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  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
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  • H05B33/00—Electroluminescent light sources
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  • H10K85/6565—Oxadiazole compounds

Definitions

• the present invention relates to electroluminescent materials and to electroluminescent devices.
• Liquid crystal devices and devices which are based on inorganic semiconductor systems are widely used; however these suffer from the disadvantages of high energy consumption, high cost of manufacture, low quantum efficiency and the inability to make flat panel displays.
• Organic polymers have been proposed as useful in electroluminescent devices, but it is not possible to obtain pure colours, they are expensive to make and have a relatively low efficiency.
• Patent application WO98/58037 describes a range of lanthanide complexes which can be used in electroluminescent devices which have improved properties and give better results.
• Patent Applications PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028, PCT/GBOO/00268 describe electroluminescent complexes, structures and devices using rare earth chelates.
• Another compound which has been proposed as an electroluminescent material for use in electroluminescent device is aluminium quinolate.
• US Patent 3,995,299 discloses an electroluminescent device comprising in sequence, an anode, an organic hole injecting and transporting zone, a luminescent zone, an electron transporting zone and a cathode.
• the luminescent zone can be an organic polymer such as a polyvinyl carbazole doped with a fluorescent dye such as a perylene, an acridine, etc.
• US Patent 4769292 discloses an electroluminescent device comprising in sequence, an anode, an organic hole injecting and transporting zone, a luminescent zone, and a cathode.
• the EL device is characterized in that the luminescent zone is formed by a thin film of less than 1 ⁇ m in thickness comprised of an organic host material and a fluorescent material capable of emitting light.
• the luminescent zone exemplified in the specification contains aluminium quinolate, and other metal quinolates with a valency of 1 to 3 are also refe ⁇ ed to and claimed.
• electroluminescent compounds of formula M(L) n and MO(L) n - 2 where M is a metal in a valency state n of greater than 3 and L is an organic ligand, the ligands L can be the same or different, e.g. M(L ⁇ ) (L ) (1-3) 0-4)... or MO(L (L 2 )....
• the invention also provides an electroluminescent device comprising sequentially an anode, a layer of an electroluminescent material comprising a compounds of fo ⁇ nula M(L) n and MO(L) n -2 where M is a metal in a valency state n of greater than 3 and L is an organic ligand; the ligands L can be the same or different, e.g. M(L ⁇ (L 2 ) (L 3 ) (L 4 ) ... or MO(L ⁇ ) (L 2 ) ....and a cathode.
• the metal M is a transition metal such as titanium, zirconium or hafnium in the four valency state or vanadium, niobium or tantulum in the five valency state.
• the electroluminescent compound is doped with a minor amount of a fluorescent material as a dopant, preferably in an amount of 5 to 15% of the doped mixture.
• a fluorescent material as a dopant, preferably in an amount of 5 to 15% of the doped mixture.
• the hue light emitted from the luminescent zone can be modified.
• a minor amount of a fluorescent material capable of emitting light in response to hole-electron recombination the hue light emitted from the luminescent zone can be modified.
• each material should emit light upon injection of holes and electrons in the luminescent zone.
• the perceived hue of light emission would be the visual integration of both emissions.
• the fluorescent material Since imposing such a balance of the organo metallic complex and fluorescent materials is highly limiting, it is prefe ⁇ ed to choose the fluorescent material so that it provides the favoured sites for light emission. When only a small proportion of fluorescent material providing favoured sites for light emission is present, peak intensity wavelength emissions typical of the organo metallic complex can be entirely eliminated in favour of a new peak intensity wavelength emission attributable to the fluorescent material. While the minimum proportion of fluorescent material sufficient to achieve this effect varies by the specific choice of organo metallic complex and fluorescent materials, in no instance is it necessary to employ more than about 10 mole percent fluorescent material, based on moles of organo metallic complex and seldom is it necessary to employ more than 1 mole percent of the fluorescent material.
