Electrically doped organic semiconducting material and organic light emitting device comprising it

Abstract

The invention relates to electrically doped semiconducting material comprising iii) at least one electrical dopant selected from metal salts consisting of at least one metal cation and at least one anion and iv) at least one matrix compound of formula 1 ##STR00001##
wherein each of R.sup.1, R.sup.2, R.sup.1, R.sup.2 is independently selected from H, C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 haloalkyl and C.sub.6-C.sub.14 aryl or both substituents on the same aromatic ring of the xanthene skeleton are hydrocarbyl groups linked with each other to form together an anelated divalent C.sub.2-C.sub.10 hydrocarbyl group and A and A are independently selected from C.sub.1-C.sub.20 heteroaryl group comprising at least one sp.sup.2 hybridized nitrogen atom as well as an electronic device and a compound.

Claims

1. An electrically doped semiconducting material comprising i) at least one electrical dopant selected from metal salts consisting of at least one metal cation and at least one anion and ii) at least one matrix compound of formula 1 ##STR00019## wherein each of R.sup.1, R.sup.2, R.sup.1, R.sup.2 is independently selected from the group consisting of H, C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 haloalkyl, and C.sub.6-C.sub.14 aryl, or both substituents on the same aromatic ring of the xanthene skeleton are hydrocarbyl groups linked with each other to form together an anelated divalent C.sub.2-C.sub.10 hydrocarbyl group, and A and A are selected from a C.sub.1-C.sub.20 heteroaryl group comprising at least one sp.sup.2 hybridized nitrogen atom; wherein R.sup.1 and R.sup.1 are the same, R.sup.2 and R.sup.2 are the same, and A and A are the same; and wherein a) the metal salt is selected from metal complexes comprising a 5-, 6- or 7-membered ring that contains the metal cation attached to other atoms of the ring through atoms independently selected from nitrogen and oxygen; or b) the metal salt is a metal complex having the structure according to formula (I) ##STR00020## wherein A.sup.1 is a C.sub.6-C.sub.30 arylene or C.sub.2-C.sub.30 heteroarylene comprising at least one atom selected from O, S, or N in an aromatic ring and each of A.sup.2 and A.sup.3 is independently selected from a C.sub.6-C.sub.30 aryl or C.sub.2-C.sub.30 heteroaryl comprising at least one atom selected from O, S, or N in an aromatic ring; or c) the metal salt is selected from lithium salts comprising an anion having formula (II) ##STR00021## wherein each of G.sup.1-G.sup.4 is independently selected from H, substituted or unsubstituted C.sub.6-C.sub.20 aryl, or substituted or unsubstituted C.sub.2-C.sub.20 heteroaryl; and wherein the metal cation is Li.sup.+.

2. The electrically doped semiconducting material according to claim 1, wherein A and A are selected from the group consisting of pyridyl and quinolinyl.

3. The electrically doped semiconducting material according to claim 1, wherein at least two of substituents G.sup.1-G.sup.4 are pyrazolyl.

4. An electronic device comprising the electrically doped semiconducting material of claim 1 between a cathode and an anode.

5. The electronic device according to claim 4, wherein the electrically doped semiconducting material forms a layer adjacent to the cathode.

6. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 50 nm.

7. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 40 nm.

8. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 30 nm.

9. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 20 nm.

10. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 15 nm.

11. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 10 nm.

12. The electronic device according to claim 5, wherein the layer of the electrically doped semiconducting material has a thickness less than 7 nm.

13. The electronic device according to claim 4 further comprising a light emitting layer between the anode and the cathode, wherein the electrically doped semiconducting material forms a layer between the cathode and the light emitting layer.

14. The electronic device according to claim 13, wherein the electrically doped semiconducting material forms a layer adjacent to the light emitting layer.

15. The electronic device according to claim 13, wherein a hole blocking layer is provided between the light emitting layer and the layer of the electrically doped semiconducting material.

Description

IV. BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic illustration of a device in which the present invention can be incorporated.

(2) FIG. 2 shows the current density versus the applied bias of in devices of Example 1.

(3) FIG. 3 shows the density of the luminous intensity versus the applied bias in devices of Example 1.

V. DETAILED DESCRIPTION OF THE INVENTION

(4) Device Architecture

(5) FIG. 1 shows the scheme of experimental blue OLED used in Example 1 for the comparison of the inventive semiconducting materials with analogous materials comprising xanthene-based matrix compounds that lack nitrogen containing heterocyclic substituents.

(6) The skilled person can design devices for other purposes by choosing the supporting materials known in the art, layer thicknesses, deposition methods and other parameters appropriately.

(7) For example, other layers can be inserted between those depicted, or some layers may be omitted. Following short overview has only informative character and does not limit the scope of the invention.

