Organic light emitting device comprising polar matrix, metal dopant and silver cathode
11355721 · 2022-06-07
Assignee
Inventors
Cpc classification
H10K2102/321
ELECTRICITY
H10K85/6574
ELECTRICITY
H10K2101/40
ELECTRICITY
H10K2101/50
ELECTRICITY
H10K85/615
ELECTRICITY
International classification
Abstract
The present invention relates to an electronic device comprising at least one light emitting layer between an anode and a substantially silver cathode, the device further comprising between the cathode and the anode at least one mixed layer comprising (i) at least one substantially covalent electron transport matrix compound comprising at least one polar group selected from phosphine oxide group or diazole group, and (ii) in substantially elemental form, an electropositive element selected from substantially non-radioactive alkali metals, alkaline earth metals, rare earth metals, and transition metals of the fourth period of the Periodic table having proton numbers 22, 23, 24, 25, 26, 27, 28, 29.
Claims
1. Electronic device comprising at least one light emitting layer between an anode and a substantially silver cathode, the device further comprising between the cathode and the anode at least one mixed layer comprising (i) at least one substantially covalent electron transport matrix compound comprising at least one polar group selected from phosphine oxide group or diazole group, and (ii) in substantially elemental form, an electropositive element selected from substantially non-radioactive alkali metals, alkaline earth metals, rare earth metals, or transition metals of the fourth period of the Periodic table having proton numbers 22, 23, 24, 25, 26, 27, 28, 29, wherein the mixed layer is an electron transporting layer, an electron injecting layer, or a charge generating layer, wherein the electron transporting layer or the electron injecting layer is adjacent to and in direct contact with the cathode.
2. Electronic device according to claim 1, wherein the reduction potential of the electron transport matrix compound, if measured by cyclic voltammetry under the same conditions, has the value which is more negative than the value obtained for at least one of tris(2-benzo[d]thiazol-2-yl)phenoxyaluminum, 9,9′,10,10′-tetraphenyl-2,2′-bianthracene, 2,9-di([1,1′-biphenyl]-4-yl)-4,7-diphenyl-1,10-phenanthroline, 2,4,7,9-tetraphenyl-1,10-phenanthroline, 9, 10-di(naphthalen-2-yl)-2-phenylanthracene, 2,9-bis(2-methoxyphenyl)-4,7-diphenyl-1,10-phenanthroline, 9,9′-spirobi[fluorene]-2,7-diylbis(diphenylphosphine oxide), 4,7-diphenyl-1,10-phenanthroline, 1,3,5-tris(1-phenyl -1H-benzimidazol-2-yl)benzene, pyrene, and [1,1′-binaphthalen]-2,2′-diylbis(diphenylphosphine oxide).
3. Electronic device according to claim 1, wherein the silver content in the cathode is at least 99.5 weight %.
4. Electronic device according to claim 1, wherein the electropositive element is selected from Li, Na, K, Be, Mg, Ca, Sr, Ba, Sc, Y, La, Sm, Eu, Tb, Yb, Lu, Ti, V, or Mn.
5. Electronic device according to claim 1, wherein the phosphine oxide group is part of a substantially covalent structure comprising at least three carbon atoms directly attached to the phosphorus atom of the phosphine oxide group and having overall count of covalently bound atoms in the range 16-250 atoms.
6. Electronic device according to claim 1, wherein the phosphine oxide group is selected from phosphine oxide substituted with three monovalent hydrocarbyl groups or one divalent hydrocarbylene group forming with the phosphorus atom a ring and one monovalent hydrocarbyl group, and the overall count of carbon atoms in the hydrocarbyl groups and the hydrocarbylene group is 8-80 carbon atoms.
7. Electronic device according to claim 1, wherein the diazole group is an imidazole group.
8. Electronic device according to claim 1, wherein the electron transport matrix compound comprises a conjugated system of at least ten delocalized electrons.
9. Electronic device according to claim 1, wherein the electron transport matrix compound comprises at least one aromatic or heteroaromatic ring.
10. Electronic device according to claim 9, wherein the electron transport matrix compound comprises at least two aromatic or heteroaromatic rings which are either linked by a covalent bond or condensed.