• any organo metallic complex capable of emitting light in the absence of fluorescent material limiting the fluorescent material present to extremely small amounts, typically less than about 10 "3 mole percent, based on organo metallic complex, can result in retaining emission at wavelengths characteristic of the organo metallic complex.
• a fluorescent material capable of providing favoured sites for light emission either a full or partial shifting of emission wavelengths can be realized. This allows the spectral emissions of the EL devices of this invention to be selected and balanced to suit the application to be served.
• the organo metallic complex can be viewed as a collector for injected holes and electrons with the fluorescent material providing the molecular sites for light emission.
• One important relationship for choosing a fluorescent material capable of modifying the hue of light emission when present in a organo metallic complex is a comparison of the reduction potentials of the two materials.
• the fluorescent materials demonstrated to shift the wavelength of light emission have exhibited a less negative reduction potential than that of the organo metallic complex. Reduction potentials, measured in electron volts, have been widely reported in the literature along with varied techniques for their measurement.
• a second important relationship for choosing a fluorescent material capable of modifying the hue of light emission when present in a organo metallic complex is a comparison of the bandgap potentials of the two materials.
• the fluorescent materials demonsfrated to shift the wavelength of light emission have exhibited a lower bandgap potential than that of the organo metallic complex.
• the bandgap potential of a molecule is taken as the potential difference in electron volts (eV) separating its ground state and first singlet state. Bandgap potentials and techniques for their measurement have been widely reported in the literature.
• bandgap potentials herein reported are those measured in electron volts (eV) at an absorption wavelength which is bathochromic to the absorption peak and of a magnitude one tenth that of the magnitude of the absorption peak. Since it is a comparison of bandgap potentials rather than their absolute values which is desired, it is apparent that any accepted technique for bandgap measurement can be employed, provided both the fluorescent and organo metallic complex band gaps are similarly measured.
• One illustrative measurement technique is disclosed by F. Gutman and L. E. Lyons, Organic Semiconductors, Wiley, 1967, Chapter 5.
• an organo metallic complex which is itself capable of emitting light in the absence of the fluorescent material
• suppression of light emission at the wavelengths of emission characteristics of the organo metallic complex alone and enhancement of emission at wavelengths characteristic of the fluorescent material occurs when spectral coupling of the organo metallic complex and fluorescent material is achieved.
• spectral coupling it is meant that an overlap exists between the wavelengths of emission characteristic of the organo metallic complex alone and the wavelengths of light absorption of the fluorescent material in the absence of the organo metallic complex.
• Optimal spectral coupling occurs when the m ⁇ 25nm the maximum absorption of the fluorescent material alone.
• spectral coupling can occur with peak emission and absorption wavelengths differing by up to 100 nm or more, depending on the width of the peaks and their hypsochromic and bathochromic slopes.
• a bathochiOmic as compared to a hypsochiOmic displacement of the fluorescent material produces more efficient results.
• organo metallic complexes which are known to themselves emit light in response to hole and electron injection
• light emission by the organo metallic complex itself can entirely cease where light emission by the fluorescent material is favoured by any one or combination of the various relationships noted above.
• shifting the role of light emission to the fluorescent material allows a still broader range of choices of organo metallic complexes.
• one fundamental requirement of a material chosen to emit light is that it must exhibit a low extinction coefficient for light of the wavelength it emits to avoid internal absorption.
• the present invention permits use of organo metallic complexes which are capable of sustaining the injection of holes and electrons, but are themselves incapable of efficiently emitting light.
• Useful fluorescent materials are those capable of being blended with the organo metallic complex and fabricated into thin films satisfying the thickness ranges described above forming the luminescent zones of the EL devices of this invention. While crystalline organo metallic complexes do not lend themselves to thin film formation, the limited amounts of fluorescent materials present in the organo metallic complex materials permits the use of fluorescent materials which are alone incapable of thin film formation. Prefe ⁇ ed fluorescent materials are those which form a common phase with the organo metallic complex material. Fluorescent dyes constitute a prefe ⁇ ed class of fluorescent materials, since dyes lend themselves to molecular level distribution h the organo metallic complex.
