WO2013190377A1

WO2013190377A1 - Composition and device

Info

Publication number: WO2013190377A1
Application number: PCT/IB2013/001420
Authority: WO
Inventors: Simon Goddard
Original assignee: Sumitomo Chemical Company Limited
Priority date: 2012-06-21
Filing date: 2013-06-19
Publication date: 2013-12-27
Also published as: GB201210989D0; WO2013190377A8; TW201402781A

Abstract

A light-emitting composition comprises a semiconducting material such as an at least partially conjugated polymer, a polymer electrolyte comprising ethylene oxide repeat units having a viscosity averaged molecular weight of less than 300,000 and two different salts.

Description

COMPOSITION AND DEVICE

Background

Electronic devices comprising active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes, organic

photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices comprising organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.

An organic light-emitting electrochemical cell (LEG) may have a substrate carrying an anode, a cathode and an organic light-emitting layer between the anode and cathode comprising a light-emitting material, a salt providing mobile ions and a polymer electrolyte. LECs are dislosed in, for example, WO 96/0O9S3.

During operation of the device, holes are injected into the device through the anode and electrons are injected through the cathode. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of the Ught-emttting material combine in the light-emitting layer to form an exciton that releases its energy as light The cations and anions of the salt may respectively p- and n-dope the light-emitting material, which may provide for a low drive voltage.

Suitable light-emitting materials include small molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers for use in the ligbt-emitting layer include poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and polyarylenes such as polyfluorenes.

US 5900327 discloses a LEC comprising the polymer BDOH-PF:

BDOH-PF The ethylene oxide side groups of BDOH-PF are said to improve compatibility with the ion-conducting polymer polyethylene oxide) and increase solubility of the polymer in common organic solvents.

WO 2011/032010 discloses luminescent ink formulations containing a plurality of salts providing at least two cations or two anions.

WO 2003/053707 discloses screen-printable light-emitting polymer based inks containing a non-electroluminescent polymer with a molecular weight between about 300,000 and 20,000,000 to provide a viscosity of above about 50 centipoises.

It is an object of the invention to provide LECs with improved turn-on time.

It is a further object of the invention to provide thin LECs.

Summary of the Invention

In a first aspect the invention provides a light-emitting composition comprising a semiconducting material, a polymer electrolyte having a viscosity averaged molecular weight of less than 300,000 and a sal

Optionally, the polymer electrolyte has a viscosity averaged molecular weight of less than 200*000, optionally less than 100,000, optionally less than 50,000.

Optionally, the polymer electrolyte comprises ethylene oxide repeat units.

Optionally, the polymer electrolyte is a polyethylene oxide homopolymer.

Optionally, the composition comprises at least two different salts.

Optionally, the salt or salts are ammonium salts.

Optionally, light is emitted directly from the semiconducting material.

Optionally, the composition further comprises a light-emitting dopant. Optionally, the semiconducting material is a semiconducting polymer.

Optionally, the semiconducting polymer is an at least partially conjugated polymer.

Optionally, the semiconducting polymer comprises substituted or unsubstituted arylene repeat units.

Optionally, the at least partially conjugated polymer comprising repeat units of formula (XT):

(DC) wherein Ar⁸ and Ar⁹ in each occurrence are independently selected from substituted or unsubstituted aryl or heteroaryl, g is greater tban or equal to 1, preferably 1 or 2, R¹³ is H or a substituent, preferably a substituent; c and d are each independently 1, 2 or 3; and any of Ar⁸, Ar° and R¹³ that are bound directly to a N atom of formula (EX) may be linked by a direct bond or divalent linking group to another of Ar⁸, Ar⁹ and R¹³ that is bound directly to the same N atom.

Optionally, the polymer is a partially conjugated polymer comprising non-conjugating repeat units that do not provide any conjugation path between repeat units adjacent to the non-conjugating repeat units.

In a second aspect the invention provides a formulation comprising a light-emitting composition according to any preceding claim and at least one solvent

Optionally according to the second aspect, the formulation comprises at least two solvents.

Optionally according to the second aspect, the at least two solvents are selected from one or more of benzene substituted with one or more Ci. oaUcyl groups and enzene substituted with one or more halogens. In a third aspect the invention provides an organic light-emitting electrochemical cell comprising an anode for injecting positive charge earners, a cathode for injecting negative charge carriers and a light-emitting layer between the anode and the cathode wherein the light-emitting layer comprises a composition according to the first aspect

In a fourth aspect the invention provides a method of forming a light-emitting electrochemical cell according to the third aspect, the method comprising the steps of: depositing the formulation according to the second aspect over one of the anode and cathode; evaporating the at least one solvent to form a light-emitting layer; and depositing the other of the anode and cathode over the light-emitting layer.

Optionally according to the fourth aspect the formulation is deposited by a method selected from screen printing, gravure printing, spin-coating and bar-coating.

