WO2002075820A1 - Electroluminescent devices - Google Patents

Electroluminescent devices Download PDF

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Publication number
WO2002075820A1
WO2002075820A1 PCT/GB2002/001264 GB0201264W WO02075820A1 WO 2002075820 A1 WO2002075820 A1 WO 2002075820A1 GB 0201264 W GB0201264 W GB 0201264W WO 02075820 A1 WO02075820 A1 WO 02075820A1
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Prior art keywords
electroluminescent
metal
layer
compound
poly
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PCT/GB2002/001264
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French (fr)
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Poopathy Kathirgamanathan
Juan Antipan Lara
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Elam-T Limited
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Priority claimed from GB0106555A external-priority patent/GB0106555D0/en
Priority claimed from GB0106558A external-priority patent/GB0106558D0/en
Priority claimed from GB0106556A external-priority patent/GB0106556D0/en
Priority claimed from GB0106554A external-priority patent/GB0106554D0/en
Priority claimed from GB0106557A external-priority patent/GB0106557D0/en
Application filed by Elam-T Limited filed Critical Elam-T Limited
Publication of WO2002075820A1 publication Critical patent/WO2002075820A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/30—Coordination compounds
    • H10K85/351—Metal complexes comprising lanthanides or actinides, e.g. comprising europium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/16—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
    • H01L33/18—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous within the light emitting region
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
    • H10K2102/10—Transparent electrodes, e.g. using graphene
    • H10K2102/101—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO]
    • H10K2102/103—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO] comprising indium oxides, e.g. ITO
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/80—Constructional details
    • H10K50/805—Electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
    • H10K85/1135—Polyethylene dioxythiophene [PEDOT]; Derivatives thereof
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/115—Polyfluorene; Derivatives thereof
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/30—Coordination compounds
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/30—Coordination compounds
    • H10K85/321—Metal complexes comprising a group IIIA element, e.g. Tris (8-hydroxyquinoline) gallium [Gaq3]
    • H10K85/324—Metal complexes comprising a group IIIA element, e.g. Tris (8-hydroxyquinoline) gallium [Gaq3] comprising aluminium, e.g. Alq3

Definitions

  • the present invention relates 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.
  • aluminium quinoiate Another compound which has been proposed is aluminium quinoiate, but this requires dopants to be used to obtain a range of colours and has a relatively low efficiency.
  • Kido et al disclosed that a terbium III acetyl acetonate complex was green electroluminescent and in an article in Applied Physics letters 65 (17) 24 October 1994 Kido et al disclosed that a europium III triphenylene diamine complexes was red electroluminescent but these were unstable in atmospheric conditions and difficult to produce as films.
  • 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.
  • US Patent 5128587 discloses an electroluminescent device which consists of an organometallic complex of rare earth elements of the lanthanide series sandwiched between a transparent electrode of high work function and a second electrode of low work function with a hole conducting layer interposed between the electroluminescent layer and the transparent high work function electrode and an electron conducting layer interposed between the electroluminescent layer and the electron injecting low work function anode.
  • a structure comprising (i) a layer of porous silicon and (ii) a layer of an electroluminescent compound.
  • the invention also provides an electroluminescent device comprising (i) a first electrode, (ii) a layer of an electroluminescent compound (iii) a layer of porous silicon (iv) a second electrode.
  • the layer of porous silicon can be formed by etching the surface of a silicon substrate as described below.
  • the band structure for single crystal silicon exhibits a conduction band minimum which does not have the same crystal momentum as the valence band maximum, yielding an indirect gap. Therefore, in silicon, radiative recombination can only take place with the assistance of a photon, making such transitions inefficient. This has prevented silicon from being used as a solid state source of light, unlike group III-N semiconductors which have a direct gap at the centre of the Brillouin zone.
  • group III-N semiconductors which have a direct gap at the centre of the Brillouin zone.
  • Porous silicon is formed using electrochemical etching, photochemical etching or stain etching of bulk silicon or silicon-on- sapphire (SOS) wafers as described in the above references.
  • the substrate may be suitably patterned lithographically prior to the etch to define device structures or confine the region exposed to the etch solution.
  • the typical emission spectrum of porous silicon is in the red, orange and yellow region (nominally 500 to 750 nm) although green and blue emission has also been demonstrated. Blue shift of the peak emission wavelength has been shown by increased oxidation and etching of the porous silicon as described in "Control of porous Si photoluminescence through dry oxidation" by S. Shih al., Appl. Phys.
  • electroluminescent compounds which can be used in the present invention include electroluminescent organo metal compounds, electroluminescent polymers, and electroluminescent metal quinolates.
  • a particular class of electroluminescent organo metal compounds are the rare earth chelates.
  • Rare earth chelates are known which fluoresce in ultra violet radiation and A. P. Sinha (Spectroscopy of Inorganic Chemistry Vol. 2 Academic Press 1971) describes several classes of rare earth chelates with various monodentate and bidentate ligands.
  • Group III A metals and lanthanides and actinides with aromatic complexing agents have been described by G. Kallistratos (Chimica Chronika, New Series, 11, 249-266 (1982)). This reference specifically discloses the Eu (10), b (III), U (III) and U (TV) complexes of diphenyl-phosponamidotriphenyl-phosphoran.
  • EP 0744451A1 and 0556005 Al also disclose fluorescent chelates of transition or lanthanide or actinide metals and the known chelates which can be used are those disclosed in the above references including those based on diketone and triketone moieties.
  • the preferred electroluminescent rare earth metal chelates which can be used in the present invention are of formula
  • L ⁇ and Lp are organic ligands
  • M is a rare earth, transition metal, lanthanide or an actinide and n is the valence state of the metal M.
  • the ligands L ⁇ can be the same or different and there can be a plurality of ligands Lp which can be the same or different.
  • L (L 2 )(L 3 )(L..)M (Lp) where M is a rare earth, transition metal, lanthanide or an actinide and (L ⁇ )(L 2 )(L 3 )(L...) are the same or different organic complexes and (Lp) is a neutral ligand.
  • the total charge of the ligands (L ⁇ )(L 2 )(L 3 )(L..) is equal to the valence state of the metal M.
  • the complex has the formula (L ⁇ )(L 2 )(L 3 )M (Lp) and the different groups (L ⁇ )(L 2 )(L 3 ) may be the same or different
  • any metal ion having an unfilled inner shell can be used as the metal and the preferred metals are selected from Sm(i ⁇ ), Eu(U), Eu(m), Tb(ffl), Dy(III), Yb(IH), Lu(IIi), Gd (IH), U(III), U(VI)O 2 , Tm(IU), Th(IN), Ce (ITI), Ce(IN), Pr(ffl), ⁇ d(IH), Pm(m), Dy(i ⁇ ), Ho(ffl), Er(ffl).
