, in which pixel device one of said source and drain contacts of the electrochemical transistor device A is in electrical contact with one of the electrodes of the electrochromic device B. Also provided are matrices of such electrochemical pixel devices, and pixelated displays incorporating the matrices. A process for the production of an electrochemical pixel device is also provided.

Description

ELECTROCHEMICAL PIXEL DEVICE

Field of the invention

The present invention is related to electrochemical devices, in particular to printable, electrochemical pixel devices based on conducting organic materials and electrochromic materials. The invention also relates to a process for the production of an electrochemical pixel device, and to matrices of electrochemical pixel devices.

Background of the invention Semiconducting and conducting organic materials, both polymers and molecules, have successfully been included in a large range of electronic devices, e g electrochemical devices, for instance as dynamic colorants in smart windows and in polymer batteries. Reversible doping and de-doping involving mobile ions switches the material between different redox states.

Use has been made of semiconducting polymers for the realisation of field effect transistor (FET) devices. The transistor channel of these devices comprises the semi- conducting polymer in question, and their function is based on changes in charge carrier characteristics in the semiconducting polymer, caused by an externally applied electric field. In such transistors, the polymer is used as a traditional semiconductor, in that the electric field merely redistributes charges within the polymer material. One such transistor has been realised, which is adapted for miniaturisation and can be used for the production of integrated circuits consisting entirely of polymer material (PCT publication WO99/10939) . A stack of sandwiched layers is described, with either a top-gate or a bottom-gate structure. A transistor device with a similar architecture, also using a polymer as semiconducting

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tinuous layers of electrochromic material and electrolyte (as well as other layers of e g ion reservoir material) are confined between two electrodes that completely cover the layers of electrochromic material and electrolyte. For the electrochromic device to be of use, at least one of said electrodes has to be transparent to let light through the device. This requirement is met in the prior art through the use of electrode materials such as indium-doped tin oxide (ITO) , tin dioxide or fluorine-doped tin dioxide. The electrochromic materials used in these applications vary, but are often based on heavy metal oxides such as W0₃ or conducting polymers such as polyani- line or polypyrrole. The conducting, electrochromic polymer poly- (3 , 4-ethylendioxythiophene) (PEDOT) has at- tracted much study, and sandwich devices incorporating this polymer have been realised.

The second category of electrochromic devices aim at providing an electrically updateable display for realisation on a flexible support. US patent 5 754 329 describes such a display, in which the electrodes of the electrochromic device are placed in one and the same plane, contacting a layer of electrochromic material for the generation of local colour effects at the interface between the electrochromic material and the electrodes. US 5 877 888 represents a further development of this device, describing a two-sided display. However, the arrangement of the component layers of the electrochromic device is similar to that of the device of the US 5 754 329 patent, considering that the electrodes on either side of the display support contact electrochromic material only, and the generation of electrochromic effects is confined to the area of the electrodes. The electrochromic materials that are used in these devices are described in detail in US 5 812 300. Active addressing of pixel displays is described e g by Firester AH, in "Active Matrix Technology", chapter 5 of "Flat-Panel Display Technologies", eds Tannas, Glenn, Doane et al, 1995 (ISBN 0-8155-1387-9) . The prior art in this field may furthermore be represented by US patents 6 157 356, 6 023 259 and 6 072 517. Active matrix driven OLED-displays (organic light emitting displays) have been realised by e g Philips and Cambridge Display Technology (CDT) . In parallel to what was noted in connection with transistors above, the transistors used in all of these applications, when employing a polymer material, utilise the polymer material as a traditional semiconductor. Problems with the pixel matrices in the displays of the prior art mentioned above include the fact that they are difficult and expensive to manufacture. In particular, no electrochemical pixel devices have been disclosed which are truly capable of being mass produced. Further- more, the practical use of the pixel elements in the prior art devices has been hampered by their comparatively high power consumption. Also, materials used in prior art devices suffer from a lack of environmental friendliness, processability and economic production pos- sibilities. There is therefore a need for new and improved pixel devices for incorporation in matrices that may be used in displays.

Summary of the invention One of the objects of the present invention is then to meet this demand, by developing the art of electrochemical pixel devices, and by providing a device with handling, production, disposal and other characteristics superior to those of the prior art . Another object of the present invention is to provide an electrochemical pixel device which can be deposited on a large range of different rigid or flexible substrates by conventional printing methods .

Yet another object of the present invention is to provide an environmentally safe electrochemical pixel device, so that the disposal of the device, along with any support onto which it has been deposited, doesn't give ) ω to DO M I-¹

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electrons between source contact and drain contact is controllable by means of a voltage applied to said gate electrode (s) , and

(B) an electrochromic device comprising: at least one electrochromic element comprising (i) at least one material that is electrically conducting in at least one oxidation state and (ii) at least one electrochromic material, wherein said materials (i) and (ii) can be the same or different; at least one layer of a solidified electrolyte which is in direct electrical contact with said electrochromic element; and at least two electrodes adapted for application of a voltage therebetween; each of said electrodes being in direct electrical contact with a component selected from said electrolyte layer (s) and said electrochromic element; in which pixel device one of said source and drain contacts of the electrochemical transistor device A is in electrical contact with one of the electrodes of the electrochromic device B. Thus, the invention is based on the finding that a so called "smart pixel", comprising a combination of a transistor and a colour cell, may be assembled by the novel components as described above. Depending on the electrochemical properties of the precise materials used in the electrochemical transistor device A and the electrochromic device B, the electrochromic device B may be connected to either of the source and drain contacts of the electrochemical transistor device A. The electrochemical pixel device is advantageous in that a voltage applied to the electrochromic display B for colouring or decolouring the electrochromic element may be modulated by controlling the gate voltage of the electrochemical transistor device A. This beneficial property of the electrochemical pixel device of the invention makes it suitable for construction of matrix assemblies of such pixels. The electrochemical pixel devices of the inven- tion may thus be used to form a matrix that may be actively addressed, in a manner known per se in the art.

Electrochemical transistor device A : The architecture of the electrochemical transistor device A in the electrochemical pixel device according to the invention is advantageous in that it makes possible the realisation of a layered transistor device with only a few layers, having for example one patterned layer of material comprising a conducting organic material, which layer comprises source and drain contacts and gate electrode (s), as well as the electrochemically active element. The source and drain contacts and the electrochemically active element are then preferably formed by one continuous piece of said material . The source and drain contacts could alternatively be formed from another electrically conducting material in direct electrical contact with the electrochemically active element. The gate electrode (s) may also be of another electrically conducting material. To provide for the necessary electrochemical reactions, whereby the conductivity in the active element is changed, a solidified electrolyte is arranged so that it is in direct electrical contact with both the active element and the gate electrode (s) . In a preferred embodiment, the source and drain contacts and gate electrode (s) , as well as the active element, are all arranged to lie in a common plane, further simplifying production of the device by ordinary printing methods. Thus, the electrochemical device according to this embodiment of the invention uses a lateral device architecture. A layer of solidified electrolyte can advantageously be deposited so that it covers, at least partly, the gate electrode (s) as well as covering the electrochemically active element. This layer of solidi- fied electrolyte may be continuous or interrupted, depending partly on which of two main types of transistor architectures is to be realised (see below) . ω ω t to I-¹

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3 Φ tr Φ Ω Φ ii 0 0 SD rt ti tr μ- 1 SD O tr rt 03 0 rt Φ SD Φ

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Φ O Ω SD Φ 3 tr O Pi tr 3 Ω 3 ti tr IQ rt SD 3 rt Ω Ω tr D SD Φ ti φ CO tr i φ Ti tr Φ rt O ti μ- Φ μ- fϋ P. Φ Φ 0 μ- tr ti O SD Φ 0 SD

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Ul o Ul O Ul o Ul

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Ω μ- Ti Φ 0 rt rt rt :^> φ μ- rr Ω rt Φ rt μ- μ- φ Φ rt Φ Ti 3 rt CQ O Ω rt rt rt Ω Φ 0 μ- if " Φ 3 if μ- μ- Ω CQ ti Φ 03 Ω 03 l-¹ μ- if Φ 3 rt tr Ω ^ tr ϋ Φ H H ti O φ φ Φ μ- φ μ- ø μ- H O φ ø t-¹ O O fD Ω Φ rt 3 μ- ti μ- o rt

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1 ø ø I-¹

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Ω φ 1 Ω 1 03 - 1

material in the electrochromic element. This makes it possible to realise devices with more than one colour, with for example one colour-generating oxidation reaction and one colour-generating reduction reaction taking place simultaneously at different locations in the device. As a further example, redox reactions giving rise to different colours at the same location, but at different applied voltages, can be designed. This further electrochromic material can be provided within the solidified electro- lyte or within the electrochromic element, which then for example comprises an electrochromic redox pair.