Viscosity average molecular weight Mv of a polymer is given by:

where N is the number of moles in a sample of the polymer having mass M, N*M is the mass of the sample, and a is the exponent in the Mark-Hou ink equation that relates the intrinsic viscosity to molar mass

Description of the Drawings

The invention will now be described in more detail with reference to the drawings in which:

Figure 1 illustrates an organic LEC according to an embodiment of the invention; Figure 2 is a graph illustrating variation of composition roughness ( a) with Mv Figure 3 is images of a composition containing a first white light-emitting polymer and 300,000 Mv polyethylene oxide) and compositions according to embodiments of the invention containing the first white light-emitting polymer and 2,000 Mv and 35,000 Mv polyethylene oxide); and

Figure 4 is ima es of a composition of a second white light emitting polymer and 300,000 Mv polyethylene oxide) and compositions according to embodiments of the invention containing the second white light-emitting polymer and 2,000 Mv, 10,000 Mv, 35,000 Mv and 100,000 Mv polyethylene oxide).

Detailed Description of the Invention

Figure 1 illustrates an organic TJEC 100 according to an embodiment of the invention. The cell 100 has an anode 101, for example ITO, a metal or a conductive organic materia] such as a polythiophene, for injection of positive charge carriers, a cathode 105 fox injection of negative charge carriers and a light-emitting layer 103 between the anode and the cathode. Further layers may be provided between the anode and the cathode, for example a hole-injection layer may be provided between the anode 101 and the light-emitting layer 103.

The light emitting layer contains at least one organic semiconducting polymer, a polymer electrolyte and at least one salt. In operation, light may be emitted directly from the one or more semiconducting polymers, or a light-emitting dopant may be provided in the light-emitting layer. The light-emitting dopant may be a fluorescent dopant that accepts singlet excitons from the semiconducting polymer wherein fluorescence is produced by radiative decay of singlet excitons, or a phosphorescent dopant that accepts triplet excitons, and optionally singlet excitons, from the semiconducting polymer and emits light by radiative decay of triplet excitons.

If a light-emitting dopant is present then all light may be emitted by the dopant, or both the semiconducting polymer and light-eoiitting dopant may emit light. More than one h^t-eraitting dopant may be present. light-emission from multiple light- emitting materials (either polymers or dopants) may combine to produce white light. The light-emitting layer may have a thickness in the range of about 100 ran - 2 microns, preferably 100 ran - 1 micron; preferably 100 mm - 750 nm, preferably 100- 500 nm.

Polymer electrolyte

Exemplary polymer electrolytes include: polyaJkylene oxides, for example polyethylene oxide (PEQ) and polypropylene oxides; copolymers of alkylene oxide, for example polyethylene-block(ethylen3 glycol) polymer and poIy(ethyIene glycol}- block-poly _jpropylene glycol)-block poJy(ethylene glycol) polymer; esters of polyalkyleueglycols such as polycarbonates; polyolefins; and polysiloxanes,

A olyalkylene oxide polymer electrolyte may carry hydroxyl end-capping groups.

The polymer electrolyte has a viscosity averaged molecular weight of less than 300,000, optionally less than 200,000, optionally less than 100,000 optionally less than 50,000, optionally less than 40,000.

The polymer electrolyte preferably makes up at least 1 weight %, 2 weight %, 5 weight %_f optionally at least 10 weight % of the composition, and is optionally provided in an amount of up to 20 weight % or up to 30 weight %.

Salts

Salts with relatively small anions or cations may be more mobile than salts with bulkier ions.

Preferred cations of the salt include alkali, alkali earth and ammonium cations.

Ammonium cations include Hi⁺ cations and mono-, di-tri and tetraalkylammonium ations.

Preferred anions of the salt include halogen-containing anions, in particular fluorine- containing anions, for example hexafiuorophosphate and tetrafluoroborate.

The light-emitting composition may include only one salt or more than one salL The ionic salt or salts may be provided in an amount in tire range 0.1 - 25 % by weight, optionally 1-15 % by weight, of the composition. Semiconducting material

The semiconducting material may be a small molecule or polymeric material.

Preferably, the semiconducting material is a polymer.

The semi co ducting polymer may be a homopolymer or a copolymer comprising two or more repeat units.

The semiconducting polymer may have a backbone containing repeat units that are conjugated to adjacent repeat units, or may contain a substantially non-conjugated backbone with conjugated groups pendant from the non-conjugated backbone.

An exemplary polymer with a non-conjugated backbone is poly(vinylcarbazole).

Exemplary polymers with at least partially conjugated backbones include polymers containing arylene, heteroarylene, aryletievinylene or heteroarylenevib yleoe repeat units in the polymer backbone, wherein said arylene, heteroarylene, axylenevinylene or heteroarylenevinylene repeat units may be substituted or unsubstituted, for example substituted with one or more hydrocarbyl groups, for example one or more Cinto hydrocarbyl groups, wherein one or more non-adjacent carbon atoms in a carbon chain of the hydrocarbyl groups may be replaced with O. Exemplary C,^

hydrocarbyl groups include Ci-a alkyl groups and phenyl substituted with one or more Q.,o alkyl groups.

