The present invention addresses this problem, at least in part. In a first aspect, the present invention provides an organic light-emitting device comprising:
an anode;
a cathode; and
an organic light emissive region between the anode and the cathode, the region comprising electroluminescent material; wherein the emitted light from the electroluminescent material is colour shifted by a non-emissive colour shifting unit present in the organic light emissive region.
Preferably, the electroluminescent material comprises electroluminescent molecules comprising colour shifting units. Most preferably, the electroluminescent material comprises an electroluminescent polymer comprising colour shifting units.
The color shift of the emission from the blue electroluminescent material or the red electroluminescent material can be measured with reference to the EL spectra (measured in the solid state) of the electroluminescent material in the absence and in the presence of a color shifting unit. The degree of movement can be measured in comparison to the movement observed in peak emission (peak emission). The degree of shift can also be measured with reference to the observed long wavelength edge shift (edge shift) or short wavelength edge shift.
Each of the red and blue electroluminescent materials emits light by exciton radiative decay after charge carrier injection. Some exciton decay from the blue electroluminescent material may be transferred to the red electroluminescent material and cause the red electroluminescent material to emit by a process known as Forster transfer.
For the purposes of the present invention, a blue electroluminescent material may be defined as an organic material which emits radiation by electroluminescence, said radiation having a wavelength range of 400-500nm, more preferably 430-500 nm. For the purposes of the present invention, blue emission light can be defined as light having a CIE x coordinate less than or equal to 0.25, more preferably less than or equal to 0.2, and a CIE y coordinate less than or equal to 0.25, more preferably less than or equal to 0.2, most preferably having CIE coordinates (0.15, 0.20).
For the purposes of the present invention, a red electroluminescent material may be defined as an organic material emitting radiation by electroluminescence, said radiation having a wavelength range of 600-750nm, preferably 600-700nm, more preferably 610-650nm, and most preferably having an emission peak of approximately 650-660 nm. For the purposes of the present invention, red emitted light can be defined as light having a CIE x coordinate greater than or equal to 0.4, preferably 0.64, and a CIE y coordinate less than or equal to 0.4, preferably 0.33.
Preferably, the colour of the composite emission from the red and blue electroluminescent materials observed in the presence of the colour shifting unit is white or near-white. White light can be defined as radiation emitted by a black body at 3000-. In this case, the skilled person will understand that a straight line drawn between the first and second CIE coordinates of the emitted light from the red and blue electroluminescent materials, respectively, will pass through a region of white or near-white light in the presence of the color-shifting unit.
Typically, the device comprises a dual emission assembly system, which results in no other emissive material being present than the red and blue electroluminescent materials. In this regard, the device generally does not contain a green electroluminescent material. Further, a blue electroluminescent material not doped with an emission dopant is preferred.
Preferably, the color shifting unit is present in either of the color shifted blue or red electroluminescent materials, i.e.: the blue or red electroluminescent material comprises a color shifting unit. However, this is not essential and the colour shifting unit may be included in a separate material to either the colour shifted blue or red electroluminescent material. The individual (single) materials may include a color shifting unit, a red electroluminescent material and a blue electroluminescent material.
It will be appreciated that the non-emissive colour shifting unit shifts the frequency of the emitted light from the red or blue electroluminescent material. This is shown in figure 2 a. This is contrasted with other structural units that can emit light themselves, so that the color of the light seen by the naked eye appears color shifted (see fig. 2 b).
Preferably, the color shifting unit green-shifts the color of the emitted light.
Preferably, the color shifting unit comprises a stilbene unit:
the stilbene units may be substituted or unsubstituted.
Preferred concentrations of migrating units are from 1% to 20%, preferably from 5% to 15%, most preferably 10%, based on the monomer proportion of repeating units.
Preferably, the blue electroluminescent material comprises a blue electroluminescent polymer, more preferably a conjugated polymer, typically a copolymer. Preferably, the polymer is solution processable. Preferably, the blue electroluminescent material is fluorescent.