Embodiments of the electrochromic device B in the electrochemical pixel device of the invention may also comprise a redox active material which does not in itself give rise to electrochromic effects . Such a material may fulfil any or both of the following two roles: (i) In some arrangements of the electrochromic device B, the electrochromic material of the entire volume of the electrochromic element can not be completely oxidised or re- duced in the absence of a complementary redox reaction; rather, only part of the material will be oxidised or reduced, respectively. Thus, the addition of a further redox active material makes it possible to fully oxidise or reduce the electrochromic material, (ii) The electro- cromic material may be sensitive to over-oxidation, occurring at too high an applied voltage, and destroying the electrochromic material rendering it useless. A further redox active material comprised in the device may serve the function of protecting the electrocromic mate- rial from such over-oxidation, through restricting the electric polarisation in the electrochromic element to a value below a threshold value. At this threshold value, the protective, further redox active material will instead be oxidised, protecting the electrochromic material from a polarisation that would otherwise destroy it. As is readily appreciated by the skilled man in the light of what is discussed above, a suitably chosen redox active ω OJ to DO μ¹ μ¹ l o Jl O l o Ul rr CQ 3 Hi Ti Φ tr μ- fD 3 Hi rt Ω μ- co μ- rt Ω O SD rr tr 01 Ω P. 0 μ- rt SD rt CQ rt 3 μ- 0 tr 0 ti ø μ^j fu ti tr if ø i 3 μ- 0 0 0 fi Φ 0 0 μ- Φ SD ø μ- CQ tr Φ tr SD

0 μ- μ- fi 0 Φ ^ 03 rt O φ φ < Φ SD < 0 ti O 3 ø Hi <! 3 O SD Φ 0 Φ rr ø rt Ω T⁾ Ω rt 0 Φ 3 3 φ Φ CQ μ- rt Φ μ- Φ f Hi μ- μ- r ø μ- ti Φ Φ

SD tr rt Φ rt if fi φ μ- ø fi Φ rt SD fi ^ 0 0 Φ Ω Ω tr 0 ti Hi ti tr tr if ti fi fϋ φ ø μ- rt Ω rt 03 Ω

^ Φ Φ rt 0 Ω ti φ Φ H 0 03 0 SD 0 μ-

Φ μ- Φ rt 0 H CQ fD if φ SD μ- 03 φ rt Ω Ω Φ fi Hi rt Φ O 0 X rt ti rt 0 SD

Φ 03 H- fi ω φ Φ Φ Ω h-> 0 H-" 0 rt CQ μ- μ- 0 3 fi φ μ- μ- Ω

0 fi Φ Φ 0 Pi rt ø P. Φ $. S ti • ii fD <! rt fD CQ P. O tr ø rr

S 03 Ω μ- CQ 03 φ tr CO ti ^• ; φ 3 if μ- 0 o Φ μ- < φ 0 fϋ <! 0 CQ μ-

. 0 o Hi . Hi Ω Hi SD fD 0 03 Φ μ- rt 0 td Ω Ti rt 03 fD Ω 3 rt φ rt O Φ

Ω ø Hi O 0 rr 0 CO 3 Ω SD r Ω 0 Ω if fi "< rt (-^■ μ- 0 tr fi rt Φ μ- ti if fi ø X tr P. φ Hi CQ ti ti fi Φ if Ω if fi rt tr rr φ 0 Φ Φ μ- ti 0 1 Φ tr ø ti 0 O Φ Φ rt Φ μ- 03 SD Hi Φ Ω Φ ti 03 μ- fϋ O Φ 0 O 0 SD O μ-

T Ω φ 03 μ- rt Ω rt 3 3 μ- tr 3 ø SD rt fD • Pi CQ tr Ω 3 X Hi Ω Hi tr

0 rt ø SD rr if if ø" φ SD μ- <! 03 φ $, fD 03 tr ϋ φ μ- Φ tr t O μ- rr μ- μ- rr μ- SD Φ ti Φ Ω rt Ω φ O fi μ- W Φ r SD O Ω μ- *ti Hi 0 φ φ o Hi Pi rt μ- Ti rr

^■<: ø Pi tr 0 rt Φ SD ø rt Φ Φ <J Ω rr rt fD μ- Φ 3 SD if O ϋ μ-

3 CQ Ω Hi 3 Hi fi ti φ ti SD tr CQ φ ti μ- tr ti ^ ti φ ti Ω μ- μ- rt rt φ ø O ø

Φ O 3 ^ o μ- 0 O μ- < Ω tr Ω ø ti μ- rt P- SD o Ω 3 tr μ- <! CQ ii μ- 3 fϋ ti Ω ti Ω fu rt φ Φ 0 fi Ti rt rt CQ O Ω O CD rt fϋ Φ φ O tr μ-

03 ø Ti rt 3 3 if ti 3 <! μ- 0 ti if 3 SD Hi φ Φ 0 ø ø Φ SD Pi Φ

0 Φ μ- fD i fϋ ti • SD Φ SD Φ l-h CQ 0 SD tr μ- 0 fi 0 rt Hi ø rt μ-

SD SD ø ti ø rt Φ rt 0 0 ø 0 - Hi 03 0 μ- Ω Φ Hi φ ti Ti 03 μ- SD Φ ø Φ fi rt Φ μ- μ- < μ- 3 CQ CO rt P. φ μ- ^> CQ Ω Ω rt μ- μ- fi ø Hi rt Q Ω

Φ ø SD < o μ- 0 μ- 0 μ- μ- fi tr rt Φ tr SD O Φ SD rr if ø X 0 03 ϋ μ- tr rt -> rr μ- 0 Ω ø Ω μ- 01 SD Pi ø φ Φ Φ ti ø Ω 0 fi ti CQ φ Hi rt Ω Φ SD ti

Φ 03 φ Φ rt rt 0 ti ø Φ Φ fi Φ rt rt O O Φ μ- O , μ- SD s 0 0 T5 fϋ O fi SD T3 rt tr Ω SD SD fi Φ ø Φ rt Φ 0 SD CQ Ω

Cfl 03 μ- rt Hi td Hi ti tr fi μ- ti fi SD rt μ- 03 Ω 0 H^{1 ■}<: CQ Hi ϋ if SD SD 0 ^Ωy ω rt rt 03 tr 0 - O rt ø Φ Ω μ- < fi 0 rt Ω Φ rt if Hi φ φ Φ tr 3 3 ti φ Φ Hi rt rt Ti ^ ϋ if Hi 0 Hι μ- O ø rt tr Ω Φ Φ < Ω Φ Φ Ti 0

P. 0 fD tr fD tr φ Φ φ Ω Φ Hi ø Ω μ- tr t. fi rt CD ø Ω μ- φ rt μ- Hi 3

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03 Φ Ti tr SD P. Hi Φ μ- rt fi — ' rt O ø 03 Ω rt ^ •» rt O Ω O μ- fi 0 φ

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Ω φ Φ ø CQ Φ Ω μ- -> Ω ø μ- μ- 1 Φ

1 fi rt 1 ø 1 1 Ω Ω 1

For the successful operation of the electrochemical pixel device, both the electrochemical transistor device A and the electrochromic device B comprise a solidified electrolyte. In A, the electrolyte makes possible the electrochemical reactions that change the conductivity in the transistor channel, whereas in B, it enables the electrochemical reactions resulting in a colour change in the electrochromic element. The solidified electrolytes in A and B may be the same or different, and is as de- fined in the "Materials" section below. For reasons of processability and ease of design, the solidified electrolytes in A and B are preferably the same.

