WO2015144204A1

WO2015144204A1 - Light-emitting electrochemical cell and method of its manufacture

Info

Publication number: WO2015144204A1
Application number: PCT/EP2014/055868
Authority: WO
Inventors: Andreas SANDSTRÖM; Ludvig Edman; Mattias LINDH
Original assignee: Lunalec Ab
Priority date: 2014-03-24
Filing date: 2014-03-24
Publication date: 2015-10-01

Abstract

This document discloses a light-emitting electrochemical cell which comprises a first electrode (2), an electrolyte material (3) which comprises ions and optionally ionizing solvent, an organic semiconducting material (4) capable of emitting light, and a second electrode (5). The organic semiconducting material is in electrical contact with the first and second electrode. The electrolyte material and the organic semiconducting material form separate regions and each consists essentially of the respective material, and the electrolyte material region presents a predetermined pattern in an area of overlap between the first and second electrode.

Description

LIGHT-EMITTING ELECTROCHEMICAL CELL AND METHOD OF ITS

MANUFACTURE

Technical Field

The present disclosure relates to a light-emitting electrochemical cell and a method for manufacturing a light-emitting electrochemical cell.

Background

Light-emitting devices based on electroluminescent organic materials offer a plethora of desirable advantages, such as conformable and extremely thin form factors, sharp contrasts in displays, etc. High-performance small displays based on light-emitting diodes have been commercialized, but the current drawback that hinders their introduction into low-cost and large-area applications is that they comprise either a vacuum-processed and therefore expensive active material (small-molecule OLEDs) or a reactive low-work- function cathode (polymer OLEDs).

Light-emitting electrochemical cells (LECs) are distinguished from the

OLEDs in that an electrolyte with mobile ions is blended with a light-emitting semiconducting organic material in the active layer. Disadvantages with this LEC structure are phase separation of the two materials, and occurrence of uneven and non-homogenous active layer which may result in poor light emitting properties.

Recently a bilayer light-emitting electrochemical surface cell structure, in which the ion- and electron-transport channels are separated, was presented (A. Sandstrom, et al. J. Am. Chem. Soc. 2010, 132, 6646-6647). This device was manufactured by sequentially spin-coating and drying a solution of the organic semiconductor superyellow (SY, Merck) and a solution of electrolyte on top of pre-patterned lateral Au electrodes. This lateral device structure results in improved device operation, such as shorter turn-on time and increased operational life time. However, it would be highly desirable to also improve the light-emitting properties of sandwich LECs and to make the manufacturing process more effective.

Hence, it is highly desirable to develop a new light-emitting electrochemical cell structure with improved light emission properties and to provide a new manufacturing process of such a light-emitting electrochemical cell.

Summary

An object of the present invention is to provide a new light-emitting electrochemical cell structure with improved light emission properties.

The invention is defined by the appended independent claims.

Embodiments are set forth in the appended dependent claims, in the following description, and in the drawings.

According to a first aspect, there is provided a light-emitting electrochemical cell which comprises a first electrode, an electrolyte material which comprises ions and optionally ionizing solvent, an organic semiconducting material capable of emitting light, and a second electrode. The organic semiconducting material is in electrical contact with the first and second electrode and the electrolyte material and the organic semiconducting material form separate regions, each consisting essentially of the respective material, and the electrolyte material region presents a predetermined pattern in an area of overlap between the first and second electrode.

By "cell" is hereby meant an individually addressable unit.

By "electrolyte material" is meant a material with free mobile ions which makes the material electrically conducting but which preferably does not conduct electrons or holes.

The organic semiconducting material may be a polymer, an oligomer or small molecules. The material may be a homogenous material or a mixture of materials, e.g. a "host-guest system".

By "electrical contact" is meant that electrons and/or holes can be electrically injected from the electrode into the organic semiconductor. Hence, there may be physical contact between the organic semiconducting material and the electrode, or there may be a contact improving layer, forming an extension of the electrode, between the organic semiconducting layer and one or both electrode(s). Moreover, there may be a layer of electrolyte between the organic semiconducting material and the electrode, which is so thin as to allow tunneling of electrons or holes between the electrode and the organic semiconducting material.

By "region" is here meant an essentially homogenous area of electrolyte material or organic semiconducting material, respectively.

By "consisting essentially" is meant that the electrolyte and/or organic semiconducting material may comprise traces of other materials, which do not materially affect the function of the respective material. For example, materials of the different regions may migrate, especially upon operation of the light-emitting electrochemical cell. Preferably, each region consists of the respective material.

A "predetermined pattern" is defined as a pattern or shape that is intentionally created as opposed to a pattern which is spontaneously and/or randomly formed, e.g. as a consequence of a mixing and/or a phase separation of the constituents.

For example, the electrolyte material forming part of a cell may have the form of a layer having a general outline with one or more through recesses being formed as slits, holes or cut-away portions within the outline. The shape and size of said slits, holes or cut-away portions are determined by the predetermined pattern.

As another example, the electrolyte material of the cell may present at least two distinct portions, having a respective shape and size and being connected to each other or separated from each other. The shape and size of the portions are determined by the predetermined pattern.