  • electroluminescent compounds which can be used in the present invention are of general formula (L ⁇ ) n M ⁇ Mq where Mi is the same as M above, Mq is a non rare earth metal, L ⁇ is a as above and n is the combined valence state of M ⁇ and Mq.
  • the complex can also comprise one or more neutral ligands Lp so the complex has the general formula (L ⁇ ) n Mi Mq (Lp), where Lp is as above.
  • the metal Mq can be any metal which is not a rare earth, transition metal, lanthanide or an actinide
  • metals which can be used include lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper (I), copper (II), silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin (IT), tin (TV), antimony (H), antimony (IV), lead (H), lead (TV) and metals of the first, second and third groups of transition metals in different valence states e.g.
  • organometallic complexes which can be used in the present invention are binuclear, trinuclear and polynuclear organometallic complexes e.g. of formula
  • L is a bridging ligand and where Mi is a rare earth metal and M 2 is Mi or Mq, Lm and Ln are the same or different organic ligands L ⁇ as defined above, x is the valence state of Mi and y is the valence state of M 2 .
  • trinuclear there are three rare earth metals joined by a metal to metal bond i.e. of formula
  • M 3 is the same as M 2 and they can be the same or different metals and Lm
  • Ln and Lp are organic ligands L ⁇ and x is the valence state of Mi, y is the valence state of M 2 and z is the valence state of M 3 .
  • Lp can be the same as Lm and Ln or different.
  • the rare earth metals and the non rare earth metals can be joined together by a metal to metal bond and/or via an intermediate bridging atom, ligand or molecular group.
  • metals can be linked by bridging ligands e.g.
  • polynuclear there are more than three metals joined by metal to metal bonds and/or via intermediate ligands
  • L ⁇ is selected from ⁇ diketones such as those of formulae
  • Ri , 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; Ri, 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.
  • 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 trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
  • Ri and/or R 2 and or R 3 examples 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.
  • 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
  • Ri, R and R 3 can also be
  • 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- anthroyltrifluoroacetonetrifluoroacetone, 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 quinoiate derivatives such as
  • 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 Ln 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
  • R, Ri and R 2 are as above.
  • 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 ⁇ is 2-ethylhexanoate or R 5 can be a chair structure so that L shadow is 2-acetyl cyclohexanoate
  • the groups Lp can be selected from
  • each Ph which can be the same or different and can be a phenyl (OPNP) or a substituted phenyl group, other substituted or unsubstituted aromatic group, a substituted or unsubstituted heterocyclic or polycyclic group, a substituted or unsubstituted fused aromatic group such as a naphthyl, anthracene, phenanthrene, perylene or pyrene group.
  • the substituents can be for example an alkyl, aralkyl, alkoxy, aromatic, heterocyclic, polycyclic group, halogen such as fluorine, cyano, amino and substituted amino groups etc. Examples are given in figs.
  • R, Ri , R 2> R 3 and R 4 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, Ri , R 2> R 3 and R 4 can also be unsaturated alkylene groups such as vinyl groups or groups where R is as above.
  • L p can also be compounds of formulae
  • L p can also be Ph Ph Ph
  • L p chelates are as shown in figs. 4 and fluorene and fluorene derivatives e.g. a shown in figs. 5 and compounds of formulae as shown as shown in figs. 6 to 8.
  • L ⁇ and Lp are tripyridyl and TMHD, and TMHD complexes, ⁇ , ⁇ ', ⁇ " tripyridyl, crown ethers, cyclans, cryptans phthalocyanans, porphoryins ethylene diamine tetramine (EDTA), DCTA, DTPA and TTHA.
  • TMHD 2,2,6,6-tetramethyl-3,5-heptanedionato
  • OPNP is diphenylphosphonimide triphenyl phosphorane.
  • the formulae of the polyamines are shown in fig. 9.
  • the electroluminescent layer comprises a layer of a light emitting metal compound selected from organic complexes of non rare earth metals
  • the complexes have the formula (M)q(L ⁇ ) n where Mq is the metal as defined above and n is the valency state of the metal and L ⁇ is as defined above.
  • the light emitting metal compound can be formed from any metal compound selected from non rare earth metals e.g. lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper, silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin, antimony, lead, and metals of the first, second and third groups of transition metals e.g.
  • non rare earth metals e.g. lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper, silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin, antimony, lead, and metals of the first, second and third groups of transition metals e.g.
  • L ⁇ . defined as above is selected from ⁇ diketones such as those of formulae above.
  • ⁇ -diketones Tris -(l,3-diphenyl-l-3-propanedione) (DBM) and suitable metal complexes are Al(DBM) 3 , Zn(DBM) 2 and Mg(DBM) 2 ., Sc(DBM) 3 etc.
  • a preferred ⁇ -diketone is when Ri and/or R 3 are alkoxy such as methoxy and the metals are aluminium or scandium i.e. the complexes have the formula
  • R 4 is an alkyl group, preferably methyl and R 3 is hydrogen, an alkyl group such as methyl or R 4 O.
  • the electroluminescent compound has the formula (L ⁇ ) m (L 2 ) n M where M is as defined above , (Li) is a compound of formula
  • L 2 is another organic ligand
  • m + n equals the valency of M and m is at least 1.
  • the complex can be non-stoichiometric i.e. of formula M x Ly where M is the metal and L is an organic ligand.
  • M is the metal
  • L is an organic ligand.
  • a stoichiometric complex x will be one and y will be the valence state of the metal
  • examples include Pt 2 (DBM) 3 and Pd 2 (DBM) 3 where Pt and Pd are nominally in the II valence state. It is possible that some kind of linked or polymeric structure is formed and/or the metal is present in more than one valence state.
  • the metal M is a metal with an unfilled inner orbital such as scandium, yttrium, niobium etc.
  • an uncharged ligand which forms a complex with the metal so the complex has the formula
  • Mr is as a metal with an unfilled inner orbital L ⁇ and Lp are as above
  • the metal quinoiate can be any metal quinoiate which emits light when an electric current is passed through it.
  • Suitable metal quinolates include the quinolates of lithium, aluminium, zinc, barium, cadmium, sodium, potassium, magnesium etc.
  • the preferred metal quinolates are lithium quinoiate and aluminium quinoiate.
  • the lithium quinoiate is preferably made by the reaction of a lithium alkyl or alkoxide with 8-hydroxy quinoline or substituted 8-hydroxy quinoline, preferably in a solvent incorporating acetonitrile..
