Patent Application
20170229672
The present invention relates to organic light-emitting devices and methods of making them. More specifically, it relates to organic light-emitting devices comprising polymer light-emitting layers and non-polymeric (also known as “small-molecule”) electron-transporting layers. Such devices are sometimes known as “hybrid devices”.
Electronic devices comprising active organic materials are attracting increasing attention for use in devices such as organic light-emitting diodes (OLEDs), organic photo responsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory devices. Devices comprising organic materials offer benefits such as low weight, low power consumption and flexibility, and they can be employed in the manufacturing of displays or lighting appliances. Use of soluble organic materials, either polymers or small-molecules, allows use of solution processing in device layer manufacture, for example inkjet printing, spin-coating, dip-coating, slot dye printing, nozzle printing, roll-to-roll printing, gravure printing and flexographic printing. Moreover, use of non-soluble small-molecules enables the manufacturing of device layers by vacuum deposition. Examples of vacuum deposition methods are vacuum sublimation and the co-evaporation (or simultaneous evaporation) of a plurality of different small-molecule materials.
An OLED may comprise a substrate carrying an anode, a cathode, one or more organic light-emitting layers, and one or more charge injecting and/or charge transporting layers between the anode and cathode.
Holes are injected into the device by the anode and electrons are injected by the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of a light-emitting material combine to form an exciton that releases its energy as light upon recombination.
A light-emitting layer consists of or includes light-emitting materials which may include small-molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers include poly(arylene vinylenes), such as poly(p-phenylene vinylenes) as disclosed in WO 90/13148, and polyarylenes, such as polyfluorenes. In U.S. Pat. No. 4,539,507 the light-emitting material is (8-hydroxyquinoline) aluminium (“Alq3”, ET3). WO 99/21935 discloses dendrimer light-emitting materials.
A light-emitting layer may alternatively consist of or include a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant. For example, J. Appl. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton) and Appl. Phys. Lett., 2000, 77, 904 discloses a host material doped with a phosphorescent light emitting dopant (that is, a light-emitting material in which light is emitted via decay of a triplet exciton).
A charge transporting layer consists of or includes materials suitable for transporting holes and/or electrons, which may include small-molecule, polymeric and dendrimeric materials. Suitable electron-transporting polymers include triazines and pyrimidines, such as those disclosed in U.S. Pat. No. 8,003,227. Suitable hole-transporting polymers include triarylamines, such as those disclosed in the Applicant's earlier applications WO 02/066537 and WO 2004/084260.
In a typical OLED structure, the electron-transporting layer comprising host-dopant small-molecule materials may be vapour deposited directly onto a light-emitting layer comprising a polymer, and then capped with a thermally evaporated metal layer. The metal layer typically forms a cathode metal contact of the device.
According to a first aspect of the present invention, an organic light emitting device comprises a light emitting layer comprising a light emitting polymer; and an electron transporting layer on the light emitting layer and comprising an electron transporting material and an n-donor material. The electron transporting layer comprises at least 20 percent by weight of the n-donor material.
By doping the electron transporting layer with 20 percent or more by weight of the n-donor material, it has been found that the thickness of the electron transporting layer can be reduced to less than 20 nm while maintaining desirable electron injection properties of the OLED device. Reducing the thickness of the electron transporting layer is beneficial as it allows the optical cavity properties for the OLED device to be optimised and therefore colour stability of the device to be optimised.
In an embodiment, the electron transporting layer has a thickness of less than 20 nm.
In an embodiment, the electron transporting layer has a thickness of less than 10 nm.
In an embodiment, the electron transporting layer has a thickness of less than 5 nm.
The electron transport layer of the invention preferably has a thickness of greater than 1 nm.
In an embodiment, the electron transporting layer comprises at least 40 percent by weight of the n-donor material.
In an embodiment, the electron transporting layer comprises at least 50 percent by weight of the n-donor material.
The electron transport layer of the invention preferably comprises less than or equal to 80 percent by weight of the n-donor material.
In an embodiment, substantially all molecules of the n-donor material are complexed with molecules of the electron transporting material.
According to a second aspect of the present invention an organic light emitting device comprises a light emitting layer comprising a light emitting polymer; and an electron transporting layer. The electron transporting layer comprises an electron transporting material and an n-donor material, at least 20 percent of the molecules of the electron transporting material are complexed with molecules of the n-donor material.