The light in the device may arise in the p-n junction in lateral proximity to an interface between the electrolyte material and the organic

semiconducting material, and near an electrode.

The light-emitting electrochemical cell may display desired

information by patterning of the electrolyte material instead of the common way of patterning of the electrode. The light-emitting electrochemical cell may exhibit excellent flexibility in the information content, i.e. option to create distinct and high resolution patterns in small series.

The light-emitting electrochemical cell may allow the use of

electrochemically unstable electrolytes as the interaction between electrolyte and semiconducting material is minimized.

An advantage with this patterned sandwich LEC structure is that it may lead to improved light out coupling and increased luminous flux.

Yet another advantage is that only the electrolyte material needs to be patterned, while electrodes can be formed as substantially planar layers. Also the organic semiconducting material may be formed as a layer while filling out any slits, holes or cut-away portions formed in the electrolyte.

A region of electrolyte material may have a volume of at least 0.001 (pm)³, preferably at least 0.01 (pm)³, or at least 0.1 (pm)³.

A region of organic semiconducting material may have a volume of at least 0.001 (pm)³, preferably at least 0.01 (pm)³, or at least 0.1 (pm)³.

The organic semiconducting material may be substantially free from mobile ions in its pristine state.

By "substantially free from mobile ions" is meant an organic

semiconducting material contains <0.05 wt-% electrolyte, <0.5 wt-%

electrolyte, <5 wt-% electrolyte.

One region of electrolyte material may form a layer and the organic semiconducting material may be in electrical contact with the first and second electrode via one or several through recesses formed in the layer of electrolyte material.

By "layer" is meant a continuous region having a mainly 2-dimensional extension and a substantially uniform thickness.

A "through recess" may be a through hole, slot or pattern in the electrolyte material.

A region of electrolyte material may only partially cover the first electrode. Thereby the electrolyte material may have less lateral extension than the electrode.

The light-emitting electrochemical cell may comprise at least two co- planar regions of electrolyte material.

Such co-planar regions may be completely separated from each other, or there may be a portion linking them to each other.

Each of the regions of electrolyte material may be in physical contact with both of the electrodes.

By "physical contact" is hereby meant that the there is no other material between the regions of electrolyte material and the electrodes.

Each of the regions of electrolyte material may be spaced from both the first and second electrode.

"Spaced from" is herein defined as that a region of electrolyte material is not in physical contact with any of the electrodes.

At least one of the electrodes is transparent for visible light.

By "transparent" is meant that at least 5 %, preferably at least 10 % or most preferably at least 25 % of the visible light is transmitted.

One or both of the first electrode and second electrodes may be transparent.

At least one of the electrodes may be non-transparent for visible light, and may preferably be reflecting.

At least a part of the predetermined pattern may provide a diffraction grating, such as a Bragg grating, adapted to couple out light from the electrochemical cell.

Techniques for providing diffraction gratings in planar structures are known as such. Providing such a diffraction grating through the patterning of the electrolyte implies improved out-coupling of light without increasing the number of parts or the complexity of the structure and without adding further process steps in the manufacturing.

According to a second aspect, there is provided a method of manufacturing a light-emitting electrochemical cell. The method comprises providing a first electrode, providing at least one patterned region of electrolyte material comprising ions and optionally ionizing solvent, providing at least one organic semiconducting material capable of emitting light and providing a second electrode. The organic semiconducting material is provided such that it electrically contacts both the first and second electrode, and the electrolyte material is provided in an area of overlap between the first and second electrode.

By this method it may be possible to add more than one region/layer of organic semiconducting material, more than one region/layer of electrolyte material, to add electrolyte regions/layers and/or organic semiconducting layers/regions in several steps etc.

The order in which the layers/regions are deposited may be altered, e.g. the organic semiconducting material may be deposited first and the region(s)/layer of electrolyte subsequently.

LECs may be stacked on top of each other, all with their own

electrodes. An electrode may be shared by two or more electrochemical cells. More than one organic semiconducting material may be used in the same active layer and share two electrodes, either separated from each other or as several layers.

The electrolyte material may be added continuously, e.g. by roll-to-roll fabrication, or it may be deposited as small regions or droplets.

An advantage of this method is that the electrolyte, instead of the electrode, is patterned and therefore the method is scalable to large areas.

Providing at least one patterned region of electrolyte material may comprise forming a continuous electrolyte material layer and patterning the layer by a subtractive process.

By "subtractive process" is meant that regions/lines are

removed/displaced from a layer/region of electrolyte material.

Providing a patterned region of electrolyte material may comprise depositing the electrolyte material by an additive process.

By "additive process" is here meant that regions of electrolyte material are added to an electrode or a layer of organic semiconducting material. Hence, an advantage of the method is that it allows for both additive and subtractive patterning of electrolyte.

The organic semiconducting material may be provided by a second additive process.

The organic semiconducting material may be added by the same additive process or by another additive process as compared to the electrolyte layer.

The region of electrolyte material may be provided at least partially on a portion of the organic semiconducting material.

The organic semiconducting material may be provided on at least part of the discrete region of electrolyte material.