  • the alkyl can be ethyl, propyl or butyl and the alkoxide can be an ethoxide, propoxide or a butoxide.
  • the lithium quinoiate can be doped the preferred dopants are coumarins such as those of formula
  • Ri, R 2 , and R 3 are hydrogen or an alkyl group such as a methyl or ethyl group, amino and substituted amino groups e.g.
  • R 3 is hydrogen or alkyl group such as a methyl or ethyl group
  • dopants include salts of bis benzene sulphonic acid such as
  • Ri, R 2 , R 3 and t are R, Ri, R 2> R 3 and t 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 Rt can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer e.g. styrene. R, Ri, R 2> R 3 and can also be unsaturated alkylene groups such as vinyl groups or groups
  • organometallic complexes such as those of general formula (L ⁇ ) n M where (L ⁇ ), M and n are as above.
  • the conjugated polymer used can be any of the conjugated polymers disclosed or referred to in US 5807627, PCT/WO90/13148 and PCT/WO92/03490.
  • the preferred conjugated polymers are poly (p-phenylenevinylene)-PPV and copolymers including PPV.
  • Other preferred polymers are poly(2,5 dialkoxyphenylene vinylene) such as poly (2-methoxy-5-(2-methoxypentyloxy-l,4-phenylene vinylene), poly(2-methoxypentyloxy)- 1 ,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 fiuorenes 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 ⁇ oly(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.
  • Fluorescent polymers are well known compounds which fluoresce in ultra violet or visible light. Fluorescent polymers include condensed aromatic compounds such as anthracene and its derivatives, chrysene and its derivatives etc. and conjugated aromatic aromatic compounds. Fluorescent polymers are widely used in light emitting diodes and any of these polymers can be used in the present invention; examples of such polymers are given in figs. 1 and figs. 2.
  • the electroluminescent material can be deposited on the porous silicon substrate directly by evaporation from a solution of the material in an organic solvent.
  • the solvent which is used will depend on the material but chlorinated hydrocarbons such as dichloromethane, n-methyl pyrrolidone, dimethyl sulphoxide, tetra hydrofuran dimethylformamide etc. are suitable in many cases.
  • the material can be deposited by spin coating from solution or by vacuum deposition from the solid state e.g. by sputtering or any other conventional method can be used.
  • the first electrode can be a metal which is in contact with the electroluminescent layer directly or through a layer such as a hole transporting layer.
  • the electrode is an opaque metal the light is emitted from the device around the edges of the metal and interdigitated structures are preferred e.g. the electrode is formed of strips of the metal.
  • the first electrode is a transparent substrate such as a conductive glass or plastic material which acts as the anode
  • preferred 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 porous silicon layer is formed on the surface of the silicon substrate and the second electrode can be directly attached to the silicon using conventional techniques e.g. by means of indium/gallium contact.
  • the electron transmitting material is a material which will transport electrons when an electric current is passed through electron transmitting materials include a metal complex such as a metal quinoiate e.g. an aluminium quinoiate, lithium quinoiate a cyano anthracene such as 9,10 dicyano anthracene, a polystyrene sulphonate and compounds of formulae shown in fig. 10.
  • a metal quinoiate e.g. an aluminium quinoiate, lithium quinoiate a cyano anthracene such as 9,10 dicyano anthracene, a polystyrene sulphonate and compounds of formulae shown in fig. 10.
  • the electron transmitting material can be mixed with the electroluminescent material and co-deposited with it. In general the thickness of the layers is from 5nm to 500nm.
  • the hole transporting layer serves to transport holes and to block the electrons, thus preventing electrons from moving into the electrode without recombining with holes.
  • the recombination of carriers therefore mainly takes place in the emitter layer.
  • Hole transporting layers are used in polymer electroluminescent devices and any of the known hole transporting materials in film form can be used.
  • hole transporting materials are aromatic amine complexes 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.
  • aromatic amine complexes 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
  • R is in the ortho - or meta-position and is hydrogen, CI -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.
  • 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 , PF 6 , H 2 PO 3 , H 2 PO , arylsulphonate, arenedicarboxylate, polystyrenesulphonate, 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% e.g. about 50% for example.
  • 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 "1 Siemen cm "1 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 preferred 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.
  • the polyanilines can be deposited on the first electrode by conventional methods e.g. by vacuum evaporation, spin coating, chemical deposition, direct electrodeposition etc. preferably the thickness of the polyaniline layer is such that the layer is conductive and transparent and can is preferably from 20nm to 200nm.
  • the polyanilines can be doped or undoped, when they are doped they can be dissolved in a solvent and deposited as a film, when they are undoped they are solids and can be deposited by vacuum evaporation i.e. by sublimation.
  • polymers of an amino substituted aromatic compound such as polyanilines referred to above can also be used as buffer layers with or in conjunction with other hole transporting materials.
  • R J 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; Ri, 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.
  • R J 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
  • 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 trifluoryl 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 second electrode attached to the silicon functions as the cathode and can be any low work function metal e.g. aluminium, calcium, lithium, silver/magnesium alloys, rare earth metal alloys etc., aluminium is a preferred metal.
  • a metal fluoride such as an alkali metal, rare earth metal or their alloys and preferably lithium fluoride can be used as the second electrode for example by having a metal fluoride layer formed on a metal.
  • first electrode an electron injection layer, the electroluminescent layer, a hole transportation layer, a porous silicon layer and the second electrode.
  • Porous silicon layers (5 ⁇ were grown by anodisation of ap-type silicon wafer [p- Si, 535, ⁇ m thick, orientation ⁇ 100> , 10 + ⁇ cm, boron doped, ohmic contact with In/Ga (60/40) eutectic] at a current density of 6mA cm “2 in HF(40%)/ethanol ( 1: 1) for a period of 12 minutes to give a porosity of 65 +5 %.
  • Rare earth chelates were coated on the porous silicon (PSi) by adding 1 ml of a solution of chelates dropwise on to the active area of the device. Once the PSi layers had been impregnated with the chelate solutions, they were dried in air (24 hours) and then dried in vacuum (1 x 10 "6 torr) at 30°C for a further period of 6 hours. The thickness of the adduct layer on each device was 800+200nm. Al top contacts (190 nm) were then deposited by vacuum sputtering. The electrical examinations were carried out at room temperature.
  • Electroluminescent structures were fabricated with a structure as shown in fig. 1, the structures comprise an indium gallium alloy electrode (1) attached to silicon layer (2) on the surface of which is a PSi layer (3) formed as above, there is a chelate layer (4) deposited on the PSi layer as described above and an alviminium electrode attached to the surface.
  • Example 1 The procedure of Example 1 was repeated using aluminium quinoiate as the electroluminescent material.