If used in the same layer as, or in a layer adjacent to, a light-emitting material with a high singlet or triplet energy level then the extent of conjugation along the backbone of the polymer may be limited by selection f repeat units. Exemplary repeat units that may limit the extent of conjugatio include:

(i) repeat units that are twisted out of the plane of adjacent repeat units,

limiting the extent of p-orbital overlap between adjacent repeat units;

(ii) conjugation-breaking repeat units that do not provide a conjugation path between repeat units adjacent to the conjugation breaking repeat units; and (iii) repeat units that are linked to adjacent repeat units through positions that limit the extent of conjugation between repeat units adjacent to the repeat unit.

One preferred class of arylene repeat units is phenylene repeat units, such as phenylene epea units of formula (ID):

(ΠΙ) wherein p in each occurrence is independently 0, 1, 2, 3 or 4, optionally 1 or 2; n is 1, 2 or 3; and R* independently in each occurrence is a substituenL

Where present, each R¹ may independently be selected from the group consisting ot

- alkyl, optionally CJ.M alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C=0 or -COO-, and one or more H atoms may be replaced with F;

- aryl and heteroaryl groups that may be unsubstituted or substituted with one or more substituents, preferably phenyl substituted with one or more C|_-2o alkyl groups; and

- a linear or branched chain of aryl or heteroaryl groups, each Of which groups may independently be substituted, for example a group of formula -(Ai³^ wherein each Ar³ is independently an aryl or heteroaryl group and r is at least 2, preferably a branched or linear chain of phenyl groups each of which may be unsubstituted or substituted with one or more Ci-a> alk l groups- Substituted N, where present, may be -NR²- wherein R² is C_halk ]; tmsubstitnted phenyl; or phenyl substituted with one or more C1-20 alkyl groups.

One or more substituents R¹ may be polar substituents. Polar substituents R¹ may improve compatibility of the semiconducting polymer with polymer electrolytes such as polyethylene oxide. Polar substituents R¹ include substituents having the following formula (X):

--(Sp^O-CCR^ fi

00

wherein * represents a point of attachment of the substituent to the repeat unit; Sp² is a spacer group; b is 0 or 1; c is at least 1, optionally 1, 2 or 3; m independently in eacb occurrence is at least 1, optionally 1, 2 or 3; p is at least 1, optionally 1, 2 or 3; and R⁹ in each occurrence is independently H or a substituent, preferably H or Ci.₅ alkyl.

Sp² is preferably a Ci-iohydr catbyl group, preferably unsubstltuted phenyl or phenyl substituted wim one or more Q-io alkyl groups.

Polar substituents R¹ may contain one or more polar oligo-ether groups, for example substituents containing one Or more polar groups -(O CH₂CH2)w-R^S wherein w is at least 1, optionally 1-5, and R⁸ is H or a substituent, optionally H, C^o alkyl or Q-jo alkoxy.

Preferably, each R is independently selected from

wherein one or more non-aromatic C atoms in a chain of the hydrocarbyl group may be replaced with 0, and is more preferably selected from Cj-a) alkyl wherein one or more non-adjacent C atoms may be replaced with O; unusubstituted phenyl; and phenyl substituted with one or more CJ.JQ alkyl groups wherein one or more non-adjacent C atoms of the alkyl group or groups may be replaced with O.

A further class of arylene repeat units are optionally substituted fluorene repeat units, such as repeat units of formula (TV):

wherein R^? in each occurrence is the same or different and is H ox a substituent, and wherein the two groups R³ may be linked to form a ring. Each R³ is preferably a substituent, and each R³ may independently be selected from the group consisting of:

- alley], optionally O.2₀ alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C-0 or -COO-, and one or more H atoms may be replaced with F;

- aryl or heteroaryl that may be unsubstihited or substituted with one or more substituents; and

- a linear or branched chain of aryl or heteroaryl groups, each of which groups may independently be substituted- for ex m le a group of formula -(Ar³),- as described above with reference to formula (III).

In the case where R³ comprises an aryl or heteroaryl group, or a linear or branched chain of aryl or heteroaryl groups, the or each aryl or heteroaryl group may be substituted with one or more substituents R* selected from the group consisting of: alkyl, for example C₁.₂₀ alkyl, wherein one or more non-adjacent C atoms may be replaced with 0, S, substituted N, C=0 and -COO- and one or more H atoms- of the alkyl group may be replaced with F;

NR⁵ ₂, OR⁵, SR⁵, and

fluorine, nitro and cyano;

wherein each R⁵ is independently selected from the group consisting of alkyl, preferably C].zo alkyl; and aryl or heteroaryl, preferably phenyl, optionally substituted with one or more C1.20 alkyl groups*

The aromatic carbon atoms of the fhiorene repeat unit may be unsubstituted, or may be substituted with one or more substituents. Exemplary substituents are alkyl, for example C_J-¾> alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, NH or substituted N, C=0 and -COO-, optionally substituted aryl, optionally substituted heteroaryl, alkoxy, alkylthio, fluorine, cyano and arylalkyl. Particularly preferred substituents include Ci-₂₀ alkyl and substituted or unsubstituted aryl, for example phenyl. Optional substituents for the aryl include one or more Ci-zo alkyl groups. Substituted N, where present, may be -NR²- wherein R² is Q.₂oalkyl; unsubstituted phenyl; Or phenyl substituted with one or more C₁.₂₀ alkyl groups.