11. Electronic device according to claim 1, wherein the molar ratio of the electropositive element to the electron transport compound is lower than 0.5.
12. Electronic device according to claim 1, wherein the molar ratio of the electropositive element to the electron transport compound is higher than 0.01.
13. Electronic device according to claim 1, which is an inverted device.
14. Electronic device according to claim 1, which is a top-emitting device with the cathode having thickness less than 30 nm.
15. Electronic device according to claim 1, wherein the silver cathode is corrugated and/or combined with a light-scattering layer.
16. Electronic device according to claim 5, wherein the covalently bound atoms are selected from C, H, B, Si, N, P, 0, S, F, Cl, Br, or I.
17. Electronic device according to claim 5, wherein the overall count of covalently bound atoms is in the range 64-160 atoms.
18. Electronic device according to claim 6, wherein the overall count of carbon atoms in the hydrocarbyl groups and the hydrocarbylene group is 32-54 carbon atoms.
19. Electronic device according to claim 1, wherein the molar ratio of the electropositive element to the electron transport compound is lower than 0.10.
20. Electronic device according to claim 1, wherein the molar ratio of the electropositive element to the electron transport compound is higher than 0.08.
21. Electronic device according to claim 1, wherein the substantially silver cathode is a single-layer cathode.
Description
III. BRIEF DESCRIPTION OF DRAWINGS
(1)
(2)
(3)
IV. DETAILED DESCRIPTION OF THE INVENTION
(4) Device Architecture
(5)
(6)
(7) The wording “device” comprises the organic light emitting diode.
(8) Material Properties—Energy Levels
(9) A method to determine the ionization potentials (IP) is the ultraviolet photo spectroscopy (UPS). It is usual to measure the ionization potential for solid state materials; however, it is also possible to measure the IP in the gas phase. Both values are differentiated by their solid state effects, which are, for example the polarization energy of the holes that are created during the photo ionization process. A typical value for the polarization energy is approximately 1 eV, but larger discrepancies of the values can also occur. The IP is related to onset of the photoemission spectra in the region of the large kinetic energy of the photoelectrons, i.e. the energy of the most weakly bounded electrons. A related method to UPS, the inverted photo electron spectroscopy (IPES) can be used to determine the electron affinity (EA). However, this method is less common. Electrochemical measurements in solution are an alternative to the determination of solid state oxidation (E.sub.ox) and reduction (E.sub.red) potential. An adequate method is, for example, cyclic voltammetry. To avoid confusion, the claimed energy levels are defined in terms of comparison with reference compounds having well defined redox potentials in cyclic voltammetry, when measured by a standardized procedure. A simple rule is very often used for the conversion of redox potentials into electron affinities and ionization potential: IP (in eV)=4.8 eV+e*E.sub.ox (wherein E.sub.ox is given in volts vs. ferrocenium/ferrocene (Fc.sup.+/Fc)) and EA (in eV)=4.8 eV+e*E.sub.red (E.sub.red is given in volts vs. Fc.sup.+/Fc) respectively (see B. W. D'Andrade, Org. Electron. 6, 11-20 (2005)), e* is the elemental charge. Conversion factors for recalculation of the electrochemical potentials in the case other reference electrodes or other reference redox pairs are known (see A. J. Bard, L. R. Faulkner, “Electrochemical Methods: Fundamentals and Applications”, Wiley, 2. Ausgabe 2000). The information about the influence of the solution used can be found in N. G. Connelly et al., Chem. Rev. 96, 877 (1996). It is usual, even if not exactly correct, to use the terms “energy of the HOMO” E.sub.(HOMO) and “energy of the LUMO” E.sub.(LUMO), respectively, as synonyms for the ionization energy and electron affinity (Koopmans Theorem). It has to be taken into consideration that the ionization potentials and the electron affinities are usually reported in such a way that a larger value represents a stronger binding of a released or of an absorbed electron, respectively. The energy scale of the frontier molecular orbitals (HOMO, LUMO) is opposed to this. Therefore, in a rough approximation, the following equations are valid: IP=−E.sub.(HOMO) and EA=E.sub.(LUMO) (the zero energy is assigned to the vacuum).