  • the device had the structure
  • ⁇ -NPB is as shown in fig. 5 and the figures are in nanometers.
  • the current density against bias voltage is shown in figs. 32 and 33, the device gave off a yellowish light.
  • Example 1 The procedure of Example 1 was repeated using lithium quinoiate as the elecfroluminescent material.
  • the devices had the structures Example 3 - Porous silicon / CuPc(8.5nm) / m-MTDATA(25nm)/Liq(37nm) Al
  • Example 4 Porous silicon / CuPc(8.3nm) / m-MTDATA(60nm)/Liq(35nm) Al
  • the current density against bias voltage is shown in figs. 34 and 35, the device of example 3 gave off a yellowish blue emission at 15V and the device of example 4 gave a yellow green emission at 22V.
  • Example 5 The procedure of Example 1 was repeated to form a device of structure Porous silicon/PEDOT(50nm)/OF(75nm)/Al Where PEDOT is poly(ethylenedioxythiophene) and OF is oligofluorene
  • n 2 - 20 PEDOT OF The current density against bias voltage is shown in fig. 36 and the device gave off a dark yellow emission at 22v.

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Abstract

An electroluminescent device comprises (i) a first electrode, (ii) a layer of an electroluminescent compound (iii) a layer of porous silicon and (iv) a second electrode.

Description

Electroluminescent Devices
The present invention relates to electroluminescent devices.
Materials which emit light when an electric current is passed through them are well known and used in a wide range of display applications. 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.
Another compound which has been proposed is aluminium quinoiate, but this requires dopants to be used to obtain a range of colours and has a relatively low efficiency.
In an article in Chemistry letters pp 657-660, 1990 Kido et al disclosed that a terbium III acetyl acetonate complex was green electroluminescent and in an article in Applied Physics letters 65 (17) 24 October 1994 Kido et al disclosed that a europium III triphenylene diamine complexes was red electroluminescent but these were unstable in atmospheric conditions and difficult to produce as films.
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. US Patent 5128587 discloses an electroluminescent device which consists of an organometallic complex of rare earth elements of the lanthanide series sandwiched between a transparent electrode of high work function and a second electrode of low work function with a hole conducting layer interposed between the electroluminescent layer and the transparent high work function electrode and an electron conducting layer interposed between the electroluminescent layer and the electron injecting low work function anode.
We have now devised improved electroluminescent devices and structures using a porous silicon electrode.
The use of light emitting porous silicon has to date been limited to moderately low light levels. Methods of increasing the intensity of the emitted light are needed for most commercial and technological applications such as displays, light emitting diodes (LED's), optical interconnects and optoelectronic circuits and the present invention provides this.
According to the invention there is provided a structure comprising (i) a layer of porous silicon and (ii) a layer of an electroluminescent compound.
The invention also provides an electroluminescent device comprising (i) a first electrode, (ii) a layer of an electroluminescent compound (iii) a layer of porous silicon (iv) a second electrode.
The layer of porous silicon can be formed by etching the surface of a silicon substrate as described below.
The band structure for single crystal silicon exhibits a conduction band minimum which does not have the same crystal momentum as the valence band maximum, yielding an indirect gap. Therefore, in silicon, radiative recombination can only take place with the assistance of a photon, making such transitions inefficient. This has prevented silicon from being used as a solid state source of light, unlike group III-N semiconductors which have a direct gap at the centre of the Brillouin zone. A review of these materials properties can be found in S. M. Sze, Physics of Semiconductor Devices, 2nd. Edition (New York: John Wiley & Sons, 1981). The discovery of photoluminescence in porous silicon has therefore generated a new optoelectronic material for study. A selected review of the fabrication techniques and properties of porous silicon can be found in the articles entitled: "Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers" by L. T. Canham, Appl. Phys. Lett., 57, 1046 (1990); "Visible light emission due to quantum size effects in highly porous crystalline silicon" by A. G. Cullis et al., Nature, 353, 335 (1991 ); "Visible luminescence from silicon wafers subjected to stain etches" by R. W. Fathauer et al., Appl. Phys. Lett., 60, 995 (1992); "Demonstration of photoluminescence in nonanodized silicon" by J. Sarathy et al., Appl. Phys. Lett., 60, 1532 (1992); and "Photoluminescent thin-film porous silicon on sapphire", by W. B. Dubbelday et al., Appl. Phys. Lett., 62,1694 (1993).
Porous silicon is formed using electrochemical etching, photochemical etching or stain etching of bulk silicon or silicon-on- sapphire (SOS) wafers as described in the above references. The substrate may be suitably patterned lithographically prior to the etch to define device structures or confine the region exposed to the etch solution. The typical emission spectrum of porous silicon is in the red, orange and yellow region (nominally 500 to 750 nm) although green and blue emission has also been demonstrated. Blue shift of the peak emission wavelength has been shown by increased oxidation and etching of the porous silicon as described in "Control of porous Si photoluminescence through dry oxidation" by S. Shih al., Appl. Phys. Lett., 60, 833 (1992) and in "Large blue shift of light emitting porous silicon by boiling water treatment" by X. Y. Hou et al., Appl. Phys. Lett., 62, 1097 (1993). The electroluminescent compounds which can be used in the present invention include electroluminescent organo metal compounds, electroluminescent polymers, and electroluminescent metal quinolates.
A particular class of electroluminescent organo metal compounds are the rare earth chelates.
Rare earth chelates are known which fluoresce in ultra violet radiation and A. P. Sinha (Spectroscopy of Inorganic Chemistry Vol. 2 Academic Press 1971) describes several classes of rare earth chelates with various monodentate and bidentate ligands.
Group III A metals and lanthanides and actinides with aromatic complexing agents have been described by G. Kallistratos (Chimica Chronika, New Series, 11, 249-266 (1982)). This reference specifically discloses the Eu (10), b (III), U (III) and U (TV) complexes of diphenyl-phosponamidotriphenyl-phosphoran.
EP 0744451A1 and 0556005 Al also disclose fluorescent chelates of transition or lanthanide or actinide metals and the known chelates which can be used are those disclosed in the above references including those based on diketone and triketone moieties.
The preferred electroluminescent rare earth metal chelates which can be used in the present invention are of formula
Figure imgf000005_0001
where Lα and Lp are organic ligands, M is a rare earth, transition metal, lanthanide or an actinide and n is the valence state of the metal M. The ligands Lα can be the same or different and there can be a plurality of ligands Lp which can be the same or different.
For example (L (L2)(L3)(L..)M (Lp) where M is a rare earth, transition metal, lanthanide or an actinide and (Lι)(L2)(L3)(L...) are the same or different organic complexes and (Lp) is a neutral ligand. The total charge of the ligands (Lι)(L2)(L3)(L..) is equal to the valence state of the metal M.