• prefe ⁇ ed fluorescent dyes are those which can be vacuum vapor deposited along with the organo metallic complex materials.
• fluorescent laser dyes are recognized to be particularly useful fluorescent materials for use in the organic EL devices of this invention. Dopants which can be used include diphenylacridine, coumarins, perylene and their derivatives.
• Ri is chosen from the group consisting of hydrogen, carboxy, alkanoyl, alkoxycarbonyl, cyano, aryl, and a heterocylic aromatic group
• R 2 is chosen from the group consisting of hydrogen, alkyl, haloalkyl, carboxy, alkanoyl, and alkoxycarbonyl
• R 3 is chosen from the group consisting of hydrogen and alkyl
• R 5 is hydrogen, or Ri or R 2 together form a fused carbocyclic ring, and/or the amino group forming R 4 completes with at least one of R 4 and R 6 a fused ring.
• the alkyl moieties in each instance contain from 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms.
• the aryl moieties are preferably phenyl groups.
• the fused carbocyclic rings are preferably five, six or seven membered rings.
• the heterocyclic aromatic groups contain 5 or 6 membered heterocyclic rings containing carbon atoms and one or two heteroatoms chosen from the group consisting of oxygen, sulfur, and nitrogen.
• the amino group can be a primary, secondary, or tertiary amino group. When the amino nitrogen completes a fused ring with an adjacent substituent, the ring is preferably a five or six membered ring.
• R 4 can take the form of a pyran ring when the nitrogen atom forms a single ring with one adjacent substituent (R or R ) or a julolidine ring (including the fused benzo ring of the coumarin) when the nitrogen atom forms rings with both adjacent substituents R 3 and R 5 .
• FD-1 7-Diethylamino-4-methylcoumarin FD-2 4,6-Dimethyl-7- ethylaminocoumarin
• FD-3 4-Methylumbelliferone FD-4 3-(2'-Benzothiazolyl)-7- diethylaminocoumarin, FD-5 3 -(2'-Benzimidazolyl)-7-N,N-diethylaminocoumarin, FD-6 7-Amino-3-phenylcoumarin, FD-7 3-(2'-N-Methylbenzimidazolyl)-7- N,Ndiethylaminocoumarin, FD-8 7-Diethylamino-4-trifluoromethylcoumarin, FD-9 2,3,5,6-lH,4H-Tetrahydro-8-methylquinolazino[9,9a,l-gh]coumarin, FD-10
• dopants include salts of bis benzene sulphonic acid such as
• Ri, R 2 , 3 and R 4 are R, Ri, R j R 3 and R4 can be the same or different and are selected from hydrogen, hydrocarbyl groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; R, Ri , R 2, R 3 and R 4 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer e.g. styrene. R, R ⁇ ; R 2, R 3 and R 4 can also be unsaturated alkylene groups such as vinyl groups or groups C CH 2 — CH 2 R where R is as above.
• dopants are dyes such as the fluorescent 4-dicyanomethylene-4H-pyrans and 4- dicyanomethylene-4H-thiopyrans, e.g. the fluorescent dicyanomethylenepyran and thiopyran dyes .
• Useful fluorescent dyes can also be selected from among known polymethine dyes, which include the cyanines, merocyanines, complex cyanines and merocyanines (i.e. tri-, tetra- and poly-nuclear cyanines and merocyanines), oxonols, hemioxonols, styryls, merostyryls, and streptocyanines.
• polymethine dyes include the cyanines, merocyanines, complex cyanines and merocyanines (i.e. tri-, tetra- and poly-nuclear cyanines and merocyanines), oxonols, hemioxonols, styryls, merostyryls, and streptocyanines.