Another aspect of the invention provides a matrix of electrochemical pixel devices as described above. The beneficial process characteristics of the electrochemical pixel device makes it suitable for incorporation in a matrix comprising a plurality of similar or identical pixel devices, in order to form an actively addressed pixel matrix. As is known to the person skilled in the art of displays incorporating actively addressed matrices, such a matrix of pixels exploits the possibility provided by a transistor coupled to a pixel to control the current flows to the colour elements of the pixels. If a matrix according to this aspect of the invention consists of, for example, three rows and three columns of the novel electrochemical pixel devices described herein, there will be nine electrochromic devices B whose colour may be changed individually. There will also be nine electrochemical transistor devices A to control the current. One row or column of the matrix may be updated at a time. In other words, e g all the transistors in the two lowest rows are set to the "off" state, and are thus in a nonconducting state. The transistors in the upper row are set to the conducting or "on" state, so that the colour of all electrochromic devices in this row may be individually changed. After completion of the process for the displays in the first row, the transistors in the first and third row will be set to their "off" states, whereas the transistors in the second row are set to their "on" state in order that the displays in the second row may now be individually updated. By setting the transistors in a row to the "off" state after updating of this row, the charges loaded into the electrochromic elements in question will be trapped there, which in turn means that a certain electrochromic element can stay in its colour changed state for some time. In summary, the transistors make control of the current applied to the electrochromic elements possible, and thereby also the selection of individual display cells to be switched. The skilled person may create a matrix of electrochemical pixel devices according to the invention, having any number of pixels without undue experimentation, using the teachings herein. Specific embodiments showing alternative matrix designs and variants of the electrochemical pixel device to be used in such matrices are shown in the detailed description below. Especially, the electrochemical transis- tor devices A in the pixels forming part of such a matrix may have one or two electrodes for supply of gate voltage to the transistor channel. Different characteristics are obtained in the different cases, as explored in further detail below. Briefly, a design having two gate elec- trodes generally provides for better control of the currents in the matrix system. However, a design of only one gate electrode prevents cross-talk between the second gate electrodes of all the pixels in a row, which may occur as a disadvantage in the two-gate design. The one- gate design also makes for fewer crossings of conductors.

The problem of cross-talk between gate electrodes in a row may also be addressed by the provision of resistances, which prevent the current from a certain pixel from spreading to other pixels in the same row. The invention in a further aspect also extends to a pixelated display which comprises such a matrix of electrochemical pixel devices. > ω to DO ¹

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printing techniques listed above. After deposition, the encapsulant can be hardened for example by ultraviolet or infrared irradiation, by solvent evaporation, by cooling or through the use of a two-component system, such as an epoxy glue, where the components are mixed together directly prior to deposition. Alternatively, the encapsulation is achieved through lamination of a solid film onto the electrochemical pixel device. In preferred embodiments of the invention, in which the components of the electrochemical pixel device are arranged on a support, this support can function as the bottom encapsulant. In this case encapsulation is made more convenient in that only the top of the sheet needs to be covered with liquid phase encapsulant or laminated with solid film. Further objects and purposes of the present invention will be clear from the following drawings and detailed description of specific embodiments thereof. These specifications and drawings are intended as illustrations of the invention as claimed, and are not to be seen as limiting in any way.

Brief description of the drawings

Figure 1 shows a top view of elements of one embodiment of an electrochemical pixel device according to the invention.

Figure 2 is a diagram showing current during colouring of a pixel as shown in figure 1. V_ds = 2 V, V_g = 0 V.

Figure 3 is a diagram showing currents during decolouring of a pixel as shown in figure 1. A: V_g = 1.4 V. B : V_g = 0 V.

Figure 4 is a diagram showing current during decolouring of a pixel as shown in figure 1. V_g = 1,4 V during the first 50 seconds, thereafter V_g = 0 V.

Figure 5 shows a top view of a 5x1 matrix of elec- trochemical pixel devices like the one shown in figure 1.

Figure 6 shows a top view of a 5x5 matrix of electrochemical pixel devices like the one shown in figure 1. Figure 7 shows a top view of a 3x3 matrix of electrochemical pixel devices according to another embodiment of the invention.

Figures 8A-8D illustrate an alternative design of a 3x3 matrix of electrochemical pixel devices according to another embodiment of the invention, having a vertical, three-layered design. Figure 8A shows a top view of the bottom layer only. Figure 8B shows a top view of the middle layer only. Figure 8C shows a top view of the top layer only. Figure 8D is a cross section from the side showing the three layers of figures 8A-8C stacked together to form the electrochemical pixel device matrix.

Description of preferred embodiments

Definitions :

Source contact: an electrical contact which provides charge carriers to a transistor channel.

Drain contact: an electrical contact which accepts charge carriers from a transistor channel.

Gate electrode: an electrical contact of which any fraction of the surface area is in direct electrical contact with solidified electrolyte, and therefore in ionic contact with the electrochemically active element. Electrochemically active element: an "electrochemically active element" according to the present invention, is a piece of a material comprising an organic material having a conductivity that can be electrochemically altered through changing of the redox state of said organic material. The electrochemically active element is in ionic contact with at least one gate electrode via a solidified electrolyte. The electrochemically active element may furthermore be integrated with each of the source and drain contacts individually or with both of them, being composed of the same or different materials. The electrochemically active element in the electrochemi- cal transistor device A in the electrochemical pixel device of the invention comprises a transistor channel.

Transistor channel: the "transistor channel" of the electrochemically active element establishes electrical contact between source and drain contacts .

Redox sink volume: in certain embodiments of the electrochemical transistor device A, the electrochemically active element further comprises a "redox sink volume" . This is a part of the electrochemically active ele- ent adjacent to and in direct electrical contact with the transistor channel, which can provide or accept electrons to or from the transistor channel. Thus, any redox reactions within the transistor channel are complemented by opposing reactions within the redox sink volume. Redox state: when reference is made to changes in the "redox state" of the electrochemically active element or electrochromic element, this is intended to include cases where the material in the element is either oxidised or reduced, as well as cases where there is a re- distribution of charges within the element, so that one end is reduced and the other end is oxidised. In the latter case, the element as a whole retains its overall redox state, but its redox state has nevertheless been changed according to the definition used herein, due to the internal redistribution of charge carriers.

Electrochromic element: an "electrochromic element" in the devices of the invention is a continuous geometrical body, which can be patterned to different shapes, and is composed of one material or a combination of materi- als. The material (s) may be organic or inorganic, molecular or polymeric. Such an electrochromic element, whether it is composed of one material or is an ensemble of more than one material, combines the following properties: at least one material is electrically conducting in at least one oxidation state, and at least one material is electrochromic, i e, exhibits colour change as a result of electrochemical redox reactions within the material . Solidified electrolyte: for the purposes of the invention, "solidified electrolyte" means an electrolyte, which at the temperatures at which it is used is sufficiently rigid that particles/flakes in the bulk therein are substantially immobilised by the high viscosity/rigidity of the electrolyte and that it doesn't flow or leak. In the preferred case, such an electrolyte has the proper rheological properties to allow for the ready application of this material on a support in an integral sheet or in a pattern, for example by conventional printing methods. After deposition, the electrolyte formulation should solidify upon evaporation of solvent or because of a chemical cross-linking reaction, brought about by additional chemical reagents or by physical effect, such as irradiation by ultraviolet, infrared or microwave radiation, cooling or any other such. The solidified electrolyte preferably comprises an aqueous or organic solvent-containing gel, such as gelatine or a polymeric gel. However, solid polymeric electrolytes are also con- templated and fall within the scope of the present invention. Furthermore, the definition also encompasses liquid electrolyte solutions soaked into, or in any other way hosted by, an appropriate matrix material, such as a paper, a fabric or a porous polymer. In some embodiments of the invention, this material is in fact the support upon which the electrochemical pixel device is arranged, so that the support forms an integral part of the operation of the device .

Electrodes: "electrodes" in devices according to the invention are structures that are composed of an electrically conducting material. Such electrodes allow the application of an external voltage to electrolyte, whereby an electric field within the solidified electrolyte is sustained for a time period long enough for the desired electrochemical reactions to occur.

Direct electrical contact: Direct physical contact (common interface) between two phases (for example elec- trode and electrolyte) that allows for the exchange of charges through the interface . Charge exchange through the interface can comprise transfer of electrons between electrically conducting phases, transfer of ions between ionically conducting phases, or conversion between electronic current and ionic current by means of electrochemistry at an interface between for example electrode and electrolyte, electrolyte and electrochromic element, or electrolyte and electrochemically active element, or by occurrence of capacitive currents due to the charging of the Helmholtz layer at such an interface.