Where there are 3 groups Lα which corresponds to the in valence state of M the complex has the formula (Lι)(L2)(L3)M (Lp) and the different groups (Lι)(L2)(L3) may be the same or different
Any metal ion having an unfilled inner shell can be used as the metal and the preferred metals are selected from Sm(iπ), Eu(U), Eu(m), Tb(ffl), Dy(III), Yb(IH), Lu(IIi), Gd (IH), U(III), U(VI)O2, Tm(IU), Th(IN), Ce (ITI), Ce(IN), Pr(ffl), Νd(IH), Pm(m), Dy(iπ), Ho(ffl), Er(ffl).
Further electroluminescent compounds which can be used in the present invention are of general formula (Lα)nMιMq where Mi is the same as M above, Mq is a non rare earth metal, Lα is a as above and n is the combined valence state of M\ and Mq. The complex can also comprise one or more neutral ligands Lp so the complex has the general formula (Lα)n Mi Mq (Lp), where Lp is as above. The metal Mq can be any metal which is not a rare earth, transition metal, lanthanide or an actinide examples of metals which can be used include lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper (I), copper (II), silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin (IT), tin (TV), antimony (H), antimony (IV), lead (H), lead (TV) and metals of the first, second and third groups of transition metals in different valence states e.g. manganese, iron, ruthenium, osmium, cobalt, nickel, palladium(II), ρalladium(IV), platinum(II), ρlatinum(rV), cadmium, chromium, titanium, vanadium, zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium, scandium, yttrium.
Further organometallic complexes which can be used in the present invention are binuclear, trinuclear and polynuclear organometallic complexes e.g. of formula
Figure imgf000007_0001
(Lm )x M1^M2 (Ln )y
where L is a bridging ligand and where Mi is a rare earth metal and M2 is Mi or Mq, Lm and Ln are the same or different organic ligands Lα as defined above, x is the valence state of Mi and y is the valence state of M2.
In these complexes there can be a metal to metal bond or there can be one or more bridging ligands between Mi and M2 and the groups Lm and Ln can be the same or different.
By trinuclear is meant there are three rare earth metals joined by a metal to metal bond i.e. of formula
(Lm)xM , (Ln )y— 2 ( LP )Z
or
Figure imgf000007_0002
where Mi and M are as above and M3 is the same as M2 and they can be the same or different metals and Lm, Ln and Lp are organic ligands Lα and x is the valence state of Mi, y is the valence state of M2 and z is the valence state of M3. Lp can be the same as Lm and Ln or different.
The rare earth metals and the non rare earth metals can be joined together by a metal to metal bond and/or via an intermediate bridging atom, ligand or molecular group.
For example the metals can be linked by bridging ligands e.g.
(Lm M ! M3 (|_n )y M2( p )z
X.Ls L
or
Figure imgf000008_0001
where L is a bridging ligand
By polynuclear is meant there are more than three metals joined by metal to metal bonds and/or via intermediate ligands
M1 2 M3 M4 or
MΛ M M4 M3 or
Figure imgf000009_0001
or
Figure imgf000009_0002
M, M, M. M,
V, V, where Mi, M2, M3 are as above and j is the same as M2 Mi, M2, M3 and Mi can be the same or different; L is a bridging ligand.
Preferably Lα is selected from β diketones such as those of formulae
Figure imgf000009_0003
(TV) where Ri, R2 and R3 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; Ri, R2 and R3 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 trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
Examples of Ri and/or R2 and or R3 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.
Some of the different groups Lα 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 L2, L3... can be charged groups such as
Figure imgf000010_0001
(V) where R is Ri as defined above or the groups Li, L2 can be as defined above and L3.. etc. are other charged groups .
Ri, R and R3 can also be
Figure imgf000010_0002
where X is O, S, Se or NH. (VI) A preferred moiety Ri is trifluoromethyl CF3 and examples of such diketones are, banzoyltrifluoroacetone, p-chlorobenzoyltrifluoroacetone, p-bromotrifluoroacetone, p-phenyltrifluoroacetone, 1 -naphthoyltrifluoroacetone, 2-naphthoyltrifluoroacetone, 2-phenathoyltrifluoroacetone, 3-phenanthoyltrifluoroacetone, 9- anthroyltrifluoroacetonetrifluoroacetone, cinnamoyltrifluoroacetone, and 2- thenoyltrifluoroacetone. The different groups Lα may be the same or different ligands of formulae
Figure imgf000011_0001
(VII) where X is O, S, or Se and Ri R2 and R3 are as above
The different groups Lα may be the same or different quinoiate derivatives such as
Figure imgf000011_0002
(vm) (LX) where R is hydrocarbyl, aliphatic, aromatic or heterocyclic carboxy, aryloxy, hydroxy or alkoxy e.g. the 8 hydroxy quinoiate derivatives or
Figure imgf000012_0001
(X) (Xa) where R is as above or H or F or
Figure imgf000012_0002
(XI) (XII)
where R5 is a substituted or unsubstituted aromatic, polycyclic or heterocyclic ring a polypyridyl group, R5 can also be a 2-ethyl hexyl group so Ln is 2-ethylhexanoate or R5 can be a chair structure so that Ln is 2-acetyl cyclohexanoate or L can be
Figure imgf000012_0003
R
(Xffl) where R is as above e.g. alkyl, allenyl, amino or a fused ring such as a cyclic or polycyclic ring.
The different groups Lα may also be
Figure imgf000013_0001
(xrv) (XV)
Figure imgf000013_0002
(XVI) (XNII)
Where R, Ri and R2 are as above. As stated above the different groups Lα may also be the same or different carboxylate groups e.g.
Figure imgf000014_0001
(XVIII)
where R5 is a substituted or unsubstituted aromatic, polycyclic or heterocyclic ring a polypyridyl group, R5 can also be a 2-ethyl hexyl group so Lπ is 2-ethylhexanoate or R5 can be a chair structure so that L„ is 2-acetyl cyclohexanoate
The groups Lp can be selected from
Ph Ph
O : N Ph
Ph Ph
(XIX)
Where each Ph which can be the same or different and can be a phenyl (OPNP) or a substituted phenyl group, other substituted or unsubstituted aromatic group, a substituted or unsubstituted heterocyclic or polycyclic group, a substituted or unsubstituted fused aromatic group such as a naphthyl, anthracene, phenanthrene, perylene or pyrene group. The substituents can be for example an alkyl, aralkyl, alkoxy, aromatic, heterocyclic, polycyclic group, halogen such as fluorine, cyano, amino and substituted amino groups etc. Examples are given in figs. 1 and 2 of the drawings where R, Ri, R2> R3 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 R2 R3 and R4 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer e.g. styrene. R, Ri, R2> R3 and R4 can also be unsaturated alkylene groups such as vinyl groups or groups
Figure imgf000015_0001
where R is as above.