Brief Description of the Drawings

The appended drawings contain, in addition to the schematic drawings and graphs illustrating the different LEC structures, performance and manufacturing of LECs, photos/micrographs taken while testing the various embodiments. These photos/micrographs are intended merely to illustrate the fact that light was actually generated by the respective device.

Fig. 1 a-1 e schematically illustrates different examples of LEC structures.

Fig. 2a-2d schematically illustrates a subtractive method of

manufacturing an LEC.

Fig. 3a-3d schematically illustrates another subtractive method of manufacturing an LEC.

Fig. 4a-4d schematically illustrates an additive method of

manufacturing an LEC.

Fig. 5 is a graph showing optoelectronic characteristics of a bilayer LEC with a filled micrometer sized array pattern.

Fig. 6a is a height profile graph of a dry ink-jetted electrolyte droplet as recorded by a stylus profiler.

Fig. 6b is a micrograph of the initial light emission from a

corresponding one-droplet region in a bilayer LEC. Fig. 6c is a micrograph of the same cell as in Fig. 6b, during diascopic illumination.

Fig. 6d is a photograph of the patterned light-emission from a bilayer

LEC.

Fig. 7 is a photograph showing the light-emission from a bilayer LEC patterned by scratching in the layer of electrolyte material.

Description of Embodiments

The concept disclosed herein will now be explained in more detail. Initially, different LEC structures and examples of materials used for the constituents are described. Thereafter different methods of manufacturing these LECs are described and finally some examples of device performances are shown.

Fig. 1 a schematically illustrates a layered electrochemical cell structure. The structure has a first electrode 2 on a substrate 1 , which may be planar. On top of the electrode there is a layer of electrolyte material 3 followed by a layer of organic semiconducting material 4. Finally the structure is provided with a second electrode 5 which completely or partially covers the organic semiconducting material. Hence, in this structure, the organic semiconducting material is only in electrical contact with the second electrode. Since the organic semiconducting material is not in electrical contact with both the first and second electrode this electrochemical cell does not function, i.e. it does not emit light when voltage is applied between the first and second electrode. However, if the layer of electrolyte material is very thin, e.g. on the order of 1 nm or less, electrons and holes may tunnel through the layer such that the organic semiconducting material will be in effective electrical contact with both the first and second electrode.

In Fig. 1 b schematically illustrates another layered LEC structure. The structure is similar to the one shown in Fig. 1a but with one key difference being that the organic semiconducting material 4 is in electrical (and physical) contact with both the first and second electrode 2, 5 by a through recess formed in the layer of electrolyte material. The through recess is filled with semiconducting material 4. On both sides of the through recess the layer of electrolyte material is in physical contact, with both the first and second electrode. Since the electrolyte material is a good electrical insulator (i.e. does not conduct electrons or holes), there is no problems with short-circuit in this LEC structure.

Fig. 1c schematically illustrates yet another layered electrochemical cell structure. The structure is generally the same as the one described in Fig. 1a, but with the difference that there is a through recess in the layer of electrolyte material 3 such that the organic semiconducting material 4 is in electrical contact with both the first and second electrode 2, 5.

Fig. 1d shows yet another layered LEC structure. The structure is similar to the one described in Fig. 1 c, but here the layer of electrolyte material 3 with the through recess is spaced from both the first electrode and the second electrode 2, 5. Furthermore, the layer of electrolyte material with the through recess may be embedded in the organic semiconducting material 4 such that no electrolyte material is in physical contact with any of the first or second electrodes. The organic semiconducting material is in electrical contact with both the first and second electrode.

In Fig. 1e, a LEC structure with more than two regions of electrolyte material/more than two layers of electrolyte material with recesses is shown. This structure is similar to the one in Fig. 1 c, but has an additional layer of electrolyte material with a through recess on top of the organic

semiconducting material. The two layers of electrolyte material are hence spaced from each other by the organic semiconducting material. There is organic semiconducting material in the through recesses of the layers of electrolyte material. The organic semiconducting material is thereby in electrical contact with both the first and second electrode.

It is important to note that Figs a-1e show vertical structures which do not have to be limited in the lateral direction.

The patterned layer(s)/regions of electrolyte material may be provided at different distances from the respective electrode, and/or at different distances from each other. Furthermore, the regions of electrolyte material may be provided in more than two surface planes. One of the regions of electrolyte material may be in contact with the first electrode, and the other region of electrolyte material may be in contact with the second electrode or both regions of electrolyte material may be in contact with the same electrode.

Substrate

The substrate may be made of a conducting or non-conducting material. If the substrate is made of a conducting material, such as a metal, it may function as a combined substrate/first electrode in a LEC device. In this case, the combined substrate/first electrode may be any type of conducting material, such as a metal structure, plate or foil, or a conducting polymeric material or a doped semi-conducting material.

As an alternative, the substrate may be made of a non-conducting material, such as glass, crystals (e.g. quartz or sapphire), wood, paper, ceramics or polymeric material.

Moreover, the substrate may be transparent to visible light. Examples of substrates that may be transparent are e.g. glass, polymeric materials or ceramics.

The substrate may be rigid or flexible such that it can be bent and possibly also folded.