• the cyanine dyes include, joined by a methine linkage, two basic heterocyclic nuclei, such as azolium or azinium nuclei, for example, those derived from pyridinium, quinolinium, isoquinolinium, oxazolium, thiazolium, selenazolium, indazolium, pyrazolium, py ⁇ olium, indolium, 3H-indolium, imidazolium, oxadiazolium, thiadioxazolium, benzoxazolium, benzothiazolium, benzoselenazolium, benzotellurazolium, benzimidazolium, 3H- or lH-benzoindolium, naphthoxazolium, naphthothiazolium, naphthoselenazolium, naphthotellurazolium, carbazolium, py ⁇ olopyridinium, phenanthrothia
• fluorescent dyes are 4-oxo-4H-benz-[d,e]anthracenes and pyrylium, thiapyrylium, selenapyrylium, and telluropyrylium dyes.
• prefe ⁇ ed ligands L are quinolate, porphoryin, porphines, pyrazalones, such as 5,10,15,20-tetra(4-pyridyl) 21H,23H-porphine 5,10,15,20-tetra(p-tolyl) 21H,23H- porphine and meso- tetraphenyl poiphine and ⁇ diketones such as dibenzoyl methane and ligands of formula
• R ⁇ R 2 and R 3 can be the same or different and are selected from hydrogen, and substituted and unsubstituted hydrocarbyl groups such as substituted and unsubstituted aliphatic groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; R ⁇ ; R 2 and R 3 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer, e.g. styrene.
• X is Se, S or O
• Y can be hydrogen, substituted or unsubstituted hydrocarbyl groups, such as substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorine, fluorocarbons such as frifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
• Ri and/or R 2 and/or R 3 include aliphatic, aromatic and heterocyclic alkoxy, aryloxy and carboxy groups, substituted and substituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene, naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclic groups such as carbazole.
• Ri and R 3 are phenyl groups and R 2 is hydrogen.
• Other ligands L can be R3 R4
• groups R can be the same or different and are selected from hydrogen, and substituted and unsubstituted hydrocarbyl groups such as substituted and unsubstituted aliphatic groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as frifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; R 1; R 2 and R 3 can also fo ⁇ n substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer, e.g. styrene.
• Some of the different groups L may also be the same or different charged groups such as carboxylate groups so that the group Li can be as defined above and the groups L 2 , L 3.. . can be charged groups such as
• R is Ri as defined above or the groups L ls L 2 can be as defined above and L 3. etc. are other charged groups.
• X is O, S, Se or ⁇ H.
• a prefe ⁇ ed moiety Ri is trifluoromethyl CF 3 and examples of such diketones are, banzoyltrifluoroacetone, p-chlorobenzoyltrifluoroacetone, p-bromotrifluoroacetone, p-phenyltrifluoroacetone, 1 -naphthoyltrifluoroacetone, 2-naphthoyltrifluoroacetone, 2-phenathoyltrifluoroacetone, 3-phenanthoyltrifluoroacetone, 9- anthroyltrifluoroacetonetrifluoiOacetone, cinnamoyltrifluoroacetone, and 2- thenoyltrifluoroacetone.
• the different groups L may be the same or different ligands of formulae
• the different groups L may be the same or different quinolate derivatives such as
• the different groups L may also be the same or different carboxylate groups e.g.
• R 5 is a substituted or unsubstituted aromatic, polycyclic or heterocyclic ring a polypyridyl group
• R 5 can also be a 2-ethyl hexyl group so L n is 2-ethylhexanoate or R 5 can be a chair structure so that L n is 2-acetyl cyclohexanoate or L ⁇ can be
• R is as above e.g. alkyl, allenyl, amino or a fused ring such as a cyclic or polycyclic ring.
• the different groups L may also be
• prefe ⁇ ed ligand is quinolate and prefe ⁇ ed electroluminescent compounds are the metal salts of substituted or unsubstituted 8 -hydroxy quinoline which are refe ⁇ ed to herein as metal quinolates.
• prefe ⁇ ed elctroluminecent compounds are titanium, zirconium, hafnium, vanadium, niobium and tantalum quinolates.