Lp can also be compounds of formulae
Figure imgf000015_0002
where Ri, R2 and R3 are as referred to above, for example bathophen shown in fig. 3 of the drawings in which R is as above.
Lp can also be Ph Ph Ph
N- 0: N- O
Ph Ph or Ph Ph
(xxrv) (XXV) where Ph is as above.
Other examples of Lp chelates are as shown in figs. 4 and fluorene and fluorene derivatives e.g. a shown in figs. 5 and compounds of formulae as shown as shown in figs. 6 to 8.
Specific examples of Lα and Lp are tripyridyl and TMHD, and TMHD complexes, α, α', α" tripyridyl, crown ethers, cyclans, cryptans phthalocyanans, porphoryins ethylene diamine tetramine (EDTA), DCTA, DTPA and TTHA. Where TMHD is 2,2,6,6-tetramethyl-3,5-heptanedionato and OPNP is diphenylphosphonimide triphenyl phosphorane. The formulae of the polyamines are shown in fig. 9.
When the electroluminescent layer comprises a layer of a light emitting metal compound selected from organic complexes of non rare earth metals the complexes have the formula (M)q(Lα)n where Mq is the metal as defined above and n is the valency state of the metal and Lα is as defined above.
The light emitting metal compound can be formed from any metal compound selected from non rare earth metals e.g. lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper, silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin, antimony, lead, and metals of the first, second and third groups of transition metals e.g. manganese, iron, ruthenium, osmium, cobalt, nickel, palladium, platinum, cadmium, chromium, titanium, vanadium, zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium, scandium, yttrium etc. which emit light when an electric current is passed through it.
Preferably Lα. defined as above, is selected from β diketones such as those of formulae above.
Examples of β-diketones are Tris -(l,3-diphenyl-l-3-propanedione) (DBM) and suitable metal complexes are Al(DBM)3, Zn(DBM)2 and Mg(DBM)2., Sc(DBM)3 etc.
A preferred β-diketone is when Ri and/or R3 are alkoxy such as methoxy and the metals are aluminium or scandium i.e. the complexes have the formula
Figure imgf000017_0001
where R4 is an alkyl group, preferably methyl and R3 is hydrogen, an alkyl group such as methyl or R4O.
There can be other ligands in place of some of the β-diketone complex such as
Figure imgf000017_0002
so that the electroluminescent compound has the formula (Lι)m(L2)n M where M is as defined above , (Li) is a compound of formula
Figure imgf000018_0001
where Ri, R2, and R3 are as defined above, L2 is another organic ligand, m + n equals the valency of M and m is at least 1.
When M is platinum or palladium the complex can be non-stoichiometric i.e. of formula MxLy where M is the metal and L is an organic ligand. In a stoichiometric complex x will be one and y will be the valence state of the metal, in a non- stoichiometric complex x and y can have different values e.g. x is two and y is three, examples include Pt2(DBM)3 and Pd2(DBM)3 where Pt and Pd are nominally in the II valence state. It is possible that some kind of linked or polymeric structure is formed and/or the metal is present in more than one valence state.
Where the metal M is a metal with an unfilled inner orbital such as scandium, yttrium, niobium etc. there can be an uncharged ligand which forms a complex with the metal so the complex has the formula
Figure imgf000018_0002
where Mr is as a metal with an unfilled inner orbital Lα and Lp are as above
When the electroluminescent compound is a metal quinoiate the metal quinoiate can be any metal quinoiate which emits light when an electric current is passed through it.
Suitable metal quinolates include the quinolates of lithium, aluminium, zinc, barium, cadmium, sodium, potassium, magnesium etc. The preferred metal quinolates are lithium quinoiate and aluminium quinoiate. The lithium quinoiate is preferably made by the reaction of a lithium alkyl or alkoxide with 8-hydroxy quinoline or substituted 8-hydroxy quinoline, preferably in a solvent incorporating acetonitrile..
The alkyl can be ethyl, propyl or butyl and the alkoxide can be an ethoxide, propoxide or a butoxide.
The lithium quinoiate can be doped the preferred dopants are coumarins such as those of formula
R,
Figure imgf000019_0001
(I)
where Ri, R2, and R3 are hydrogen or an alkyl group such as a methyl or ethyl group, amino and substituted amino groups e.g.
R3
Figure imgf000019_0002
where R3 is hydrogen or alkyl group such as a methyl or ethyl group,
Other dopants include salts of bis benzene sulphonic acid such as
Figure imgf000020_0001
(IH) and perylene and perylene derivatives and dopants of the formulae of figs. 17 to 19 of the drawings where Ri, R2, R3 and t are R, Ri, R2> R3 and t 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, R2> R3 and Rt can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer e.g. styrene. R, Ri, R2> R3 and can also be unsaturated alkylene groups such as vinyl groups or groups
C CH2 CH2 R where R is as above.
Other dopants which can be used are organometallic complexes such as those of general formula (Lα)nM where (Lα), M and n are as above.
When the electroluminescent compound is a conjugated polymer the conjugated polymer used can be any of the conjugated polymers disclosed or referred to in US 5807627, PCT/WO90/13148 and PCT/WO92/03490.
The preferred conjugated polymers are poly (p-phenylenevinylene)-PPV and copolymers including PPV. Other preferred polymers are poly(2,5 dialkoxyphenylene vinylene) such as poly (2-methoxy-5-(2-methoxypentyloxy-l,4-phenylene vinylene), poly(2-methoxypentyloxy)- 1 ,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 fiuorenes and oligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes and oligo anthracenes, ploythiophenes and oligothiophenes.
In PPV 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 ρoly(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.
Other polymers which can be used are electroluminescent fluorescent polymers. Fluorescent polymers are well known compounds which fluoresce in ultra violet or visible light. Fluorescent polymers include condensed aromatic compounds such as anthracene and its derivatives, chrysene and its derivatives etc. and conjugated aromatic aromatic compounds. Fluorescent polymers are widely used in light emitting diodes and any of these polymers can be used in the present invention; examples of such polymers are given in figs. 1 and figs. 2.
The electroluminescent material can be deposited on the porous silicon substrate directly by evaporation from a solution of the material in an organic solvent. The solvent which is used will depend on the material but chlorinated hydrocarbons such as dichloromethane, n-methyl pyrrolidone, dimethyl sulphoxide, tetra hydrofuran dimethylformamide etc. are suitable in many cases. Alternatively the material can be deposited by spin coating from solution or by vacuum deposition from the solid state e.g. by sputtering or any other conventional method can be used.