One or more substituents R³ may be polar substituents. Polar substituents R³ may improve compatibility of the semiconducting polymer with polymer electrolytes such as polyethylene oxide- Polar substituents R³ may contain one or more polar oligo- ether groups, for example substituents containing one or more polar groups - (OC¾Cl¾V-R^s as described above with reference to formula (III)

Preferably, each R³ is independently selected from C].« hydrocarbyl wherein one or more non-aromatic C atoms in a chain of the bydrocarbyl group may be replaced with O, and is more preferably selected from: C1.2₀ alkyl wherein one or more non-adjacent C atoms may be replaced with 0; unusubstituted phenyl; and phenyl substituted with one or more QJZO alkyl groups wherein one or more non-adjacent C atoms of the alkyl group or groups may be replaced with O.

The repeat unit of formula (IV) may be a 2,7-linked repeat unit of formula IVa):

(IVa)

Optionally; the repeat unit of formula (TVa) is not substituted in a position adjacent to the 2- or 7- positions.

The extent of conjugation of repeat units of formulae (IV) may be limited by (a) linking the repeat unit through the 3- and / or 6- positions to limit the extent of conjugation across the repeal unit, and / or (b) substituting the repeat unit with one or more further substituents R^J in or more positions adjacent to the linking positions in order to create a twist with the adjacent repeat unit or units, for example a 2,7-linked fluorene carrying a C1.20 alkyl substituent in one or both of the 3- and o^ppositions.

The semiconducting polymer may contain repeat units carrying polar substituents, fox example substituents of formula *-(SpV((0-(CR¾m)pVH or -(OCH₂CH₂)w-R⁸ as described above, and repeat units carrying non-polar substituents, for example Q 0 bydrbcarbyl substituents. For example, a semiconduaing polymer may contain repeat units of formula (TV) having polar substituents such as substituents of formula * -

or -{OCHaCHz R⁵ and rep**¹ unite of formula (IV) having non-polar substituents such as Ci .40 hydrocarbyl.

The polymer may contain amine repeat units in particular amines of formula (IX):

(IX) wherein Ar⁸ and Ai⁵ in each occurrence are independently selected from substituted Or unsubstituted aryl or heteroaryl, g is greater than or equal to 1, preferably 1 or 2, R is H or a substituent, preferably a substituent, and c and d are each independently 1, 2 or 3.

R¹³, which may be the same or different in each occurrence when g > 1, is preferably selected from the group consisting of alkyl, for example Q_-2o alkyl, Ar¹⁰, or a branched or linear chain of Ar¹⁰ groups, wherein Ax^w in each occurrence is independently optionally substituted aryl or heteroaryl. Exemplary spacer groups are Ci-_¾) alkyl, phenyl and phe yl-Ci.20 alkyl.

Any of Ar⁸, Ar⁹ and, if present, Ar¹⁰ bound directly to a N atom in the repeat unit of Formula (IX) may be linked by a direct bond or a divalent linking atom or group to another of Ar⁸, Ar⁹ and Ar¹⁰ bound directly to the same N atom. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C.

Any of Ar⁸, Ar⁹ and, if present, Ar¹⁰ may be substituted with one or more substituents. Exemplary substituents are substituents R¹⁴, wherein each R may independently be selected from the group consisting of:

- substituted or unsubstihited alkyl, optionally C_I.M alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted I¾ C=0 or -COO- and one or more H atoms may be replaced with F. Substituted N or substituted C, where present, may be N or C substituted with a hydrocarbyl group (in the case of substituted N) or two hydrocarbyl groups (in the case of substituted C), for example a Q._to alkyl, unsubstituted phenyl or phenyl substituted with one or more CJ-J_O alkyl groups.

Preferred repeat units of formula (IX have formulae 1-3:

1 2 3

In one preferred arrangement, R¹³ is Ar¹⁰ and each of At⁸, Ar⁹ and Ar¹⁰ are independently unsubstituted Or substituted with one or more C m alk l groups.

Ar⁸, Ar⁹ and Ar¹⁰ are preferably phenyl, each of which may independently be Substituted with one or more substituents as described above.

In another preferred arrangement, Ar³ and Ar⁹ are phenyl, each of which may be substituted with one or more C1.2₀ alkyl groups, and ^K is 3,5-diphenylbenzene wherein each phenyl may be substituted with one or more CK_M alkyl groups.

In another preferred arrangement, c, c and g are each 1 and Ar⁸ and Ar⁹ are phenyl linked by an oxygen atom to form a phenoxazine ring.

Amine repeat units may be provided in a molar amount in the range of about 0.5 mol % up to about SO mol %, optionally up to 40 mol %■

The semiconducting material may itself emit light directly. Alternatively, excitons formed on the semiconducting material may be transferred to one or more light- emitting dopants such that light is emitted from the dopant. Suitable dopants include fluorescent dopants and phosphorescent dopants. Fluorescent dopants suitably have an excited singlet energy level that is no higher than, and optionally lower than, that of the semiconducting material such that singlet excitons may be transferred from the semiconducting material to the dopant. Phosphorescent dopants suitably have an excited triplet energy level that is no higher than, and optionally lower than, that of the semiconducting material such that triplet excitons may be transferred from the semiconducting material to the dopant.

