GB2513378A

GB2513378A - Device

Info

Publication number: GB2513378A
Application number: GB1307466.1A
Authority: GB
Inventors: Thomas Johannes Kugler; Andrey Nikolaenko; Sarah Tyler
Original assignee: Cambridge Display Technology Ltd
Current assignee: Cambridge Display Technology Ltd
Priority date: 2013-04-25
Filing date: 2013-04-25
Publication date: 2014-10-29
Also published as: GB201307466D0

Abstract

A layer for an organic electronic device comprises of a charge transport polymer having polar side chains and a salt and/or salt precursor. Also disclosed, is an organic electronic device, comprising the layer and a method of making the layer.

Description

Device

FIELD OF THE INVENTION

The present invention relates to a layer for an organic electronic device, and preferably an electron injection layer, comprising a charge transporting polymer and a salt or a salt precursor, wherein the charge transporting polymer comprises polar side chains. The invention is also concerned with blends comprising the charge transporting polymer and the salt or a salt precursor as well as methods for making the layer. Organic electronic devices comprising the layer and methods for making the devices also form a part of the invention.

BACKGROUND

Organic electronic devices provide many potential advantages including inexpensive, low temperature, large scale fabrication on a variety of substrates including glass and plastic. Organic light emitting diode displays provide additional advantages as compared with other display technologies -in particular they are bright, colourful, last-switching and provide a wide viewing angle. OLED devices (which here includes organometallic devices and devices including one or more phosphors) may be fabricated using either polymers or small molecules in a range of colours and in multicoloured displays depending upon the materials used. For general background information reference may be made, for example, to W090/13148, W095/06400, W099/48160 and US4,539,570, as well as to "Organic Light Emitting Materials and Devices" edited byzhigang Li and Hong Meng, CRC Press (2007), ISBN 10: 1-57444- 574X, which describes a number of materials and devices, both small molecule and polymer.

In its most basic form an organic light emitting diode (OLED) comprises a light emitting layer which is positioned in between an anode and a cathode. Frequently a hole injection layer is incorporated in between the anode and the light emitting layer. It functions to decrease the energy difference between the work function of the anode and the highest occupied molecular orbital (HOMO) of the light emitting layer thereby increasing the number of holes introduced into the light emitting layer. In operation holes are injected through the anode, and if present the hole injection layer, into the light emitting layer and electrons are injected into the light emitting layer through the cathode. The holes and electrons combine in the light emitting layer to form an exciton which then undergoes radiative decay to provide light.

For an OLED to achieve optimum electronic performance it is necessary for electrons to be efficiently injected into the light emitting layer. To achieve this effect the cathode present in an OLED may be prepared from materials that have a low work function, usually a work function of less than 3.5 eV and more typically a work function of less than 3 eV. The cathode of the device may, for example, be made from a low work function metal such as calcium. Low work function metals are, however, very sensitive to solvents such as water. This has a deleterious effect on the display, causing defective pixels (known as black spots) and reduces the operational lifetime of the display.

Alternatively it has been proposed to use a layer of metal fluoride located between the light emitting layer and a higher work function, more robust, metal cathode such as Al-Ag. LiF, BaF2 and NaF have all been suggested for use in this role. The presence of the metal fluoride can result in an improvement in device efficiency -see for example AppI. Phys. Lett. 70, 152, 1997. This improvement is believed to result from a reduction in the barrier height at the light emitting polymer/cathode interface, allowing improved electron injection into the light emitting layer. Devices comprising metal fluoride layers are, however, still sensitive to degradation by moisture and require a high level of encapsulation. These devices are also expensive to fabricate by thermal evaporation processing.

In an alternative approach to improving injection of electrons into the light emitting layer from the cathode it has been proposed to combine a cathode comprising higher work function metals (e.g. Al-Ag) with an electron injection layer that is located between it and the light emitting layer. The role of the electron injection layer is to assist the injection of electrons into the light emitting layer. A number of different types of electron injection layers have been proposed including charge transporting polymers. Such polymers can advantageously be deposited by solution processing and thus easily be incorporated into larger displays.

Thermally evaporated Cs2CO3 has also been proposed as an electron injection layer. The need to use thermal evaporation to deposit 032003 onto a light emitting layer is, however, a major drawback.

Consequently there is a need for further electron injection layers that can be prepared by solution processing, preferably in air, which significantly reduces the cost of device fabrication.

SUMMARY OF INVENTION

Thus viewed from a first aspect the present invention provides a layer for an organic electronic device comprising: a charge transporting polymer; and a salt and/or a salt precursor, wherein said charge transporting polymer comprises polar side chains.

Preferably the layer is an electron injection layer.

Viewed from a further aspect the present invention provides a blend comprising a charge transporting polymer and a salt and/or a salt precursor, wherein said charge transporting polymer comprises polar side chains.

Viewed from a further aspect the present invention provides an organic electronic device comprising a layer as hereinbefore defined.

Preferably the device is an organic light emitting device and the layer is an electron injection layer.

Viewed from a further aspect the present invention provides use of a layer as hereinbefore defined in the preparation of an organic electronic device, wherein said device has at least two of, and preferably all of, the following properties: (i) Lifetime at 1000 cd/m2: at least 1300 hours, preferably at least 1400 hours (ii) Current density (mNcm2) at 5 V: at least 30 mA/cm2, more preferably at least 35 mA/cm2 (Ui) Drive voltage (V) at 1000 Cd/m2: less than 4.5 V, more preferably less than 4 V. Viewed from a further aspect the present invention provides a method of making a layer of an organic electronic device as hereinbefore defined comprising: depositing a solution of a charge transporting polymer and a salt and/or a salt precursor to form said layer.

Viewed from a further aspect the present invention provides a method of making a layer of an organic electronic device as hereinbefore defined comprising: (i) depositing a solution of a charge transporting polymer to form a first layer; and (ii) depositing a solution of salt and/or a salt precurosr to form a second layer on said first layer.

Viewed from a further aspect the present invention provides a method of making an organic electronic device comprising a step of depositing a layer by the method as hereinbefore defined.

DEFINITIONS

As used herein the term layer" refers to a complete or functioning structure that, when incorporated into an organic electronic device, performs a specific function.

Examples of layers include an electron injection layer, an electron transport layer, a hole injection layer, a hole transport layer, a light emitting layer and an interlayer. In the present invention, the layer is preferably an electron injection layer. A layer may be a single layer. Alternatively a layer may comprise a plurality of layers, i.e a layer when prepared for incorporation into an organic electronic device may itself comprise more than one single layer.

As used herein the term "single layer" refers to a layer that is homogeneous throughout the entirety of the layer. Thus the different components comprising the layer are evenly distributed throughout the single layer.

As used herein the phrase "a plurality of layers" refers to two or more single layers that have been joined together. When a second single layer is spin coated onto a first single layer and then they are annealed together, a bilayer is formed. When a third single layer is spin coated onto a bilayer and then they are annealed together, a trilayer is formed and so on. The solution from which each single layer is deposited is homogeneous at the start of spin coating. When layers are spin coated and annealed together, there may be some intermixing of the contents of the two layers and the interface between the two single layers may not be clearly defined. Thus the number of different solutions deposited by spin coating during fabrication of a multilayer structure determines the number of layers present therein.

As used herein the term polymer" refers to a compound comprising repeating units. Preferred polymers of the present invention comprise 4 or more repeat units.

Polymers usually have a polydispersity of greater than 1. Polymers generally comprise a backbone and side chains. The backbone is the linear chain to which all side chains may be regarded as being pendant. The side chains are the groups that are pendant to the backbone or branch off the backbone.

As used herein the term "polar' refers to a separation of charge within the structure of a molecule. Thus polar side chains' are side chains wherein a separation of charge is present within their structure. "Polar groups" are those groups wherein there is a covalent bond between two atoms wherein the electrons forming the bond are unequally distributed. The term encompasses electrical dipole moments where the distribution of charge in the bond is only slightly uneven creating a slightly positive end and a slightly negative end. The term also encompasses zwitterions and ionic groups where the charge separation is complete.

As used herein the term "zwitterioniC' refers to group that comprises both a positive charge and a negative charge.

As used herein the term salt" refers to an ionic substance comprising a cation and a counteranion.

As used herein the term salt precursor" refers to a substance which, when in contact with the charge transporting polymer, forms a salt.

As used herein the term alkyl" refers to saturated, straight chained, branched or cyclic groups. Alkyl groups may be substituted or unsubstituted.

As used herein the term haloalkyl refers to saturated, straight chained, branched or cyclic groups in which one or more hydrogen atoms are replaced by a halo atom, e.g. F or Cl, especially F. As used herein, the term "cycloalkyl" refers to a saturated or partially saturated mono-or bicyclic alkyl ring system containing 3 to 10 carbon atoms. Cycloalkyl groups may be substituted or unsubstituted.

As used herein, the term "heterocycloalkyl" refers to a cycloalkyl group in which one or more ring carbon atoms are replaced by at least one hetero atom such as -0-, -N-or -S-. Heterocycloalkyl groups may be substituted or unsubstituted.

As used herein the term alkenyl" refers to straight chained, branched or cyclic group comprising a double bond. Alkenyl groups may be substituted or unsubstituted.

As used herein the term "alkynyl" refers to straight chained, branched or cyclic groups comprising a triple bond. Alkynyl groups may be substituted or unsubstituted.

Optional substituents that may be present on alkyl, cycloalkyl, heterocycloalkyl, alkenyl and alkynyl groups as well as the alkyl moiety of an arylalkyl group include C1-15 alkyl or cycloalkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, N, C=O and -COO-, substituted or unsubstituted C514 aryl, substituted or unsubstituted 05-14 heteroaryl, alkoxy, C115 alkylthio, halo, e.g. fluorine and chlorine, cyano and arylalkyl.

As used herein, the term "aryl" refers to a group comprising at least one aromatic ring. The term aryl encompasses heteroaryl as well as fused ring systems wherein one or more aromatic ring is fused to a cycloalkyl ring. Aryl groups may be As used herein, the term "heteroaryl" refers to a group comprising at least one aromatic ring in which one or more ring carbon atoms are replaced by at least one hetero atom such as -0-, -N-or -S-.

Optional substituents that may be present on aryl or heteroaryl groups as well as the aryl moiety of arylalkyl groups include halide, cyano, C1-16 alkyl, C1-16 fluoroalkyl, C116 alkoxy, C116 fluoroalkoxy, C514 awl and C514 heteroaryl.

As used herein, the term "arylalkyl" refers to an alkyl group as hereinbefore defined that is substituted with an awl group as hereinbefore defined.

As used herein the term "halogen" encompasses atoms selected from the group consisting of F, Cl, Br and I. As used herein the term "alkoxy" refers to 0-alkyl groups, wherein alkyl is as defined above.

As used herein the term "blend" refers to a mixture of at least two compounds and/or polymers. Generally a blend will be a solid, e.g. powder.

As used herein the term "solution" refers to a homogeneous mixture of a compound or blend in a solvent.

optional substituents for different groups As used herein the term "dielectric constant" is used herein as an indicator of the polarity of a solvent. The dielectric constants of a large number of solvents can be found in the 92nd Edition, 2011-2012, of the CRC Handbook of Chemistry and Physics.

As used herein the term "work function" refers to the minimum energy (in electronvolts) needed to remove an electron from the Fermi level of a material into vacuum. The work function is measured by photoelectron spectroscopy.

As used herein the term "bright waving" refers to a transient luminance increase that increases the lifetime of an organic light emitting device.

As used herein the term "T luminance" refers to the time in hours it takes the luminance of a device to decrease to half its value at turn on.

As used herein the term "T90 luminance" refers to the time in hours it takes the luminance of a device to decrease to 90% of its value at turn on.

DESCRIPTION OF INVENTION

The layer of the present invention is preferably incorporated into an organic electronic device as an electron injection layer. The presence of the layer of the invention advantageously improves the transport of electrons from the cathode to, for example, a light emitting layer. As a result the electrical performance of devices comprising a layer of the present invention is significantly improved. The need for a low work function cathode is also avoided so cathodes comprising less moisture and oxygen sensitive materials may be used. This, in turn, reduces the encapsulation requirements of the device.

The presence of the layer of the present invention advantageously also improves the luminance performance of devices comprising the layer. Specifically the luminance of the devices may increase rather than decrease after the device is turned on. This is highly beneficial since it ultimately extends the device lifetime.

In some embodiments, the layer of the present invention is preferably a single layer. Thus the charge transporting polymer and salt and/or salt precursor comprising the layer are preferably evenly distributed throughout the layer. Preferably the layer is homogeneous. Single layers are preferred when a salt precursor is present.