Colour change: when reference is made to "colour change" , this is also meant to include changes in optical density or reflectance, so that "colour change" for exam- pie takes into account changes from blue to red, blue to colourless, dark green to light green, grey to white or dark grey to light grey alike.

Materials Preferably, the solidified electrolyte in either or both of the electrochemical transistor device A and the electrochromic device B comprises a binder. It is preferred that this binder have gelling properties. The binder is preferably selected from the group consisting of gelatine, a gelatine derivative, polyacrylic acid, po- lymethacrylic acid, poly (vinylpyrrolidone) , polysaccha- rides, polyacrylamides, polyurethanes, polypropylene oxides, polyethylene oxides, poly(styrene sulphonic acid) and poly (vinyl alcohol) and salts and copolymers thereof; and may optionally be cross-linked. The solidified electrolyte preferably further comprises an ionic salt, preferably magnesium sulphate if the binder employed is gelatine. The solidified electrolyte preferably further contains a hygroscopic salt such as magnesium chloride to maintain the water content therein.

The organic material for use in the electrochemical transistor device A in the electrochemical pixel device of the present invention preferably comprises a polymer which is electrically conducting in at least one oxidation state and optionally further comprises a polyanion compound. Organic materials comprising combinations of more than one polymer material, such as polymer blends, or several layers of polymer materials, wherein the different layers consist of the same polymer or different polymers, are also contemplated. Conductive polymers for use in the electrochemical transistor device of the in- vention are preferably selected from the group consisting of polythiophenes, polypyrroles , polyanilines, polyiso- thianaphthalenes, polyphenylene vinylenes and copolymers thereof such as described by J C Gustafsson et al in Solid State Ionics, 69 , 145-152 (1994) ; Handbook of Oligo- and Polythiophenes, Ch 10.8, Ed D Fichou, Wiley- VCH, Weinhem (1999) ; by P Schottland et al in Macromole- cules, 33, 7051-7061 (2000); Technology Map Conductive Polymers, SRI Consulting (1999) ; by M Onoda in Journal of the Electrochemical Society, 141, 338-341 (1994) ; by M Chandrasekar in Conducting Polymers, Fundamentals and Applications, a Practical Approach, Kluwer Academic Publishers, Boston (1999) ; and by A J Epstein et al in Mac- romol Chem, Macromol Symp, 51, 217-234 (1991) . In an especially preferred embodiment, the organic material is a polymer or copolymer of a 3 , 4-dialkoxythiophene, in which said two alkoxy groups may be the same or different or together represent an optionally substituted oxy- alkylene-oxy bridge. In the most preferred embodiment, the polymer is a polymer or copolymer of a 3 , 4-dialkoxy- thiophene selected from the group consisting of poly (3, 4- methylenedioxythiophene) , poly (3 , -methylenedioxythio- phene) derivatives, poly (3 , 4-ethylenedioxythiophene) , poly (3,4-ethylenedioxythiophene) derivatives, poly (3,4- propylenedioxythiophene) , poly (3 , 4-propylenedioxythio- phene) derivatives, poly(3 , 4-butylenedioxythiophene) , poly (3, 4-butylenedioxythiophene) derivatives, and copoly- mers therewith. The polyanion compound is then preferably poly(styrene sulphonate) .

In preferred embodiments, the electrochromic element for use in the electrochromic device B in the electro- chemical pixel device of the present invention comprises, as electrochromic material, an electrochromic polymer which is electrically conducting in at least one oxidation state, and optionally also comprises a polyanion compound. Electrochromic polymers for use in the electro- chromic element of the electrochromic device of the invention are preferably selected from the group consisting of electrochromic polythiophenes, electrochromic polypyr- roles, electrochromic polyanilines, electrochromic poly- isothianaphthalenes, electrochromic polyphenylene vi- nylenes and copolymers thereof, such as described by J C Gustafsson et al in Solid State Ionics, 69, 145-152 (1994); Handbook of Oligo- and Polythiophenes, Ch 10.8, Ed D Fichou, Wiley-VCH, Weinhem (1999) ; by P Schottland et al in Macromolecules, 33, 7051-7061 (2000); Technology Map Conductive Polymers, SRI Consulting (1999); by M Onoda in Journal of the Electrochemical Society, 141, 338-341 (1994); by M Chandrasekar in Conducting Polymers, Fundamentals and Applications, a Practical Approach, Klu- wer Academic Publishers, Boston (1999) ; and by A J Ep- stein et al in Macromol Chem, Macromol Symp, 51, 217-234 (1991) . In a preferred embodiment, the electrochromic polymer is a polymer or copolymer of a 3 , 4-dialkoxythiophene, in which said two alkoxy groups may be the same or different or together represent an optionally substituted oxy-alkylene-oxy bridge. In the most preferred embodiment, the electrochromic polymer is a polymer or copolymer of a 3 , 4-dialkoxythiophene selected from the group consisting of poly (3 , 4-methylenedioxythiophene) , poly- (3, 4-methylenedioxythiophene) derivatives, poly (3 , 4-eth- ylenedioxythiophene) , poly (3 ,4-ethylenedioxythiophene) derivatives, poly (3 , 4-propylenedioxythiophene) , poly(3,4- propylenedioxythiophene) derivatives, poly (3 , 4-butylene- u> co DO to μ> μ> σi o Ul o Ul o Ul

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Some embodiments of the invention comprise a further electrochromic material for realisation of pixel devices with more than one colour. This further electrochromic material can be provided within the electrochromic ele- ment or the solidified electrolyte of the electrochromic device B, which then for example comprises an electrochromic redox system, such as the redox pair of colourless Fe²⁺ and SCN^" ions on one hand, and of red Fe³⁺(SCN) (H₂0)₅ complex on the other. By way of further, non-limiting example, such materials may be selected from different phenazines such as DMPA - 5, 10-dihydro-5, 10- dimethylphenazine, DEPA - 5 , 10-dihydro-5, 10-diethyl- phenazine and DOPA - 5, 10-dihydro-5 , 10-dioctylphenazine, from TMPD - N,N,N' ,N' -tetramethylphenylenediamine, TMBZ - N,N,N' ,N' -tetramethylbenzidine, TTF - tetrathiafulvalene, phenanthroline-iron complexes, erioglaucin A, diphenylamines, p-ethoxychrysoidine, me- thylene blue, different indigos and phenosafranines, as well as mixtures thereof . As described above, the electrochromic device B in the electrochemical pixel device of the invention may comprise a redox active material for reasons other than additional colouring effects. This redox active material may be the same or different from any of the further electrochromic materials listed immediately above. Thus, any suitable anti-oxidant or anti-reductant may be used, for example organic substances like vitamin C, alcohols, polyalcohols (e g glycerol) or sugars, the alcohols, polyalcohols or sugars where appropriate being present at a high pH, conjugated polymers, oligomers and single molecules; inorganic substances like salts comprising species that may be oxidised (e g Fe²⁺ to Fe³⁺, Sn²⁺ to Sn⁺) , metal clusters (e g a Cu cluster or a Fe cluster) , or salts comprising species that may be reduced (e g Fe³⁺ to Fe²⁺, Sn⁴⁺ to Sn²⁺) ; metal organic complexes like ferro- cenes, phthalocyanines, metallo-porphyrines .