The doping properties leading to a reduction in thickness of the electron transporting layer can also be defined in terms of the percentage of molecules of the electron transporting material that are complexed with molecules of the n-donor material.
In an embodiment, at least 50 percent of the molecules of the electron transporting material are complexed with molecules of the n-donor material.
In an embodiment, at least 80 percent of the molecules of the electron transporting material are complexed with molecules of the n-donor material.
In an embodiment, the ratio of molecules of the electron transporting material to molecules of the n-donor material is 1:1.
In an embodiment, the device further comprises a metal cathode disposed on the electron transporting layer.
In an embodiment, the electron transporting layer comprising the n-donor material is formed directly on the light emitting layer.
By doping the electron transporting layer with 20 percent or more by weight of the n-donor material, it has been found that the electron transporting layer comprising the n-donor material can be formed directly on the light emitting layer while maintaining desirable electron injection properties of the OLED device. Reducing the number of layers in the device is beneficial as it allows faster, easier and cheaper manufacturing processes.
In an embodiment, the n-donor material is a molecular dopant material.
In an embodiment, the n-donor material is a molecular redox dopant material.
In an embodiment, the n-donor material is a substantially organic redox dopant material.
In an embodiment, the n-donor material is a transition metal complex, preferably a paddle wheel complex.
In an embodiment, the n-donor material is tetrakis (1,3,4,6,7,8-hexahydro-2H-pyrimido [1,2-a] pyrimidinato) ditungsten (II) (ND1).
In an embodiment, the n-donor material is free of Lithium salt or Lithium organic metal complex.
By doping the electron transporting layer with at least 20 percent by weight of an n-donor material which is a molecular dopant material, preferably a molecular redox dopant material, and which is free of Lithium salt or Lithium organic metal complex, electron injection properties can be achieved which are suitable for commercial products.
In an embodiment, the electron transporting material comprises a phenanthroline compound or a metal quinolate.
In an embodiment, the electron transporting material comprises a phenanthroline compound.
In an embodiment, the electron transporting material comprises a metal quinolate.
In an embodiment, the electron transporting material comprises ET1 or ET2 which are illustrated below:
In an embodiment, ET1 is used for the electron transporting material and a doping ratio of at least 30% by weight of ND1 is used and the electron transporting layer is less than 10 nm thick.
In an embodiment ET1 is used for the electron transporting material and a doping ratio of 30% to 50% by weight of ND1 is used and the electron transporting layer is less than 10 nm thick.
In an embodiment ET2 is used for the electron transporting material and a doping ratio of at least 70% by weight of ND1 is used and the electron transporting layer is less than 10 nm thick.
In an embodiment ET2 is used for the electron transporting material and a doping ratio of 70% to 90% by weight of ND1 is used and the electron transporting layer is less than 10 nm thick.
According to a third aspect of the present invention, a process for the preparation of an organic light emitting device comprises depositing a solution of a light emitting polymer over an anode layer; and vapour depositing an electron transporting material and an n-donor material to form an electron transporting layer over the light emitting polymer.
The electron transporting layer comprises at least 20 percent by weight of an n-donor material.
In an embodiment, the electron transporting layer has a thickness of less than 20 nm.
In an embodiment, the electron transporting layer has a thickness of less than 10 nm.
In an embodiment, the electron transporting layer has a thickness of less than 5 nm.
In an embodiment, the electron transporting layer comprises at least 40 percent by weight of the n-donor material.
In an embodiment, the electron transporting layer comprises at least 50 percent by weight of the n-donor material.
In an embodiment, depositing a solution of a light emitting polymer is conducted by spin-coating, inkjet-printing, slot die coating, screen printing or dip-coating.
In the following, embodiments of the invention will be described, by way of example, with reference to the drawings in which:
Anode
The anode typically comprises a transparent conducting material such as an inorganic oxide or a conducting polymer.
Cathode
The cathode typically comprises a conductive metal such as Al or Cu or Ag or a highly conductive alloy, with an optional alkali metal halide or oxide or an alkaline earth halide or oxide layer in electrical contact with the electron transport layer.