The first electrode can be a metal which is in contact with the electroluminescent layer directly or through a layer such as a hole transporting layer. When the electrode is an opaque metal the light is emitted from the device around the edges of the metal and interdigitated structures are preferred e.g. the electrode is formed of strips of the metal.
Preferably the first electrode is a transparent substrate such as a conductive glass or plastic material which acts as the anode, preferred 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 porous silicon layer is formed on the surface of the silicon substrate and the second electrode can be directly attached to the silicon using conventional techniques e.g. by means of indium/gallium contact.
Optionally there is a layer of an electron transmitting material between the cathode and the electroluminescent material layer, the electron transmitting material is a material which will transport electrons when an electric current is passed through electron transmitting materials include a metal complex such as a metal quinoiate e.g. an aluminium quinoiate, lithium quinoiate a cyano anthracene such as 9,10 dicyano anthracene, a polystyrene sulphonate and compounds of formulae shown in fig. 10. Instead of being a separate layer the electron transmitting material can be mixed with the electroluminescent material and co-deposited with it. In general the thickness of the layers is from 5nm to 500nm.
Preferably there is a hole transporting layer deposited on the transparent substrate and the electroluminescent material is deposited on the hole transporting layer. The hole transporting layer serves to transport holes and to block the electrons, thus preventing electrons from moving into the electrode without recombining with holes. The recombination of carriers therefore mainly takes place in the emitter layer.
Hole transporting layers are used in polymer electroluminescent devices and any of the known hole transporting materials in film form can be used.
Examples of such hole transporting materials are aromatic amine complexes 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. Examples of polyanilines are polymers of
Figure imgf000023_0001
(XXVI) where R is in the ortho - or meta-position and is hydrogen, CI -18 alkyl, Cl-6 alkoxy, amino, chloro, bromo, hydroxy or the group
Figure imgf000023_0002
where R is alky or aryl and R' is hydrogen, Cl-6 alkyl or aryl with at least one other monomer of formula I above.
Polyanilines which can be used in the present invention have the general formula
Figure imgf000024_0001
(xxvπ) 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, SO4, BF , PF6, H2PO3, H2PO , arylsulphonate, arenedicarboxylate, polystyrenesulphonate, polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate, cellulose sulphonate, camphor sulphonates, cellulose sulphate or a perfluorinated polyanion.
Examples of 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.
We have found that protonated polymers of the unsubstituted or substituted polymer of an amino substituted aromatic compound such as a polyaniline are difficult to evaporate or cannot be evaporated, however we have surprisingly found that if the unsubstituted or substituted polymer of an amino substituted aromatic compound is deprotonated the it can be easily evaporated i.e. the polymer is evaporable.
Preferably 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% e.g. about 50% for example.
Preferably the polymer is substantially fully deprotonated
A polyaniline can be formed of octamer units i.e. p is four e.g.
Figure imgf000025_0001
The polyanilines can have conductivities of the order of 1 x 10"1 Siemen cm"1 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 preferred 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.
The polyanilines can be deposited on the first electrode by conventional methods e.g. by vacuum evaporation, spin coating, chemical deposition, direct electrodeposition etc. preferably the thickness of the polyaniline layer is such that the layer is conductive and transparent and can is preferably from 20nm to 200nm. The polyanilines can be doped or undoped, when they are doped they can be dissolved in a solvent and deposited as a film, when they are undoped they are solids and can be deposited by vacuum evaporation i.e. by sublimation.
The polymers of an amino substituted aromatic compound such as polyanilines referred to above can also be used as buffer layers with or in conjunction with other hole transporting materials.
The structural formulae of some other hole transporting materials are shown in Figures 11, 12, and 13 of the drawings, where RJ; R2 and R3 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; Ri, R2 and R3 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 trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
Examples of Ri and/or R2 and/or R3 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 second electrode attached to the silicon functions as the cathode and can be any low work function metal e.g. aluminium, calcium, lithium, silver/magnesium alloys, rare earth metal alloys etc., aluminium is a preferred metal. A metal fluoride such as an alkali metal, rare earth metal or their alloys and preferably lithium fluoride can be used as the second electrode for example by having a metal fluoride layer formed on a metal.
In a preferred structure there is a first electrode, an electron injection layer, the electroluminescent layer, a hole transportation layer, a porous silicon layer and the second electrode.
The invention is further described in the Examples.
Example 1
Porous silicon layers (5μιη were grown by anodisation of ap-type silicon wafer [p- Si, 535, μm thick, orientation < 100> , 10 + Ω cm, boron doped, ohmic contact with In/Ga (60/40) eutectic] at a current density of 6mA cm"2 in HF(40%)/ethanol ( 1: 1) for a period of 12 minutes to give a porosity of 65 +5 %.
Rare earth chelates were coated on the porous silicon (PSi) by adding 1 ml of a solution of chelates dropwise on to the active area of the device. Once the PSi layers had been impregnated with the chelate solutions, they were dried in air (24 hours) and then dried in vacuum (1 x 10"6torr) at 30°C for a further period of 6 hours. The thickness of the adduct layer on each device was 800+200nm. Al top contacts (190 nm) were then deposited by vacuum sputtering. The electrical examinations were carried out at room temperature.
Electroluminescent structures were fabricated with a structure as shown in fig. 1, the structures comprise an indium gallium alloy electrode (1) attached to silicon layer (2) on the surface of which is a PSi layer (3) formed as above, there is a chelate layer (4) deposited on the PSi layer as described above and an alviminium electrode attached to the surface.
A range of structures with different chelates were made and an electric current was passed through the structures between the electrodes and light was emitted, the results shown in the Table. The EL was measured using spectrophotometer. 25f is the porous silicon with no chelate and ηELREL was given a value of 1 and the values of the other structures compared to this.
Table
Figure imgf000029_0001
The spectra were determined and the current density against bias voltage plotted and the results shown on figs. 19 to 31.
Example 2
The procedure of Example 1 was repeated using aluminium quinoiate as the electroluminescent material. The device had the structure
Porous silicon / CuPc(15nm) / α-NPB(60nm) / Alq(75nm) / LiF(2nm) / Al(200nm)
where CuPc is a copper phthalocyanine buffer layer, α-NPB is as shown in fig. 5 and the figures are in nanometers.
The current density against bias voltage is shown in figs. 32 and 33, the device gave off a yellowish light.