(8) Substrate

(9) It can be flexible or rigid, transparent, opaque, reflective, or translucent. The substrate should be transparent or translucent if the light generated by the OLED is to be transmitted through the substrate (bottom emitting). The substrate may be opaque if the light generated by the OLED is to be emitted in the direction opposite of the substrate, the so called top-emitting type. The OLED can also be transparent. The substrate can be either arranged adjacent to the cathode or anode.

(10) Electrodes

(11) The electrodes are the anode and the cathode, they must provide a certain amount of conductivity, being preferentially conductors. In OLEDs, at least one of the electrodes must be semi-transparent or transparent to enable the light transmission to the outside of the device. Typical electrodes are layers or a stack of layer, comprising metal and/or transparent conductive oxide. Other possible electrodes are made of thin busbars (e.g. a thin metal grid) wherein the spaces between the busbars is filled (coated) with a transparent material with a certain conductivity, such as graphene, carbon nanotubes, doped organic semiconductors, etc.

(12) In one mode, the anode is the electrode closest to the substrate, which is called non-inverted structure. In another mode, the cathode is the electrode closest to the substrate, which is called inverted structure.

(13) Typical materials for the anode are indium tin oxide (ITO) and Ag. Typical materials for the cathode are magnesium-silver alloy (10 vol. % Mg), Ag, ITO, aluminium. Mixtures and multilayer are also possible.

(14) Hole Transporting Layer (HTL)

(15) It is a layer comprising a large gap semiconductor responsible to transport holes from the anode or holes from a CGL to the emitting layer (EML). The HTL is comprised between the anode and the EML or between the hole generating side of a CGL and the LEL. The HTL can be doped with a p-dopant. P-doping the HTL lowers its resistivity and avoids the respective power loss due to the otherwise high resistivity of the undoped semiconductor. The doped HTL can also be used as optical spacer, because it can be made very thick, up to 1000 nm or more without significant increase in resistivity.

(16) Hole Injecting Layer (HIL)

(17) It is a layer which facilitates the injection of holes from the anode or from the hole generating side of a CGL into an adjacent HTL. Typically the HIL is a very thin layer (<10 nm). The hole injection layer can be a pure layer of p-dopant and can be about 1 nm thick. When the HTL is doped, an HIL may not be necessary, since the injection function is already provided by the HTL.

(18) Suitable compounds for the hole transport matrix material of the hole transport layer may be selected from the known hole transport matrices (HTMs), e.g. from triaryl amine compounds. Preferred HTMs for the inventive doped hole transport material are compounds comprising a conjugated system of delocalized electrons, wherein the conjugated system comprises lone electron pairs of at least two tertiary amine nitrogen atoms. Examples are N4,N4-di(naphthalen-1-yl)-N4,N4-diphenyl-[1,1-biphenyl]-4,4-diamine (HT1), and N4,N4, N4,N4-tetra([1,1-biphenyl]-4-yl)-[1,1:4,1-terphenyl]-4,4-diamine (HT2). The synthesis of terphenyldiamine HTMs is described e.g. in WO2011/134458, US2012/223296 or WO2013/135237; 1,3-phenylenediamine matrices are described e.g. in WO2014/060526.

(19) These documents are herein incorporated by reference. Many triaryl amine HTMs are commercially available.

(20) Emitting Layer (EML)

(21) The light emitting layer must comprise at least one emitter and can optionally comprise additional layers. A mixture of different types of emitters can be provided for higher efficiency. Mixed light can be realized by using emission from an emitter host and an emitter dopant.

(22) Blocking layers can be used to improve the confinement of charge carriers in the EML, as explained e.g. in U.S. Pat. No. 7,074,500 B2.

(23) Electron Transporting Layer (ETL)

(24) It is a layer comprising a large gap semiconductor responsible to transport electrons from the cathode or electrons from a CGL to the ETL. The ETL is comprised between the anode and the EML or between the electron generating side of a CGL and the LEL. The ETL can be mixed with an electrical n-dopant, in which case it is said the ETL is n-doped. The ETL can be comprised by several layers, which can have different compositions. Electrical n-doping the ETL lowers its resistivity and/or improves its ability to inject electrons into an adjacent layer and avoids the respective power loss due to the otherwise high resistivity (and/or bad injection ability) of the undoped semiconductor. The doped ETL can also be used as optical spacer, because it can be made very thick, up to 1000 nm or more without significant increase in resistivity.

(25) Hole blocking layers and electron blocking layers can be employed as usual.