In some other embodiments, the layer of the present invention comprises a plurality of single layers. The layer may be, for example, a bilayer or trilayer, but is preferably a bilayer. Preferably the layer comprises a first single layer comprising a charge transporting polymer and a second single layer comprising a salt and/or salt precursor. Preferably the layer is a bilayer. Preferably the first layer is solution processed. Preferably the second layer is solution processed.

When the second single layer is deposited on the first single layer and they are annealed together, a bilayer is formed. During spin coating and/or annealing there may be some intermixing of the contents of the first and second single layers. Thus some salt and/or salt precursor from the second single layer may diffuse into the first single layer and some charge transporting polymer from the first single layer may extend into the second single layer. Thus the interface between the first and second single layers in some cases may not be clearly defined. Since a first single layer comprising charge transporting polymer and a second single layer comprising salt and/or salt precursor form the layer it is regarded as a bilayer.

When the layer is a single layer, the layer is preferably solution processed.

When the layer comprises a plurality of layers, each of its single layers is preferably solution processed. Thus when the layer is a bilayer, the first single layer is preferably solution processed. Similarly when the layer is a bilayer, preferably the second single layer is solution processed. Still more preferably, the first and second single layers are preferably solution processed.

A key feature of the layer of the present invention is the presence of a charge transporting polymer comprising polar side chains. The polar side chains confer polarity on the charge transporting polymer that enables it to dissolve in solvents that are orthoganol to the other layers, e.g. light emitting layer, typically present in an organic electronic device. As a result, the charge transporting polymer can be readily deposited by solution processing onto, for example, a light emitting layer of a partially assembled OLED without damaging the underlying light emitting layer. Moreover the polar side chains of the charge transporting polymer also form a polar environment with which a salt will form a solid solution. Thus in the case of single layer devices the polar side chains of the charge transporting polymer solubilise the salt and prevent it precipitating. In the case of devices comprising a plurality of layers, the polar side chains of the charge transporting polymer form a polar surface which acts as a wetting layer onto which the salt and/or salt precursor can be deposited as a blanket layer, without the formation of salt islands at the interface.

The polarity of the charge transporting polymer is therefore an important feature of the layer of the present invention. The polarity may be characterised by the solvents in which the charge transporting polymer is soluble. Preferred charge transporting polymers are soluble in a solvent having a dielectric constant of 15 to 65, preferably 20 to 60 and more preferably 25 to 50. Particularly preferred charge transporting polymers are soluble in a solvent selected from dimethylformamide (DMF), dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide (DMSO), acetone, butanone, pentanone, methyl butyl ketone, diethyl ether, methyl t-butyl ether, tetrahydrofuran (THE), acetonitrile, phenyl acetate, ethyl acetate, triethylphosphate, a,a,cz,-trifluorotoluene, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3-methylbutan-1 -01, 2-methylbutan-1 -01, 2,2-dimethylpropan-1 -ol, pentan-3-ol, pentan-2-ol, 3-methylbutan-2-ol, 2-methylbutan- 2-ol, methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane or 2-butoxyethanol. Still more preferred charge transporting polymers are soluble in a solvent selected from DMSO, methanol and 2-butoxyethanol.

Preferred charge transporting polymers present in the layers of the present invention comprise a repeat unit of formula (Xa) or (Xb):

A

(A) C 2) (A) a b (Xa) a (Xb) wherein Ar is a C520 substituted or unsubstituted aryl or heteroaryl group; L is a bond or a linker group; A is a polar group; and B is a polar group, hydrogen, substituted or unsubstituted C116 alkoxy, substituted or unsubstituted C514 aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted C514 heteroaryl, substituted or unsubstituted heteroarylalkyl and substituted or unsubstituted alkyl wherein one or more non-adjacent C atoms may be replaced with -0-, -Nfl-, -NH-, -S-, -COO-, -NHCO-, -NHSO2-, -NHCOO-groups wherein P is C18 alkyl; and each of a and b are independently an integer selected from 1 to 5 When either of a or b is greater than 1, there are more than 1 A and B groups respectively attached to the linker, e.g. when a is 2, there are 2 A groups attached to the linker. When multiple A and/or B groups are present, they may be attached to the linker at different atoms.

Preferred charge transporting polymers comprise a repeat unit of formula X shown below: cçf (ç3)) (A)a W ()h Xc Xci Xe (1). 1 (A) 1 (A)a (A)a (A) Xli Xg wherein L, A, B, a and b are as defined above in relation to formula Xa and Xb.

Particularly preferably the charge transporting polymer comprises repeat units of formula (Xi): Xi (Xi) wherein L, A, B, a and b are as defined above in relation to formula Xa and Xb.

In preferred charge transporting polymers, (B)b is (A)a, i.e. the repeat unit comprises identical polar groups per unit. In further preferred charge transporting polymers a is 1 or 2.

In further preferred charge transporting polymers, L is a linker group selected from substituted or unsubstituted C514 aryl, substituted or unsubstituted C514 heteroaryl and substituted or unsubstituted C116 alkyl wherein one or more non-adjacent C atoms may be replaced with -0-, -NE-, -NH-, -S-, -COO-, -NHCO-, -NHSO2-, -NH000-groups wherein R is C18 alkyl. More preferably L is a linker group selected from substituted or unsubstituted 0514 aryl and substituted or unsubstituted C116 alkyl wherein one or more non-adjacent C atoms may be replaced with -0-, -Nfl-, -NH-, -S- -COO-, -NHCO-, -NHSO2-, -NHCOO-groups wherein R is 01-8 alkyl. In some charge transporting polymers, L is a 0514 aryl, especially a C5 or 05 aryl, e.g. phenyl. In other charge transporting polymers, L is a C1-16 alkyl, more preferably a 016 alkyl and yet more preferably a C14 alkyl.

Particularly preferably the charge transporting polymer comprises a repeat unit of formula (Xii) or (XiH): A A (Xu) a (Xvi) wherein n is an integer between 1 and 16, nore preferably an integer between 1 to 6 and yet more preferably an integer between 1 and 4, e.g. 2 and a is 1 or 2. In formula (XUi) when one A group is present (i.e. a is 1) it is preferably present in the 4 position.

In formula (Xiii) when two A groups are present (i.e. a is 2), they are preferably present at the 3 and 4 positions.

In some charge transporting polymers present in the layer of the present invention A preferably comprises a zwitterionic group. Preferred zwitterionic groups comprise a positively charged N, F, S or 0 atom, preferably a positively charged N atom. Particularly preferably the zwitterionic group comprises an oxonium, sulfonium, phosphonium or ammonium, still more preferably an ammonium. Further preferred zwitterionic groups comprise a sulfonate, sulfinate, sulfite, thiosulfate, thiosulfonate, phosphate, phosphite, phosphonate, thiophosphate, thiophosphonate, orthophosphate, pyrophosphate, polyphosphate, carboxy, thiocarboxy or alkoxy group. Sulfonate and carbonate are particularly preferred.

Further preferred zwitterionic groups are those of formula (i): / KY (i) wherein Z is N, A, 0 or S; R1 is substituted or unsubstituted C18 alkyl, substituted or unsubstituted C28 alkenyl, substituted or unsubstituted C514 aryl or substituted or unsubstituted C514 heteroaryl; R2 is present when 7 is N or P and is R1; R8 is a C110 alkylene chain in which non-adjacent carbon atoms may optionally be replaced by -0-, -Nfl-, -NH-, -5-, -000-, -NHCO-, -NHSO2-, -NH000-groups wherein P is 018 alkyl; and Y is SO3, S02, 0S02, SS03, S02S, C02, P03, 0P032-, OP(OR)0 where P is 01-6 alkyl, OP(S)022-, P(S)022-, OPO(OH)OPO(OH)0, 0-(P0(0H)0)P0(0H)0 wherein n is 1 to 6, C02, CSO, or 0group.

In preferred groups of formula (i) Z is N or P, particularly N. In further preferred groups of formula (i) R1, and when present fl2, is an substituted or unsubstituted alkyl or substituted or unsubstituted C514 aryl. More preferably fl1, and when present R2, is a 018 alkyl, still more preferably a 013 alkyl, e.g. methyl.

In further preferred groups of formula (i) R3 is a C18 alkyl, more preferably a C26 alkyl, e.g. a C or 04 alkyl.

In further preferred groups of formula (i) Y is SOc or C02.

In some charge transporting polymers present in the layer of the present invention A comprises a non-charged polar group. Preferred examples of such polar groups include amide, sulfonamide, ester, carboxylic acid, carbonate, carbamate, ether, alcohol, amine, thioether, sulfide or haloalkyl. Particularly preferred polar groups are those of formula (ii): _4.

i (u) wherein M is 0, Nfl, NH, S or CO wherein R is Ci alkyl; Q is Br, Cl, F, I or H, preferably Cl, F or H; TisBr,Cl,F,lorH; o is an integer from 1 to 4; p is an integer from ito 16; and P4 is H or C alkyl.

In preferred groups of formula (ii), M is 0, Nfl or NH, particularly 0.

In further preferred groups of formula (ii), I is Cl, F or H, particularly H. In further preferred groups of formula (ii), o is 2 or 3, particularly 2.

In further preferred groups of formula (ii), p is 1 to 12. In some groups p is more preferably 3 to 10, and still more preferably 4 to 8. In other groups p is more preferably 2 to 6 and still more preferably 2 or 3.

In further preferred groups of formula (ii), P4 is H, -OH3 or -CH2CH3.

In some charge transporting polymers present in the layer of the present invention A comprises an ionic group. Preferred ionic groups comprise a covalently bound anion, particularly a covalently bound anion selected from SOS, S02, 0S02, SS03, S02S, C02, P03, 0P032, OP(OR)0 where R is C16a1ky1, OP(S)022, P(S)022, OPO(OH)OPO(OH)0, O-(PO(0H)O)PO(OH)O wherein n is 1 to 6, C02 0(3)0-, or C. Still more preferably the covalently bound anion is C02.

Preferably the ionic group comprises a counter cation selected from Lit, Nat, Kt, flb, Cs, Be2, Mg2, Ca2, Sr2 and Ba2 Still more preferably the cation is Cs.

Particularly preferred charge transporting polymers present in the layer of the present invention comprise a repeat unit of formula (Xii) and still more preferably a repeat unit of formula (Xii) wherein a is 1. In such polymers A is preferably a zwitterionic group.

Other particularly preferred charge transporting polymers present in the layer of the present invention comprise a repeat unit of formula (XUi) and still more preferably a repeat unit of formula (Xiii) wherein a is 1. In such polymers A is preferably a non-charged polar group.

Other particularly preferred charge transporting polymers present in the layer of the present invention comprise a repeat unit of formula (XUi) and still more preferably a repeat unit of formula (Xiii) wherein a is 2. In such polymers one A is preferably a non-charged polar group and one A is preferably an ionic group.

Particularly preferred charge transporting polymers present in the layer of the present invention comprises a repeat unit of formula (Xiv), (Xv),(Xvi) or (Xvii): so3 (Xiv) p=8 (Xv) j (Xvi) tcs oo c a cxi + H30(OH2CH2C)aO O(0H20H20)3OH3 (Xvii) The charge transporting polymer present in the layer of the present invention optionally comprises further repeat units. Some preferred electron transporting polymers comprise a repeat unit of formula (R) which is an substituted or unsubstituted, 2,7-linked fluorene and more preferably a repeat unit of formula (R) as shown below: R1° R11 (R) wherein R1° and R11 are independently selected from hydrogen, substituted or unsubstituted C115 alkyl, substituted or unsubstituted C115 alkoxy, substituted or unsubstituted C514 aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted C514heteroaryl and substituted or unsubstituted heteroarylalkyl.

In preferred repeat units of formula (R) R1° and R11 are the same. In particularly preferred repeat units at least one and more preferably both of R1° and R11 comprise a substituted or unsubstituted C-alkyl or a substituted or unsubstituted C514 aryl, e.g. a C6 aryl. Preferred substituents of aryl groups are C116 alkyl and still more preferably an A particularly preferred repeat unit of formula (R) for use in the charge transporting polymer is (Ri) as shown below: C3H17 (Ri) Repeat units of formula (R) may be incorporated into charge transporting polymers using monomers as described in W02002/092723.

One preferred charge transporting polymer of the present invention comprises repeat units of formulae (Xii) and (R). Particularly preferred charge transport polymers comprise repeat units of formulae (Xiv) and (Ri). One preferred charge transporting polymer comprises 30-70 %wt repeat unit (Xiv) and 30-70 %wt repeat unit (Ri), more preferably 40-60 %Wt repeat unit (Xiv) and 60-40 %wt repeat unit (Ri) and still more preferably about 50 %wt repeat unit (Xiv) and about 50 %wt repeat unit of formula (Ri).