Light-Emitting Layer
The light-emitting material(s) of the light-emitting layer may be selected from polymeric and non-polymeric light-emitting materials. Exemplary light-emitting polymers are conjugated polymers, for example polyphenylenes and polyfluorenes examples of which are described in Bernius, M. T., Inbasekaran, M., O'Brien, J. and Wu, W., Progress with Light-Emitting Polymers. Adv. Mater., 12: 1737-1750, 2000, the contents of which are incorporated herein by reference.
A conjugated light-emitting polymer may comprise one or more amine repeat units of formula (I):
wherein Ar8, Ar9 and Ar10 in each occurrence are independently selected from substituted or unsubstituted aryl or heteroaryl, g is 0, 1 or 2, preferably 0 or 1, R13 independently in each occurrence is H or a substituent, preferably a substituent, and c, d and e are each independently 1, 2 or 3.
R13, which may be the same or different in each occurrence when g is 1 or 2, is preferably selected from the group consisting of alkyl, for example C1-20 alkyl, Ar11 and a branched or linear chain of Ar11 groups wherein Ar11 in each occurrence is independently substituted or unsubstituted aryl or heteroaryl.
Any two aromatic or heteroaromatic groups selected from Ar8, Ar9, and, if present, Ar10 and Ar11 that are directly bound to the same N atom may be linked by a direct bond or a divalent linking atom or group. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C.
Ar8 and Ar10 are preferably C6-20 aryl, more preferably phenyl, that may be unsubstituted or substituted with one or more substituents.
In the case where g=0, Ar9 is preferably C6-20 aryl, more preferably phenyl, that may be unsubstituted or substituted with one or more substituents.
In the case where g=1, Ar9 is preferably C6-20 aryl, more preferably phenyl or a polycyclic aromatic group, for example naphthalene, perylene, anthracene or fluorene, that may be unsubstituted or substituted with one or more substituents.
R13 is preferably Ar11 or a branched or linear chain of Ar11 groups. Ar11 in each occurrence is preferably phenyl that may be unsubstituted or substituted with one or more substituents.
Exemplary groups R13 include the following, each of which may be unsubstituted or substituted with one or more substituents, and wherein * represents a point of attachment to N:
c, d and e are preferably each 1.
Ar8, Ar9, and, if present, Ar10 and Ar11 are each independently unsubstituted or substituted with one or more, optionally 1, 2, 3 or 4, substituents. Exemplary substituents may be selected from substituted or unsubstituted alkyl, optionally C1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl (preferably phenyl), O, S, C═O or —COO— and one or more H atoms may be replaced with F.
Preferred substituents of Ar8, Ar9, and, if present, Ar10 and Ar11 are C1-40 hydrocarbyl, preferably C1-20 alkyl.
Preferred repeat units of formula (I) include unsubstituted or substituted units of formulae (I-1), (I-2) and (I-3):
A light-emitting polymer comprising repeat units of formula (I) may further comprise one or more arylene repeat units. Exemplary arylene repeat units are phenylene, fluorene, indenofluorene and phenanthrene repeat units, each of which may be unsubstituted or substituted with one or more substituents, optionally one or more C1-40 hydrocarbyl groups. Exemplary hydrocarbyl groups include C1-20 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1-20 alkyl groups.
Polymers as described herein including, without limitation, inert polymers and light-emitting polymers, may have a polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography in the range of about 1×103 to 1×108, and preferably 1×103 to 5×106. The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers described herein may be 1×103 to 1×108, and preferably 1×104 to 1×107.
Polymers as described herein including, without limitation, inert polymers and light-emitting polymers, are preferably amorphous.
The light emitting layer may comprise a fluorescent or phosphorescent dopant provided in light-emitting layer 103 with a host material. Exemplary phosphorescent dopants are row 2 or row 3 transition metal complexes, for example complexes of ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum or gold. Iridium is particularly preferred.
Hole-Transporting Layer
A hole transporting layer may be provided between the anode and the light-emitting layer or layers of an OLED.
If present, a hole transporting layer located between the anode and the light-emitting layer(s) preferably has a material having a HOMO level of less than or equal to 5.5 eV, more preferably around 4.8-5.5 eV or 4.9-5.3 eV as measured by cyclic voltammetry. The HOMO level of the material in the hole transport layer may be selected so as to be within 0.2 eV, optionally within 0.1 eV of the light-emitting material of the light-emitting layer.