Examples 3 and 4
The procedure of Example 1 was repeated using lithium quinoiate as the elecfroluminescent material. The devices had the structures Example 3 - Porous silicon / CuPc(8.5nm) / m-MTDATA(25nm)/Liq(37nm) Al Example 4 - Porous silicon / CuPc(8.3nm) / m-MTDATA(60nm)/Liq(35nm) Al The current density against bias voltage is shown in figs. 34 and 35, the device of example 3 gave off a yellowish blue emission at 15V and the device of example 4 gave a yellow green emission at 22V.
Example 5 The procedure of Example 1 was repeated to form a device of structure Porous silicon/PEDOT(50nm)/OF(75nm)/Al Where PEDOT is poly(ethylenedioxythiophene) and OF is oligofluorene
Figure imgf000030_0001
where n = 2 - 20 PEDOT OF The current density against bias voltage is shown in fig. 36 and the device gave off a dark yellow emission at 22v.

Claims

Claims
1. A structure comprising (i) a layer of porous silicon and (ii) a layer of an electroluminescent compound.
2. An electroluminescent device comprising (i) a first electrode, (ii) a layer of an electroluminescent compound (iii) a layer of porous silicon (iv) a second electrode.
3. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is a chelate of a rare earth, transition metal, lanthanide or an actinide
4. A structure or device as claimed in claim 3 in which the chelate is of the formula
Figure imgf000031_0001
where Lα, n, M, Lp are as defined herein.
5. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is (Lα)nMιM2 where Mi, is as defined herein, M2 is a non rare earth metal, Lα is as defined herein and n is the combined valence state of Mi and M2.
6. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is the general formula (Lα)n Mi M2 (Lp), where Mi, M2, Lα and Lp are as defined herein and n is the combined valence state of Mi and M2.
7. A structure or device as claimed in claim 5 or 6 in which M2 is lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper (I), copper (H), silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin (H), tin (IN), antimony (II), antimony (IV), lead (ϋ), lead (IN) and metals of the first, second and third groups of transition metals in different valence states e.g. manganese, iron, ruthenium, osmium, cobalt, nickel, palladium(H), ρalladium(TV), ρlatinum(II), platinum(IN), cadmium, chromium, titanium, vanadium, zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium, scandium, or yttrium.
8. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is a binuclear, trinuclear and polynuclear organometallic complexes of formula
(Lm )χ L L M2(Lπ)y or
(l_m)x ι M3 (Ln )y— M2(|_p )z or
(Lπiλ (|_n)y
Figure imgf000032_0001
or
Figure imgf000032_0002
(Lm)xMι M3(Ln)y M2(|_p)E
N. ^L /
or
Figure imgf000032_0003
or
M1 M2 M3 4 or M, M, M4 M 3 or
Figure imgf000033_0001
or
Figure imgf000033_0002
M1 M2 M4 M3 xL XLX _ where Mi, M2, M3 and Mi are rare earth metals where Mi , M2 and Ms are the same or different rare earth metals and Lm, Ln and Lp are organic ligands Lα as defined herein, and x is the valence state of Mi, y is the valence state of M2 and z is the valence state of M3, Lp can be the same as Lm and Ln or different, and L is a bridging ligand.
9. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is an electroluminescent non rare earth metal complex of formula
(Mq)n(Lα)n where Mq is the metal, n is the valency state of the metal and Lα is as specified herein.
10. A structure or device as claimed in claim 9 in which the metal is selected from lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper, silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin, antimony, lead, and metals of the first, second and third groups of transition metals e.g. manganese, iron, ruthenium, osmium, cobalt, nickel, palladium, platinum, cadmium, chromium, titanium, vanadium, zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium, scandium, yttrium etc. which emit light when an electric current is passed through it.
11. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is an electroluminescent metal quinoiate.
12. A structure or device as claimed in claim 11 in which the metal quinoiate is selected from lithium, aluminium, zinc, barium, cadmium, sodium, potassium and magnesium quinoiate.
13. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is an electroluminescent conjugated polymers.
14. A structure or device as claimed in claim 13 in which the electroluminescent conjugated polymer is selected from poly (ρ-phenylenevinylene)-PPV and copolymers including PPV, poly(2,5 dialkoxyphenylene vinylene), poly (2-methoxy- 5-(2-methoxypentyloxy-l,4-phenylene vinylene, poly(2-methoxypentyloxy)-l,4- phenylenevinylene), poly(2-methoxy-5-(2-dodecyloxy- 1 ,4-phenylenevinylene), 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.
15. A structure or device as claimed in claim 1 or 2 in which the electroluminescent compound is an electroluminescent fluorescent polymer.
16. A structure or device as claimed in claim 15 in which the fluorescent polymer is selected form condensed aromatic compounds, anthracene and its derivatives, chrysene and its derivatives.
17. A structure or device as claimed in any one of the preceding claims in which the electroluminescent layer is deposited on the porous silicon layer by vapour deposition or deposition from solution.
18. A structure or device as claimed in any one of claims 2 to 17 in which there is a layer of a hole transmitting material between the porous silicon and the electroluminescent compound layer.
19. An electroluminescent device as claimed in claim 18 in which the hole transmitting material is a film of a polymer selected from poly(vinylcarbazole), N,N'- diphenyl-N,N'-bis (3-methylphenyl) -1,1' -biphenyl -4,4'-diamine (TPD), polyaniline, substituted polyanilines, polythiophenes, substituted polythiophenes, polysilanes and substituted polysilanes.
20. An electroluminescent device as claimed in claim 18 or 19 in which the hole transmitting material is a film of a compound of formula (II) or (III) herein or as in Figure 11, 12, 13, or 14 of the drawings.
21. An electroluminescent device as claimed in any one of claims 2 to 20 in which there is a layer of an electron transmitting material between the cathode and the electtoluminescent material layer.
22. An electroluminescent device as claimed in claim 21 in which an electron transmitting material and the light emitting metal compound are mixed to form one layer.
23. An electroluminescent device as claimed in claim 21 or 22 in which the electron transmitting material is a metal quinoiate.
24. An electroluminescent device as claimed in claim 23 in which the metal quinoiate is an aluminium quinoiate or lithium quinoiate
25. An electroluminescent device as claimed in claim 21 or 22 in which the electron transmitting material is selected from cyanoanthracenes such as 9,10 dicyanoanthracenes, polystyrene sulphonates or a compound of formulae shown in Fig. 10.
26. An elecfrohiminescent device as claimed in any one of claims 18 to 25 in which a hole transmitting material and an electron transmitting material and the light emitting metal compound are mixed to form one layer.
PCT/GB2002/001264 2001-03-16 2002-03-18 Electroluminescent devices WO2002075820A1 (en)

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