The area of the substrate may be ranging from 1 mm² up to 20 m² for example in roll-to-roll fabrication. First Electrode

As described above, one possibility is to utilize a combined

substrate/first electrode. Another possibility is to utilize a non-conducting substrate which may be coated by a thin layer of an electrical conductive material forming a first electrode.

Various depositing techniques may be used for this coating, such as electron beam evaporation, physical vapor deposition, sputter deposition techniques, etc. For solution processable materials, such as conducting polymers etc., various printing and coating techniques may be utilized.

A transparent electrical conductive material may be selected from a group consisting of: graphene, graphene oxide, carbon nanotubes, thin metal films, metal meshes, metallic nanowires, a doped transparent conductive oxide (TCO), and transparent conducting polymers (TCP).

The metallic nanowires may be selected from a group consisting of any conductive material or blend thereof, such as Ag, Cu, Ni, and CuNi.

The TCO may be selected from a group consisting of SnO2, ln₂O₃, ZnO, CdO, Sb2O3, and mixtures thereof.

Specific, non-limiting examples include indium tin oxide, fluorine tin oxide, Al zinc oxide, indium cadmium oxide, gallium zinc oxide, and indium zinc oxide.

The TCP may be selected from a group consisting of polythiophenes, polypyrroles, polyanilines, polyisothiana phthalenes, polyfluorenes, polyphenylene vinylenes and copolymers thereof. Specific, non-limiting examples include Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), PEDOT:tosylate and/or other transparent conducting polymers, and/or blends thereof.

Alternatively the first electrode may be reflective to visible light, e.g. different types of metals, such as Al, Au or Ag.

Electrolyte material

The electrolyte material is a material with free mobile ions but which does not conduct electrons or holes. Preferably, a functional electrolyte material may be a material that exhibits an average ion mobility of at least 1 ^*10^~14 m²A s, and an electronic conductivity below 1 ^*10^-8 S/m.

The electrolyte material may be selected from a group consisting of: a gel electrolyte, a substantially solid electrolyte, a substantially liquid electrolyte, a salt comprising electrolyte, an electrolyte comprising an ionic liquid, an electrolyte comprising an ionizing material, or combinations thereof. The salt comprising electrolyte may comprise at least one metal salt, the salt comprising a cation, such as Li, Na, K, Rb, Mg, or Ag, and a molecular anion, such as CF3SO3, CI0₄, or (CF₃S0₂)2N .

The electrolyte material may in addition comprise an ionizing material, preferably a material comprising one or more ether oxygen groups. Examples of such materials includepoly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG), trimethylolpropane ethoxylate (TMPE), polypropylene oxide), methoxyethoxy-ethoxy substituted polyphosphazane, and polyether based polyurethane, or combinations thereof.

The ionizing material may have functionalized end groups. One example of such an end group is dimethacrylate (DMA).

The electrolyte material may comprise further constituents which do not alter the function as an electrolyte. Such constituents may be additives providing e.g. increased viscosity and improved wetting properties in the ink phase, a certain texture or color, etc.

The electrolyte material may be in physical contact with the first and/or second electrode. As an alternative there may be a layer of a contact- improving material provided between the layer of electrolyte material and the first electrode. Examples of such contact-improving materials may be PEDOT:PSS, Ag nanowires, ZnO, polyaniline (PANI) or carbon nanotubes (CNT). The layer of electrolyte material in this LEC structure is spaced from the first electrode by a distance of 0.002 to 50 pm, preferably 0.1 pm.

The electrolyte material may be patterned such that an organic semiconducting material, when deposited on the patterned electrolyte material, is in electrical contact with both the first and second electrode in a LEC device. The patterning may be performed by either a subtractive or an additive method.

If patterning the electrolyte material by a subtractive method, electrolyte material may be removed and/or displaced such that through recess(es) is/are formed in an already applied layer of electrolyte material.

Subtractive patterning may be performed by a mechanical process. The patterning may be in the form of a line pattern, an array pattern, etc., and may be effectuated by an object providing a line or point contact, e.g. a scraper, knife, stylus or a nanoimprinter. Such patterning may provide a result as illustrated by fig. 7. Other options include milling or drilling type operations. It may also be effectuated by punching holes in the layer of electrolyte material.

As an alternative, subtractive patterning may be performed by a chemical process for removing/displacement of electrolyte material. A material capable of etching or dissolving the electrolyte material may then be provided on the layer of electrolyte material were the through recess(es) is desired. Depending on the chosen electrolyte materials, materials capable of etching or dissolving electrolyte materials can be e.g. cyclohexanone, ethanol, isopropanol or THF.

As a further alternative, subtractive patterning may be performed by a radiation process where regions in the layer of electrolyte material are subjected to radiation or ablation such that a through recess is created. This may be performed by e.g. radiation of laser, UV-light, plasma, an electron or ion beam, particles etc.

As mentioned above, the layer of electrolyte material may be patterned in one or several steps by an additive method.

Upon additive patterning, regions of electrolyte material are added as droplets or regions on the first electrode or on the organic semiconducting material.

The deposition of the regions of electrolyte material may be performed by printing techniques such as ink-jet, screen-, flexo- or gravure printing, slot- die coating or Mayer rod coating. It is also possible to add the electrolyte material by spray-coating, curtain coating or by simply adding droplets of electrolyte material by a pipette.