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Ω Φ tr ti φ rt ø fi 0 0 <

O μ- 0 ^■<; Ω SD μ- μ> fi tr ø Ω 0 ι-3 T3 φ rt O φ Ti Ω μ- Ω μ- ti Ω

0 Ω μ- Φ 0 Φ Ω Φ 0 Ω o Ω 0 Φ rt fu l-h tr fu fi Φ 3 <! Ti tr Ω SD if Ω ti r ø rt 03 rt Φ fD rt 0 0 ϋ SD 1 0 ø Φ Ti φ ~.. μ- 0 Φ Φ rt 0 ti SD Φ ti rt fi fD SD Ω Φ fϋ Hi Φ r fi M 3 CQ Φ 0 (U Φ CQ Ti rt Ω ϋ 3 if O fi O

SD 0 Ti Ω rt CQ Ω SD SD H Ti if I-¹ Hi Φ 0 03 ti μ- o Ti if φ rt μ- td φ φ 3 Ω

Ω fi μ- rt fi φ ^ Φ £ rt Ω μ- rt — ti Φ 0 tr ø o φ Ω μ- rr tr tr rt Φ φ 03 0 Ω if fi rt ø ϋ μ- Ti Ω rt Φ CD Ti 0 CO ^ O μ- SD μ- φ φ Ω ti O Φ

Ω Hi rt fϋ rt μ- 0 fϋ SD 01 fϋ rr tr Ω Ti fD Ti ^ CQ Hi ø 01 I—¹ Ω SD rt 3 tr Ul φ 0 t ^ ti Ω 0 Ω Ω s Ω 0 0 φ rt ti Φ rt CD 0 ti ti φ ti Φ rr 3 ø tr μ-

Φ _^ ti _^ rr 0 rt tr tr μ- 0 01 fi 01 rt O ti O ti fi Ti 0 rt 0 rt CO rt rt Ω ti Sϋ 03 Ω rt μ- 3 J Φ fi μ- fϋ Φ rt ø μ- Φ Ω μ- O rt rr o Ti if 0 if 0 ti tr rt 0 rr μ- rt SD s: 03 03 φ Φ <! 3 3 tr rr 01 fϋ fϋ ti tr ø Ω ii ^ ^ Ti φ 3 fD Φ ti Ω Φ 03 tr

Φ 0 fi Sϋ H Φ Ti fu μ- SD rt 0 ø 0 φ < tr 0 μ- Ω ^ !-^■ Φ ø O tr ti rt SD

Φ 03 0 o Ul 0 ^ Ω Ω 0 μ- 3 φ Φ O 03 o Φ φ Φ Ω Ti CO 01 Ω ti μ- 0 rt Ti ø rt Φ tr ϋ • Φ 03 SD rt rt fi φ φ ø μ- ø 3 tr ti rt 0 0 0 ti Φ μ- SD if O SD H μ- if Ti ^ SD μ- tr tr CQ Ω rt μ- Φ SD fi tr φ Φ 0 Φ 3 01 3 ti 3 rt X rt fD SD rr H ti φ rt Φ H" φ ω fi Φ φ fu μ- Ω B ø ^■<; ~. 03 03 cT rt Φ 0 μ- fi tr Φ tr rt ti fϋ if 0 Φ 3 μ- ^ • Φ Ω Ω 0 0 fD μ- 03 CQ 0 μ- Φ 0 O 3 Ω μ- Φ Φ μj DO

Φ SD Φ Φ <! SD 03 <J rt rt Hi 0 0 O SD φ Ti fD CD ø Pi fi 3 μ- ø < cn rt rt Ω rr Ω ø φ I-¹ SD o td μ- ti fi Ti 0⁾ rt ø fϋ Ti r rt μ- SD Ω TJ μ- 0 P.

Φ if Φ o Φ tr 0 rt rt Ω 0 φ Ω 0 0 Sϋ μ- μ- Ti H Ti Φ φ Ti if μ- 3 fi rt O rt Ω ti φ

Φ fi ø μ- <i CQ Φ r fi rt Φ Ω Ω X 03 μ- ti fi - φ rt ø μ- Φ Φ Φ Ti tr φ CQ <!

Φ ii rt Φ 03 Φ . SD fi μ- Ω t tr tr 03 Φ X "d Φ ti if CQ 0 ø <! fi 0 ^ Φ fϋ μ-

Ω Φ tr μ- Ω ti rr Φ < Φ Φ Ω ti Φ 0 H CO φ H- Hi tr 0 >. fϋ < rt μ- μ- 3 0 Ω rr ^ ø rt φ Φ SD Φ Si Φ Φ 0 0 3 μ- if X φ 0 ti O φ 03 Ω SD l« Φ Φ μ- φ ϋ μ- ø ti 3 fi 0 Sϋ ø 3 3 μ- rt ϋ o CD ti SD Ω φ Hi 0 φ 3 ti μ- Ω CD

0 03 fϋ 0 0 tr ϋ Φ rt Φ 0 Ti μ- Ω SD φ s; fi H fD ti Ti 0 0 rr 0 φ Φ o

Ω 0 Ω 0 3 if P. ti Ω SD tr <! ø φ tr P. O fϋ φ Ti μ- Hi > fu ti Ω 3 o if ø ø CD tr P. μ- Ti Φ ti Φ SD μ- μ- < P. rt 0 0 01 H rt fD Sϋ Hi

Φ 0 fD φ μ- rt SD Ω 0 3 P- 0 01 fi Φ Ω 03 μ- Φ >< Φ fi I-" 0 rt μ- 0 ti r

3 i Ti 3 3 tr ti rt ø φ ti ϋ φ Φ rr φ Ω Ω < CQ Ti P- μ- ^ tr rt ø 0 Ti φ rt μ- fi ti μ- μ- φ rt ti CQ ø SD CQ <! fi 3 if φ H- ti μ< ti Ω Φ μ- Φ tr rt Ω O ti tr

Ω μ- 0 Φ Ω ø ϋ 0 ø" rt μ- μ- μ- SD SD Φ 0 φ SD 0 Ti fD rt 03 φ rt tr if μ- φ fϋ ϋ * Ω SD rt 0 Si ø ø Sϋ Ω ø rr 3 Sϋ Φ Hi CO Ti fD ti if Φ if Φ ti • ; SD

Φ φ _^ l-¹ Hi Φ fϋ φ CD Φ μ- SD Ω 03 ^ Ti tr ^> Ti Ti φ o 3 μ-

Ω ⁽Q SD Ti Ω Si 03 μ- ti 03 rr Ω Φ Φ o i— ^■ ti φ 0 3 3 Φ ø

^ rt fu o •<; rt rt Ul Ti 0 μ- o , — . CD μ- μ- O Ω fϋ Φ fi X Φ Φ Ω φ o μ- ti μ- <!

Ti Hi tr Φ tr • I-¹ rt 0 ti 0 en rt SD Ω Ω fi r 0 0 ^ ø Hi rt ^ 03 Ω ø φ fu fϋ Φ fi φ μ- tr rt φ ti 1 0 H¹ 0 fϋ fi μ- fi Φ μ" Φ Φ ti g Φ rt fD ø

Ω Hi rt Ω H Ω Φ SD Ω Ω V£> ti 0 μ- <! Φ SD fi 0 Φ Ω Si ø rt rt rr ti if rt CD 0 tr SD Ω rt Φ ^^ _^^ 1 ø Φ Ti rt SD Ω ti r Ti Φ ϋ tr μ- μ- 0 φ μ- 0 Hi φ rt rt • ϋ 03 ^■ : CQ . 0 Ti CQ Φ tr tr ti ti < φ O

<! 3 <! ø μ- 01 Ω Φ Φ fϋ ~. Φ μ- 0 Φ μ- rt 0

Φ φ fi 0 0 t-3 1 Φ μ- rt Ti ^ 3 ø I 1 Ω if Ω ø μ- 0 if ø 0 1 Φ μ- Φ fϋ Φ 01 1 φ fi 1 r

tact between the electrochemically active element 4 and the gate electrode 5.

The electrochromic device comprises an electrochromic element 6, as well as two electrodes 7,8. Covering the electrochromic element 6 and the first electrode 7 is a layer of solidified electrolyte 9. There is no direct electrical contact between the first electrode 7 and the electrochromic element 6, but between the electrochromic element 6 and the second electrode 8. The first electrode 7 of the electrochromic device is in direct electrical contact with, or rather coincides with, the source contact 2 of the electrochemical transistor device.