The blue electroluminescent material is preferably a semiconducting polymer and may comprise triarylamine repeat units. Particularly preferred triarylamine repeat units are shown in formulas 1-6:
wherein X, Y, A, B, C and D are independently selected from H or a substituent. More preferably, one or more of X, Y, A, B, C and D is independently selected from the group consisting of optionally substituted, branched or straight chain alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl, and arylalkyl groups. Most preferably, X, Y, A and B are C1-10An alkyl group. The repeating unit of formula 4 is most preferred. Any two phenyl groups of repeating units 1-6 may be linked by a direct bond or by a divalent moiety, preferably a heteroatom, more preferably O or S. Polymers in units 1-3 in the case where the units are linkedLinkage of the phenyl repeat units in the backbone is most preferred.
More preferably, the blue electroluminescent polymer is a copolymer, in particular an intrinsic blue electroluminescent copolymer, comprising one or more repeat units of formulae 1-6, most preferably a repeat unit of formula 4, and at least one arylene repeat unit. Particularly preferred arylene repeat units are those described above in connection with longer wavelength emitters.
Preferably, the red electroluminescent material comprises a red electroluminescent polymer, more preferably a conjugated polymer, typically a copolymer. Preferably, the polymer is solution processable. Red electroluminescent polymers having a shallow LUMO energy level, for example much less than (2.5 eV), are preferred. This facilitates electron transport in the device.
The red fluorescent material of the light LUMO may comprise a copolymer of fluorene repeat units and Se-containing repeat units as described anywhere herein. The Se-containing repeat unit can include formula 52:
wherein X is O, S, Se, CR2、SiR2Or NR, more preferably O, S or Se; and each R is independently alkyl, aryl, or H. The repeating unit of formula (52) may be substituted or unsubstituted. Preferred substituents for the repeating unit of formula (52) are C which may be present on one or more rings of the repeating unit of formula (52)1-20An alkyl group.
Such red fluorescent materials of shallow LUMO are known, for example, from Macromolecules2005, 38, 244-.
A red phosphorescent material is a desirable choice as the red electroluminescent material of the shallow LUMO. Preferably, the red phosphorescent material comprises a dendrimer comprising a core and one or more conjugated dendrons comprising surface groups. However, this is not essential and the red phosphorescent material may comprise a red phosphorescent small molecule of a metal (M) surrounded by three bidentate ligands, for example, or a red phosphorescent linear polymer.
Solution processability of the dendrimer is very adaptable because the surface groups controlling processability can be modified independently of the light-emissive core.
The red phosphorescent material may include a metal complex. Preferred metal complexes include optionally substituted complexes of formula (53):
ML1qL2rL3s
(53)
wherein M is a metal; l is1、L2And L3Each of which is a ligand; q is an integer; r and s are each independently 0 or an integer; and the sum of (a.q) + (b.r) + (c.s) equals the number of coordination sites available on M, where a is L1Number of coordination sites on, b is L2Number of coordination points on, and c is L3The number of coordination sites on the substrate.
The red phosphorescent material may have formula (54) or (55):
wherein M represents a metal and R represents H, a substituent or a dendron comprising a surface group.
When the red phosphorescent material is a small molecule, R represents H or a substituent. Examples of the substituent include, for example, C1-20Solubilizing groups for alkyl or alkoxy groups, electron-withdrawing groups such as fluorine, nitro or cyano groups, and methods for increasing the glass transition temperature (T) of polymersg) A substituent of (1).
R may represent a dendron having a surface group, which makes the red light emitting material a dendrimer.
Preferably, the red phosphorescent dendrimer has formula (56) or (57):
wherein M and R are as defined above and R' represents H or a surface group.
Examples of surface groups R' include, for example, C1-20Solubilizing groups for alkyl or alkoxy groups, electron-withdrawing groups such as fluorine, nitro or cyano groups, and methods for increasing the glass transition temperature (T) of polymersg) A substituent of (1).
Preferably, R' represents an alkyl or alkoxy group, preferably a C1 to C20 alkyl or alkoxy group, more preferably.
M may represent any suitable metal, in particular a d-block metal such as the metals in the second and third rows, i.e. elements 39 to 48 and elements 72 to 80, especially ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, tungsten and gold. Preferably, M represents iridium (Ir).