• n is the valency state of the metal and the where the substituents are the same or different in the 2, 3, 4, 5, 6 and 7 positions and are preferably selected from alky, alkoxy, aryl, aryloxy, sulphonic acids, esters, carboxylic acids, amino and amido groups or are aromatic, polycyclic or heterocyclic groups.
• the prefe ⁇ ed quinolates are the 2-methyl and the 5- methyl quinolates.
• Metal quinolates can be synthesised by the reaction of a metal compound such as a salt, ethoxide or alkyl 8-hydroxyquinoline in accordance with well known methods.
• a metal compound such as a salt, ethoxide or alkyl 8-hydroxyquinoline
• the reaction preferably takes place in a nitrile solvent such as acetonitrile, phenyl nitrile, tolyl nitrile, etc.
• the invention also provides an electroluminescent device which comprises (i) a first electrode, (ii) a layer of a electroluminescent compound as described above and (iii) a second electrode.
• the first electrode can function as the anode and the second electrode can function as the cathode and preferably there is a layer of a hole transporting material between the anode and the layer of the electroluminescent compound.
• the hole transporting material can be any of the hole transporting materials used in electroluminescent devices.
• the hole transporting material can be an amine complex such as poly (vinylcarbazole), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1' -biphenyl -4,4'- diamine (TPD), an unsubstituted or substituted polymer of an amino substituted aromatic compound, a polyaniline, substituted polyanilines, polythiophenes, substituted polythiophenes, polysilanes etc.
• polyanilines are polymers of
• R is in the ortho - or meta-position and is hydrogen, Cl-18 alkyl, Cl-6 alkoxy, amino, chloro, bromo, hydroxy or the group
• R is alky or aryl and R' is hydrogen, Cl-6 alkyl or aryl with at least one other monomer of formula I above.
• the hole transporting material can be a polyaniline
• polyanilines which can be used in the present invention have the general formula
• XX where p is from 1 to 10 and n is from 1 to 20, R is as defined above and X is an anion, preferably selected from CI, Br, SO 4 , BF 4 , PF 6 , H 2 PO 3 , H 2 PO 4 , arylsulphonate, arenedicarboxylate, poiystyrenesulphonate, polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate, cellulose sulphonate, camphor sulphonates, cellulose sulphate or a perfluorinated polyanion.
• arylsulphonates are p-toluenesulphonate, benzenesulphonate, 9,10- anthraquinone-sulphonate and anthracenesulphonate; an example of an arenedicarboxylate is phthalate and an example of arenecarboxylate is benzoate.
• evaporable deprotonated polymers of unsubstituted or substituted polymer of an amino substituted aromatic compound are used.
• the de-protonated unsubstituted or substituted polymer of an amino substituted aromatic compound can be formed by deprotonating the polymer by treatment with an alkali such as ammonium hydroxide or an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.
• the degree of protonation can be controlled by forming a protonated polyaniline and de-protonating.
• Methods of preparing polyanilines are described in the article by A. G. MacDiarmid and A. F. Epstein, Faraday Discussions, Chem Soc.88 P319 1989.
• the conductivity of the polyaniline is dependant on the degree of protonation with the maximum conductivity being when the degree of protonation is between 40 and 60%, for example, about 50%.
• the polymer is substantially fully deprotonated.
• a polyaniline can be formed of octamer units, i.e. p is four, e.g.
• the polyanilines can have conductivities of the order of 1 x 10 " Siemen cm or higher.
• the aromatic rings can be unsubstituted or substituted, e.g. by a CI to 20 alkyl group such as ethyl.
• the polyaniline can be a copolymer of aniline and prefe ⁇ ed copolymers are the copolymers of aniline with o-anisidine, m-sulphanilic acid or o-aminophenol, or o- toluidine with o-aminophenol, o-ethylaniline, o-phenylene diamine or with amino anthracenes.