Upon function of the electrochemical pixel device 1, a colouring or decolouring current is supplied to the electrochromic element 6 through application of a voltage between drain contact 3 and electrode 8, corresponding to a drain-source-voltage V_ds. The current actually supplied to the electrochromic element 6 is controlled by the con- ductivity in the electrochemically active element 4. This conductivity, in turn, is controlled by a gate voltage V_g at the positive gate electrode 5. The gate voltage V_g may, in certain embodiments, be applied between the positive gate electrode 5 and a second, negative gate elec- trode 11, which may or may not be in direct electrical contact with the electrochemically active element 4. Alternatively, the gate voltage is applied between the positive gate electrode 5 and either of the source contact 2 or the drain contact 3. In an experiment using this embodiment of an electrochemical pixel device according to the invention, the device was manufactured as follows: a starting material of Orgacon™ foil, commercially available from Agfa and comprising the conducting and electrochromic polymer PE- DOT-PSS (poly- (3,4-ethylendioxythiophene) doped with poly(styrene sulfonate) ) was used. Patterning of the PE- DOT-PSS substrate was done using a plotter tool equipped ω ω to DO μ> M

Ul o l O Ul o Ul

φ > fi Hi fi s rr μ- Ω ω rt φ fi Φ (D tr rt tr o

Φ < 0 fi 01 ti fi o

3 SD μ- 3 ø 0 =^> 0

Φ Ω Ω SD 0 fD 3 1= ø tQ φ H rt Φ ti CQ 03 μ- ! rt SD 0 tr P. 0 tr Ω rt 53 φ 0 Hi μ-

S Φ SD rr 0 rt ø φ ø fϋ CD tr fi 0 fi tr

CO <! φ μ- o I-¹ rt

0 fi CD 01 0 Ul ^ 3 tr

Hi ti Φ Ti o Φ φ φ

0 rt μ- Ω I—¹ 03 ø

Sϋ < Φ fϋ 0 τ= φ SS rt tr

CQ φ ; 0 Ω μ- Φ

Φ ø Ti Pi rt rt fD CQ φ Ω 0 ti Ω ti μ-

Ω 0 tr ti Φ Ω m 0 if Φ ø

O Hi ^ μ- rt tr Ω Φ SD ø

0 3 μ- Φ tr ti μ- fi o CQ Φ 0 ti 0 ø ø ϋ ø tQ ti 0 fD Hi tQ

Ω < rt r Φ 3 0 rt Φ 03 01 SD μ- i μ- - rt 03 Ω fD

0 rt < fϋ 0 03 DO rt Q if 0 rt rt ø fi fϋ

Φ if Φ Φ rt Ω fϋ rt φ Hi <! ø 3 oo fϋ Φ SD O O μ- H < ø I-" CQ φ Hi ti Ω fϋ fi Φ Φ φ rt

Ω 01 φ td rr Φ fϋ rt Ω td tr μ- o fi Hi rt Hi rt ti tr r O μ- ø •

0 φ ti O 03 Φ ι-3 ti DO

Ω rt 0 m rt ^{^} s: Ω Ω tr tr ui Φ Φ if TI 0 μ- <

3 Φ Φ CD ti CQ Ti μ- ø 3 ' CD ti Ω Ti fu

Ω μ- Φ CQ 0 ti 0 o Ω μ- 0 0 Pi

SD SD li μ- SD 01 rt rt fi X SD rt μ^J SD ø φ μ-

^> 0 Φ ti t ø 3 0

S Pi r φ <! fϋ rr fu fD ti fϋ Φ rt rt Φ

1— >

CO Ω H SD ?v 0 Φ Hi Φ

Φ rt • 0 SD fi μ- μ- Ul CD π iQ μ- 0 rt ø < μ- φ ø 03 $. 3 rr ti

Φ < 0 μ- μ- rt rt fD o ø O rt 0 tr rt tQ

01 ti φ Φ 03

"off" state. Already at 0.3-0.4 V it was evident from the appearance of blue colouring that the transistor channel

long as the voltage was applied.

Effects of four possible combinations of voltages

Figures 2-4 are diagrams of measurements performed on a PEDOT-PSS pixel device with the design shown in figure 1. Figure 2 shows colouring of the electrochromic device using a V_ds of 2 V. The transistor channel was in the "on" state, i e V_g = 0 V. The current through the channel was about 150 μA at the outset, and then decreased because of the reduction to a non-conducting state of the electrochromic element in the display cell. The electrochromic element area in this measurement was 64 mm², and the area of the counter-electrode was 90 mm². After about five seconds, the pixel was fully switched.

Figure 3 is a diagram showing decolouring of a pixel in two different cases. The upper curve, A, corresponds to the current from the electrochromic element at a V_g of 1.4 V, i e with the transistor channel closed. The lower curve, B, shows the current from the electrochromic element at a V_g of 0 V, i e with the transistor channel open.

Figure 4 shows decolouring of one pixel at different values of V_g. The transistor channel was closed

(V_g = 1.4 V) for the first 50 s, whereupon it was opened (V_g = 0 V) for the last 10 s. After 50 s of decolouring with a closed transistor channel, there were still a lot of charges in the electrochromic element, as evident from figure 4. When the transistor channel was opened, i e the gate voltage was set to 0 V, a decolouring current peak occurred. The size of this peak was almost 20 μA, which shall be compared to the few hundred nA of leak current when the channel was closed.

Lateral matrices of electrochemical pixel devices

Several different matrices of electrochemical pixel devices have been realised, using the same materials as in the electrochemical pixel device embodiment described in the previous section.

Shown in figure 5 is a column of five such pixels, or a 5x1 matrix. Using the reference numerals of figure ω 00 to to μ> μ> l O Ul o Ul o in

Pi rt Φ μ- <! tr H- < SD O fi TS fi O ø ω O Ω rt μ- Ul Ω r O 1-3 Hi rt fϋ rt rt 0 μ¹ φ 0 ø Φ p. (D Φ μ- P. Hi ø ti Φ 0 0 X Hi ø if ø φ O μ- Hi if μ- ti Ti ti O Φ

< CQ rr 03 φ ii I-" Pi P. Ω O < Φ oo ti Φ fi rr 0 3 Φ < O Ti fu Ω μ- Φ μ- ø rt O 0 φ ti 0 rr tr μ- ø rt ti Φ rt 0 Φ Sϋ CD Ω 03 fD rr rt

Ω rt CQ rt H- ^ 03 φ 0 0 Ω Φ 3 tr φ ø Ti μ- Φ Ω if μ- rt Φ if

Φ if fϋ ø μ- *J 0 -— rt SD 03 ti Φ φ φ CQ fϋ Φ ø ø •*] Φ ø Ω Ω 0 Ω Φ φ fi Φ

CQ Φ ^ Ω Φ fu ti 03 * CO 3 03 03 fD rt rt O ø cQ ti^¬ £ O 0 O 3 p. ti Φ μ- SD Hi H fD ti μ- 03 03 rt ti Φ ^* ti fi ro ø' rr H μ- 3 fϋ Ti rt fi ti 03 Φ rt φ ø O Ω rt μ- μ- l-¹ rt Φ Φ r P. μ- 0 fϋ 0 Ω 0 rt fi μ- O ti

3 03 ii 3 Φ 03 CQ ø 0 € if Ω <! φ O ti CO 0 O \-> ø Ω 3 fϋ fi O ti X fD tr fu to φ ti PJ ϋ μ- φ ø μ- fD 0 φ Ω μ- rt 03 φ ti ti^¬ ø Φ fD φ SD μ-

Φ tr μ- r CQ rt ø rt rt 0 rt rt 0 s 0 μ- ro 03 Φ ø ø

Φ fϋ 0 Φ ø »i μ- rt tr CQ Φ tr fi CQ SD ti tr Hi Ti ^ O rt ø Ti Ω fϋ CQ CO Ω tr Ul 0 s; Ω tQ H- ø Su μ- SD Ω ø 0 fD CQ O Φ 0_, fD if tQ rt 0 μ- O Ω Φ O Ω o fi ø rt X ø 03 rr rt Ω rr Ω ti^¬ Ω Ω μ- O 03 Φ O Hi X J≡l tr α 0 O rt 0 ti ø rr Ω Φ μ- fi μ- rt ro μ- if <! fi Hi Hi O φ Ti H 0- ø rt Ti fϋ 0 0 0 tr φ Ti ø O O Φ SD O μ- O rt tQ ti rt Hi 0 CQ if

Φ Hi ø rt

0 ι-3 Ω 3 Hi φ ti Φ tQ CO μ- ti CD 3 ti 01 Ω rt fi O fϋ if μ- 0 Φ Ω fϋ

3 rt 03 tr if O O 03 03 ø μ- μ- 01 fϋ if tifi φ <! fi X rt Ω tr fD Φ Φ rt Ω> Ω ø tr φ rt 1 φ μ- ro 01 Ω O μ- rt Φ s CD ro φ CD φ rr rt CQ O rt