The "ligand" or "L" in formulae 53 to 57 may represent a carbon donor or a nitrogen donor, such as a porphyrin or a bidentate ligand of formula (58):
wherein Ar is4And Ar5May be the same or different and is independently selected from optionally substituted aryl or heteroaryl; x1And Y1May be the same or different and is independently selected from carbon or nitrogen; and Ar4And Ar5Can be fused together. Particularly preferred is X1Is carbon and Y1Is a ligand for nitrogen.
Examples of bidentate ligands are shown below:
Ar4and Ar5Each of which may bear one or more substituents. Particularly preferred substituents include: fluorine or trifluoromethyl which can be used to blue-shift the emitted light of the complex, as disclosed in WO 02/45466, WO 02/44189, US 2002-; alkyl or alkoxy groups, as disclosed in JP 2002-324679; carbazoles, which, when used as emissive materials, can be used to assist in the transport of holes to the complex, as disclosed in WO 02/81448; bromine, chlorine or iodine, which can be used to functionalize ligands for attachment of remote groups (further groups), as disclosed in WO02/68435 and EP 1245659; and dendrons, which can be used to obtain or enhance the solution processability of the metal complex, as disclosed in WO 02/66552.
Other ligands suitable for use with the d block elements include diketonates (diketonates), particularly acetylacetonates (acac), triarylphosphines, and pyridines, each of which may be substituted.
The red phosphorescent dendrimer may have formula (59) or (60):
wherein R is 2-ethyl, hexyl.
Any suitable host material may be used with the red phosphorescent material. The host material may be a small molecule or a polymer. Preferably, the host material is a polymer, more preferably a conjugated polymer.
The concentration of the red light emitting material in the polymer host may be sufficient to make the emitted light from the polymer host invisible. The concentration of the red light emitting material in the polymer host may be greater than 7.5 wt%. The concentration of the red light emitting material in the polymer host may be at least 10 wt%.
The concentration of the red light emitting material in the polymer host may be sufficient to make the emitted light from the polymer host visible.
Preferred red and blue electroluminescent polymers are substituted. Examples of the substituent include, for example, C1-20Solubilizing groups for alkyl or alkoxy groups, electron-withdrawing groups such as fluorine, nitro or cyano groups, and methods for increasing the glass transition temperature (T) of polymersg) A substituent of (1).
The red electroluminescent material may be a separate material from the blue electroluminescent material. In this case, the red and blue electroluminescent materials may be mixed together in the organic light-emitting region. When the red electroluminescent material is a red phosphorescent material, the blue electroluminescent material may function as a host for the red electroluminescent material.
Alternatively, the red and blue electroluminescent materials may be contained in separate sub-layers of the organic light emissive region. In this case, the blue electroluminescent material may also function to transport holes to the red electroluminescent material, or vice versa.
A hole transport layer comprising a hole transport material may be present between the anode and the organic light emissive region. Suitable materials for the hole transport material include hole transport polymers, in particular polymers comprising triarylamine repeat units. Preferred triarylamine repeat units include repeat units having the general formula 1 to 6.
Particularly preferred hole transport polymers of this type are AB type copolymers of fluorene repeat units and triarylamine repeat units.
In a first embodiment, the emission from the blue electroluminescent material is color shifted by the color shifting unit.
Preferably, the emitted light from the blue electroluminescent material is green-shifted. In this regard, the peak emission is preferably shifted by 10nm to 40nm, more preferably by 15nm to 35nm, still more preferably by 20nm to 30 nm. The long wavelength edge is preferably shifted by 10nm to 35nm, more preferably 20nm to 25 nm. The short wavelength edge is preferably shifted from 0nm to 16nm, preferably from 4nm to 16nm, more preferably from 8nm to 12 nm.
In this embodiment, the emission from the color-shifted blue electroluminescent material preferably has CIE coordinates (0.15 < x < 0.3, 0.3 < y < 0.45), more preferably (0.18 < x < 0.25, 0.36 < y < 0.44), and most preferably (0.22, 0.4). In this embodiment, the emitted light from the color-shifted blue electroluminescent material preferably has a wavelength in the range of 420 to 520nm, more preferably 450 to 520 nm. The color of the emitted light can be described as cyan.