A hole-transporting layer may contain polymeric or non-polymeric hole-transporting materials. Exemplary hole-transporting polymers are homopolymers and copolymers comprising repeat units of formula (I) as described above.
A hole-transporting layer may be crosslinked, particularly if a layer overlying that charge-transporting or charge-blocking layer is deposited from a solution. The crosslinkable group used for this crosslinking may be a crosslinkable group comprising a reactive double bond such and a vinyl or acrylate group, or a benzocyclobutane group. The crosslinkable group may be provided as a substituent of, or may be mixed with, a hole-transporting material used to form the hole-transporting layer.
A hole-transporting layer adjacent to a light-emitting layer containing a phosphorescent light-emitting material preferably contains a charge-transporting material having a lowest triplet excited state (T1) excited state that is no more than 0.1 eV lower than, preferably the same as or higher than, the T1 excited state energy level of the phosphorescent light-emitting material(s) in order to avoid quenching of triplet excitons.
A hole-transporting layer as described herein may be non-emissive, or may contain a light-emitting material such that the layer is a charge transporting light-emitting layer. If the hole-transporting material a polymer then a light-emitting dopant may be provided as a side-group of the polymer, a repeat unit in a backbone of the polymer, or an end group of the polymer. Optionally, a hole-transporting polymer as described herein comprises a phosphorescent polymer in a side-group of the polymer, in a repeat unit in a backbone of the polymer, or as an end group of the polymer.
The polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography of the polymers described herein may be in the range of about 1×103 to 1×108, and preferably 1×104 to 5×106. The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers described herein may be 1×103 to 1×108, and preferably 1×104 to 1×107.
Polymers as described herein are suitably amorphous.
Electron Transport Layer (ETL)
Advantageously, an electron-transporting layer comprises a semiconducting host material and a semiconducting dopant material. Suitable host-dopant material systems include small-molecule materials. The host and the dopant materials can be deposited simultaneously by vapour deposition to form an electron-transporting layer comprising a mixture or blend of the host and dopant materials.
The anode electrode 20, typically made of ITO (indium tin oxide), is 45 nm thick and is deposited by physical vapour deposition such as vacuum or thermal evaporation. The HIL 30 is 50 nm thick and is deposited by spin coating a solution of a hole-injecting material called Plexcore© OC AQ-1200 as available from Plextronics Inc. The IL 40 is 22 nm thick, and is deposited by spin coating a solution of the hole-transporting polymer P10. The polymer P10 comprises the monomers M11 to M14 in the following weight percentages: 50% M11, 30% M12, 12.5% M13 and 7.5% M14. The chemical structures of these monomers are shown below:
The LEP layer 50 is 60 nm thick and is deposited by spin coating a solution of the light-emitting polymer P20. The polymer P20 comprises the monomers M21 to M25 in the following weight percentages: 36% M21, 14% M22, 45% M23, 4% M24 and 1% M25. The chemical structures of these monomers are shown below:
The polymers P10 and P20 were synthesized using the Suzuki polymerisation method, as it is well known in the art. Monomer M11 has been disclosed in WO2002/092723, M12 in WO2005/074329, M13 in WO2002/092724, M14 in WO2005/038747, M21 in WO2002/092724, M22 in U.S. Pat. No. 6,593,450, M23 in WO2009/066061, M24 in WO2010/013723, and M25 in WO2004/060970.
The cathode electrode 60 consists of three stacked layers of NaF 60a, Al 60b and Ag 60c, having a thickness of 4 nm, 100 nm and 100 nm respectively. The NaF is deposited by thermal evaporation on the LEP layer 50 and then encapsulated by the thermally evaporated bi-layer stack of Al and Ag.
In operation, holes injected from the anode electrode 20 and electrons injected from the cathode electrode 60 combine in the LEP layer 50 to form excitons which may decay radiatively to provide light upon recombination.