A further preferred charge transporting polymer of the present invention comprises repeat units of formula (Xiii). Particularly preferred charge transport polymers comprise repeat units of formulae (Xv) and (Xvi). One preferred charge transporting polymer comprises 30-70 %wt repeat unit (Xv) and 30-70 %wt repeat unit (Xvi), more preferably 40-60 %wt repeat unit (Xv) and 60-40 %wt repeat unit (Xvi) and still more preferably about 50 %wt repeat unit (Xv) and about 50 %wt repeat unit of formula (Xvi).

A further preferred charge transporting polymer of the present invention is a homopolymer of repeat units of formula (Xvii).

The layers and devices of the present invention comprise a salt. The salt may be incorporated into the layer of the present invention as a salt. Alternatively the salt may be generated in situ (i.e. within the layer and device) from a salt precursor. When the salt is generated in situ it is preferably generated by reaction between a salt precursor and residual moisture present in the charge transporting polymer, e.g. a charge transporting polymer comprising repeat units of formula (Xvii).

The salt and/or salt precursor present in the layer of the present invention is preferably soluble in water and an organic solvent. Preferred salts comprise an organic anion. Preferred salts and salt precursors are soluble in a solvent having a dielectric constant of greater than 15, preferably greater than 20 and preferably greater than 25.

There is no upper limit on the dielectric constant and it may be, for example, 85.

Particularly preferred salts and salt precursors are soluble in a solvent selected from water, DMF, dimethylacetamide, N-methyl-2-pyrrolidone, DMSO, acetone, butanone, pentanone, methyl butyl ketone, diethyl ether, methyl t-butyl ether, THF, acetonitrile, phenyl acetate, ethyl acetate, triethylphosphate, a.,a.,cz,-trifluorotoluene, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3-methylbutan-1 -ol, 2-methylbutan-1 -ol, 2,2-dimethylpropan-1 -ol, pentan- 3-ol, pentan-2-ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane or 2-butoxyethanol. Still more preferred salts and salt precursors are soluble in a solvent selected from DMSO, methanol and 2-butoxyethanol.

Preferred layers of the invention comprise a salt. Particularly preferred salts present in the layer of the present invention comprise an alkali metal or an alkaline earth metal or a transition metal. More preferably the salt comprises an alkali metal.

Preferred salts comprise a cation selected from LL, Nat, K, Rb, Cs, Be2, Mg2t Ca2, Sr2 and Ba2. More preferred salts comprise a cation selected from K, Rb, Cs, Be2, Mg2, Ca2, Sr2 and Ba2. Still further preferred salts comprise a cation selected from Rb, Cs, Ca2t Sr2, yet more preferably RV, Cs, e.g. Cst As mentioned above, preferred salts present in the layer of the present invention comprise an organic anion. More preferred salts comprise an anion selected from hydroxide, halide, C14 alkoxide, C14 carboxylate, C14 halocarboxylate, C14 diketonate, perhalogenate, nitrate, C14 phosphate. Particularly preferred salts comprise a C14 carboxylate anion, preferably CO2 or HC03, especially C032.

An especially preferred salt present in the layer of the present invention is Cs2CO3.

Further preferred layers of the present invention comprise a salt precursor.

Preferably the salt precursor is a compound which reacts with water to form an acid or a compound with at least one acidic bond. Preferred salt precursors include metal alkoxides, metal halogenides, silanes, acid chlorides, acid anhydrides and sulfonyl or phosphoryl chlorides. All of these compounds can generate mobile anions and cations upon reaction with water. More preferably the salt precursor is a metal alkoxide or metal halogenide and particularly preferably a metal alkoxide.

When the salt precursor is a metal alkoxide, the metal present is preferably a metal that can form a high oxidation state, e.g. an oxidation state of Ill or IV or higher and preferably Ill or IV, particularly IV. Preferably the metal is selected from group 3, 4 or 14 of the periodic table, e.g. Sc, Y, Ti, Zr, Si, Ge or Sn. Particularly preferably the metal is selected from Ti, Zr, Si and Sn. Preferred metal alkoxides are those of formula M(OR')4 wherein M is Ti, Zr, Si and Sn and fl is C18 alkyl or C610 aryl.

When the salt precursor is a metal halogenide, the metal present may be any transition metal or main group element. Preferably the metal is selected from group 3, 4, 5, 6, 7, 8, 13 or 14 of the periodic table, e.g. Sc, Ti, Zr, V, Ta, Cr, Mn, Fe, Al, Si, Ge or Sn. Particularly preferably the metal is selected from Ti, Zr, Fe, Al, Sn or Si. Further preferred halogenides are chlorides. Preferred metal halogenides are those of formula M(halogen)4 wherein M is Ti, Zr, Si and Sn and halogen is chloride and M(halogen)3 wherein M is Fe or Al and halogen is chloride.

Particularly preferably the salt precursor is selected from Ti(iPrO)4, Sn(iPrO)4, SiOPrO)4, SiCl4 and ZrCI4. Particularly preferably the salt precursor is Ti(iPrO)4.

When the salt precursor contacts the charge transporting polymer, it undergoes partial hydrolysis due to the presence of residual water in the charge transporting polymer. For example, when the salt precursor is Ti(iPrO)4 partial hydrolysis to Ti(iPrO)4(OH), occurs, wherein x is 4 or less. This reaction generates iPrCH, titanate species (i.e. titanium oxide anions) and protons. The titanate anions can migrate with cations in ion pairs. The protons can function as countercations that interact with the charge transporting polymer, e.g. a polymer comprising repeat units of formula (Xvii).

This is discussed below in more detail.

When the leaving group generated upon contact with residual water in the charge transporting polymer is a strong acid, then the strong acid may be the main source of mobile anions. For example if SiCl4 is the salt precursor, this reacts with water to generate Si(OH)4 and HCI and the HCI reacts with water to generate cr and H3O. The C1 anion can migrate with cations in ion pairs as discussed below in more detail.

An analogous reaction occurs when the salt precursor is a silane. Preferred silanes are those of formula R'R"R"SiCI wherein each of R', R" and R" may be Cl, H, C18 alkyl or C0 aryl. When such a silane contacts water, the corresponding silanol is formed along with HCI. The HCI reacts with water to generate or and H3O as described above.

Alternatively the salt precursor may be an acid chloride or an acid anhydride.

The acids may be organic or inorganic. Examples of suitable inorganic acid chlorides are sulfonyl chloride and phosphoryl chloride. Suitable organic acid chlorides include those of formula R'COCI and R'SO2CI wherein R' is C18 alkyl or C8 aryl. Preferred acid anhydrides are those of formula R'COOCOFl" wherein R' and R" are each independently 01-8 alkyl or C610 aryl. As above when the leaving group generated is a strong acid, then the strong acid may be the main source of mobile anions.

The layers of the invention may comprise a charge transporting polymer, a salt and a salt precursor. More preferably, however, the layers of the present invention comprise a charge transporting polymer and either a salt or a salt precursor. When the charge transporting polymer is a polymer comprising polar side chains comprising zwitterionic or non-charged polar groups (e.g. a polymer comprising repeat units of formula (Xiv), (Xv) and/or (Xvi)), the layer preferably comprises a salt. Particularly preferably such layers are bilayers.

When the charge transporting polymer is a polymer comprising polar side chains comprising ionic groups (e.g. a polymer comprising repeat units of formula (Xvii), the layer preferably comprises either a salt or a salt precursor, particularly a salt precursor.

Some particularly preferred layers of the present invention comprise: * A charge transporting polymer comprising polar side chains comprising zwitterionic groups (e.g. a polymer comprising repeat units of formula (Xiv) and a salt (e.g. 052003) in a bilayer structure; * A charge transporting polymer comprising polar side chains comprising non-charged polar groups (e.g. a polymer comprising repeat units of formula (Xv) and/or (Xvi)), a salt (e.g. Cs2CO3) in a bilayer structure; * A charge transporting polymer comprising polar side chains comprising non-charged polar groups (e.g. a polymer comprising repeat units of formula (Xv) and/or (Xvi)), a salt (e.g. Cs200s) in a single layer structure; and * A charge transporting polymer comprising polar side chains comprising an ionic group and a non-charged polar group (e.g. a polymer comprising repeat units of formula (Xvii), a salt precursor (e.g. Ti(iPrO)4) in a bilayer structure.

Preferred blends of the present invention comprise a charge transporting polymer as hereinbfore defined. Preferred blends of the present invention comprise a salt and/or a salt precursor as hereinbefore defined. Preferred falibacks recited in relation to the charge transporting polymer, salt and salt precursor above also apply in relation to their presence in the blend.

Further preferred blends of the present invention comprise charge transporting polymer and salt, more preferably in a weight ratio of 1:1 to 20:1, more preferably 1.5:1 to 15:1, still more preferably 2:1 to 5:1 and yet more preferably about 2.5:1 to 3.5:1.

Further preferred blends of the present invention comprise charge transporting polymer and salt precursor, more preferably in a weight ratio of 1.5:1 to 1:4, more preferably 1:1 to 1:3 and still more preferably about 1:1.5.

When the blends of the present invention are used in the manufacture of organic electronic devices, they are preferably in the form of solutions. The solutions may be used in conventional solution processing techniques to form the layer of the invention. The solvent present in the solution is preferably selected from DMF, dimethylacetamide, N-methyl-2-pyrrolidone, DMSO, acetone, butanone, pentanone, methyl butyl ketone, diethyl ether, methyl t-butyl ether, THF, acetonitrile, phenyl acetate, ethyl acetate, triethylphosphate, a,a,a,-trifluorotoluene, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3- methylbutan-1 -ol, 2-methylbutan-1 -ol, 2,2-dimethylpropan-1 -ol, pentan-3-ol, pentan-2- ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane, 2-butoxyethanol or mixtures of the afore-going.

More preferably the solvent is selected from DMSO, methanol, 2-butoxyethanol or mixtures of the aforegoing. When a mixture of solvents is used, the solvents are preferably miscible. One preferred solvent mixture is DMSO and 2-butoxyethanol.

The concentration of the charge transporting polymer in the solution is preferably in the range 0.2 to 3 wt% and more preferably 0.3 to 1 wt%. The concentration of the salt in the solution is preferably 0.05 to 1 %wt and more preferably 0.1 to 0.5 %wt. The concentration of the salt precursor in the solution is preferably in the range 0.01 to 1 wt% and more preferably 0.04 to 0.1 wt%.

A layer, e.g. electron injection layer, of the present invention may be prepared by depositing a solution of a charge transporting polymer and a salt and/or salt precursor to form said layer. Preferably the layer, e.g. electron injection layer, is prepared using a blend as hereinbefore described. In preferred methods at least some solvent is removed (e.g. by evaporation) following deposition of the layer.

The charge transporting polymer and salt and/or salt precursor may be dissolved in the same solvent. More preferably, however, the charge transporting polymer is dissolved in a solvent to form a solution of charge transporting polymer and separately a salt and/or salt precursor is dissolved in a solvent to form a solution of salt and/or salt precursor. The solution of charge transporting polymer and solution of salt and/or salt precursor are then mixed to form a blend as hereinbefore described.

Thus a preferred method of the present invention comprises: (i) dissolving a charge transporting polymer as hereinbefore defined in a first solvent to form a solution of charge transporting polymer; (U) dissolving a salt and/or salt precursor as hereinbefore defined in a second solvent to form a solution of salt and/or salt precursor; (Ui) mixing said solution of charge transporting polymer and said solution of salt and/or salt precursor; and (iv) depositing said mixture to form said layer.

The solvents used may be the same or different. The solvent in each case is preferably selected from DMF, dimethylacetamide, N-methyl-2-pyrrolidone, DMSO, acetone, butanone, pentanone, triethylphosphate, a,a,a,-trifluorotoluene, methyl butyl ketone, diethyl ether, methyl t-butyl ether, THF, acetonitrile, phenyl acetate, ethyl acetate, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3-methylbutan-1 -ol, 2-methylbutan-1 -ol, 2,2-dimethylpropan- 1 -ol, pentan-3-ol, pentan-2-ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane or 2-butoxyethanol or mixtures thereof. The first solvent is preferably DMSO. The second solvent is preferably 2-butoxyethanol.

Alternatively the layer, e.g. electron transport layer, of the present invention may be prepared by a method comprising: (i) depositing a solution of a charge transporting polymer to form a first layer; and (ii) depositing a solution of salt and/or salt precursor to form a second layer on said first layer.

In preferred methods at least some solvent is removed (e.g. by evaporation) following deposition of the first layer and prior to deposition of the second layer. In further preferred methods, at least some solvent is removed (e.g. by evaporation) following deposition of the second layer.