These additive or subtractive patternings may result in a patterned layer area of 100 (nm)²- 50 m², preferably 1 (Mm)²- 5 m², 10 (Mm)²- 0.5 m², 100 (Mm)²- 0.1 m², 100 (Mm)²- 0.01 m² or 100 ( m)²- 0.001 m², and a thickness of at least 10 nm, preferably at least 100 nm, or at least 10 Mm. The additive patterning may also result in circular features with a diameter of at least 10 nm, preferably at least 100 nm, at least 1 μιτι, at least 10 pm or at least 100 pm. It is important to note that these numbers are only examples and not limiting intervals.

Organic Semiconducting Material

The organic semiconducting material may be a light-emitting molecular, oligomeric or polymeric material.

A light-emitting molecular material may be selected from a group of ionic transition metal complexes, such as Ru(bpy)₃ ²⁺(X^")₂, where bpy is bipyridine and X^" is an anion, or from a group of non-metallic complexes such as rubrene or 4,7-bis(4-(4-sec-butoxyphenyl)-5-(3,5-di(1- naphthyl)phenyl)thiophen-2-yl)-2, 1 ,3-benzothiadiazole.

A light-emitting polymeric material may be selected from a group of conjugated polymers comprising poly(para-phenylene vinylene (PPV), polyfluorenylene (PF), poly(1 ,4-phenylene) (PP), polythiophene (PT), and neutral and ionic derivatives thereof, and any type of co-polymer structure thereof. The conjugated polymer may be a phenyl-substituted PPV

copolymer, such as "superyellow" (SY, Merck, PDY-132), poly[2-methoxy-5- (2-ethyl-hexyloxy)-1 ,4-phenylenevinylene] (MEH-PPV), and a

polyspirobifluorene-based copolymer, such as "superblue" (SB, Merck, SPB- 02T).

The semiconducting material may be in physical contact with both the first and second electrode, or a contact-improving layer may be provided between the organic semiconducting material and the first and/or second electrode. Examples of such contact-improving materials may be

PEDOT:PSS, Ag nanowires, ZnO, PANI or CNT.

The organic semiconducting material may be deposited in one or several additive steps by various printing techniques (inkjet-, screen- or offset printing) or coating techniques (e.g. spin-coating or spray-coating) on the patterned layer of electrolyte material and/or on the first electrode. When depositing in several steps it may be advantageous to employ materials with orthogonal solubility such that the solvents of the subsequently, for example immediately adjacent, deposited organic semiconducting materials do not dissolve the beneath (dry) layer(s). This is valid for most types of solution-based deposition and for all materials/layers being

deposited.

Second Electrode

The second electrode is made of an electrical conductive material. It may be made of the same or a different material as the first electrode.

Examples of suitable materials for the second electrode are the same as the ones discussed in the paragraph about the first electrode.

Like the first electrode, the second electrode may be transparent for visible light. One or both of the first electrode and second electrodes may be transparent. Alternatively, one of the electrodes may be transparent, and the other non-transparent and optionally reflective, such that the light can be emitted from only one side of the LEC device.

The second electrode may be provided using the same deposition techniques as the ones mentioned above for the deposition of the first electrode.

In Fig. 2a-2d a subtractive method of manufacturing the LEC structures described above is depicted. Fig. 2a schematically illustrates a planar substrate 1 on which a first electrode 2 followed by a layer of electrolyte material 3 has been deposited.

In Fig. 2b an object 6 is punched, pressed, stamped or drawn through or almost through the layer of electrolyte material 3 forming a through recess in the electrolyte material. The through recess is formed by removing or displacing the electrolyte material. The shape of the tool that

removes/displaces the electrolyte material determines the shape of the through recess. The through recess may be provided to a depth that allows effective electrical contact between the electrodes (or contact improving layer, as the case may be) and the organic semiconducting material. In Fig. 2c an organic semiconducting material 4 is deposited on the patterned layer of electrolyte material 3' (with several through recesses), such that there is organic semiconducting material in the through recesses in the layer of electrolyte material and the organic semiconducting material is in electrical contact with the first electrode 2.

A second electrode 5 is then deposited on the organic semiconducting material 4 as depicted in Fig. 2d. When a voltage is applied between the first and second electrode, light is emitted in proximity of the edges of the layer of electrolyte material in the interface region between the patterned electrolyte material and the organic semiconducting layer.

In Fig. 3a-3d a similar manufacturing method as the one described in Figs. 2a-2d is shown. Fig. 3a shows a layered structure with a substrate 1 with a first electrode 2 and a layer of electrolyte material 3, respectively. In Fig. 3b a sharp object 7 is moved over the layer of the electrolyte material such that a pattern is scratched in the layer of electrolyte material. An organic semiconducting layer 4 is deposited on top of the patterned electrolyte 3" material such that the organic semiconducting material fills the

recesses/scratches in the layer of electrolyte material, see Fig. 3c. Fig. 3d schematically illustrates a complete structure of a LEC with a second electrode 5 deposited on top of the organic semiconducting material. When a voltage is applied between first and second electrodes light is emitted from the scratched pattern formed in the layer of electrolyte material.