(26) Charge Generation Layer (CGL)

(27) The OLED can comprise a CGL which can be used in conjunction with an electrode as inversion contact, or as connecting unit in stacked OLEDs. A CGL can have the most different configurations and names, examples are pn-junction, connecting unit, tunnel junction, etc. Best examples are pn junctions as disclosed in US 2009/0045728 A1, US 2010/0288362 A1. Metal layers and or insulating layers can also be used.

(28) Stacked OLEDs

(29) When the OLED comprises two or more EMLs separated by CGLs, the OLED is named a stacked OLED, otherwise it is named a single unit OLED. The group of layers between two closest CGLs or between one of the electrodes and the closest CGL is named a electroluminescent unit (ELU). Therefore a stacked OLED can be described as anode/ELU.sub.1/{CGL.sub.X/ELU.sub.1+X}.sub.X/cathode, wherein x is a positive integer and each CGL.sub.X or each ELU.sub.1+X can be equal or different. The CGL can also be formed by the adjacent layers of two ELUs as disclosed in US2009/0009072 A1. Further stacked OLEDs are explained e.g. in US 2009/0045728 A1, US 2010/0288362 A1, and references therein.

(30) Deposition of Organic Layers

(31) Any organic semiconducting layers of the inventive display can be deposited by known techniques, such as vacuum thermal evaporation (VTE), organic vapour phase deposition, laser induced thermal transfer, spin coating, blade coating, slot dye coating, inkjet printing, etc. A preferred method for preparing the OLED according to the invention is vacuum thermal evaporation.

(32) Preferably, the ETL is formed by evaporation. When using an additional material in the ETL, it is preferred that the ETL is formed by co-evaporation of the electron transporting matrix (ETM) and the additional material. The additional material may be mixed homogeneously in the ETL. In one mode of the invention, the additional material has a concentration variation in the ETL, wherein the concentration changes in the direction of the thickness of the stack of layers. It is also foreseen that the ETL is structured in sub-layers, wherein some but not all of these sub-layers comprise the additional material.

(33) Electrical Doping

(34) The present invention can be used in addition or in combination with electrical doping of organic semiconducting layers.

(35) The most reliable and at the same time efficient OLEDs are OLEDs comprising electrically doped layers. Generally, the electrical doping means improving of electrical properties, especially the conductivity and/or injection ability of a doped layer in comparison with neat charge-transporting matrix without a dopant. In the narrower sense, which is usually called redox doping or charge transfer doping, hole transport layers are doped with a suitable acceptor material (p-doping) or electron transport layers with a donor material (n-doping), respectively. Through redox doping, the density of charge carriers in organic solids (and therefore the conductivity) can be increased substantially. In other words, the redox doping increases the density of charge carriers of a semiconducting matrix in comparison with the charge carrier density of the undoped matrix. The use of doped charge-carrier transport layers (p-doping of the hole transport layer by admixture of acceptor-like molecules, n-doping of the electron transport layer by admixture of donor-like molecules) in organic light-emitting diodes is, e.g., described in US 2008/203406 and U.S. Pat. No. 5,093,698.

(36) US2008227979 discloses in detail the charge-transfer doping of organic transport materials, with inorganic and with organic dopants. Basically, an effective electron transfer occurs from the dopant to the matrix increasing the Fermi level of the matrix. For an efficient transfer in a p-doping case, the LUMO energy level of the dopant is preferably more negative than the HOMO energy level of the matrix or at least slightly more positive, not more than 0.5 eV, to the HOMO energy level of the matrix. For the n-doping case, the HOMO energy level of the dopant is preferably more positive than the LUMO energy level of the matrix or at least slightly more negative, not lower than 0.5 eV, to the LUMO energy level of the matrix. It is further more desired that the energy level difference for energy transfer from dopant to matrix is smaller than +0.3 eV.

(37) Typical examples of known redox doped hole transport materials are: copperphthalocyanine (CuPc), which HOMO level is approximately 5.2 eV, doped with tetrafluoro-tetracyanoquinonedimethane (F4TCNQ), which LUMO level is about 5.2 eV; zincphthalocyanine (ZnPc) (HOMO=5.2 eV) doped with F4TCNQ; a-NPD (N,N-Bis(naphthalen-1-yl)-N,N-bis(phenyl)-benzidine) doped with F4TCNQ. a-NPD doped with 2,2-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (PD1). a-NPD doped with 2,2,2-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) (PD2). All p-doping in the device examples of the present application was done with 5 mol. % of PD2. Typical examples of known redox 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) ditung-sten (II) (W.sub.2(hpp).sub.4); naphthalene tetracarboxylic acid di-anhydride (NTCDA) doped with 3,6-bis-(dimethyl amino)-acridine; NTCDA doped with bis(ethylene-dithio) tetrathiafulvalene (BEDT-TTF).