The charge transporting polymer is preferably dissolved in a solvent selected from DMF, dimethylacetamide, N-methyl-2-pyrrolidone, DMSO, acetone, butanone, pentanone, methyl butyl ketone, diethyl ether, methyl t-butyl ether, THF, acetonitrile, phenyl acetate, ethyl acetate, triethylphosphate, a,a,a,-trifluorotoluene, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3-methylbutan-1 -ol, 2-methylbutan-1 -01, 2,2-dimethylpropan-1 -01, pentan- 3-ol, pentan-2-ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane or 2-butoxyethanol or mixtures thereof. DMSO and methanol are preferred. The salt and/or salt precursor is preferably dissolved in a solvent selected from DMF, DM50, acetone, acetonitrile, methanol, ethanol, propanol, isopropanol, n-butanol or 2-butoxyethanol. Methanol or 2-butoxyethanol is preferred.

When the layer comprises a plurality of layers, the layers are preferably annealed after deposition of the final layer, e.g. after deposition of the second layer.

Annealing may be carried out by microwave radiation and/or by heating. Suitable heating conditions include 100-150 0Cin a glove box.

Without wishing to be bound by theory it is thought that the layers of the present invention improve electron injection into the light emitting layer by a number of mechanisms including: (1) The very deep HOMO level of the charge transporting polymer makes it an efficient hole blocking layer. Holes accumulating at the light emitting layer/charge transporting polymer interface will then increase the local electric field at the interface, and thereby facilitate electron injection from the cathode into the electron injection layer.

(2) Due to the presence of the polar sidechains on charge transporting polymer, the first layer of cathode, e.g. Al, atoms landing on the charge transporting polymer surface during vapour deposition of the cathode are more likely to react with the polar atoms of the sidechains than reacting with the C=C double bonds of the conjugated pi-system.

Because of this, the pi-system of the charge transporting polymer remains intact at the cathode interface, and is available for injecting electrons into.

(3) Adding a salt, e.g. Cs2CO3, to the charge transporting polymer enables the formation of an n-doped interface between the charge transporting polymer and the, e.g. Al, cathode. The Al-cations formed during electron transfer to the pi-system of the charge transporting polymer are thought to be stabilised by complex formation with the carbonate anions in Cs2CO3.

Without wishing to be bound by theory, it is thought that the layers of the present invention achieve bright waving and improve the luminance performance of devices incorporating the layers by two main mechanisms. Devices comprising electron injection layers comprising a charge transporting polymer and a salt such as Cs2003 (whether it is added as a salt or generated in situ) display characteristic transient changes in luminance during lifetime experiments. These changes occur within two separate timescales: (i) an initial, fast increase in luminance occurs within minutes after the start of device operation, followed by a luminance decrease during the first hours of operation and (ii) the onset of a second, much slower luminance increase is then observed after several tens of hours, and may continue for hundreds of hours before reaching its peak value, after which the luminance decreases again.

These effects combine to overall significantly improve the lifetime of the device.

The initial, fast increase in luminance is most probably due to a drift of ions at the interface between the electron injection layer and the, e.g. aluminium, cathode upon application of the externally applied forward bias. The resulting ionic space charges at the cathode interface can then result in band bending and thereby improve electron injection.

The second, slower luminance increase observed may be due to a number of mechanisms including an initial diffusion of, e.g. Cs, cations into the light emitting layer (the driving force for this diffusion being complex formation between the electron-rich units in the light emitting polymer and the Cs cations) resulting in the formation of electron traps and partial quenching of electroluminescence. This effect is therefore a slow, bulk effect. When the device is subsequently turned on, application of the forward bias is thought to pull the Cs cations out of the [ER layer, thereby reducing the number of electron traps and quenching sites, which then results in a transient luminescence increase (i.e. bright-waving).

In the methods of the invention the layer, preferably the electron injection layer, is deposited on a light emitting layer. Any conventional solution-based processing method may be used. Representative examples of solution-based processing methods include spin coating, gravure printing, flexographic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In preferred methods, however, depositing is by spin coating. The parameters used for spin coating the electron injection layer or layers such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the layer.

The layers and blends of the present invention are preferably used in the manufacture of organic electronic devices. Organic electronic devices comprising a layer of the present invention therefore form a further aspect of the present invention.

Examples of electronic devices that may be prepared using the layers and blends of the present invention include organic light emitting diodes (OLEDs), organic photovoltaic devices (OPVs), organic photosensors, organic transistors and organic memory array devices. Such devices comprise an anode, a cathode and an active organic layer in between the anode and cathode. The layer of the present invention is preferably present in between the active organic layer and the cathode. The electrodes are preferably deposited by thermal evaporation. The active layer is preferably deposited by solution processing, e.g. spin coating. The layer of the present invention is also preferably deposited by solution processing, e.g. spin coating.

The layer and blends of the present invention are particularly beneficial in the manufacture of CLEDs. In CLEDs the active organic layer is an organic light-emitting layer. In OLEDs the layer of the present invention is preferably an electron injection layer.

Preferably the device, e.g. OLED, comprises: (i) an anode; (ii) optionally an interlayer; (iii) a light emitting layer; (iv) an electron injection layer; and (v) a cathode, wherein the electron injection layer is as hereinbefore defined.

Still more preferably the device, e.g. OLED, comprises: (i) a substrate; (ii) an anode on said substrate; (iii) a hole injection layer on said anode; (iv) optionally an interlayer on said hole injection layer; (v) a light emitting layer on said hole injection layer or where present said interlayer; (vi) an electron injection layer on said light emitting layer; and (vii) a cathode on said electron injection layer, wherein the electron injection layer is as hereinbefore defined.

Particularly preferred devices, e.g. OLEDs, additionally comprise an interlayer.

Preferably the interlayer is in between the hole injection layer and the light emitting layer and/or in between the anode and the hole injection layer. Preferred OLEDs of the present invention comprise an interlayer in between the hole injection layer and the light emitting layer.

Preferred devices of the invention are also encapsulated to avoid ingress of moisture and oxygen. Conventional encapsulation techniques may be used. An advantage of the devices of the present invention, however, is that they are more resistant to degradation and therefore have longer lifetimes than conventional devices lacking an electron injection layer but having instead a low work function cathode.

The substrate may be any material conventionally used in the art such as glass or plastic. Optionally the substrate is pre-treated to improve adhesion thereto.

Preferably the substrate is transparent. Preferably the substrate also has good barrier properties to prevent ingress of moisture or oxygen into the device.

The anode may comprise any material with a worki unction suitable for injection of holes into the light emitting layer. Preferably the anode is transparent.

Representative examples of materials for use as a transparent anode include indium tin oxide (ITO) and indium zinc oxide (IZO). If the anode is not required to be transparent (e.g. if the cathode is transparent) then opaque conducting materials such as opaque metals may be used as the anode.

The anode may comprise a single layer or may comprise more than one layer.

For example, the anode may comprise a first anode layer and an auxiliary conductive layer between the anode and the hole injection layer such as a layer of organic conductive material between the anode and the hole injection layer.

Preferably the anode is deposited on the substrate by thermal evaporation. The anode is preferably 20 to 200 nm thick and more preferably 10 to 100 nm thick.

The hole injection layer preferably comprises a conducting material. It assists hole injection from the anode into the light emitting layer. Representative examples of materials that may be used to form the hole injection layer include PEDOT:PSS, PANI (polyaniline), polypyrole, optionally substituted, doped poly(ethylene dioxythiophene) (PEDI), in particular PEDT doped with a charge-balancing polyacid such as polystyrene sulfonate (PSS) as disclosed in EPO9O1 176 and EP0947123, polyacrylic acid or a fluorinated sulfonic acid, for example Nafion (R); polyaniline as disclosed in US 5723873 and US 5798170; and optionally substituted polythiophene or poly(thienothiophene). Other suitable materials are summarized in the book by Zigang Li and Hong Meng, Chapter 3.3 page 303 -12. Examples of conductive inorganic materials include transition metal oxides such as VO<, MO and RuO as disclosed in Journal of Physics D: Applied Physics (1996), 29(11), 2750-2753. Suitable materials for use as the hole injection layer are commercially available, e.g. from Plextronics Inc. Preferably the hole injection layer is deposited by a solution-based processing method. Any conventional solution-based processing method may be used.

Representative examples of solution-based processing methods include spin coating, gravure printing, flexographic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In preferred methods, however, depositing is by spin coating. The parameters used for spin coating the hole injection layer such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the layer.

After deposition, the hole injection layer is preferably annealed by heating, e.g. at 150 to 200 °C for 5 to 30 minutes in air.

The thickness of the hole injection layer is preferably 15 to 100 nm and more preferably 30 to 50 nm One preferred interlayer comprises a repeat unit of formula (R) as described above in relation to the charge transport polymer. Preferred repeat units are those described as preferred in relation to charge transport polymers, especially (Ri).

Further preferred interlayer polymers comprise a repeat unit of formula (S): Ar (S) wherein Ar5, Ar6 and Ar represent 05-14 aryl or C14 heteroaryl.

In preferred units of formula (S) Ar5 and Ar6 are the same. In particularly preferred repeat units Ar5 and Ar° comprise substituted or unsubstituted C514 aryl.

When present, preferred substituents for Ar5 and Ar6 include C116 alkyl and C116 alkoxy groups. Especially preferred Ar5 and Ar6 groups are unsubstituted C5 aryl.

In further preferred repeat units of formula (S), Ar comprises substituted or unsubstituted C514 awl. When present, preferred substituents for Ar include straight chain or branched C116 alkyl and C1-16 alkoxy groups. Preferably Ar is substituted, particularly preferably by a branched 026 alkyl group.

A particularly preferred repeat unit (Si) is shown below: (Si) Repeat units of formula (S) may be incorporated into interlayer polymers using monomers as described in W099/54385.

Further preferred interlayer polymers comprise a repeat unit of formula (1): A N A rQ X (1) wherein Ar7 and Ar8 represent 05-14 aryl or 05-14 heteroaryl and X' is a crosslinkable or thermosettable group.

In preferred units of formula (T) Ar' and Ar8 are the same. In particularly preferred repeat units Ar' and Ar8 comprise substituted or unsubstituted 05-14 aryl.

When present, preferred substituents for Ar7 and Ar8 include C116 alkyl and C116 alkoxy groups. Especially preferred Ar' and Ar8 groups are unsubstituted C6 aryl.

Examples of crosslinkable or thermosettable group X' in repeat unit X include moieties containing a double bond, a triple bond, a precursor capable of in situ formation of a double bond, or an unsaturated heterocyclic group. In preferred repeat units of formula (X) the crosslinkable or thermosettable group X' contains a precursor capable of in situ formation of a double bond. More preferably X' contains a benzocyclobutanyl group. Especially preferred X' groups comprise a C5-1, aryl group substituted with a benzocyclobutanyl group, particularly preferably 06 aryl substituted with a benzocyclobutanyl group.

A particularly preferred repeat unit (Ti) is shown below: (Ti) Repeat units of formula (T) may be incorporated into interlayer polymers using monomers as described in W02005/052027.

One preferred interlayer of the devices of the present invention comprise repeat units of formulae (R), (S) and (T). Particularly preferred interlayer polymers comprise repeat units of formulae (Ri), (Si) and (Ti). Especially preferred interlayer polymers comprise 40-60 %wt (Ri), 30-50% (Si) and 2.5-10 %wt (Ti).

Preferably the interlayer is deposited by a solution-based processing method.

Any conventional solution-based processing method may be used. Representative examples of solution-based processing methods include spin coating, gravure printing, flexigraphic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In preferred methods, however, depositing is by spin coating. The parameters used for spin coating the interlayer such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the layer.

After deposition, the interlayer is preferably crosslinked by heating, e.g. at 150 to 200 °C for 30 to 120 minutes in a glove box.

The thickness of the interlayer is preferably 5 to 50 nm and more preferably 10 to 40 nm.

The light emitting layer present in the devices of the present invention may comprise any conventional light emitting compound and/or light emitting polymer.

Preferably the light emitting layer comprises a light emitting polymer. The light emitter may be a red emitter or a green emitter, but is preferably a green emitter.

Preferred light emitting polymers comprise a repeat unit of formula (R) as described above in relation to the charge transporting polymer. A particularly preferred repeat unit of formula (R) for use in the light emitting polymer is (Ru) as shown below: CoHn 6 13 (Ru) Repeat units of formula (Ru) may be incorporated into charge transporting polymers using monomers as described in W02002/092723.

Preferred light emitting polymers further comprise a repeat unit formula (S) as described above in relation to the interlayer. A particularly preferred repeat unit of formula (S) is (Si) as shown above.

Further preferred light emitting polymers further comprise a repeat unit of formula (I) as described above in relation to the interlayer. A particularly preferred repeat unit of formula (T) is (Ti) as shown above.

A particularly preferred light emitting polymer is a block copolymer of the formula (RS)a(RT)b wherein a is 30-70 (e.g. 50-65) and b is 70-30 (e.g. 50-35).