In this first embodiment, the red and blue electroluminescent materials are preferably separate materials, typically mixed together in the organic light-emissive region. Preferably, the organic light emissive region is a layer having a thickness in the range of 65-70 nm.
The blue electroluminescent material may be any suitable material. In this first embodiment, the blue electroluminescent material preferably comprises a color shifting unit. Preferably, the blue electroluminescent material includes a polymer, and the color-shifting unit is included in a main chain of the polymer, for example, as shown in the following formula 7:
other repeat units may be present in the polymer of formula 7 shown above. For example, the polymer may further comprise one or more different arylene or heteroarylene repeat units, such as, for example, a fluorene repeat unit (preferably a substituted 2, 7 linked fluorene repeat unit) having general formula 8:
wherein R is1And R2Independently selected from hydrogen or optionally substituted alkyl, alkoxy, aryl, arylalkyl, heteroaryl and heteroarylalkyl. More preferably, R1And R2At least one of (A) includes optionally substituted C4-C20Alkyl or aryl.
Other arylene repeat units include: polyarylene vinylenes such as polyparaphenylene vinylenes; 2, 7-linked 9, 9 diaryl polyfluorenes; polyspirofluorene (polyspirofluoroene), which is in particular 2, 7-linked poly-9, 9-spirofluorene; polyindenofluorenes, in particular 2, 7-linked polyindenofluorenes; polyphenylene, in particular alkyl-or alkoxy-substituted poly-1, 4-phenylene. Such polymers are disclosed, for example, in adv. mater.200012 (23)1737-1750 and references therein. Preferably, the blue electroluminescent material comprises the colour shifting units in a concentration of from 1% to 20%, preferably from 5% to 15%, most preferably 10%, based on the monomeric proportion of the repeat units. Preferably, the blue electroluminescent material comprises 1 mol% to 30 mol% of the blue light-emitting unit. Preferably, the blue electroluminescent material comprises from 3 to 10 mol% of one or more different fluorene repeat units.
Preferred blue light-emitting units are shown above in formulas 1 to 6.
Preferred red light emitting materials include polymers comprising optionally substituted repeat units of formula (I):
wherein X1、Y1And Z1Each independently O, S, CR2、SiR2Or NR, more preferably O or S, most preferably S; and each R is independently alkyl, aryl, or H. Preferred substituents for the repeating unit of formula (I) are C which may be present on one or more rings of the repeating unit of formula (I)1-20An alkyl group.
More preferably, the red light emitting material is a copolymer comprising optionally substituted repeat units of formula (I) and arylene co-repeat units (co-repeat units) selected from: optionally substituted 1, 4-phenylene repeat units as disclosed in j.appl.phys.1996, 79, 934; fluorene repeat units, as disclosed in EP 0842208; indenofluorene repeat units, as disclosed, for example, in Macromolecules 2000, 33(6) 2016-; and spirofluorene repeat units as disclosed in, for example, EP 0707020. Examples of the substituent include, for example, C1-20Solubilizing groups for alkyl or alkoxy groups, electron-withdrawing groups such as fluorine, nitro or cyano groups, and methods for increasing the glass transition temperature (T) of polymersg) A substituent of (1).
Particularly preferred arylene repeat units include optionally substituted 2, 7-linked fluorenes, most preferably repeat units of formula (II):
wherein R is1And R2Independently selected from hydrogen or optionally substituted alkyl, alkoxy, aryl, arylalkyl, heteroaryl and heteroarylalkyl. More preferably, R1And R2At least one of (A) includes optionally substituted C4-C20Alkyl or aryl.
In a first embodiment, it has been found that a more stable white emission and significantly longer device lifetime results from the combined emission of the mixed red electroluminescent material and blue-green (colour shifted towards the blue) electroluminescent material when compared to the previously known three-component mixture of red, green and blue electroluminescent materials. DC device lifetime and pulsed device lifetime extensions have been observed for devices according to the invention with a combined emission of mixed red and blue-green electroluminescent materials when compared to known three-component mixtures of red, green and blue electroluminescent materials.