The semiconducting polymer may comprise com^'ugation-breaking repeat units that break any conjugation path between repeat units adjacent to the conjugation-breaking repeal unit. An exemplary conjugation-breakiag repeat unit has formula (I):

wherein Ar² in each occurrence independently represents a substituted or

unsubstituted aryl or heteroaryl group; Sp¹ represents a spacer group that does not provide any conjugation path between the two groups Ar².

Ar² is preferably phenyl that may be unsubstituted or substituted with one or more substituents, preferably one or more C_halky! groups.

Sp¹ may contain a single non-conjugating atom only between the two groups Ar², or Sp¹ may contain αοπ-conjugating chain of at least 2 atoms separating the two groups Ar².

A non-conjugating atom may be, for example, -0-, -S-, -CR⁷ ₂- or -SiRV wherein R⁷ in each occurrence is H or a substituent, optionally Ci-_¾> alkyl.

A spacer chain Sp¹ may contain two or more atoms separating tbe two groups Ar^for example a (¼._¾) alkyl chain wherein one or more non-adjacent C atoms of the chain may be replaced with 0 Or S. Preferably, the spacer chain Sp¹ contains at least one sp³-hybridised carbon atom separating the two groups Ar².

Preferred groups Sp* are selected from C₁.₂₀ alkyl wherein one or more non-adjacent C atoms may be replaced with O. An ether spacer or oligo-ether spacer chain, for example a chain of formula— (CH2CH₂OV, wherein v is 1 or more, optionally 1-10, may improve misdbility of the semiconducting polymer with electrolytes such as polyethylene oxide).

Examples of cyclic non-conjugating spacers are optionally substituted cyclohexane or adaraantane repeat units that may have the structures illustrated below:

Exemplary substituents for cyclic conjugation repeat units include Cj.joalkyl- Conjugation breaking repeat units may make up 0.5-30 mol % of repeat units Of a. polymer, preferably 1-20 mol % of repeat units.

The semiconducting polymer may have a weight average molecular weight in the range of about 100,000 - 1,000,000, optionally 100-000 - 500,000 as measured by GPC calibrated against polystyrene Standards.

A formulation of one or more salts, a polymer electrolyte, a semiconducting polymer and (if present) one or more dopants may contain 40-97, optionally 50-95 weight % of the semiconducting polymer.

Phosphorescent light-emitting materials

Exemplary phosphorescent light-emitting materials include metal complexes comprising substituted or unsubstituted complexes of formula (Π)

wherein M is a metal, each of L¹, L² and I? is a coordinating group; q is an integer; r and s are each independently 0 or an integer; and the sum of (a. q) + (b. r) + (c.s) is equal to the number of coordination sites available on , wherein a is the number of coordination sites on L¹, b is the number of coordination sites on L² and c is the number of coordination sites on L³<

Heavy elements M induce strong spin-orbit coupling to allow rapid intersyStem crossing and emission from triplet or higher states. Suitable heavy metals M include d-block metals, in particular those in rows 2 and 3 i.e. elements 39 to 48 and 72 to 80, in particular ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum and gold. Iridium is particularly preferred. Exemplary ligands J-¹, L and Lr include carbon or nitrogen donors such as r aphyrin or bidentate ligands of formula (IK):

(III) wherein AJ⁵ and Ar⁶ may be the same or different and are independently selected from substituted or unsubstituted aryl or heteroaryl; X¹ and Y¹ may be the s me or different and are independently selected from carbon or nitrogen; and Ar⁵ and Ar⁶ may be fused together. Ligands wherein X¹ is carbon and Y¹ is nitrogen are preferred, in particular ligands in which Ar⁵ is a single ring or fused heteroaromatic of N and C atoms only, for example pytidyl or isoquinoline, and Ax⁶ is a single ring o fused aromatic,, for example phenyl or naphthyl.

Examples of bidentate ligands are illustrated below:

Other ligands suitable for use with d-block elements include diketonates, in particular acetylacetonate (acac); triarylphosphines and pyridine, each of which may be substituted.

Each of Ar⁵ and Ar" may carry one or more substituents. Two or more of these substituents may be linked to form a ring, for example n aromatic ring.

Exemplary substituents of ligands of formula (III) include groups R³ as described above with reference to Formula (TV), preferably Ci-_fljhydrocarbyl. Particularly preferred substituents include fluorine or trifluoromethyl which may be used to blue- shift the emission of the complex, for example as disclosed in WO 02/45466, WO 02/44189, US 2002-117662 and US 2002-182441; alkyl or alkoxy groups, for example Cj-aoalkyl or alkoxy, which may be as disclosed in JP 2002-324679;

carbazole which may be used to assist hole transport to the complex when used as n emissive material, for example as disclosed in WO 02/81448; bromine, chlorine or iodine which can serve to functioiialise the ligand for attachment of further groups, for example as disclosed i WO 02/68435 and EP 1245659; and dendrons which may be used to obtain or enhance solution protessability of the metal complex, for example as disclosed in WO 02/66552.