In Figs. 4a-4d an additive manufacturing method is shown. Fig. 4a schematically illustrates a substrate 1 coated with a first electrode 2. In Fig. 4b the electrolyte material has been deposited as small regions/droplets 3"' on top of the first electrode. Then an organic semiconducting material 4 is deposited, as shown in Fig. 4c, which covers the regions/droplets of electrolyte material. Finally, in Fig. 4d the complete LEC device structure is shown with a second electrode 5 deposited on top of the organic

semiconducting material. When a voltage is applied between the first and second electrode, light is emitted. Figure 5 presents an optoelectronic examination of an ITO|{PEG + KCF₃S0₃}|superyellow|AI bilayer LEC. The dry {PEG + KCF₃S0₃} electrolyte material drop diameter and pitch were 50 and 90 pm respectively, and the drops were positioned in all of the array cells for the formation of a filled micrometer sized array pattern. Characteristic LEC features of increasing luminance and decreasing voltage with time during constant-current drive mode were observed, thus providing further evidence for that the ions in the drops of electrolyte material can redistribute and perform balanced

electrochemical doping of superyellow in the bilayer structure. To get an indication of the luminance of the emissive area (the droplets), the "measured luminance" has been divided with a scaling factor A^* = (π?)/(ά²) where r is the drop radius and d is the drop pitch, for the calculation of a "pixel luminance". As A^* corresponds to the ratio between the nominal area of electrolyte material and the device area, and since it is only a minor part of each droplet of electrolyte material that is emissive, this procedure adds a rather conservative measure of the pixel luminance. The pixel luminance is of relevance for display applications where the contrast between an emissive pixel and the background is of interest, whereas the measured luminance is of more significance in filled micrometer sized array devices that feature a uniform emission to the eye. 50 different bilayer LECs were tested with filled micrometer sized array patterns, and a peak power conversion efficacy of 1.6 Im/W at a measured luminance of 61 cd/m² (corresponding to a pixel luminance of 274 cd/m²) was obtained for the champion device.

An optimization of the doping structure via the electrolyte material/light- emissive-compound ratio is a viable path for the attainment of high efficiency and long operational lifetime in conventional LEC devices, which comprise a blend of a light-emitting compound and an electrolyte material as the active material. However, for the herein studied bilayer devices, it is uncertain whether the basic criteria for this optimization procedure are valid. Thus, it is at this stage difficult to tune the active material composition for optimized operation, but an improved performance through better process control and improved understanding of the device operation is anticipated. Moreover, the attention is called to that planar emissive devices, such as LECs and OLEDs, typically only allow 20 percent of the generated photons to be coupled out of the device structure, but that an appropriately designed microscopic structure at the ITO interface can increase this out-coupling efficiency significantly. Hence, a designed patterning of the electrolyte material array for improved light out-coupling will facilitate for higher efficiencies.

Importantly, despite the notably uneven emission on the microscopic level (see Fig. 6b and 6c), it is possible to realize bilayer LEC devices with homogenous emission to the external observer.

The inset in Figure 5 is a photograph of the emission from an

ITO|{PEG + KCF₃S0₃}|superyellow|AI bilayer LEC, comprising a filled micrometer sized array pattern with a drop diameter and pitch of 60 and 120 μιτ), respectively. The device was driven with a constant current of 1 mA, and featured relatively uniform emission intensity and color over the entire device area of 113 mm², despite that the light-emissive regions only covered less than 20 percent of the device area.

Fig. 6a shows the height profile of a typical dry {PEG + KCF₃SO₃} droplet of electrolyte material, which demonstrates a "broken coffee ring" or "crown-like" structure following drying. More specifically, the electrolyte material has agglomerated into distinct and relatively regularly shaped small circular spots, with a typical diameter < 5 m, and with a peak height ranging from a few nm up to 500 nm. These small circular-shaped features are primarily positioned around the droplet circumference, but exist also in its interior.

Fig. 6b illustrates a photomicrograph of the initial light-emission from a single-droplet region (or micrometer sized array cell) in a biased bilayer device. The yellow-green light emission is preferentially emitted from micrometer-thick circular lines, located both along the perimeter and in the interior of each droplet. Since hole injection and light emission depend on a physical contact between the anode and the light-emitting compound in the device structure (or if there is a contact-improving layer provided, the physical contact between the contact-improving layer and the light-emitting compound), the emissive regions must be proximate to contact points between the indium-tin oxide (ITO) anode and the light-emitting compound (here superyellow). In other words, physical ITO-superyellow contact points, or "pinholes", must exist in the interior of the droplets of electrolyte material; a common problem for inkjetted printed OLEDs, here turned into our favor.

Fig. 6c presents the light-emission from the same micrometer sized array cell (as photographed during diascopic, or "backside", illumination) at a later time, and a comparison with Fig. 6a reveals that the spatial locations of the emissive regions have changed. The diascopic illumination allows for identification of doped superyellow regions as darkened areas. The observed spatial correlation between the initial but quickly decaying light emission and heavy doping, implies that these regions suffer from too-high doping levels. High doping levels are undesired in LECs as they can quench the light emission.