The more stable white emission can be attributed to the longer lifetime of the green-blue polymer under both pulsed and direct current conditions and to the significantly reduced change in the emission spectrum of the green-blue polymer over the operating lifetime of the device. For a three-component mixture of red, green and blue electroluminescent materials, the color of the emitted light tends to vary significantly, becoming more blue due to the associated reduction in the emitted light of the red component, especially the green component.
In a second embodiment, the emission from the red electroluminescent material is color shifted by the color shifting unit.
Preferably, the emitted light from the red electroluminescent material is green-shifted. As described above, the degree of movement can be measured by referring to the EL spectra of the red electroluminescent material in the absence and presence of the color-shifting unit. In this regard, the peak emission is preferably shifted by 5nm to 30nm, preferably 5nm to 15nm, more preferably 8nm to 12nm, and still more preferably about 10 nm. The long wavelength edge is preferably shifted by 3nm to 12nm, more preferably 5nm to 10 nm. The short wavelength edge is preferably shifted by 12nm to 23nm, more preferably by 15nm to 20 nm.
In this embodiment, the emission from the color-shifted red electroluminescent material preferably has CIE coordinates of about (0.64, 0.33), and more preferably about (0.60, 0.38). The color of the emitted light may be described as red-orange.
In this second embodiment, it is preferred that the blue electroluminescent material comprises a colour shifting unit. In this regard, a preferred blue electroluminescent material includes a polymer having a main chain including a plurality of color-shifting units, and a side chain depending from the main chain including a blue light-emitting unit, for example, the polymer may include a repeating unit as shown in the following formula 9:
the blue light-emitting unit preferably comprises a triarylamine.
In this second embodiment, the red electroluminescent material may be any suitable material.
The device according to the first aspect of the invention may be used for backlighting of flat panel displays, but also for other lighting applications, in particular as an ambient lighting source.
In a second aspect of the invention there is provided an electroluminescent material comprising a blue or red electroluminescent material as described anywhere above in relation to the first aspect and a non-emissive colour shifting unit. Also provided is the use of an electroluminescent material for emitting light.
The invention will now be described in more detail with reference to the accompanying drawings, in which:
Referring to fig. 1, the structure of an electroluminescent device according to the invention comprises a transparent glass or plastic substrate 1, an indium tin oxide anode 2 and a cathode 4. An organic light emissive region 3 is disposed between the anode 2 and the cathode 4.
Additional layers may be located between the anode 2 and the cathode 3, such as charge transport layers, charge injection layers or charge blocking layers.
In particular, it is desirable to provide a conductive hole injection layer formed of a doped organic material located between the anode 2 and the electroluminescent layer 3 to assist in the injection of holes from the anode into the layer or layers of semiconducting polymer. Examples of doped organic hole injecting materials include poly (ethylene dioxythiophene) (PEDT), in particular PEDT doped with polystyrene sulfonate (PSS) as disclosed in EP 0901176 and EP0947123, or polyaniline as disclosed in US 5723873 and US 5798170.
If present, the hole transport layer, located between the anode 2 and the electroluminescent layer 3, preferably has a HOMO level of less than or equal to 5.5eV, more preferably about 4.8-5.5 eV.
If present, the electron transport layer between the electroluminescent layer 3 and the cathode 4 preferably has a LUMO level of about 3-3.5 eV.
The organic light emissive region 3 may be composed of a color shifting unit, a blue electroluminescent material and a red electroluminescent material, or may comprise a combination of these components with one or more additional materials. In particular, these components may be mixed with hole and/or electron transport materials, as disclosed in, for example, WO 99/48160. Alternatively, the blue and/or red electroluminescent materials may be covalently bound to the charge transport material.