(38) In devices demonstrating the present invention, redox doping has been used in the HTL.

(39) Preferred ETL matrix compounds of the present invention are

(40) ##STR00018##

(41) C6 and C7 are the most preferred compounds.

VI. EXAMPLES

(42) Synthesis Procedures

(43) All manipulations were carried out under argon in thoroughly dried glass vessels, without any further purification of commercial chemicals except for the use of dried and degassed solvents (solvent purification system (SPS) quality).

(44) General synthesis procedure, syntheses of precursor compounds, and syntheses of inventive C2, C and C6 as well as of comparative compounds were reported in WO2013/14998. Inventive compound C7 has been synthesized analogously and characterized as follows: TLC (silica, ethyl acetate): R.sub.f=0.25

(45) DSC: Melting point: 345 C. (peak), sublimed material Glass transition Tg: 163 C. (onset), heating rate 10 K/min, sublimed material

(46) .sup.1H-NMR (CD.sub.2Cl.sub.2 referenced to 5.31 ppm, 500.13 MHz): J[ppm]=6.50 (d, J=8.5 Hz, 2H), 7.19 (dd, J=8.0 Hz, 5.0 Hz, 2H), 7.32 (d, J=9.0 Hz, 2H), 7.42 (d, J=2.0 Hz, 2H, fluorene H-1), 7.58 (t with fine splitting, J=7.5 Hz, 2H, xanthene H-2 or H-3), 7.70 (t, J=2.0 Hz, 2H), 7.72 (signal pattern not clear due to overlapping signals, 2H), 7.73 (ddd, J=8.0 Hz, 7.0 Hz, 1.0 Hz, 2H, xanthene H-2 or H-3), 7.78 (d, J=8.0 Hz, 2H), 8.06 (d, J=8.0 Hz, 2H), 8.42 (dd, J=4.5 Hz, 1.5 Hz, 2H), 8.68 (d, J=2.5 Hz, 2H, pyridine H-2), 8.82 (d, J=8.5 Hz, 2H, pyridine H-6).

(47) .sup.13C-NMR (CD.sub.2Cl.sub.2 referenced to 53.73 ppm, 125.76 MHz): [ppm]=54.82 (s, spiro-sp.sup.3 C), 117.72, 121.27, 121.93, 123.49, 123.56, 124.90, 125.14, 125.61, 126.68, 127.10, 127.53, 127.87, 133.93, 134.23, 136.15, 138.73, 139.54, 146.18, 148.36, 148.79, 157.56 (d, C.sub.ArO).

Example 1

(48) A bottom emitting blue OLED schematically shown in shown in FIG. 1 was fabricated by standard vacuum thermal evaporation (VTE) technique. On a glass substrate (not shown) provided with a 90 nm thick ITO anode (1), following layers were deposited subsequently:

(49) (2) 10 nm thick hole injecting and hole transporting layer consisting of hole transport matrix HT1 and p-dopant 2,2,2-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile) (PD2) in a weight ratio 92:8,

(50) (3) 120 nm thick hole transporting and electron blocking layer of HT1,

(51) (4) 20 nm thick emitting layer consisting of the commercially available host ABH113 and emitter NUBD370 (both from SFC, Korea),

(52) (5) 31 nm thick hole blocking layer made of compound E1,

(53) (6) 5 nm thick electron injecting and electron transporting layer consisting of the inventive or comparative compounds given in the Table 1 co-deposited with the additive D4 in the weight ratio given in the Table 1, and

(54) (7) 100 nm thick aluminium cathode.

(55) In FIGS. 2 and 3, the curve (1) refers to compound E1, (2) refers to compound E4, (3) refers to compound C2, (4) refers to compound C5, (5) refers to compound C6 and (6) refers to compound C7. The compounds were co-deposited with either 30% or 35% (in weight ratio) of compound D4. It is clearly seen that OLEDs comprising the inventive doped semiconducting materials perform well only if they comprise the xanthene matrices substituted with nitrogen containing substituents as defined in this invention.

(56) The voltages and efficiencies reported in the Table 1 show that xanthene matrices comprising nitrogen-containing heterocyclic substituent as specified above can be, oppositely to other xanthene matrices having very similar structures and frontier orbital energy levels, successfully doped with air stable metal salt n-dopants.

(57) The features disclosed in the foregoing description, in the claims and the accompanying drawings may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof.

Used Abbreviations

(58) DSC differential scanning calorimetry Fc.sup.+/Fc ferrocenium/ferrocene reference system HPLC high performance liquid chromatography SPS solvent purification system TLC thin layer chromatography UV UV/Vis spectroscopy eq chemical equivalent mol. % molar percent vol. % volume percent