A light-emitting dendrimer comprises a light-emitting core, such as a metal complex of formula (Π), bouod to one or more dendions, wherein each dendron comprises a branching point and two or more dendritic branches. Preferably, the dendron is at least partially conjugated, and at least one of the branching points and dendritic branches comprises an ar l or heteioaryl group, for example a phenyl group. In one arrangement, the branching point group and the branching groups are all phenyl, and each phenyl may independently be substituted with one or more substituents, for example alkyl or alkoxy.

A dendron may have optionally substituted formula (TV)

(TV)

wherein BP represents a branching point for attachment to a core and Gt represents first generation branching groups.

The dendron may be a first, second, third or higher generation dendron. Gi may be substituted with two or more second generation branching groups 2, and so on, as in optionally substituted formula (TVa):

(IVa) wherein u is 0 or 1; v is 0 if u is 0 or may be 0 or 1 if u is 1; BP represents a branching point for attachment to a core and Gj, G₂ and G3 represent first, second and third generation dendron brandling groups. In one preferred embodiment, each of BP and Gi„ G2 ... G„ is phenyl, and each phenyl BP, G|, G2 ... G„_i is a 3₇ -Hru«a' phenyl.

A preferred dendron is a substituted or unsubstituted dendron of fonnula (IVb):

(IVb) wherein * represents an attachment point of the dendron to a core.

BP and / or any group G may be substituted with one or more substituents, for example one or more C^aUcyl or alkoxy groups.

Phosphorescent light-emitting materials of a light-emitting composition may be rese in an amount of about 0.05 mol % up to about 20 mol ¾, optionally about 0.1- 0 mol % relative to their host material. A light-emitting composition may contain one or more phosphorescent light-emitting materials. A phosphorescent material be physically mixed with the semiconducting material as host or ma be chemically bound to the semiconducting material. In the case of a polymeric semiconducting host, the phosphorescent material may be provided in a side-chain, mam chain or end-group of the polymer. Where a phosphorescent material is provided in a polymer side -chain, the phosphorescent material may be directly bound to the backbone of the polymer or spaced apart therefrom by a spacer group, for example a Ci-20 alk l spacer group in which one or more non-adjacent C atoms may be replaced by O or S or -C(=0)0-.

White lieht emission

In the case of a white light-emitting LEC or composition, the light emitted may have CIE x coordinate equivalent to that emitted by a black body at a temperature in the range of 2500-9000K and a CIE y coordinate within 0.05 or 0.025 of the CIE y coordinate of said light emitted by a blade body, optionally a CIE x coordinate equivalent to that emitted by a black body at a temperature in the range of 2700- 4500K.

Formulations

An ink formulation suitable for forming a light-emitting layer may be formulated by mixing the components of the composition with one or more suitable solvents.

Optionally, more than one solvent is used wherein the semiconducting polymer is soluble in at least one of the solvents and wherein the polymer electrolyte is soluble in at least one of the other solvents.

Solvents suitable for dissolving semiconducting polymers, particularly polymers comprising atkyl substituents, include benzenes substituted with one or more Q-io alkyl or Ci.i«alkoxy groups, for example toluene, xylenes and merhylanisoles.

Solvents suitable for dissolving polymer electrolytes, for example PEO, include benzenes substituted with polar groups, for example electron-withdrawing groups, such as groups with a positive Hammett constant. Suitable polar groups include chlorine, cyano, Cj o alkoxy and benzoate substituents. Exemplary solvents include chlorobenzene., The formulation may be a solution in which all components of the composition are dissolved in the solvent or solvents, or it may be a dispersion wherein one or more components of the composition are suspended in the formulation. Preferably, the formulation is a solution.

The formulation may contain further components such as surfactants and r compatibilisers.

Deposition methods

Inks as described above may be deposited by a wide variety of coating and printing methods known to the skilled person including, without limitation, spin-coating, dip- coating, bar-coating, doctor blade coating, screen printing, gravnre printing and inkjet printing, dispense printing, nozzle printing and slot die coating.

Ink viscosity may be selected according to the deposition method used.

In the case of dispense printing, a preferred viscosity range of the ink is in the range of 4 cP to 50 cP, optionally 10-20 cP.

In the case of gravure printing a preferred viscosity range of the ink is in the range of 5-300 cP, optionally 10-100 cP.

Viscosities as described herein are measured at a shear rate of 1000 / s at 20°C using a cone and plate rheometer.

Following deposition, solvent may be allowed to evaporate from the formulation at ambient pressure and temperature or may be heated and / or placed under vacuum.

Hole injection layers

A conductive hole injection layer, which may be formed from a conductive organic or inorganic material, may be provided between the anode and the light-emitting layer of an LEG to improve hole injection from the anode into the light-emitting layer.

Examples of doped organic hole injection materials include optionally substituted, doped polyethylene dioxythiophene) (PEDT), in particular PEDT doped with a charge-balancing polyacid such a* polystyrene sulfonate (PSS) as disclosed in EP 0901176 and EP 0947123, polyacrylic acid or a fluorinated sulfonic acid, for example Nation ®; polyaniline as disclosed in US 5723873 and US 5798170; and optionally substituted polythiophene or pol^thienothiophene). Examples of conductive inorganic materials include transition metal oxides such as VOx MoOx and RuOx as disclosed in Journal of Physics D: Applied Physics (1996)» 29(11), 2750-2753.