The cathode 4 is selected from materials having a work function that allows electrons to be injected into the organic light-emissive region. Other factors such as the likelihood of adverse interactions between the cathode and the organic light-emissive region affect the choice of cathode. The cathode may be composed of a single material such as an aluminum layer. Alternatively, the cathode may comprise a plurality of metals, for example a bilayer of calcium and aluminium as disclosed in WO 98/10621, elemental barium as disclosed in WO98/57381, appl. phys.lett.2002, 81(4), 634 and WO 02/84759, or a thin layer of a dielectric material which assists electron injection, for example lithium fluoride as disclosed in WO 00/48258 or barium fluoride as disclosed in appl. phys.lett.2001, 79(5), 2001. To provide efficient electron injection into the device, the cathode preferably has a work function of less than 3.5eV, more preferably less than 3.2eV, and most preferably less than 3 eV.
Optical devices tend to be sensitive to moisture and oxygen. Therefore, the substrate preferably has excellent barrier properties for preventing moisture and oxygen from entering the device. The substrate is typically glass, however, alternative substrates may be used where flexibility of the device is particularly desirable. For example, the substrate may comprise a plastic as in US 6268695, which discloses a substrate with alternating layers of plastic and barrier layers, or a thin sheet of thin glass and plastic as disclosed in EP 0949850.
The device is preferably encapsulated with an encapsulant material (not shown) to prevent the ingress of moisture and oxygen. Suitable sealing materials include glass plates, films with suitable barrier properties, such as alternating layers of polymer and dielectric as disclosed in, for example, WO 01/81649, or gas-tight containers as disclosed in, for example, WO 01/19142. A getter material for absorbing any atmospheric moisture and/or oxygen that may permeate through the substrate or the sealing material may be arranged between the substrate and the sealing material.
In a practical device, at least one of the electrodes is semi-transparent in order that light may be absorbed (in the case of a photosensitive device) or emitted (in the case of an OLED). Where the anode is transparent, it typically comprises indium tin oxide. Examples of transparent cathodes are disclosed in, for example, GB 2348316.
The embodiment of figure 1 shows a device formed by first forming an anode on a substrate followed by deposition of an electroluminescent layer and a cathode, however it will be appreciated that the device of the invention may also be formed by first forming a cathode on a substrate followed by deposition of an electroluminescent layer and an anode.
Polymers comprising fluorene repeat units may provide one or more of the functions of hole transport, electron transport, and emission, depending on which layer of the device the polymer is used in and the nature of the co-repeat units. Preferred fluorene repeat units are for example optionally substituted 2, 7-linked fluorenes having the general formula 8.
In particular:
homopolymers of fluorene repeat units, such as 9, 9-dialkylfluorene (dialkylfluorene) -2, 7-diyl homopolymers, can be used to provide electron transport.
Copolymers comprising fluorene units and triarylamine repeat units, in particular selected from repeat units of formulae 1-6, may be used to provide hole transport and/or emission.
Copolymers comprising fluorene units and heteroarylene repeat units can be used for charge transport or emission. Preferred heteroarylene repeat units are selected from formulas 10-24:
wherein R is6And R7Are the same or different and are each independently hydrogen or a substituent, preferably alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl, or arylalkyl. For ease of processing, R6And R7Preferably the same. More preferably, R6And R7Preferably identical and each is phenyl.
The electroluminescent copolymer may comprise an electroluminescent region and at least one of a hole transporting region and an electron transporting region as disclosed in, for example, WO 00/55927 and US 6353083. If only one of the hole transporting region and the electron transporting region is provided, the electroluminescent region may also provide the other of the hole transporting and electron transporting functions.
Different regions may be provided within such polymers along the backbone of the polymer according to US6353083, or as groups pendant from the backbone of the polymer according to WO 01/62869.
Preferred methods for preparing these polymers are Suzuki polymerisation as described, for example, in WO00/53656, And Yamamoto polymerisation as described, for example, in T.Yamamoto, "Electrically connecting And Thermally Stable Pi-Conjugated Poly (arylene) s Prepared by an Organometallic process, Progress in Polymer science 1993, 17, 1153-. These polymerization techniques are all carried out by "metal insertion" in which the metal atom of the metal complex catalyst is inserted between the aryl group and the leaving group of the monomer. In the case of Yamamoto polymerization, a nickel complex catalyst is used; in the case of Suzuki polymerisation, a palladium complex catalyst is used.