Φ 0 3 0 0 Ω tr rt 01 Ω rt fD ø ø μ- O 0 Ω ti < fϋ tr tr fD H fD fi 3 μ- CD ø Φ Φ rt φ fD rt rt ti 03 CQ O rt Hi SD Φ O O Ti μ- ø Φ fD rt oo

> φ 3 Sϋ Ω Hi O rr SD 3 ti μ-¹ $ ø ti Sϋ CO 0 ti Hi tr 3 μ- Ω fi rt Φ Hi

Φ ø μ- rt SD μ- rt Φ Ω O ø W o φ 0 rr Ti Φ fϋ Φ O CO X φ Ti O O fi 03 Ω ii CQ »i X if Si φ Φ fi Φ μ- tr O 0 ro Ω ø φ CQ fϋ μ- fϋ Φ H Hi φ if μ- ø 0 rt Φ tQ tr CQ Pi Φ P- X φ Φ Hi 03 rt fi fϋ X 0

H 3 X Ti ti O 0 ø fϋ Φ SD Φ φ Ω rt μ- O fϋ fi μ- 0 03 μ- 03 φ φ O Φ ^J l μ- Φ tr 0 φ 0 TJ rt rt rt P. l-¹ μ- rt Si 03 Hi Ti O ø fi 03 O μ- Ω μ- f" , , rt μ- X 03 Φ Hi CQ rt Φ μ- 3 Φ H ø ti Φ φ rt Ti P- CQ SD 03 ø rt 3 Ω ^ω

03 Φ ti co φ 3 fϋ if ti < Φ fi O Φ CO O Sϋ φ Ω ti 03 3 P. fi ø if ^ tr 0 oo H- SD rt Φ Φ Φ Φ ^ μ- Hi Φ fi ø μ- fi H μ- CO < O φ - 0 μ- μ- O I-¹

0 0 Ω Hi > O μ- ti TJ ø 0 01 μ- <! Φ CQ 03 Ω p. I-¹ O ti ø < P. rt 0

$ Hi rt 0 fi 1 SD < <i μ- CQ Φ fi CQ μ- 03 rt ø fu 0 0 Ω 3 Φ fi μ- Φ fD Hi ø 0 ti Φ oo H φ Φ SD X Sϋ Ti Ω rt 0 ø Ω tr μ- rt rt Hi rr 3 0 ø φ P. CQ ø

Φ ti 3 <! d ti φ r μ- rt tr 01 ti φ fu Φ ø fi μ- o p 3 ø Ti ø Φ rt μ- Φ Φ μ- "- TJ rt Φ rt Φ X ti Φ φ Φ ø μ- fϋ O rt 03 tr μ- 03 φ fϋ Ul O tr ø Φ fi Ω H- μ- Φ φ O ti P. ^ P. Ω ø rt ø ø tr O μ- ø Φ

SD ø

X Ω φ ti P. Φ Si 3 fϋ 0 if to φ 0 fϋ ø Φ

Ω 0 Φ ro ø Hi P. 03

Hi rt Hi Hi 03 CD fD Ω ø φ CO Φ 0 . 03 Ω 0 O Φ μ- o φ ø φ Hi 0 φ CQ ø Hi μ- ti ti OJ H> rt SD <! Φ 03 ti ^ O fi ti CD Hi rt fD fi μ- 0 fu fi fϋ μ-

CQ O rt 0 if X ti rt μ- Ω rt Φ tr H 0 0 0 Si o rt ti o tr CQ r ti^¬ T <! ø Ω tr 3 SD U) fi 3 O μ- Ω rt if μ- 0 01 rt Ω Φ rt O < Sϋ 0 μ- ø 3 H¹ ro μ¹ TS φ ti tr Φ <! Φ ϋ fi < φ fi ti rt Ω φ fϋ rt ti tr ϋ IQ 0 1— i CD ø ti fD • : M I-¹

Φ φ 03 rt μ- 3 <! rt Φ Φ 0 O if μ- tr rt fi Ω O Φ CD " 03 μ- 0 φ rt μ- Ti

3 Φ tr ø SD H- fi P. ø φ ø if rt ti rt fi μ- fϋ fϋ ϋ o fϋ Ω μ-

OD μ- ti ⁽Q rt O μ- μ> μ- 03 Φ CQ ti 3 μ- rt 03 01 O μ- fϋ co Ti σ, μ- ti fϋ ti Φ X 03 CO tr φ 3 Φ 03 O ti ø 0 X

> Ω Φ rt Ti l • X rr φ <-r φ fϋ fu Φ SD μ- CQ O • fu fϋ CO 3 O fi O fϋ X fϋ μ-

^ X fi _^-_^ rr ø rr 3 rr ø < Hi fD ø μ- O ti ri- μ- l K O CQ O 03

Ω φ Pi < Φ rt 0 φ μ] tr SD fi CO fϋ 0 TJ ø Ul 0 rt CQ Ω Φ Hi Φ μ-

Ti ti μ- φ 0 CO if if Φ •<: μ- ti fi < T) μ- • Φ tr 0

0 cr SD ti μ- Ti * Φ Ω rr μ- 3 fϋ 3 0 3 ø μ-

3 μ- 03 Hi fi Hi μ- SD if rt fϋ Φ Φ 3 O 03

1 X Hi rr CQ 01 ti SD Ω 0 φ if fϋ ti ^ μ- ti 01 fi CD μ- rt I—¹ SD Ω Hi φ Ti Φ μ- ø 0 *< ø 0 Ω CO fϋ ø fu μ- μ- 03 O Φ O ti Φ *< O Ω t-> ø ti Ω μ- 1 CO 0 Ω rt rt fϋ Φ $ rt 1 SD 03 0 φ 1 ø ø μ- Ω 0 < O 0 O

Hi ø CQ X 1 tr I p m. ø fi Hi r Φ 1

prises the electrochemically active element 4 of each of the transistor devices. Also in this layer are positive (5) and negative (11) gate electrodes, and conductors connecting the gate electrodes of each row. In order to minimise cross-talk, the negative electrodes 11 have all been provided with a resistance, which is shown in the figures as a line interrupting each negative electrode 11. The source and drain contacts 2,3 of the electrochemical transistor device and one electrode 7 of the electrochromic device are also present in this layer. The middle layer II, or spacer layer, is shown in figure 8B. This layer comprises the elements of solidified electrolyte that are necessary for the electrochemical reactions in the electrochemical pixel device. Thus, the electrolyte 9 for the electrochromic device B is provided so that it contacts the electrode 7 of the bottom layer I and the electrochromic element 6 of the top layer III when the layers are put together. In the same fashion, the electrolyte 10 for the electrochemical transis- tor device A is provided so that it contacts the electrochemically active element 4 and the gate electrode 5 of the bottom layer when the layers are put together. The middle layer II also comprises vias 12, that are formed from an electrically conducting material and serve the purpose of mediating transport of charges to the drain contacts 3 of the bottom layer I from the top layer III, described next .

Figure 8C illustrates the top layer III. In this layer, conductors 13 supply V_ds to the top layer via the vias 12 of the middle layer. The bottom layer also comprises the electrochromic elements 6 of the vertical electrochromic devices. In this particular embodiment, the electrochromic elements 6 of all pixels in a column are formed from the same piece of electrochromic and con- ducting material, and the electrodes 8 for application of V_ds to the electrochemical pixel devices in this column may be thought of as those parts of this piece that are not in contact with the gel electrolyte underneath. This arrangement makes possible the application of V_ds to drains 3 and electrodes 8, in a fashion similar to the operation of the single, lateral electrochemical pixel device shown in figure 1. The top layer III also comprises areas 14, which have been made non-conducting or isolated, which are in contact with the electrochemical transistor device electrolytes 10 in the layer above and which serve the purpose of preventing leak currents from the electrochemically active elements 4.

Figure 8D is a simple sketch of the three layers taken together, which is primarily intended to illustrate the vias 12, which establish electrical contact between components of layers I and III.