Preferably R is Ru. Preferably S is Si. Preferably T is Ti.

The light emitting layer is preferably prepared by depositing a solution of the light emitting polymer on the anode or, when present the hole injection layer or interlayer. Any conventional solution-based processing method may be used.

Representative examples of solution-based processing methods include spin coating, gravure printing, flexographic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In preferred methods, however, depositing is by spin coating. The parameters used for spin coating the light emitting layer such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the light emitting layer. After depositing, the light emitting layer is preferably dried, e.g. at 100- °C in a glove box.

The thickness of the light emitting layer is preferably 40 to 350 nm and more preferably 50 to 150 nm.

The electron injection layer is preferably prepared by depositing a solution on the light emitting layer. The method is discussed in more detail above The thickness of the electron injection layer is preferably 1-20 nm. When the electron injection layer is a single layer, the thickness of the electron injection layer is preferably 1-10 nm and still more preferably 1-5 nm, e.g. less than 5 nm. When the electron injection layer is a bilayer, the thickness of the electron injection layer is preferably 1-20 nm and still more preferably 1-10 nm. When the electron injection layer comprises a plurality of layers, e.g. two layers, the first layer preferably has a thickness of 1 to 10 nm and still more preferably 1-5 nm. When the electron injection layer comprises a plurality of layers, e.g. two layers, the second layer preferably has a thickness of ito 10 nm and still more preferably 1-5 nm.

The cathode may comprise any material having a workfunction allowing injection of electrons into the active, e.g. light-emitting, layer. An advantage of the electron injection layer of the present invention is that this can be achieved even with cathodes having a relatively high workfunction. The cathode may, for example, have a workfunction in the range 2.1-5.1 eV, more preferably 2.3-4.5 eV, most preferably 2.9- 4.1 eV. Work functions of metals can be found in, for example, Michaelson, J. AppI.

Phys. 48(11), 4729, 1977. The cathode may consist of a single material such as a layer of aluminium. Alternatively, it may comprise a plurality of metals, for example a bilayer or trilayer of metals. A particularly preferred cathode comprises a layer of Al and a layer of Ag.

Advantageously, due to the presence of the electron injection layer of the present invention, the cathode does not require a thin layer of metal compound, in particular a fluoride of an alkali or alkali earth metal, to assist electron injection. Thus preferred cathodes of the present invention do not comprise [iF or NaF.

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.

Preferably the cathode is deposited on the substrate by thermal evaporation.

The cathode is preferably 100 to 400 nm thick and more preferably 200 to 350 nm thick.

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 as disclosed in, for example, WO 01/81649 or an airtight container as disclosed in, for example, WO 01/19142. 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 such a layer is in the range of 20-300 nm. A material for absorption of any atmospheric moisture and/or oxygen that may permeate through the substrate or encapsulant may optionally be disposed between the substrate and the encapsulant.

Preferred devices of the present invention have one or more of the following structural characteristics: Substrate: Glass surface Anode: ITO Anode thickness: 10 to 100 nm Hole injection layer: Polymeric charge conducting material Hole injection layer thickness: 30-50 nm Interlayer: Poymer comprising repeat units (Ri), (Si) and (Ti).

Interlayer thickness: 10 to 40 nm Light emitting layer: Block copolymer (RU-Si)60-(Ri-Ti)40 Light emitting layer thickness: 50 to 150 nm Electron injection layer: Polymer comprising repeat units (Xiv) and (Ri) and Cs2003 or polymer comprising repeat units (Xv) and (Xvi) and Cs2CO3 or polymer comprising repeat units (XvH) and TiOPrO)4 Electron injection layer thickness: 1-10 nm Cathode: Al/Ag Cathode thickness: 200 to 350 nm Preferred methods for making organic electronic devices of the present invention comprise: (i) depositing an anode on a substrate; (ü) depositing a hole injection layer on said anode; (iii) optionally depositing an interlayer on said hole injection layer; (iv) depositing a light emitting layer on said hole injection layer or where present said in terlayer; (v) depositing an electron injection layer on said light emitting layer; and (vi) depositing a cathode on said electron injection layer.

Preferably steps (ii)-(v) are carried out by solution processing. Preferably steps (i) and (vi) are carried out by thermal vapour deposition. Preferably the device is heated, e.g. at a temperature in the range 60-95 °C following fabrication. Preferably heating is carried out for 8 to 14 hours.

Organic electronic devices of the present invention which comprise an electron injection layer comprising a charge transporting polymer and a salt and/or salt precursor as hereinbefore defined are characterised by having a higher current density at 5 V than an identical device which comprises an electron injection layer comprising the same charge transporting polymer but no salt or salt precursor. Still more preferably the devices of the present invention are characterised by having a 4 times and more preferably 5 times higher current density at 5 V than the above-described comparative device.

Organic electronic devices of the present invention which comprise an electron injection layer comprising a charge transporting polymer and a salt and/or salt precursor as hereinbefore defined are characterised by having a lower drive voltage at 1000 cd/m2 than an identical device which comprises an electron injection layer comprising the same charge transporting polymer but no salt or salt precursor. Still more preferably the devices of the present invention are characterised by having a 25 %, and more preferably 30 %, lower drive voltage at 1000 cd/m2 than the above-described comparative device.

Organic electronic devices of the present invention which comprise an electron injection layer comprising a charge transporting polymer and a salt and/or salt precursor as hereinbefore defined are characterised by having a longer T5 luminance lifetime than an identical device which comprises an electron injection layer comprising the same charge transporting polymer but no salt or salt precursor. Still more preferably the devices of the present invention are characterised by having a T50 luminance lifetime that is at least 10 times, more preferably at least 100 times and still more preferably at least 300 times longer than the 150 luminance lifetime of the above-described comparative device.

The present invention therefore also relates to the use of a layer as hereinbefore defined in the preparation of an organic electronic device which has at least two of, and preferably all of, the following properties: (i) Lifetime at 1000 cd/m2: at least 1300 hours, preferably at least 1400 hours (ii) Current density (mA/cm2) at 5 V: at least 30 mA/cm2, more preferably at least 35 mA/cm2 (iii) Drive voltage (V): less than 4.5 V, more preferably less than 4 V. Particularly preferred devices have a T50 luminance lifetime of greater than 10 hours, more preferably greater than 100 hours and still more preferably greater than 1000 hours, e.g. lOto 2000 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic of a typical OLED; Figure 2 is a schematic of an OLED prepared according to the examples of the present invention; Figure 3 is a flow diagram of the method used to prepare the OLEDs in the examples of the present invention; Figure 4 shows a plot of current density (mNcm2) versus voltage (V) for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer or no electron injection layer but a low work function cathode; Figure 5 shows a plot of luminance (cd/m2) versus voltage (V) for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer or no electron injection layer but a low work function cathode; Figure 6 shows a plot of external quantum efficiency (EQE) versus voltage for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer or no electron injection layer but a low work function cathode; Figure 7 shows a plot of efficiency, measured as Lm/W, versus Luminance for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer or no electron injection layer but a low work function cathode; Figure 8 shows a plot of luminance (cd/m2) versus time (hours) for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer or no electron injection layer but a low work function cathode; Figure 9 shows a plot of luminance (cd/m2) versus log(time (hours)) for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer or no electron injection layer but a low work function cathode Figure 10 shows a plot of current density (mA/cm2) versus voltage (V) for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt and comparative devices comprising only the charge transporting polymer; Figure 11 shows a plot of luminance (cd/rn2) versus voltage (V) for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt and comparative devices comprising only the charge transporting polymer; Figure 12 shows a plot of EQE versus voltage for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt and comparative devices comprising only the charge transporting polymer; Figure 13 shows a plot of LmiW efficiency versus luminance (0dm2) for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt and comparative devices comprising only the charge transporting polymer; Figure 14 shows a plot of luminance (cd/m2) versus time (hours) for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt and comparative devices comprising only the charge transporting polymer; Figure 15 shows a plot of luminance (cd/m2) versus log (time (hours)) for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt and comparative devices comprising only the charge transporting polymer; Figure 16 shows a plot of current density (mA/cm2) versus voltage (V) for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer; Figure 17 shows a plot of luminance (cd/m2) versus voltage (V) for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer; Figure 18 shows a plot of EQE versus voltage for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer; Figure 19 shows a plot of efficiency, measured as LmiW, versus Luminance for devices having a bilayer electron injection layer of the present invention and comparative devices having an electron injection layer solely comprising a charge transporting polymer.

Figure 20 shows a plot of luminance (cd/m2) versus log (time (hours)) for devices of the invention having single blend layer EIL comprising different ratios of charge transporting polymer and salt precursor and a comparative device comprising only the charge transporting polymer; Figure 21 shows a plot of luminance (cd/m2) versus time (hours) for devices of the invention having a bilayer electron injection layer and a comparative device having no electron injection layer but a low work function cathode; and Figure 22 shows a plot of luminance (cd/rn2) versus time (hours) for devices having a bilayer electron injection layer of the present invention wherein the thickness of the salt layer is varied.

DETAILED DESCRIPTION OF THE INVENTION

A cross-section through a basic structure of a typical OLED 1 is shown in Figure 1 a. A glass or plastic substrate 2 supports a transparent anode layer 4 comprising, for example, indium tin oxide (ITO) on which is deposited a hole injection layer 6, a light emitting layer 8, an electron injection layer 10 and a cathode 12. The electron injection layer 10 is a layer of the present invention. The hole injection layer 6, which helps match the hole energy levels of the anode layer 4 and the light emitting layer 8, comprises a conductive transparent polymer. Cathode 12 comprises a bilayer of silver and aluminium. There is no need for an additional layer of sodium fluoride, and therefore the stability of the device to moisture and oxygen is increased. Contact wires 14 and 16 to the anode and the cathode respectively provide a connection to a power source 18.

In so-called bottom emitter" devices, the multi-layer sandwich is deposited on the front surface of a planar glass substrate, with the reflecting electrode layer, usually the cathode, furthest away from the substrate, whereby light generated internally in the light emitting layer is coupled out of the device through the substrate. An example of a bottom emitter 1 a is shown in Figure 1 a, where light 20 is emitted through transparent anode 4 and substrate 2 and the cathode 12 is reflective.

Conversely, in a so-called "top emitter", the multi-layer sandwich is disposed on the back surface of the substrate 2, and the light generated internally in the light emitting layer 8 is coupled externally through a transparent electrode layer 12 without passing through the substrate 2. An example of atop emitter lb is shown in Figure lb. Usually the transparent electrode layer 12 is the cathode, although devices which emit through the anode may also be constructed. The cathode layer 12 can be made substantially transparent by keeping the thickness of cathode layer less than around 50-100 nm, for example.

EXAMPLES

Materials * The substrate is glass obtained from Corning.

* The anode is indium tin oxide (ITO). The ITO was thermally deposited on the above substrate. Alternative substrates comprising ITO may be obtained from, e.g. Geomatic.

* The hole injection layer (HIL) is Plexcore© OC AQ-1200, available from Plextronics Inc. * The interlayer polymer comprises repeat units (Ri), (Si) and (Ti) described above. The ratio of the repeat units in the interlayer is 50% Ri, 42.5% Si and 7.5 % Ti. The interlayer was polymerised by Suzuki polymerisation as described in W00053656.

* The light emitting layer in the examples comprises a light emitting polymer comprising repeat units Ru, Si and Ti described above. It comprises these repeat units in the ratio (Rii-Si)30-(Rii-Ti)40. The light emitting layer was polymerised by Suzuki polymerisation as described in W00053656.

* The cathode is Al-Ag, or in some comparative examples NaF-Al-Ag. Sodium fluoride (in powder form), aluminium and silver wires were all obtained from Sigma Aldrich.

* Three different charge transporting polymers were prepared as follows.

Charge transporting polymer A (CTP A) comprising repeat units (Xiv) and (Ri) described above. The polymer was polymerised by Suzuki polymerisation as described in W00053656.

Charge transporting polymer B (CTP B) comprising repeat units (Xv) and (Xvi) described above. The polymer was polymerised by Suzuki polymerisation as described in W00053656.

Charge transporting polymer C (CTP C) comprising repeat units (Xvii) described above. The monomers were prepared by the method described in U52012/0181529. The polymer was polymerised by Suzuki polymerisation as described in U5201 2/0181 529.

* The salt present in the electron injection layer is Cs2CO3. The Cs2CO3 was obtained from Sigma Aldrich.

* The salt precursor present in the electron injection layer is Ti(iPrO)4. It was obtained from Sigma Aldrich.

Preparative Example for the Fabrication of Organic Light Emitting Diodes A device having the structure shown in Figure 2 was prepared. The preparative process used is set out in the flow diagram in Figure 3.