(10) For the chosen reference compounds, the inventors obtained following values of the reduction potential by standardized cyclic voltammetry in tetrahydrofuran (THF) solution vs. Fc.sup.+/Fc:
(11) ##STR00003## ##STR00004## ##STR00005## ##STR00006##
(12) Examples of matrix compounds for state-of-the-artelectrically doped semiconducting materials based on matrix compounds comprising phosphine oxide group and a conjugated system of at least 10 delocalized electrons are
(13) ##STR00007## ##STR00008## ##STR00009## ##STR00010## ##STR00011##
(14) As comparative compounds were used
(15) ##STR00012## ##STR00013## ##STR00014## ##STR00015##
(16) Substrate
(17) 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.
(18) Electrodes
(19) The electrodes are the anode and the cathode, they must provide a certain amount of conductivity, being preferentially conductors. Preferentially the “first electrode” is the cathode. 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 space between the busbars is filled (coated) with a transparent material having certain conductivity, such as graphene, carbon nanotubes, doped organic semiconductors, etc.
(20) In one embodiment, 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.
(21) Typical materials for the Anode are ITO and Ag.
(22) The inventors found that especially advantageous is the use of cathodes prepared substantially of metallic silver, because neat silver provides the best reflectivity, and thus best efficiency, specifically e.g. in bottom emitting devices built on a transparent substrate and having an a transparent conductive oxide anode. Alternatively, for top emitting devices having transparent cathodes, electropositive metals like aluminium are basically inapplicable due to high reflectivity/absorptivity even in very thin layers, and other metals with high work function which can form transparent thin layers, like gold, also afford very poor electron injection. Therefore, substantially silver cathodes could be so far hardly used in air stable devices, e.g. in devices having undoped ETLs or ETLs doped with metal salt additives, because such devices showed high operational voltages and low efficiencies due to poor electron injection from neat silver.
(23) It is equally well possible that the cathode is pre-formed on a substrate (then the device is an inverted device), or the cathode in a non-inverted device is formed by vacuum deposition of a metal or by sputtering. Thin silver cathodes having thickness less than 30 nm, preferably less than 25 nm, more preferably less than 20 nm, most preferably less than 15 nm are transparent and therefore advantageously used in top emitting devices. One embodiment of the invention is a transparent device comprising the transparent silver cathode in a combination with a transparent anode.
(24) Both thick (light reflecting) as well as thin (translucent or transparent) cathodes can be advantageously combined with a light-scattering layer and/or be corrugated, as described in WO2011/115738 or in WO2013/083712.
(25) Hole-Transporting Layer (HTL)
(26) The HTL is a layer comprising a large gap semiconductor responsible to transport holes from the anode or holes from a COL to the light emitting layer (LEL). The HTL is comprised between the anode and the LEL or between the hole generating side of a CGL and the LEL. The HTL can be mixed with another material, for example a p-dopant, in which case it is said the HTL is p-doped. The HTL can be comprised by several layers, which can have different compositions. P-doping of 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.
(27) Suitable hole transport matrices (HTM) can be, for instance compounds from the diamine class, where a delocalized pi-electron system conjugated with lone electron pairs on the nitrogen atoms is provided at least between the two nitrogen atoms of the diamine molecule. Examples are N4,N4′-di(naphthalen-1-yl)-N4,N4′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (HTM1), N4,N4,N4″,N4″-tetra([1,1′-biphenyl]-4-yl)-[1,1′:4′,1″-terphenyl]-4,4″-diamine (HTM2). The synthesis of diamines is well described in literature; many diamine HTMs are readily commercially available.
(28) Hole-Injecting Layer (HIL)
(29) The HIL is a layer which facilitates the injection of holes from the anode or from the hole generating side of a COL 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.