One advantage of the device shown in
Further, the choice of cathode material in the device shown in
Compounds which are suitable for use as electron-transporting material are disclosed for example in Yasuhiko Shirota and Hiroshi Kageyama, Chem. Rev. 2007, 107, 953-1010 and incorporated by reference. In one example, the electron-transporting material may be a phenanthroline compound. Phenanthroline compounds which can be suitably used are disclosed in EP1786050 and incorporated by reference. In one example, the electron-transporting material may be a metal quinolate. Metal quinolates which can be suitably used are disclosed in JP 2001076879 and incorporated by reference.
Further examples of doped electron transport materials are: fullerene C60 doped with acridine orange base (AOB); perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) doped with leuco crystal violet; 2,9-di (phenanthren-9-yl)-4,7-diphenyl-1,10-phenanthroline doped with tetrakis (1,3,4,6,7,8-hexahydro-2H-pyrimido [1,2-a] pyrimidinato) ditungsten (II) (W2(hpp)4, (ND1); naphthalene tetracarboxylic acid di-anhydride (NTCDA) doped with 3,6-bis-(dimethyl amino)-acridine; NTCDA doped with bis(ethylene-dithio) tetrathiafulvalene (BEDT-TTF).
In the present example the ETL 62 comprises an electron-transporting material containing one of the small-molecule hosts such as ET1 and ET2. The chemical structures of ET1 and ET2 are illustrated below:
The ETL 62 comprises an n-donor material. The n-donor material is a compound which is capable of electrically doping a matrix compound via a redox process. One or more electrons are transferred from the n-donor material to the matrix compound in a charge transfer mechanism. To achieve efficient electron transfer, the HOMO level of the n-donor material has to be energetically above the LUMO level of the matrix compound. HOMO and LUMO levels can be measured, for example by cyclic voltammetry. Energy levels can be converted from tabulated ionization potentials (IP) and electron affinities (EA) by applying Koopman's theorem. IP and EA of commonly used compounds can be found in the literature, for example Shirota and Kageyama, Chem. Rev. 2007, 107, 953-10101.
In one example, the n-donor material may be a substantially organic redox dopant material. Suitable organic redox dopant materials are for example heterocyclic radical and diradical compounds disclosed in US2007252140A1 and incorporated by reference. Particularly suitable are biimidazole compounds. Other suitable organic n-donor materials are leuko bases disclosed in US2005040390A1 and incorporated by references. Particularly suitable is leuko crystal violet.
In one example, the n-donor material may be a transition metal complex. Particularly suitable are paddle wheel complexes disclosed in US2009212280A1 and incorporated by reference. Particularly preferred is tetrakis (1,3,4,6,7,8-hexahydro-2H-pyrimido [1,2-a] pyrimidinato) ditungsten (II) (ND1).
As shown in
The table below shows the measured colour parameters for the devices described above in relation to
As shown in the table above, the reduction in the thickness of the ETL brings the CIE y colour value down to 0.18. This is a similar value to that of a NaF-based cathode device as shown in
As the doping ratio of the ETL between the host and the dopant is increased more host is complexed with the dopant. However, once the dopant level is beyond a certain point there is not enough host for the dopant to complex with. This results in non-complexed dopant being present in the ETL. The dopant is very reactive on its own; therefore the presence of uncomplexed dopant in the ETL can be detrimental to the lifetime properties of an OLED device.
This process of varying the dopant ratio has been shown to transfer to other host systems. Adjustments must be made to account for the size of the host molecule.
In an embodiment, ET2 is used as a host. For ET2 compared to ET1 for example the maximum doping percentage before non-complexed dopant is present is 80% by weight compared to 50% by weight.
When ET1 is used for the electron transporting material a doping ratio of 30-50% by weight of ND1 is may be used. When ET2 is used for the electron transporting material a doping ratio of 70-90% by weight of ND1 is may be used. These doping percentages are used for electron transporting layers less than 10 nm thick.
Various modifications will be apparent to those skilled in the art. For example, the substrate 10 may be made of plastic (e.g. of polyethylene naphthalate, PEN or polyethylene terephthalate, PET type). The HIL 30 may be preferably 20 to 100 nm thick and more preferably 40 to 60 nm thick. The IL 40 may be preferably 10 to 50 nm thick and more preferably 20 to 30 nm thick. The LEP layer 50 may be preferably 10 to 150 nm thick and more preferably 50 to 70 nm thick.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1413774.9 | Aug 2014 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2015/052197 | 7/30/2015 | WO | 00 |