(i) Depositing and Cleaning of ITO Anode The ITO anode was deposited on a glass substrate by thermal deposition. The ITO anode was then cleaned in a UV-ozone generator (15 minutes in a USHIO UV ozone generator). The thickness of the anode is 45 nm.

(ii) Spin Coating and Thermal Annealing of HIL The HIL was deposited by spin-coating Plexcore © OC AQ-1200, available from Plextronics, Inc., from water in air, to a thickness of 35 nm. The HIL was thermally annealed at 170 °C for 15 minutes in air.

(iii) Spin Coating and cross-linking of IL The IL was deposited by spin-coating the interlayer polymer, from a 0.6 wt% concentration solution in o-xylene. The IL was thermally cross-linked at 180 °C for 60 minutes in a glove box (examples 1-6) or for 200 °C for 15 minutes in a glove box (examples 7-19). The final IL has a thickness of 22 nm (iv) Spin Coating of Light emitting layer In examples 1-6 and 13-16 the light emitting layer was deposited by spin-coating the light emitting polymer, from a 0.8 wt% concentration solution in o-xylene. The light emitting layer was dried at 100 °C for 10 minutes in a glove box. The final light emitting layer has a thickness of 60 nm. In examples 7-12 the light emitting layer was deposited by spin-coating the light emitting polymer, from a 1.2 wt% concentration solution in o-xylene. The light emitting layer was dried at 100 °C for 10 minutes in a glove box. The final light emitting layer has a thickness of 79 nm. In example 17 the light emitting layer was deposited by spin-coating the light emitting polymer, from a 0.8 wt% concentration solution in o-xylene. The light emitting layer was dried at 100 °C for minutes in a glove box. The final light emitting layer has a thickness of 60 nm. In example 18 the light emitting layer was deposited by spin-coating the light emitting polymer, from a 1.2 wt% concentration solution in o-xylene. The light emitting layer was dried at 100 °C for 10 minutes in a glove box. The final light emitting layer has a thickness of 80 nm. In example 19 the light emitting layer was deposited by spin-coating the light emitting polymer, from a 1.2 wt% concentration solution in o-xylene.

The light emitting layer was dried at 100 CC for 10 minutes in a glove box. The final light emitting layer has a thickness of 80 nm.

(v) Spin coating of EIL The process used for spin coating the EIL varied depending on the form of the EIL and the materials present in the FIL.

BilayerElL

Examples 1-6

The first layer of the EIL was deposited by spin-coating of the charge transporting polymer from either a 1.0 wt% concentration solution in methanol (for CTP A) or from a 0.6 wt% concentration solution in DMSO (for CTP B). The polymer layer was dried at 120 CC for 10 minutes in a glove box. The second layer of Cs2CO3 was deposited by spin coating from a 0.1 wt% solution in methanol after drying of the charge transporting polymer layer. The Cs2CO3 layer was dried at 120 CC for 10 minutes in a glove box. The first layer of charge transporting polymer was 10 nm thick, and the layer of Cs2CO3 was 5 nm.

For comparative devices wherein the EIL solely comprises a charge transporting polymer layer, the EIL was deposited in the same way as the first layer of the above bilayered EIL. It was 10 nm thick.

Examples 13-16

The first layer of the EIL was deposited by spin-coating of the charge transporting polymer from 1.0 wt% concentration solution in DMSC. The polymer layer was dried at 120 CC for 10 minutes in a glove box. The thickness of the first charge transporting polymer layer was 5 nm. The second layer of 0s2003 was deposited by spin coating after drying of the charge transporting polymer layer. To vary the thickness of the Cs2CO3 layer various concentrations of Cs2CO3 solution in butoxyethanol were used (shown in the Table below) while keeping the spin speed constant.

Cs2CO3 solution Solvent Concentration (wt%) Solution A Butoxyethanol 0.2 Solution B Butoxyethanol 0.1 Solution C Butoxyethanol 0.05 The 052003 layer was dried at 120 °C for 10 minutes in a glove box. The thickness of the Cs2003 layer deposited from Solution A was 5 nm. Layers of Cs2003 deposited from Solution B and Solution C both had thickness smaller than 5nm and the CsCO3 layer deposited from Solution C was thinner than the Cs2003 layer deposited from Solution B). The thickness of Cs2CO3 layers deposited from Solution B and Solution C could not be measured reliably by the standard cleanroom equipment (Dektak).

For comparative devices wherein the EIL solely comprises a charge transporting polymer layer, the EIL was deposited in the same way as the first layer of the above bilayered EIL. The thickness of the layer was Snm.

Example 18: 0W-B

The first layer of the EIL was deposited by spin-coating of the charge transporting polymer from a 0.6 wt% concentration solution of CTP B in DM50. The polymer layer was dried at 120 °C for 10 minutes in a glove box. The second layer of Cs2CO3 was deposited by spin coating from a 0.2 wt% solution in butoxyethanol after drying of the charge transporting polymer layer. The 0s2003 layer was dried at 120 °C for 10 minutes in a glove box. The first layer of charge transporting polymer was 5 nm thick, and the layer of 053003 was 5 nm.

Example 18: 0W-A

The first layer of the EIL was deposited by spin-coating of the charge transporting polymer from a 1.0 wt% concentration solution of CTP A in methanol. The polymer layer was dried at 120 °C for 10 minutes in a glove box. The second layer of 0s2003 was deposited by spin coating from a 0.2 wt% solution in butoxyethanol after drying of the charge transporting polymer layer. The 052003 layer was dried at 120 °C for 10 minutes in a glove box. The first layer of charge transporting polymer was 10 nm thick, and the layer of Cs2CO3 was 5 nm.

Example 19

The first layer of the ElLs was deposited by spin-coating of the charge transporting polymer from a 1.0 wt% concentration solution of OW B in DM50. The polymer layer was dried at 120 °C for 10 minutes in a glove box. The second layer of Cs2CO3 was deposited by spin coating from 0.2 wt%, 0.lw%, and 0.05w% solutions in butoxyethanol respectively, after drying of the charge transporting polymer layer. The Cs2003 layer was dried at 120 CC for 10 minutes in a glove box. The first layer of charge transporting polymer was 5 nm thick, and the layers of Cs2CO3 were estimated to be around 5nm, 2.5nm, and 1.5nm thick.

Blended single layer EIL

Examples 7-12

A blended ElL comprising a homogenous mixture of CTP B and 052003 was deposited by spin-coating of a mixture of 1.0 wt% concentration CTP B in DMSO and a 0.2 wt% concentration of Cs2CO3 in 2-butoxyethanol. The ratio of CTP B:0s2C03 solutions was between 1:1 and 1:3 by volume as described in example 7. The layer was dried at 120 00 for 10 minutes in a glove box. This blended EIL was spun to a thickness of 7 nm except in one experiment (as indicated) where the thickness is 6 nm.

For comparative devices wherein the EIL solely comprises a charge transporting polymer layer, the EIL was deposited by spin-coating of the charge transporting polymer CTP B from a 1.0 wt% concentration solution in DMSO. The polymer layer was dried at 120 °C for 10 minutes in a glove box. The resulting thickness was 5 nm.

Example 17

For the comparative device with 6nm OTP-C only: EIL was deposited by spin-coating of the CTP-C polymer from a 0.lw% concentration solution in methanol in a glove box. The polymer layer was dried at 120 °C for 10 minutes in a glove box. The resulting EIL layer was 6 nm thick.

For devices with TiOPrO)4:CTP-C blends (40:60, 60:40, and 80:20 w%) in methanol: The EILs were deposited in the same way as the EIL of the above comparative EIL, from 0.lw% solutions in MeCH, in a glove box. After drying in the glove box, their film thickness was estimated to be less than 5 nm.

In order to vary the Ti(iPrO)4:CTP-C ratio, various concentration ratios of Ti(iPrO)4:CTP-C in methanol were used (shown in the Table below), whilst keeping the combined weight of Ti(iPrO)4 and 0W-C at 0.1w%: Solution Ti(iPrO)4: CTP-C only Combined weight ratio concentration (wt%) CTP-C only CTP-C only 0.1 Solution A 40:60 0.1 Solution B 60:40 0.1 Solution C 80:20 0.1 (vi) Deposition of cathode The cathodes are blanket-deposited by successive thermal evaporation of, when present 2 nm NaF, followed by lOOnm Al, and then followed by lOOnm Ag.

Testing of OLED Device Current, voltage, and luminance drive characteristics are collected for device performance screening using characterised silicon photodiodes and device spectral output characteristics collected using a calibrated spectrometer system and collection optics. The device is typically swept through a voltage range, and IVL data curves are collected, the condition, timings and parameters under which measurements are made are controlled. Refined drive characteristics are collected using traceably calibrated, industry standard, photometry, colour measurement systems, power supplies and meters.

Life time is screened using photodiode based measuring systems, these monitor the device luminance and applied voltage, while it being driven by calibrated power supplies under specified conditions (constant current). The environmental conditions under which tests are carried out are stringently controlled.

Example 1

Devices were prepared according to the above methods and with an EIL and cathode as described in the table below. The charge transporting polymer A was used.

The current density vs. voltage of each of these devices was measured, and the results are shown in Figure 4 and Table 1.

EIL Composition Cathode Median J (mA/cm2) @ 5V no EIL (control) NaF-Al-Ag 37.8 Charge transporting polymer Al-Ag 5.5 A layer 1st layer: charge transporting Al-Ag 35.6 polymer A 2nd layer: Cs2CO3

Table 1

It can be seen that devices with an EIL comprising solely charge transporting polymer A have significantly lower current densities than those with no EIL and a low work function cathode. However, the device with an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2CO3 demonstrates a vastly improved current density that is almost equal to the device with the low work function cathode (35.6 and 37.6 mA/cm2 © SV, respectively).

Moreover the device comprising a first layer of charge transporting polymer A and a second layer of Cs2CO3 has a much faster turn-on than the device with the EIL solely comprising charge transporting polymer. This suggests a change in mechanism for electron injection. It is thought that the Cs2CO3 layer may create a n-doped interface to the underlying polymer layers allowing for rapid turn-on. In contrast in devices with an EIL solely comprising a charge transporting polymer it is thought that the interface to the cathode is not n-doped and instead that slower electron injection occurs by band-bending.

Example 2

The same devices as described above in Example 1 were compared in terms of Luminance vs. voltage. The results are shown in Figure 5 and Table 2 below.

EIL Composition Cathode Median V @ 1000 Cd/rn2 no EIL (control) NaF-Al-Ag 3.4 Charge transporting polymer Al-Ag 5.3 A layer Vt layer: charge transporting Al-Ag 3.8 polymer A 2 layer: Cs2CO3

Table 2

It can be seen that devices with an EIL solely comprising a charge transporting polymer require a significantly higher drive voltage than the control device (5.3V © 1000 Cd/rn2 compared with 3.4V in the control). However, the device with an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2003 displays a significantly reduced drive voltage of 3.8V, which is almost equal to the control device containing a low work function cathode.

Example 3

The devices described in Example 1 were compared in terms of their External Quantum Efficiency (EQE) vs. Voltage characteristics. The results are shown in Figure 6 and in Table 3 below.

EIL Composition Cathode Median EQE @ 1000 Cd/rn2 no EIL (control) NaF-Al-Ag 5.4 Charge transporting polymer Al-Ag 3.9 A layer 1st layer: charge transporting Al-Ag 4.0 polymer A 2 layer: 052003

Table 3

Although the devices with an EIL solely comprising a charge transporting polymer and an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2CO3 have similar maximum EQE values of 3.9 and 4.0 respectively, it can be seen from Figure 6 that they display quite different EQE vs. V characteristics.

The device with the EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2CO3 has a lower turn-on voltage than the device comprising an EIL solely of charge transporting polymer. This suggests a change in mechanism for electron injection as discussed above. It can also be seen that the device comprising an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2003 also displays much slower roll-off at high voltages.

Example 4

The devices described in Example 1 were compared in terms of their efficiency, measured as LmiW as a function of Luminance. The results are shown in Figure 7 and

Table 4.

EIL Composition Cathode Median Lm/W @1000 Cd/m2 no EIL (control) NaF-Al-Ag 17.5 Charge transporting polymer Al-Ag 8.1 A layer Vt layer: charge transporting Al-Ag 11.6 polymer A 2nd layer: Cs2CO3

Table 4

It can be seen from the results that the device comprising an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2CC3 has a higher LmiW efficiency than the device having an EIL solely comprising an electron transport polymer A. This is a result of the lower drive voltages required, as illustrated in Example 2. The lower LmiW efficiency of the device an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2CO3 in comparison to the control device with a low work function cathode is a result of the higher FOE of the latter device. This could potentially be offset by optimising the charge carrier balance of the device containing an EIL comprising a first layer of charge transporting polymer A and a second layer of Cs2CO3.