For example, in the synthesis of linear polymers by Yamamoto polymerization, monomers having two reactive halogen groups are used. Similarly, according to the method of Suzuki polymerisation, at least one reactive group is a boron derivative group, such as a boronic acid or ester (boronic ester), and the other reactive group is a halogen. Preferred halogens are chlorine, bromine and iodine, most preferably bromine.
It will therefore be appreciated that repeat units and end groups comprising aryl groups as set out throughout the application may be derived from monomers bearing suitable leaving groups.
Suzuki polymerisation can be used to prepare regular (regioregular), block and random copolymers. In particular, homopolymers or random copolymers can be prepared when one reactive group is a halogen and the other reactive group is a boron derivative group. Alternatively, block or regular, in particular AB-type, copolymers can be prepared when both reactive groups of the first monomer are boron and both reactive groups of the second monomer are halogen.
As an alternative to halides, other leaving groups capable of participating in metal insertion include groups containing tosylate (tosylate), mesylate (mesylate) and triflate (triflate).
A polymer or polymers may be deposited from solution to form a layer. Suitable solvents for the polyarylene, in particular polyfluorene, include monoalkylbenzenes or polyalkylbenzenes, such as toluene and xylene. Particularly preferred solution deposition techniques are spin coating and ink jet printing.
Spin coating is particularly suitable for devices that do not require a patterned structure of electroluminescent material-for example for lighting applications or simple monochrome segmented displays.
Inkjet printing is particularly suitable for high information content displays, especially full color displays. Inkjet printing of OLEDs is described for example in EP 0880303.
If the layers of the device are formed by solution processing, the skilled person will appreciate techniques to prevent intermixing between adjacent layers, for example by crosslinking one layer before deposition of a subsequent layer of that layer or selecting materials for adjacent layers such that the material forming the first of those layers is insoluble in the solvent used to deposit the second layer.
Example 1
(a) Preparation of color-shifted blue electroluminescent polymers
A comparative blue electroluminescent polymer as described in WO 03/095586 was prepared by Suzuki polymerisation as described in WO00/53656 using diboronate, dibromo monomer of 9, 9-biphenylfluorene and 9, 9-dioctylfluorene and 5 mol% of monomer 1 below. A colour shifting blue electroluminescent polymer was prepared by the same method except that 10 mol% of the fluorene monomer was replaced with 10 mol% of the following colour shifting monomer 2.
Monomer 1
Monomer 2
Color shift as can be seen from the results in fig. 3, the EL spectra of the blue electroluminescent material and the color shifted blue (cyan) electroluminescent material are compared in fig. 3.
(b) Production of white light emitting devices using a dual mixing system according to the invention
Red electroluminescent polymers comprising 9, 9-dialkylfluorene repeat units, benzothiadiazole repeat units, triarylamine repeat units, and red light emitting repeat units derived from monomer 3 as disclosed in WO 00/46321 were prepared by Suzuki polymerisation as described in WO 00/53656.
Monomer3
Available as Baytron P from H C Starck of Leverkusen, GermanyThe polyvinyldioxythiophene/polysulfonaminostyrene (PEDT/PSS) of (a) was deposited by spin coating on an indium tin oxide anode supported on a glass substrate (available from Applied Films, Colorado, USA). A hole transport layer of F8-TFB (shown below) was deposited by spin coating from a xylene solution onto the PEDT/PSS layer to a thickness of about 10nm and heated at 180 ℃ for 1 hour. A mixture of color-shifting blue and red electroluminescent polymers in a ratio of 99.5: 0.5 was deposited by spin coating from a xylene solution onto the F8-TFB layer to a thickness of about 65 nm. A Ba/Al cathode is formed on the polymer by evaporating a first layer of barium to a thickness of up to about 10nm formed on the semiconducting polymer, and evaporating a second layer of aluminum barium to a thickness of about 100nm formed on the semiconducting polymer. Finally, the device is sealed with a metal encapsulant (encapsulant) containing a getter that is placed on the device and bonded to the substrate to form a hermetic seal.