(30) Light-Emitting Layer (LEL)
(31) The light emitting layer must comprise at least one emission material and can optionally comprise additional layers. If the LEL comprises a mixture of two or more materials the charge carrier injection can occur in different materials for instance in a material which is not the emitter, or the charge carrier injection can also occur directly into the emitter. Many different energy transfer processes can occur inside the LEL or adjacent LELs leading to different types of emission. For instance excitons can be formed in a host material and then be transferred as singlet or triplet excitons to an emitter material which can be singlet or triplet emitter which then emits light. A mixture of different types of emitter can be provided for higher efficiency. White light can be realized by using emission from an emitter host and an emitter dopant. In one of preferred embodiments of the invention, the light emitting layer comprises at least one polymer.
(32) Blocking layers can be used to improve the confinement of charge carriers in the LEL, these blocking layers are further explained in U.S. Pat. No. 7,074,500 B2.
(33) Electron-Transporting Layer (ETL)
(34) The ETL is a layer comprising a large gap semiconductor responsible for electron transport from the cathode or electrons from a CGL or EIL (see below) to the LEL. The ETL is comprised between the cathode and the LEL or between the electron generating side of a COL 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. If the used electrical doping creates new charge carriers in the extent that substantially increases conductivity of the doped semiconducting material in comparison with the undoped ETM, then 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 the operational voltage of the device comprising such doped ETL. The preferable mode of electrical doping that is supposed to create new charge carriers is so called redox doping. In case of n-doping, the redox doping corresponds to the transfer of an electron from the dopant to a matrix molecule.
(35) In case of electrical n-doping with metals used as dopants in their substantially elemental form, it is supposed that the electron transfer from the metal atom to the matrix molecule results in a metal cation and an anion radical of the matrix molecule. Hopping of the single electron from the anion radical to an adjacent neutral matrix molecule is the currently supposed mechanism of charge transport in redox n-doped semiconductors.
(36) It is, however, hard to understand all properties of semiconductors n-doped with metals and, specifically, of semiconducting materials of present invention, in terms of electrical redox doping. It is therefore supposed that semiconducting materials of present invention advantageously combine redox doping with yet unknown favourable effects of mixing ETMs with metal atoms and/or their clusters. It is supposed that semiconducting materials of present invention contain a significant part of the added electropositive element in its substantially elemental form. The term “substantially elemental” shall be understood as a form that is, in terms of electronic states and their energies, closer to the state of a free atom or to the state of a cluster of metal atoms than to the state of a metal cation or to the state of a positively charged cluster of metal atoms.
(37) Without being limited by theory, it can be supposed that there is an important difference between the n-doped organic semiconducting materials of previous art and the n-doped semiconducting materials of the present invention. In common organic ETMs of previous art (having reduction potentials roughly in the range between −2.0 and −3.0 V vs. Fc.sup.+/Fc and comprising a conjugated system of at least ten delocalized electrons), the strong redox n-dopants like alkali metals or W.sub.2(hpp).sub.4 are supposed to create the amounts of charge carriers that are commensurate to the number of individual atoms or molecules of the added dopant, and there is indeed an experience that increasing the amount of such strong dopant in conventional matrices above certain level does not bring any substantial gain in electrical properties of the doped material.
(38) On the other hand, it is difficult to speculate which role shall the n-doping strength of the electropositive element play in the matrices of the present invention comprising primarily the polar groups but only very small or none conjugated systems of delocalized electrons.
(39) It may be perhaps be supposed that in such matrices, even for the strongest electropositive element like alkali metals, only part of added atoms of the electropositive element added as the n-dopant reacts with matrix molecules by the redox mechanism under formation corresponding metal cations. It is rather supposed that even in high dilution, when the amount of the matrix is substantially higher than the amount of added metallic element, a substantial part of the metallic element is present in a substantially elemental form. It is further supposed that if the metallic element of the present invention is mixed with matrix of the present invention in a comparable amount, the majority of the added metallic element is present in the resulting doped semiconducting material in the substantially elemental form. This hypothesis seems to provide a reasonable explanation as to why the metallic elements of the present invention can be effectively used in significantly broader range of ratios to the doped matrix than the stronger dopants of previous art, even though they are weaker dopants. The applicable content of the metallic element in the doped semiconducting material of the present invention is roughly in the range from 0.5 weight % up to 25 weight %, preferably in the range from 1 to 20 weight %, more preferably in the range from 2 to 15 weight %, most preferably in the range from 3 to 10 weight %.