Example 5

This example shows comparative data for devices containing EIL5 comprising different charge transporting polymers, specifically A and B. The data for comparative devices lacking an EIL (with NaF cathode) or lacking a Cs2CO3 layer is also presented.

The results are shown in Table 5.

EIL Cathode V@ V EQE@ EQE LmIW J Composition 100 1000 1000 @ @ 1000 5V Cd/rn2 Cd/m2 Cd/m2 Max Cd/rn2 Elf no EIL (control NaF-Al-2.6 3.4 5.4 5.4 17.5 37.8 with NaF) Ag Charge Al-Ag 4.5 5.9 2.7 2.8 5.0 3.2 transporting polymer B 1st layer: charge Al-Ag 2.6 3.5 4.2 4.3 13.0 36.3 transporting polymer B 2 layer: Cs2CO3 Charge Al-Ag 4.0 5.3 3.9 4.2 8.1 5.5 transporting polymer A 1st layer: charge Al-Ag 2.6 3.8 4.0 4.1 11.6 35.6 transporting polymer A 2nd layer: Cs2CC3

Table 5

It can be soon from the table that devices comprising an EIL comprising a first layer of charge transporting polymer A or B and a second layer of Cs2CO3 perform very similarly.

Example 6

This example demonstrates the Luminance vs. Time characteristics of the following devices prepared as described above: No EIL/NaF-Al-Ag cathode (control) EIL comprising solely of charge transporting polymer B/Al-Ag cathode (comparative) EIL comprising a first layer of charge transporting polymer B and a second layer of Cs2003.

The results are shown in Figures 8 and 9. It can be seen that devices containing an EIL comprising solely of charge transporting polymer B have very short lifetimes (LT5O% of around 4 hours). In contrast, the device having an EIL comprising a first layer of a charge transporting polymer and a second layer of Cs2CC3 display lifetime characteristics which are significantly better. Notably the lifetime of these latter devices is even better than the control device with no EIL and a low work function cathode. This represents a major advantage over such devices.

Example 7

Devices were prepared according to the above methods and with an EIL and cathode as described in the table below. The charge transporting polymer B was used.

The EILs are single blend layers. Devices were prepared with different ratios of charge transporting polymer to 052003 and the variance in Intensity vs Wavelength measured.

Exp. CTP B at 1% in Cs2003 at 0.2% in Final CTP Final CTP No. DMSO (ml) 2-butoxyethanol (ml) B wt% 052003 B:Cs2CO3 wt% ratio 1 2 6 0.25 0.15 1.6:1 3 2 4 0.33 0.13 2.5:1 2 2 0.5 0.10 5:1 The results show that despite variation in the amount of 0s003 present in the EILs of the devices that all devices have similar electroluminescent properties.

For control devices wherein the EIL solely comprises a charge transporting polymer layer, the EIL was deposited by spin-coating of the charge transporting polymer CTP B from a 1.0 wt% concentration solution in DMSO. The resulting thickness was 5 nm.

Examples

Devices were prepared as described in example 7, including the control device.

The current density vs. voltage of each of these devices was measured and the results are shown in Figure 10 and Table 6.

Exp. No. Final CTP B Final Cs2003 CTP Median J wt% wt% B:Cs2003 ratio (mA/cm2) @ 5V Control: CTP 13.4 B only 1 0.25 0.15 1.6:1 8.4 3 0.33 0.13 2.5:1 11.9 0.5 0.10 5:1 10.9

Table 6

It can be seen from the table that the highest current densities were achieved with the devices having single blend-layer EILs comprising 2.5:1 CTP:Cs2CO3. The control devices with CTP B-only EILs showed higher current densities than the devices with single blend-layer EILs.

Example 9

In this example, the devices prepared as in example 7 were compared in terms of Luminance vs. Voltage. The results are shown in Figure 11 and Table 7.

Exp. No. Final CTP Final CTP Average V @ B wt% Cs2CO3 B:Cs2CO3 1000 Cd/rn2 wt% ratio Control: CTP B only 4.6 1 0.25 0.15 1.6:1 4.9 3 0.33 0.13 2.5:1 4.6 0.5 0.10 5:1 4.7

Table 7

It can be seen from the table that there is little variation between the devices.

As in example 8, the best performance (i.e. lowest drive voltage) was achieved with the devices having EILs comprising 2.5:1 CTP:Cs2CO3.

Example 10

Devices were prepared as in example 7 and their efficiency measured in terms of EQE vs. Voltage. The results are shown in Figure 12 and TableS.

Exp. No. Final CTP B Final CTP Average wt% Cs2003 B:Cs2003 ratio EQE @ wt% 1000 Cd/rn2 Control: 3.6 CTP B only 1 0.25 0.15 1.6:1 4.1 3 0.33 0.13 2.5:1 4.3 0.5 0.10 5:1 4.0

Table 8

It can be seen from Table 8 that all of the devices measured have similar EQE vs. Voltage characteristics. The devices having EILs comprising 2.5:1 CTP:Cs2003 yielded the highest EQE maxima.

Example 11

In this example, devices as described in Example 7 were compared in terms of their [mM vs. Luminance characteristics. The results are shown in Figure 13 and

Table 9.

Exp. No. Final CTP B Final Cs2CO3 CTP B:Cs2CO3 Average wt% wt% ratio Lm/W © 1000 CdIm2 Control: CTP 8.8 B only 1 0.25 0.15 1.6:1 9.3 3 0.33 0.13 2.5:1 10.2 0.5 0.10 5:1 9.4

Table 9

It can be seen that the highest [mM efficiency was measured for the devices having EILs comprising 2.5:1 CTP:Cs2CO3.

Example 12

In this example, the lifetime of devices described in example 7 were compared by measuring their Lm/W vs. Voltage characteristics. As can be seen in Figures 14 and 15 there is a trend in device lifetime as a function of Cs2003, with the shortest lifetime device containing the least Cs2CO3 and vice versa.

Example 13

Devices were prepared according to the above methods and with an FIL and cathode as described in the table above. The charge transporting polymer B was used.

The current density vs. voltage of each of these devices was measured, and the results are shown in Figure 16 and Table 10.

B

1 layer: charge transporting polymer B Al-Ag 6.7 2nd layer: Cs2CO3 deposited from solution

A

1 layer: charge transporting polymer B Al-Ag 11.8 2Hd layer: Cs2CO3 deposited from solution

B

1 layer: charge transporting polymer B Al-Ag 24.9 2nd layer: Cs2CO3 deposited from solution

C

Table 10

It can be seen that devices with an EIL comprising solely charge transporting polymer B have the lowest current densities. However, the devices with an FIL comprising a first layer of charge transporting polymer B and a second layer of Cs2003 demonstrates a vastly improved current density. The current density improvement becomes more significant with decreasing 0s2003 solution concentration (and accordingly decreasing the Cs2CO3 layer thickness).

Moreover the device comprising the first layer of charge transporting polymer B and a second layer of Cs2CO3 has a much faster turn-on that the device with the EIL solely comprising charge transporting polymer. This suggests a change in mechanism for electron injection. It is thought that the 082003 layer may create an n-doped interface to the underlying polymer layers allowing for rapid turn-on. In contrast in devices with an EIL solely comprising a charge transporting polymer it is thought that the interaction to the cathode does not result in the n-doping and instead that slower electron injection occurs by band-bending.

Example 14

The same devices as described above in Example 13 were compared in terms of Luminance vs. voltage. The results are shown in Figure 17 and Table 11 below.

EIL Composition Cathode Median V @ 1000 Cd/m2 Single layer: charge transporting polymer Al-Ag 5.8

B

layer: charge transporting polymer B Al-Ag 5.1 2 layer: Cs2003 deposited from solution

A

1 layer: charge transporting polymer B Al-Ag 4.5 2nd layer: Cs2CO3 deposited from solution

B

1 layer: charge transporting polymer B Al-Ag 3.7 2 layer: Cs2003 deposited from solution

C

Table 11

It can be seen that devices with an EIL solely comprising a charge transporting polymer require a significantly higher drive voltage than devices with an EIL comprising a first layer of charge transporting polymer B and a second layer of 0s2003. Drive voltage decreases with decreasing Cs2CO3 solution concentration (and accordingly decreasing the Cs2CO3 layer thickness) reaching 3.7V © 1000 Cd/m2 in devices with Cs2003 deposited form Solution C (compared with 5.SV in devices with the single layer of charge transporting polymer B).

Example 15

The devices described in Example 13 were compared in terms of their External Quantum Efficiency (EQE) vs. Voltage characteristics. The results are shown in Figure 18 and in Table 12 below.

EIL Composition Cathode Median EQE @ 1000 Cd/rn2 Single layer: charge transporting polymer Al-Ag 2.8

B

1 layer: charge transporting polymer B Al-Ag 3.7 2 layer: Cs2CO3 deposited from solution

A

1 layer: charge transporting polymer B Al-Ag 4.3 2 layer: Cs2CO3 deposited from solution

B

1 layer: charge transporting polymer B Al-Ag 4.7 2 layer: Cs2CO3 deposited from solution

C

Table 12

It can be seen that devices with an EIL solely comprising a charge transporting polymer have the lowest EQE of 2.8% @ 1000 Cd/m2. Devices with an EIL comprising a first layer of charge transporting polymer B and a second layer of Cs2CO3 have higher EQE increasing from 3.7% (0s2003 deposited from Solution A) to 4.7% (Cs2003 deposited from Solution A) with decreasing Cs2003 solution concentration (and accordingly decreasing the Cs2CO3 layer thickness).

It can also be seen from Figure 18 that devices with an EIL solely comprising a charge transporting polymer and an EIL comprising a first layer of charge transporting polymer B and a second layer of Cs2CO3 display quite different EQE vs. V characteristics. The device with the EIL comprising a first layer of charge transporting polymer B and a second layer of Cs2CO3 (especially deposited from Solution C) has a lower turn-on voltage and more flat dependence of EQE on the voltage than the device comprising an EIL solely of charge transporting polymer. This suggests a change in mechanism for electron injection as discussed above and better balance between electron and hole currents.

Example 16

The devices described in Example 13 were compared in terms of their efficiency, measured as LmiW as a function of Luminance. The results are shown in Figure 19 and Table 13.

B

1 layer: charge transporting polymer B Al-Ag 7.8 2 layer: Cs2CO3 deposited from solution

A

1 layer: charge transporting polymer B Al-Ag 10.4 2 layer: 052003 deposited from solution

B

1 layer: charge transporting polymer B Al-Ag 13.9 2Hd layer: Cs2003 deposited from solution

C

Table 13

It can be seen from the results that the devices comprising an EIL comprising a first layer of charge transporting polymer B and a second layer of 082003 has a higher Lm/W efficiency than the device having an EIL solely comprising an electron transport polymer A. Similarly to the previous examples, Lm,W efficiency increases with decreasing Cs2CO3 solution concentration (and accordingly decreasing the 0s2003 layer thickness). This is a result of the lower drive voltages required, as illustrated in

Example 14.

Example 17

It can be seen from Figure 20 that the use of CTP-C alone does not result in bright-waving, whereas addition of 60w% Ti(iPrO)4 results in a strong transient increase in luminance, in combination with an increase of the T90% lifetime from.clohrs for CTP-C only to >lOhrs. Adding only 40w% Ti(iPrO)4 does not result in the transient luminance increase, but still improves the T90% lifetime to a value similar to the one achieved with 60w% Ti(iPrC)4. Increasing the Ti(iPrO)4 content to 80w% results in shorter T90 lifetimes with respect to CTP-C only.

Example 18

It can be seen from Figure 21 that in contrast to the NaF control device which degrades without bright-waving, bilayer EILs with Cs2003 and either CTP A and CTP B show transient luminance variations. The bright-waving effect is most pronounced in the case of CTP B, whereas the second bright wave is much less pronounced in the case of CTP A. Despite the differences in amplitude of the bright waves produced by CW A and CTP B, the effect results in strongly increased operational lifetimes in comparison to the NaF control device that does not show bright waving.

Example 19

It can be seen from Figure 22 that increasing the thickness of the Cs2CO3 layer results in larger luminance variations during bright waving, and correspondingly longer operational lifetimes.

The results obtained in examples 17-19 suggest that bright-waving may involve a mechanism wherein an initial diffusion of Cs cations into the light emitting layer (the driving force for this diffusion being complex formation between the electron-rich units in the LEP and the Cs cations) results in the formation of electron traps and partial quenching of electroluminescence. This effect is therefore a slow, bulk effect. When the device is subsequently turned on, application of the forward bias is thought to pull the Cs cations out of the LEP layer, thereby reducing the number of electron traps and quenching sites, which then results in a transient luminescence increase (i.e. bright-waving). This is supported by the fact that increasing the amount of Cs2CO3 at the electron injection layer-light emitting polymer interface by increasing the thickness of the salt layer results in stronger bright-waving (example 19). Likewise in example 18, Cs2CO3 on top of lOnm CTP A results in less bright-waving than Cs2CO3 on top of 5nm CTP B. This result suggests that increasing the thickness of the underlying charge transport polymer may result in less diffusion of Cs-cations into the LEP due to the CTP acting as diffusion barrier. In addition, CTF A may be a belier barrier against the diffusion of Cs-cations than CTP B as a consequence of its chemical composition.