Cathode

The cathode may consist of a single material such as a layer of aluminium or silver. Alternatively, it may comprise a plurality of layers, for example a bilayer of metals such as calcium and aluminium as disclosed in WO 98/10621; elemental barium, either alone or with one or more cathode layers, for example a bilayer of barium and alTiminium as disclosed in WO 98/57381, Appl. Phys. Lett. 2002, 81(4), 634 and WO 02 84759. The cathode may contain a thin layer of metal compound, in particular an oxide or fluoride of an alkali or alkali earth metal between the light-emitting layer and one or more conductive layers to assist electron injection, for example lithium fluoride as disclosed in WO 00/48258; barium fluoride as disclosed in Appl. Phys. Lett 2001, 79(5), 2001; and barium oxide,

The cathode may be in direct contact with the light-emitting layer.

The cathode may be an air-stable metal, for example aluminium or silver. The cathode may be deposited by evaporation or sputtering, or by deposition of a paste of the metal. A paste of the metal may be deposited by a printing method, for example screen printing.

The cathode may be opaque or transparent. Transparent cathodes are particularly advantageous for active matrix devices because emission through a transparent anode in such devices is at least partially blocked by drive circuitry located underneath the emissive pixels. A transparent cathode comprises a layer of an electron injecting material that is sufficiently thin to be transparent. Typically, the lateral conductivity of this layer will be low as a result of its thinness. In this case, the layer of electron injecting material is used in combination with a thicker layer of transparent conducting material such as indium tin oxide.

It will be appreciated that a transparent cathode device need not have a transparent anode (unless, of course, a fully transparent device is desired), and so the transparent anode used for bottom-emitting devices may be repJaced or supplemented with a layer of reflective material such as a layer of aluminium. Examples of transparent cathode devices are disclosed in, for example, GB 2348316.

Encapsulation

Organic optoelectronic devices tend to be sensitive to moisture and oxygen.

Accordingly, the substrate preferably has good barrier properties for prevention of ingress of moisture and oxygen into the device. The substrate is commonly glass, however alternative substrates may be used, in particular where flexibility of the device is desirable. For example, the substrate may comprise one or more plastic layers, for example a substrate of alternating plastic and dielectric barrier layers or a laminate of thin glass and plastic

The device may be encapsulated with an encapsulant (not shown) to prevent ingress of moisture and oxygen. Suitable encapsulants include a sheet of glass, films having suitable barrier properties such as silicon dioxide, silicon monoxide, silicon nitride or alternating stacks of polymer and dielectric or an airtight container. In the case of a transparent Cathode device, a transparent encapsulating layer such as Silicon monoxide or silicon dioxide may be deposited to micron levels of thickness, although in one preferred embodiment the thickness of snch a layer is in the range of 20-300 nm. A getter material for absorption of any atmospheric moisture and / or oxygen that may permeate through the substrate or encapsulant may be disposed between the substrate and the encapsulant.

Examples

Comparative Ink !

An ink containing the following components was prepared by dissolving a light- emitting polymer, polymer electrolyte and salts in a solvent mixture of 4- methylanisole and chlorobenzene in the amounts given in Table 1.

Table 1

THA^PFe' is tetiahexylammonium hexafluorophosphate.

THP*BF4^" is tetxaheptyl-untnonium tetrafluoroborate.

300,000 Mv Folyetbylene oxide is available from Sigma-Aldrich.

White Emitting Polymer 1 was formed by Suzuki polymerisation of the following monomers as described in WO 00/53656 in which a red phosphorescent iridium complex was provided as an end-cappmg group of the polymer:

30mol % 30 mol %

0.1 mol %

A glass substrate as cleaned with acetone and isopropyl alcohol,, treated with UV light and ozone, and blown with nitrogen gas. A film of the ink was fanned by depositing the ink onto the glass substrate by bar coating using a RDS Number 20 coating bar (nominal 45μπι wet thickness) with a bead of ~3ml applied in front of the bar onto the substrate, and evaporating the solvent at S0C to give a film of about 500- 600 nm in thickness.

The roughness of the film (Ra) was measured using a Veeco Nano scope - V AFM system used in tapping mode.

The film had a roughness Ra of 30.4 am ± 2.7 nm.

With reference to Figure 2, a clear correlation can be seen between PEO molecular weight and film roughness.

Ink Example 1 An ink was prepared as described for Comparative Ink 1 except that the 300,000 Mv polyethylene oxide was replaced with 35,000 Mv polyethylene oxide, and a film of this ink was formed as described for Comparative Ink 1,

The film had a roughness Ra of 25.0 nm ± 1.3 mo.

Ink Example 2

An ink was prepared as described for Comparative Ink 1 except that the 300,000 Mv polyethylene oxide was replaced with 2,000 Mv polyethylene oxide, and a film of this ink was formed as described for Comparative Ink 1.

Tbe film had a roughness Ra of 1-6 wn ± 0-4 nm.