(40) Hole blocking layers and electron blocking layers can be employed as usual.
(41) Other layers with different functions can be included, and the device architecture can be adapted as known by the skilled in the art. For example, an Electron-Injecting Layer (EIL) made of metal, metal complex or metal salt can be used between the cathode and the ETL.
(42) Charge Generation Layer (CGL)
(43) 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.
(44) Stacked OLEDs
(45) When the OLED comprises two or more LELs separated by CGLs, the OLED is called a stacked OLED, otherwise it is called a single unit OLED. The group of layers between two closest CGLs or between one of the electrodes and the closest CGL is called 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 described e.g. in US 2009/0045728 A1, US 2010/0288362 A1, and references therein.
(46) Deposition of Organic Layers
(47) 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. Polymeric materials are preferably processed by coating techniques from solutions in appropriate solvents.
(48) 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.
(49) In is supposed that semiconducting material of present invention contains a significant part of the added electropositive element in its substantially elemental form. Consequently, the process of the present invention requires that the electropositive element is vaporized from its elemental or substantially elemental form. In this context, the term “substantially elemental” shall be understood as a form that is, in terms of electronic states and their energies and in terms of chemical bonds, closer to the form of an elemental metal, of a free metal atom or to the form of a cluster of metal atoms, than to the form of a metal salt, of a covalent metal compound, or to the form of a coordination compound of a metal. Typically, metal vapour release from metal alloys according to EP 1 648 042 B1 or WO2007/109815 is understood as the evaporation from a substantially elemental for of the evaporated metal.
(50) Electrical Doping
(51) 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.
(52) 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 not more than slightly more positive, preferably not more than 0.5 eV more positive than 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 not more than slightly more negative, preferably not more than 0.5 eV lower compared to the LUMO energy level of the matrix. It is furthermore desired that the energy level difference for energy transfer from dopant to matrix is smaller than +0.3 eV.
(53) Typical examples of known redox doped hole transport materials are: copper phthalocyanine (CuPc), which HOMO level is approximately −5.2 eV, doped with tetrafluoro-tetracyanoquinonedimethane (F4TCNQ), which LUMO level is about −5.2 eV; zinc phthalocyanine (ZnPc) (HOMO=−5.2 eV) doped with F4TCNQ; α-NPD (N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine) doped with F4TCNQ. α-NPD doped with 2,2′-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (PD1). α-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 3 mol % of PD2.
(54) 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) ditungsten (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).
(55) Besides the redox dopants, certain metal salts can be alternatively used for electrical n-doping resulting in lowering operational voltage in devices comprising the doped layers in comparison with the same device without metal salt. True mechanism how these metal salts, sometimes called “electrically doping additives”, contribute to the lowering of the voltage in electronic devices, is not yet known. It is believed that they change potential barriers on the interfaces between adjacent layers rather than conductivities of the doped layers, because their positive effect on operational voltages is achieved only if layers doped with these additives are very thin. Usually, the electrically undoped or additive doped layers are thinner than 50 nm, preferably thinner than 40 nm, more preferably thinner than 30 nm, even more preferably thinner than 20 nm, most preferably thinner than 15 nm. If the manufacturing process is precise enough, the additive doped layers can be advantageously made thinner than 10 nm or even thinner than 5 nm.
(56) Typical representatives of metal salts which are effective as second electrical dopants in the present invention are salts comprising metal cations bearing one or two elementary charges. Favourably, salts of alkali metals or alkaline earth metals are used. The anion of the salt is preferably an anion providing the salt with sufficient volatility, allowing its deposition under high vacuum conditions, especially in the temperature and pressure range which is comparable with the temperature and pressure range suitable for the deposition of the electron transporting matrix.
(57) Example of such anion is 8-hydroxyquinolinolate anion. Its metal salts, for example lithium 8-hydroxyquinolinolate (LiQ) represented by the formula D1
(58) ##STR00016##
(59) are well known as electrically doping additives.