Claims

1. A pixel device, which comprises the following components : (A) an electrochemical transistor device comprising: a source contact; a drain contact; at least one gate electrode; an electrochemically active element arranged between, and in direct electrical contact with, the source and drain contacts, which electrochemically active element comprises a transistor channel and is of a material comprising an organic material having the ability of electrochemically altering its conductivity through ' change of redox state thereof; and a solidified electrolyte in direct electrical contact with the electrochemi- cally active element and said at least one gate electrode and interposed between them in such a way that electron flow between the electrochemically active element and said gate electrode (s) is prevented; whereby flow of electrons between source contact and drain contact is controllable by means of a voltage applied to said gate electrode (s) , and

(B) an electrochromic device comprising: at least one electrochromic element comprising (i) at least one material that is electrically conducting in at least one oxidation state and (ii) at least one electrochromic material, wherein said materials (i) and (ii) can be the same or different; at least one layer of a solidified electrolyte which is in direct electrical contact with said electrochromic element; and at least two electrodes adapted for application of a voltage therebetween; each of said electrodes being in direct electrical contact with a component selected from said electrolyte layer (s) and said electrochromic element; in which pixel device one of said source and drain contacts of the electrochemical transistor device A is in electrical contact with one of the electrodes of the electrochromic device B.

2. An electrochemical pixel device according to claim 1, in which the source contact of the electrochemical transistor device A is in electrical contact with one of the electrodes of the electrochromic device B.

3. An electrochemical pixel device according to claim 1, in which the drain contact of the electrochemical transistor device A is in electrical contact with one of the electrodes of the electrochromic device B.

4. An electrochemical pixel device according to any one of the preceding claims, in which said source and drain contacts, gate electrode (s) and electrochemically active element of the electrochemical transistor device A are arranged in one common plane .

5. An electrochemical pixel device according to claim 4, in which, in the electrochemical transistor de- vice A, a continuous or interrupted layer of solidified electrolyte covers the electrochemically active element and covers at least partially said gate electrode (s) .

6. An electrochemical pixel device according to any one of the preceding claims, in which, in the electrochemical transistor device A, at least one of said source and drain contacts and gate electrode (s) is formed from the same material as the electrochemically active element .

7. An electrochemical pixel device according to claim 6, in which, in the electrochemical transistor device A, all of said source and drain contacts and gate electrode (s) are formed from the same material as the electrochemically active element.

8. An electrochemical pixel device according to any one of claims 6-7, in which, in the electrochemical transistor device A, the source and drain contacts and the electrochemically active element are formed from a con- tinuous piece of said material comprising an organic material .

9. An electrochemical pixel device according to any one of the preceding claims, in which, in the electro- chromic device B, the electrodes are formed from the same material as the electrochromic element .

10. An electrochemical pixel device according to any one of the preceding claims, in which the source and drain contacts, the electrochemically active element and the gate electrode (s) of the electrochemical transistor device A and the electrochromic element and the electrodes of the electrochromic device B are all formed from the same material .

11. An electrochemical pixel device according to any one of the preceding claims, in which, in the electrochemical transistor device A, the organic material is a polymer .

12. An electrochemical pixel device according to any one of the preceding claims, in which, in the electrochromic device B, the electrochromic material comprises an electrochromic polymer.

13. An electrochemical pixel device according to any one of claims 11-12, in which the organic material in the electrochemical transistor device A is a polymer and the electrochromic material in the electrochromic device B comprises an electrochromic polymer.

14. An electrochemical pixel device according to claim 13, in which the electrochromic polymer in the electrochromic device B is the same material as the polymer in the electrochemical transistor device A.

15. An electrochemical pixel device according to any one of claims 11-14, in which any electrochromic polymer present in the electrochromic device B and any polymer present in the electrochemical transistor device A is se- lected from the group consisting of polythiophenes, polypyrroles, polyanilines, polyisothianaphtalenes, poly- phenylene vinylenes and copolymers thereof.

16. An electrochemical pixel device according to claim 15, in which any electrochromic polymer present in the electrochromic device B and any polymer present in the electrochemical transistor device A is a polymer or copolymer of a 3 , 4-dialkoxythiophene, in which the two alkoxy groups may be the same or different or together represent an optionally substituted oxy-alkylene-oxy bridge .

17. An electrochemical pixel device according to claim 16, in which said polymer or copolymer of a 3,4-di- alkoxythiophene is selected from the group consisting of poly (3 , 4-methylenedioxythiophene) , poly (3 , 4-methylenedioxythiophene) derivatives, poly (3 , 4-ethylenedioxythio- phene) , poly (3 , 4-ethylenedioxythiophene) derivatives, poly (3 , 4-propylenedioxythiophene) , poly (3 , 4-propylenedi- oxythiophene) derivatives, poly (3 , 4-butylenedioxythiophene) , poly (3, 4-butylenedioxythiophene) derivatives, and copolymers therewith.

18. An electrochemical pixel device according to any one of the preceding claims, in which the electrochromic material in the electrochromic device B and/or the or- ganic material in the electrochemical transistor device A comprise (s) a polyanion compound.

19. An electrochemical pixel device according to claim 18, in which said polyanion compound is poly(styrene sulfonate) or a salt thereof.

20. An electrochemical pixel device according to any one of the preceding claims, in which the solidified electrolyte in the electrochemical transistor device A and/or the solidified electrolyte in the electrochromic device B comprise (s) a binder.

21. An electrochemical pixel device according to claim 20, in which said binder is a gelling agent selected from the group consisting of gelatine, a gelatine derivative, polyacrylic acid, polymethacrylic acid, poly (vinylpyrrolidone) , polysaccharides, polyacrylamides, polyurethanes, polypropylene oxides, polyethylene oxides, poly(styrene sulphonic acid) and poly (vinyl alcohol), and salts and copolymers thereof.

22. An electrochemical pixel device according to any one of the preceding claims, in which the solidified electrolyte in the electrochemical transistor device A and/or the solidified electrolyte in the electrochromic device B comprise (s) an ionic salt.

23. An electrochemical pixel device according to any one of the preceding claims, in which the same solidified electrolyte is used in both the electrochemical transistor device A and the electrochromic device B.

24. An electrochemical pixel device according to any one of the preceding claims, arranged on a support.

25. An electrochemical pixel device according to claim 24, in which said support is selected from the group consisting of polyethylene terephthalate, polyethylene naphthalene dicarboxylate, polyethylene, polypro- pylene, polycarbonate, paper, coated paper, resin-coated paper, paper laminates, paperboard, corrugated board and glass .

26. An electrochemical pixel device according to claim 24 or claim 25, in which said support is reflective .

27. An electrochemical pixel device according to any one of the preceding claims, in which, in the electro- chromic device B, the electrodes and the electrochromic element are arranged side by side in a common plane.

28. An electrochemical pixel device according to any one of claims 1-26, in which, in the electrochromic de- vice B, the electrodes and the electrochromic element are arranged vertically.

29. A matrix comprising a plurality of the electrochemical pixel device according to any one of claims 1- 28.

30. A matrix according to claim 29, in which the electrochemical pixel devices have one gate electrode each.

31. A matrix according to claim 29, in which the electrochemical pixel devices have at least two gate electrodes each.

32. A matrix according to claim 31, in which one of the gate electrodes of each electrochemical pixel device is provided with a resistance, in order to minimise cross-talk between pixels.

33. A pixelated display comprising a matrix accord- ing to any one of claims 29-32.

34. A process for the production of an electrochemical pixel device according to claim 1, which process comprises deposition of said contacts, electrodes, electro- chemically active element, electrochromic element and electrolyte (s) onto a support.

35. A process according to claim 34, wherein said contacts, electrodes, electrochemically active element, electrochromic element and/or electrolyte (s) are deposited by means of printing techniques.

36. A process according to claim 34, wherein said contacts, electrodes, electrochemically active element, electrochromic element and electrolyte (s) are deposited by means of coating techniques.

37. A process according to any one of claims 34-36, in which device said organic material of the electro- chemical transistor device A and/or said electrochromic element of electrochromic device B comprises a polymer, which process comprises deposition of said polymer on a support through in si tu polymerisation.

38. A process according to any one of claims 34-37 comprising patterning of any one of contacts, electrodes, electrochemically active element and electrochromic element using a subtractive method.

39. A process according to claim 38, in which said patterning is performed through chemical etching.

40. A process according to claim 38, in which said patterning is performed through gas etching.

41. A process according to claim 38, in which said patterning is performed by mechanical means, comprising scratching, scoring, scraping and milling.

42. A process according to any one of claims 34-41, in which said electrochemical pixel device is as defined in any one of claims 2-28.