Figure 6d presents a photograph of a small portion of a larger 8x8 mm²

ITO|{PEG + KCF₃S0₃}|superyellow|AI static display, which repeatedly presents a message in the form of the word "LEC". The emissive pixels correspond to the existence of a droplet of electrolyte material, while the dark pixels signal the absence of a droplet. It is notable that the uneven droplet emission on the microscopic level again averages out to a rather

homogenous pixel emission on a macroscopic plane. As printed droplets (with diameter of 50 pm) of electrolyte material correspond to emissive pixels of the same dimensions, and since the positioning of the droplets of electrolyte material are controlled through the software of the inkjet printer, it is a straightforward procedure to design and attain any desired emissive pattern with micrometer resolution via additive inkjet printing of an micrometer sized array pattern of electrolyte material. Finally, the attention is called to that the herein presented static-display LEC comprise solely air-stabile materials, and that the bilayer stacks are routinely fabricated under ambient atmosphere.

Embodiment 1 (subtractive LEC patterning) Patterned 15x15 mm² ITO-glass substrates were cleaned in a 1 :10 detergent-water mixture for 30 min, acetone for 10 min, iso-propylalcohol for 10 min, and finally dried in an oven at 110 °C for > 12 h. A PEDOT:PSS-water dispersion was subsequently coated onto the substrates by preheating the glass samples to 100 °C, depositing PEDOT:PSS on the substrates using a syringe with a 0.45 pm filter, spincoating at 4000 rpm, and finally drying the resulting film for > 12 h at 130 °C. The final PEDOTPSS coated ITO glass substrate was transferred to a nitrogen filled glovebox free from oxygen and water.

A 5 mg/ml SY-toluene solution was made by mixing the constituents using a magnetic stirrer at a temperature of 70 °C in a water and oxygen free environment. A 10 mg/ml PEO/KCF₃S0₃-cyclohexanone solution was similarly made, and subsequently spincoated onto the PEDOTPSS coated ITO-glass substrates using 1500 rpm for 60 s. The film was dried at 70°C for a minute before stored at room temperature for >48 h. The resulting film was then scratched with a syringe needle in order to create small holes through which electrical contact to the PEDOTPSS-ITO could be made. The SY- solution was finally spincoated on top of the stack using 2000 rpm for 60 s, and the entire device was dried at 50°C for >24 h.

The performance of these devices is very good. The turn-on time is fast, reaching a peak brightness within seconds. At 5 V, the emission is fairly stable. The Al electrode gets uneven as the potential is applied in the regions where the electrolyte material has not been scratched, indicating a formation of gaseous compound and a high degree of side reactions at these points. As the Al is protected by SY, this reaction cannot be due to PEO and Al reacting with each other.

Embodiment 2 (additive LEC patterning by inkjet printing)

The salt KCF₃SO₃ and the ion-solvating polymer PEG were separately dissolved in cyclohexanone in a concentration of 10 g/l. These master solutions were mixed in a {PEG : KCF₃SO₃} = {4 : 1} mass ratio and thereafter ultrasonicated for 20 min. The electrolyte material ink was filtered through a 0.2 μιη poly(tetrafluoroethylene) syringe filter before deposition. The light- emitting compound ink consisted of superyellow dissolved in toluene in a concentration of 7 g/l. The inks were stored in darkness, and their entire preparation process was executed under ambient air conditions. The ITO- coated glass substrates were cleaned by subsequent ultrasonication in acetone and iso-propylalcohol, and thereafter dried in an oven at 120 °C for > 12 h.

The electrolyte material ink was transferred to an inkjet cartridge and deposited with a drop-on-demand inkjet printer under ambient air conditions. The cartridge's printhead nozzles delivered drops of 10 pi. By tuning of the inkjet printer settings, repeatable printing of droplets of electrolyte material on top of the ITO-coated glass substrate could be attained at an ejection voltage of 27 V and pulse duration of 42.3 με. The inkjetted droplets of electrolyte material were dried on a hotplate at 90 °C for > 1 h, before being spincoated (2000 rpm, 60 s) with the superyellow ink. The sample was then transferred to a N₂-filled glovebox ([H₂0], [0₂] < 1 ppm), and dried on a hotplate at 90 °C for 1 h, and thereafter at 60 °C for > 1 1 h. An Al top cathode (100 nm thickness) was thermally evaporated on top of the bilayer stack. Devices to be characterized in ambient atmosphere were encapsulated by attaching a microscope cover glass plated with UV-curable epoxy.

It proved difficult to control the drying behavior of the electrolyte material ink on the ITO substrate which resulted in a broken structure as seen in Fig. 6a instead of a homogenous dry drop. At inspection by eye, it seems like the whole drop is emitting light, see Fig. 6d and inset in Fig. 5. This is probably resulting from the broken structure of each drop, without which there should only be light-emission from the drop perimeters. As seen in Figs. 6b and 6c light originates also from the interior of each drop. The highest luminance of the pixels that was achieved in a filled micrometer sized array pattern was 274 cd/m² at 1.6 Im/W. Static displays as in Fig. 6d and filled micrometer sized array devices as in Fig. 5 can be produced with this technique, and turn-on-times for the devices are quite short. Lifetimes are so far limited to a few hours and additional optimization is necessary to improve the performance in terms of lifetime, luminance, and efficiency.