Moreover example 17 shows that CTP C, which comprises Cs cations its structure, does not result in bright-waving. This suggests that in case of ElLs with Cs2CO3, it is not just the Cs-cations that diffuse into the LEF, but rather Cs:C03 ion pairs. In the case of CTF C, the anions are attached to a polymer backbone and can therefore not diffuse into the LEP layer. Diffusion of Cs-cations alone would result in the formation of ionic space charges which would self-limit such as process. Addition of Ti(iPrO)4 to CTP C is thought to lead to at least partial hydrolysis of the Ti(iPrO)4 and formation of Ti-OH bonds. Due to the high oxidation state of Ti(IV), such Ti-OH groups are acidic, and the resulting orthotitanic acid or titanium hydroxide (H4TiO4) generates mobile protons and titanate anions. The presence of mobile titanate anions would then enable Cs-titanate ion pairs to diffuse into the LEF, thereby enabling bright-waving effects similar to the ones observed with Cs2CO3-containing EILs.

Claims

CLAIMS: 1. A layer for an organic electronic device comprising: a charge transporting polymer; and a salt and/or a salt precursor, wherein said charge transporting polymer comprises polar side chains.
2. A layer as claimed in claim 1, which is an electron injection layer.
3. A layer as claimed in claim 1 or 2, which is homogeneous.
4. A layer as claimed in any one of claims 1 to 3, wherein said layer is solution processed.
5. A layer as claimed in claim 1 or 2, comprising: a first layer comprising a charge transporting polymer; and a second layer comprising a salt and/or a salt precursor.
6. A layer as claimed in claim 5, which is a bilayer.
7. A layer as claimed in claim 5 or6, wherein said first layer is solution processed.
8. A layer as claimed in any one of claims 5 to 7, wherein said second layer is solution processed.
9. A layer as claimed in any preceding claim, wherein said charge transporting polymer comprises a repeat unit of formula (Xa) or (Xb):I(I) CI) (I) a h (Xa) a (Xb) wherein Ar is a C520 substituted or unsubstituted aryl or heteroaryl group; L is a bond or a linker group; A is a polar group; B is a polar group, hydrogen, substituted or unsubstituted C1-16 alkoxy, substituted or unsubstituted C514 aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted C514 heteroaryl, substituted or unsubstituted heteroarylalkyl and substituted or unsubstituted alkyl wherein one or more non-adjacent C atoms may be replaced with -0-, -Nfl-, -NH-, -S-, -COO-, -NHCO-, -NHSO2-, -NHCOO-groups wherein P is C18 alkyl; and each of a and b are independently an integer selected from 1 to 5.
10. A layer as claimed in any preceding claim, wherein said charge transporting polymer comprises repeat units of formula (Xi): (Xi) wherein L is a bond or a linker group; A is a polar group; and B is A, hydrogen, substituted or unsubstituted C116 alkoxy, substituted or unsubstituted C514 aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted C514 heteroaryl, substituted or unsubstituted heteroarylalkyl and substituted or unsubstituted alkyl wherein one or more non-adjacent C atoms may be replaced with -0-, -NP- -NH-, -S--COO-, -NHCO-, -NHSO2, -NHCOO-groups wherein R is C18 alkyl; and each of a and b are independently an integer selected from 1 to 5
11. A layer as claimed in claim 9 or 10, wherein (B)b is (A)a.
12. A layer as claimed in any one of claims 9 to 11, wherein L is a linker group selected from substituted or unsubstituted C514 aryl, substituted or unsubstituted C514 heteroaryl and substituted or unsubstituted C116 alkyl wherein one or more non- adjacent C atoms may be replaced with -0-, -NR-, -NH-, -S-, -COO-, -NHCO-, -NHSO2-, -NHCOO-groups wherein R is C18 alkyl.
13. A layer as claimed in any one of claims 9 to 12, wherein said charge transporting polymer comprises a repeat unit of formula (Xii) or (Xiii): A A (Xu) a (Xiii) wherein n is an integer between 1 and 16.
14. A layer as claimed in any one of claims 9 to 13, wherein A comprises a zwitterionic group.
15. A layer as claimed in claim 14, wherein said zwitterionic group comprises a positively charged N, P, 0 or S atom.
16. A layer as claimed in claim 14 or 15, wherein said zwitterionic group comprises a sulfonate, sulfinate, sulfite, thiosulfate, thiosulfonate, phosphate, phosphite, phosphonate, thiophosphate, thiophosphonate, orthophosphate, pyrophosphate, polyphosphate, carboxy, thiocarboxy or alkoxy group.
17. A layer as claimed in any one of claims 14 to 16, wherein said zwitterionic group is of formula (Q: /\2 A (i) wherein Z is N, A, 0 or S; fl1 is substituted or unsubstituted C18 alkyl, substituted or unsubstituted C alkenyl, substituted or unsubstituted 05-14 aryl or substituted or unsubstituted C514 heteroaryl; R2 is present when 7 is N or P and is R1; R3 is a C110 alkylene chain in which non-adjacent carbon atoms may optionally be replaced by -0-, -Nfl-, -NH-, -S-, -COO-, -NHCO-, -NHSO2-, -NH000-groups wherein P is C18 alkyl; and Y is S0, S02, 0S02, SS03, S02S, C02, P03, 0P032, OP(0R)0 where P is C15 alkyl, CP(S)022-, P(S)022-, OPO(OH)OPC(OH)0, O-(PC(OH)C)PO(OH)C wherein n is 1 to 6, CO2H C(S)0, or 0 group.
18. A layer as claimed in any one of claims 9 to 13, wherein said polar group is a non-charged polar group comprising at least one moiety selected from -NHCO-, - NHSO2-, -COO-, -0000-, -NH000, -0-, -Nfl-, -NH-, -NO-, -S-, -CF2-and -0012-wherein P is C18 alkyl.
19. A layer as claimed in claim 18, wherein said polar group is of formula (H): 4M M A4 wherein M is 0, NR, NH, S or CO wherein R is C15 alkyl; QisBr,Cl,F,lorH; I is Br, Cl, F, I or H; o is an integer from 1 to 4; p is an integer from ito 16; and P4 is H or C alkyl.
20. A layer as claimed in any one of claims 9 to 13, wherein said polar group is an ionic group.
21. A layer as claimed in claim 20, wherein said ionic group comprises a covalently bound anion selected from S03, S02, 0S02, SSO, S02S, C02, P03, 0P032, OP(OR)0 where R is alkyl, OP(S)022, P(S)022, OPO(OH)OPO(OH)0, 0- (P0(0H)0)P0(0H)0 wherein n is 1 to 6, C02, C(S)0, or 0.
22. A layer as claimed in claim 20, wherein said anion is C02.
23. A layer as claimed in any one of claims 20 to 22, wherein said ionic group comprises a cation selected from Lie, Na, K4, Rb, Cs, Be2, Mg2, Ca2, Sr2 and Ba2
24. A layer as claimed in any preceding claim, wherein said charge transporting polymer comprises a repeat unit of formula (Xiv), (Xv),(Xvi) or (Xvii): S0 (Xiv) p=8 \(Xv) j (Xvi) osc,c, c.5" o co + H3O(H2OH2C)3O C(0H20H20)30H3 (Xvii)
25. A layer as claimed in any preceding claim, comprising a salt.
26. A layer as claimed in any preceding claim, wherein said salt comprises a cation.
27. A layer as claimed in claim 26, wherein said cation is an alkali metal or an alkaline earth metal.26. A layer as claimed in claim 26 or 27, wherein said cation is selected from LL, Nat, K, RV, Cs, Be2, Mg2, Ca2, Sr2 and Ba2.29. A layer as claimed in any preceding claim, wherein said salt comprises an anion selected from hydroxide, halide, titanate, C14 alkoxide, C14 carboxylate, 01-4 halocarboxylate, 01-4 diketonate, perhalogenate, nitrate and 01-4 phosphate.30. A layer as claimed in claim 29, wherein said anion is a C14 carboxylate.31. A layer as claimed in any preceding claim, wherein said salt is 052003.32. A layer as claimed in any preceding claim, comprising a salt precursor.33. A layer as claimed in claim 32, wherein said salt precursor comprises titanium.34. A layer as claimed in claim 32 or 33, wherein said salt precursor is Ti(iPrO)4.35. A blend comprising a charge transporting polymer and a salt and/or a salt precursor, wherein said charge transporting polymer comprises polar side chains.36. A blend as claimed in claim 35, wherein said charge transporting polymer is as defined in any one of claims 9 to 24.37. A blend as claimed in claim 35 or 36, wherein said salt is as defined in any one of claims 26 to 31.38. A blend as claimed in claims 35 or 36, wherein said salt precursor is as defined in any one of claims 32 to 34.39. An organic electronic device comprising a layer as defined in any one of claims 1to34.40. A device as claimed in claim 39, which is an organic light emitting device and said layer is an electron injection layer.41. A device as claimed in claim 39 or 40 comprising: (i) an anode; (ii) a light emitting layer; (iii) an electron injection layer; and (iv) a cathode, wherein said electron injection layer is as defined in any one of claims 1 to 34.42. A device as claimed in any one of claims 40 to 41, wherein said cathode has a 43. Use of a layer as defined in any one of claims 1 to 34 in the preparation of an organic electronic device, wherein said device has at least two of the following properties: (i) Lifetime at 1000 cd/rn2: at least 1300 hours, (ii) Current density (mA/cm2) at 5 V: at least 30 mA/cm2, (iii) Drive voltage (V) at 1000 Cd/m2: less than 4.5 V. 44. A method of making a layer of an organic electronic device as defined in any one of claims 1 to 4 and 9 to 34 comprising: depositing a solution of a charge transporting polymer and a salt and/or a salt precursor to form said layer.45. A method as claimed in claim 44, wherein said solution comprises a solvent selected from DMF, dimethylacetamide, N-methyl-2-pyrrolidone, DMSO, acetone, butanone, pentanone, methyl butyl ketone, diethyl ether, methyl t-butyl ether, THE, acetonitrile, phenyl acetate, ethyl acetate, triethylphosphate, a,ct,a,-trifluorotoluene, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3-methylbutan-1 -ol, 2-methylbutan-1 -ol, 2,2-dimethylpropan-1 -ol, pentan-3-ol, pentan-2-ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane or 2-butoxyethanol or mixtures thereof.46. A method of making a layer of an organic electronic device as defined in any one of claims 1, 5 to 8 and 9 to 34 comprising: (i) depositing a solution of a charge transporting polymer to form a first layer; and (ii) depositing a solution of salt and/or a salt precursor to form a second layer on said first layer.47. A method as claimed in claim 46, wherein said solutions of charge transporting material and salt and/or salt precursor comprise a solvent selected from DMF, dimethylacetamide, N-methyl-2-pyrrolidone, DMSO, acetone, butanone, pentanone, methyl butyl ketone, diethyl ether, methyl t-butyl ether, THE, acetonitrile, phenyl acetate, ethyl acetate, triethylphosphate, cx,a,a,-trifluorotoluene, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, pentan-1 -ol, 3- methylbutan-1 -ol, 2-methylbutan-1 -ol, 2,2-dimethylpropan-1 -ol, pentan-3-ol, pentan-2- ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, methoxyothanol, 2-ethoxyethanol, 2-propoxyethanol, dimethoxyethane or 2-butoxyethanol or mixtures thereof.48. A method as claimed in any one of claims 44 to 47, wherein depositing is carried out by spin coating.49. A method as claimed in any one of claims 46 to 48, comprising the further step of annealing.50. A method of making an organic electronic device comprising a step of depositing a layer by the method as claimed in any one of claims 44 to 49.51. A method as claimed in claim 50, comprising: (i) depositing an anode on a substrate; (ii) depositing a hole injection layer on said anode; (iii) optionally depositing an interlayer on said hole injection layer; (iv) depositing a light emitting layer on said hole injection layer or where present said i nterlayer; (v) depositing an electron injection layer on said light emitting layer; and (vi) depositing a cathode on said electron injection layer.52. A method as claimed in claim 51, wherein each of steps (ii)-(iv) are carried out by solution processing.53. A method as claimed in claim 50 or 51, comprising the further step of heating said device at a temperature between 60 and 95 °C.