• Other polymers of an amino substituted aromatic compound which can be used include substituted or unsubstituted polyaminonapthalenes, polyaminoanthracenes, polyaminophenanthrenes, etc. and polymers of any other condensed polyaromatic compound. Polyaminoanthracenes and methods of making them are disclosed in US Patent 6,153,726.
• the aromatic rings can be unsubstituted or substituted, e.g. by a group R as defined above.
• conjugated polymer and the conjugated polymers which can be used can be any of the conjugated polymers disclosed or refe ⁇ ed to in US 5807627, PCT/WO90/13148 and PCT/WO92/03490.
• the prefe ⁇ ed conjugated polymers are poly (p-phenylenevinylene)-PPV and copolymers including PPV.
• Other prefe ⁇ ed polymers are poly(2,5 dialkoxyphenylene vinylene) such as poly (2-methoxy-5-(2-methoxypentyloxy-l,4-phenylene vinylene), poly(2-methoxypentyloxy)-l,4-phenylenevinylene), poly(2-methoxy-5-(2- dodecyloxy-l,4-phenylenevinylene) and other poly(2,5 dialkoxyphenylenevinylenes) with at least one of the alkoxy groups being a long chain solubilising alkoxy group, poly fluorenes and oligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes and oligo anthracenes, ploythiophenes and oligothiophenes.
• the phenylene ring may optionally carry one or more substituents, e.g. each independently selected from alkyl, preferably methyl, alkoxy, preferably methoxy or ethoxy.
• Any poly(arylenevinylene) including substituted derivatives thereof can be used and the phenylene ring in poly(p-phenylenevinylene) may be replaced by a fused ring system such as anthracene or naphthlyene ring and the number of vinylene groups in each polyphenylenevinylene moiety can be increased, e.g. up to 7 or higher.
• the conjugated polymers can be made by the methods disclosed in US 5807627, PCT/WO90/13148 and PCT/WO92/03490.
• the thickness of the hole transporting layer is preferably 20nm to 200nm.
• polymers of an amino substituted aromatic compound such as polyanilines refe ⁇ ed to above can also be used as buffer layers with or in conjunction with other hole transporting materials.
• R ⁇ R 2 and R 3 can be the same or different and are selected from hydrogen, and substituted and unsubstituted hydrocarbyl groups such as substituted and unsubstituted aliphatic groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as frifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; R ⁇ ; R 2 and R 3 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer, e.g.
• styrene X is Se, S or O
• Y can be hydrogen, substituted or unsubstituted hydrocarbyl groups, such as substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorine, fluorocarbons such as frifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
• Ri and/or R 2 and/or R 3 include aliphatic, aromatic and heterocyclic alkoxy, aryloxy and carboxy groups, substituted and substituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene, naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclic groups such as carbazole.
• the electron injecting material is a material which will transport electrons when an electric cu ⁇ ent is passed through electron injecting materials include a metal complex such as a metal quinolate, e.g. an aluminium quinolate, lithium quinolate, zirconium quinolate, a cyano anthracene such as 9,10 dicyano anthracene, cyano substituted aromatic compounds, tetracyanoquinidodimethane a polystyrene sulphonate or a compound with the structural formulae shown in figures 2 or 3 of the drawings in which the phenyl rings can be substituted with substituents R as defined above.
• a metal complex such as a metal quinolate, e.g. an aluminium quinolate, lithium quinolate, zirconium quinolate, a cyano anthracene such as 9,10 dicyano anthracene, cyano substituted aromatic compounds, tetracyanoquinidodimethane a polys
• the electroluminescent layer in an electroluminescent device comprises a doped zirconium quinolate, then a prefe ⁇ ed electron injecting material is zirconium quinolate.
• the first electrode is preferably a transparent substrate such as a conductive glass or plastic material which acts as the anode; prefe ⁇ ed substrates are conductive glasses such as indium tin oxide coated glass, but any glass which is conductive or has a conductive layer such as a metal or conductive polymer can be used. Conductive polymers and conductive polymer coated glass or plastics materials can also be used as the substrate.