The surface morphology of the dry inkjetted droplets of electrolyte material was measured with a stylus profiler (Bruker Dektak XT). Due to the soft nature of the electrolyte material, a conformal and thin (50 nm) coating of Al was thermally evaporated on top of the printed droplets for the formation of a robust and easy-to-measure surface. Whilst driven in constant-current mode, the LECs were monitored by a data acquisition device connected to a computer via a USB-port (National Instruments USB-6009). The luminance was measured with a calibrated photodiode equipped with an eye-response filter (Hamamatsu Photonics, S9219-01). The photographs were recorded with either a digital single-lens reflex camera (Canon 60D) equipped with a macro lens (Sigma Macro 150mm F2.8 EX DG HSM) or a diascopic optical microscope (Olympus BX51 ).

Embodiment 3 Combination of bilayer structure for improved light extraction and LEC behavior

It is well known that about 80% of the light generated in planar light- emitting devices is lost within the devices. Some parts are lost due to total internal reflection between the (glass) substrate and the ambient air, and some is lost to waveguide modes within the device. It has been shown that waveguide modes in OLEDs can be reduced, thus that more of the generated light can be extracted, by introducing structures on nano- and micrometer scale. Most often these structures are periodic and placed in between the substrate and an electrode. However they can also be placed at the electrode/active material interface or within the active layer. It is possible to position the electrolyte material in the bilayer structure such that it forms a light-extraction structure in addition to delivering ions for the electrochemical doping processes and LEC-operation. Such extraction structures (usually with sub-micrometer dimensions) used today can be fabricated using laser ablation, nano-imprinting, or lithography methods.

Claims

1 . A light-emitting electrochemical cell comprising:

a first electrode,

an electrolyte material comprising ions and optionally ionizing solvent, an organic semiconducting material capable of emitting light, and a second electrode,

wherein the organic semiconducting material is in electrical contact with the first and second electrode,

the electrolyte material and the organic semiconducting material form separate regions, each consisting essentially of the respective material, and characterized in that

the electrolyte material region presents a predetermined pattern in an area of overlap between the first and second electrode.

2. The light-emitting electrochemical cell according to claim 1 , wherein a region of electrolyte material has a volume of at least 0.001 (pm)³, preferably at least 0.01 (pm)³, or at least 0.1 (pm)³.

3. The light-emitting electrochemical cell according to any one of the preceding claims, wherein a region of organic semiconducting material has a volume of at least 0.001 (pm)³, preferably at least 0.01 (pm)³, or at least 0.1 (pm)³.

4. The light-emitting electrochemical cell according to any one of the preceding claims, wherein the organic semiconducting material regions are substantially free from mobile ions in their pristine state.

5. The light-emitting electrochemical cell according to any one of the preceding claims, wherein at least one region of electrolyte material forms a layer and wherein the organic semiconducting material is in electrical contact with one or both of the first and second electrode via one or several through recesses formed in the layer of electrolyte material.

6. The light-emitting electrochemical cell according to any one of the preceding claims, wherein a region of electrolyte material only partially covers the first electrode.

7. The light-emitting electrochemical cell according to any one of the preceding claims, comprising at least two co-planar regions of electrolyte material.

8. The light-emitting electrochemical cell according to any one of the preceding claims, wherein each of the regions of electrolyte material is in physical contact with both of the electrodes.

9. The light-emitting electrochemical cell according to any one of claims 1 -5 and 7, wherein each of the regions of electrolyte material is spaced from both the first and second electrode. 10. The light-emitting electrochemical cell according to any one of the preceding claims, wherein at least one of the electrodes is transparent for visible light. 1. The light-emitting electrochemical cell according to any one of the preceding claims, wherein at least one of the electrodes is non- transparent for visible light, and optionally reflective.

12. The light-emitting electrochemical cell as claimed in any one of the preceding claims, wherein at least a part of the predetermined pattern provides a diffraction grating adapted to couple out light from the light-emitting electrochemical cell.

13. A method of manufacturing a light-emitting electrochemical cell comprising:

providing a first electrode,

providing at least one patterned region of electrolyte material comprising ions and optionally ionizing solvent,

providing at least one organic semiconducting material capable of emitting light,

providing a second electrode,

wherein the organic semiconducting material is provided such that it electrically contacts both the first and second electrode, and

wherein the electrolyte material is provided in an area of overlap between the first and second electrode.

14. The method according to claim 13, wherein providing at least one patterned region of electrolyte material comprises forming a continuous electrolyte material layer and patterning the layer by a subtractive process.

15. The method according to any one of claims 13-14, wherein providing at least one patterned region of electrolyte material comprises depositing the electrolyte material by an additive process.

16. The method according to any one of claims 13-15, wherein the organic semiconducting material is provided by a second additive process. 17. The method according to any one of claims 13-16, wherein the region of an electrolyte material is provided at least partially on a portion of the organic semiconducting material.

18. The method according to any one of claims 13-17, wherein the organic semiconducting material is provided at least partially on a discrete region of electrolyte material.