Figure 3 sho s images of Comparative Ink 1 and Ink Examples 1 and 2. Lower roughness at lower FEO Mv is apparent from these figures,

Comparative Ink 2

An ink was prepared as described for Comparative Ink 1 except that White Emitting Polymer 1 was replaced was replaced with White Emitting Polymer 2 prepared by Suzuki polymerisation of the following monomers as described in WO 00/53656:

20 mol % 4.5 mol %

30 mol % 30 mol %

0.05 mol %

A film of this ink was formed as described for Comparative Ink 1. The film had a roughness Ra of 45,7 am ± 0.4 nm. Ink Example 3

An ink was prepared as described for Comparative Ink 2 except that the 300,000 Mv polyethylene oxide was replaced with 100,000 Mv polyethylene oxide, and a film of this ink was formed as described for Comparative Ink 1.

The film had a roughness Ra of 16.3 ran ± 0-5 nm.

Ink Example 4 An ink was prepared as described for Comparative Ink 2 except that the 300,000 Mv polyethylene oxide was replaced with 35,000 Mv polyethylene oxide, and a film of this ink was formed as described for Comparative Ink 1.

The film had a roughness Ra of 12,1 nm ± 0.6 nm.

Ink Example 5

An ink was prepared as described for Comparative Ink 2 except that the 300,000 Mv polyethylene oxide was replaced with 10,000 Mv polyethylene oxide, and a film of this ink was formed as described for Comparative Ink 1,

The film had a roughness Ra of 3.7 nm ± 1.3 nm. fak, Ex mple 6

An ink was prepared as described for Comparative Ink 2 except that the 300,000 Mv polyethylene oxide was replaced with 2,000 Mv polyethylene oxide, and a film Of this ink was formed as described for Comparative Ink 1.

The film had a roughness Ra of 1.5 nm ± 0.1 nm.

Figure 4 shows images of Comparative Ink 2 and Ink Examples 3-6. Lo er roughness at lower FEO Mv is apparent from these images.

Without wishing to be bound by any theory, polymer electrolytes having a lower viscosity averaged molecular weight may have a lower tendency to aggregate, resulting in formation of smoother films.

Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims.

Claims

1. A light-emitting composition comprising a semiconducting material, a

polymer electrolyte having a viscosity averaged molecular weight of less than 300,000 and a salt.

2. A light-emitting composition according to claim 1 wherein the polymer

electrolyte has a viscosity averaged molecular weight of less than 200,000, optionally less than 100,000, optionally less than 50,000.

3. A Ught-emitting composition according to claim 1 or 2 wherein the polymer electrolyte comprises ethylene oxide repeat units.

4. A Ught-emitting composition according to claim 3 wherein the polymer

electrolyte is a polyethylene oxide lnoniopolymer.

5. A light-emitting composition according to any preceding claim wherein the composition comprises at least two different salts.

6. A light-emitting composition according to any preceding claim wherein the salt or salts are ammonium salts.

7. A light-emitting composition according to any preceding claim wherei light is emitted directly from the semiconducting materia].

8. A light-emitting composition according to any preceding claim wherein the composition further comprises a light-emitting dopant.

9. A light-emitting composition according to any preceding claim wherein the semiconducting material is a semiconducting polymer.

10» A light-emitting composition according to claim 9 wherein the

semiconducting polymer is an at least partially conjugated polymer.

11. A light emitting composition according to claim 10 wherein the

semiconducting polymer comprises substituted or nnsubstituted arylene repeat units. A Ught-emitiing composition according to claim 10 or 11 wherein the at least partially conjugated polymer comprising repeat units of formula (XX):

(ΓΧ) wherein Ar⁸ and Ar⁹ in each occurrence are independently selected from substituted or unsubstituted aryl or heteroaryl. g is greater than or equal to 1, preferably 1 or 2, R ³ is H or a Substituent, preferably a substituent; c and d are each independently 1, 2 or 3; and any of Ar⁸, Ar⁹ and R¹³ that are bound directly to a N atom of formula (IX) may be linked by a direct bond ot divalent linking group to another of Ar⁵, Ar⁹ and R¹³ that is bound directly to the same N atom.

13. A composition according to any of claims 10-12 wherein the polymer is a partially conjugated polymer comprising non-conjugating repeat units that do not provide any conjugation path between repeat units adjacent to the nod- conjugating repeat units.

14. A formulation comprising a light-emitting composition according to any

preceding claim and at least one solvent. 15. A formulation according to claim 14 wherein the formulation comprises at least two solvents. 16. A formulation according to claim 14 or 15 wherein he at least two solvents are selected from one or more of benzene substituted with one or more d.io a kyl groups and benzene substituted with one or more halogens^

17. An organic light-Emitting electrochemical cell comprising an anode for

injecting positive charge carriers, a cathode for injecting negative charge carriers and a light-emitting layer between the anode and the cathode wherein the light-emitting layer comprises a composition according to any of claims 1- 13.

18. A method of forming a Ught-emitting electrochemical cell according to claim 17, the method comprising the steps of: depositing the formulation according to any of claims 14-16 over one of the anode and cathode; evaporating the at least one solvent to form a light-emitting layer; and depositing the other f the anode and cathode over the light-emitting layer.

19. A method according to claim 18 wherein the formulation is deposited by a method selected from screen printing, gravure printing, spin-coating and bar- coating.