• the cathode is preferably a low work function metal, e.g. aluminium, calcium, lithium, silver/magnesium alloys, rare earth metal alloys etc; aluminium is a prefe ⁇ ed metal.
• a metal fluoride such as an alkali metal, rare earth metal or their alloys can be used as the second electrode, for example by having a metal fluoride layer formed on a metal.
• a pre-etched ITO coated glass piece (10 x 10cm 2 ) was used.
• the device was fabricated by sequentially forming on the ITO, by vacuum evaporation using a Solciet Machine,ULVAC Ltd. Chigacki, Japan the active area of each pixel was 3mm by 3 mm, the layers comprised :-
• ITO indium tin oxide coated glass
• Cu Pc copper phthalocyanine
• ⁇ -NPB is as defined in the specification
• Zrq 4 is zirconium quinolate
• DPQA is diphenylquinacridine.
• the Zrq 4 is zirconium quinolate and the Zrq 4 :DPQA layer was formed by concu ⁇ ent vacuum deposition to form a zirconium quinolate layer doped with DPQA.
• the weight ratio of the Zrq and DPQA is conveniently shown by a relative thickness measurement.
• the coated electrodes were stored in a vacuum desiccator over a molecular sieve and phosphorous pentoxide until they were loaded into a vacuum coater (Edwards, 10 "6 ton) and aluminium top contacts made. The devices were then kept in a vacuum desiccator until the electroluminescence studies were performed.
• the ITO electrode was always connected to the positive terminal.
• the current vs. voltage studies were ca ⁇ ied out on a computer controlled Keithly 2400 source meter. An electric cu ⁇ ent was applied across the device and the performance shown in fig. 14; the electroluminescence spectrum is shown in fig. 15.
• the device had the structure of fig. 16 and the colours are as in the CIE colour chart of fig. 17.
• a device was fabricated according to the method of Example 1 with the structure ITO /CuPc (25nm) / ⁇ -NPB (75 nm)/Zrq 4 :Nilered (75:0.38nm) /LiF (0.4 nrnVAl, where nilered is
• a device was fabricated according to the method of Example 1 with the structure ITO(100 ⁇ / sqr. m ) /CuPc (25nm) / ⁇ -NPB (75 nm)/Zrq 4 :DPQA (60:0.4nm) /Zrq 4 (10nm)/LiF (0.4 nm)/Al.
• a device was fabricated according to the method of Example 1 with the structure ITO(100 ⁇ / sqr. m ) /CuPc.TPTP (15:15nm) / ⁇ -NPB (75 nm)/Zrq 4 :DPQA (60:0.5nm) /LiF (0.2 mnVAl.
• Example 5 A device was fabricated according to the method of Example 1 with the structure
• a device was fabricated according to the method of Example 1 with the structure ITO(100 ⁇ / sqr. m ) /CuPc (25nm) / ⁇ -NPB (60 nm)/Zrq 4 :DCJT (35:0.5nm) / Zrq 4 (35nm/LiF (0.5 nm)/Al.
• DCJT is 4-(Dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran.
• a device was fabricated according to the method of Example 1 with the structure ITO(100 ⁇ / sqr. m ) /CuPc (50nm) / ⁇ -NPB (75 nm)/Zrq 4 :DCM (60:0.5nm) /
• KF potassium fluoride
• DCM 4-(Dicyanomethylene)-2-methyl-
• Example 8 A device was fabricated according to the method of Example 1 with the structure
• a device was fabricated according to the method of Example 1 with the structure ITO(100 ⁇ / sqr. m ) /CuPc (25nm) / ⁇ -NPB (40 nm)/Zrq 4 :DPQA (30:0.2nm) / Zrq (l Onm/LiF (0.5 nm)/Al.
• the devices were fabricated by the same method according to Example 1.
• the Zrq had an increase in efficiency of 40% compared with Alq 3 at 300 cd m " and a luminance 36% greater at 20 mA cm " .

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