(60) Another class of metal salts useful as electrical dopants in electron transporting matrices of the present invention represent compounds disclosed in the application PCT/EP2012/074127 (WO2013/079678), having general formula (II)
(61) ##STR00017##
(62) wherein A.sup.1 is a C.sub.6-C.sub.20 arylene and each of A.sup.2-A.sup.3 is independently selected from a C.sub.6-C.sub.20 aryl, wherein the aryl or arylene may be unsubstituted or substituted with groups comprising C and H or with a further LiO group, provided that the given C count in an aryl or arylene group includes also all substituents present on the said group. It is to be understood that the term substituted or unsubstituted arylene stands for a divalent radical derived from substituted or unsubstituted arene, wherein the both adjacent structural moieties (in formula (I), the OLi group and the diaryl prosphine oxide group) are attached directly to an aromatic ring of the arylene group. In examples of the present application, this class of dopants is represented by compound D2
(63) ##STR00018##
(64) wherein Ph is phenyl.
(65) Yet another class of metal salts useful as electrical dopants in electron transporting matrices of the present invention represent compounds disclosed in the application PCT/EP2012/074125 (WO2013/079676), having general formula (III)
(66) ##STR00019##
(67) wherein M is a metal ion, each of A.sup.4-A.sup.7 is independently selected from H, substituted or unsubstituted C.sub.6-C.sub.20 aryl and substituted or unsubstituted C.sub.2-C.sub.20 heteroaryl and n is valence of the metal ion. In examples of the present application, this class of dopants is represented by compound D3
(68) ##STR00020##
V. ADVANTAGEOUS EFFECT OF THE INVENTION
(69) The favourable effects of the inventive electrically doped semiconducting materials are shown in comparison with comparative devices comprising instead of the inventive combination of electron transporting matrices and dopants other combinations of matrices and dopants known in the art. The used devices are described in detail in examples.
(70) In the first screening phase, there were in device of example 1 tested 32 matrix compounds with 5 wt % Mg as dopant. Electron transport matrices comprising phosphine oxide matrices and having their LUMO level expressed in terms of their reduction potential vs. Fc.sup.+/Fc (measured by cyclic voltammetry in THF) higher than compound B0 (−2.21 V under standardized conditions used) performed better than C1 and C2, in terms of operational voltage and/or quantum efficiency of the device, and significantly better than matrices lacking the phosphine oxide group, irrespective of their LUMO level. These observations were confirmed also for several other divalent metals, namely Ca, Sr, Ba, Sm and Yb.
(71) The results are summarized in Table 1, wherein relative change of voltage and efficiency (both measured at current density 10 mA/cm.sup.2) is calculated against the C2/Mg system of previous art taken as the reference. The overall score is calculated by subtraction of relative voltage change from relative change of efficiency.
(72) TABLE-US-00001 TABLE 1 ETL ETL wt % U (U − U.sub.ref)/U.sub.ref EQE (EQE − EQE.sub.ref)/EQE.sub.ref matrix dopant dopant (V) (%) (%) (%) score E1 Li 0.5 3.255 −39 5.340 −5 +34 E1 Mg 5 3.2 −40 5.15 −9 +31 E1 Ca 1 3.497 −35 5.415 −4 +31 E1 Ca 5 3.633 −32 5.235 −7 +25 E1 Ba 1 3.577 −33 6.090 +8 +41 E1 Ba 5 3.491 −35 5.560 −1 +34 E2 Li 0.5 3.264 −39 5.345 −5 +34 E2 Mg 5 3.56 −34 5.33 −5 +29 E2 Ca 1 3.245 −39 5.750 +2 +41 E2 Ca 5 3.83 −29 5.83 +4 +33 E2 Ba 1 6.104 +13 6.245 +14 +1 E2 Ba 5 3.293 −39 6.055 +8 +47 E3 Mg 5 3.68 −31 4.68 −17 +14 E4 Mg 5 3.6 −33 3.9 −31 +2 E4 Ca 2 3.490 −35 5.900 +5 +40 E4 Ba 2 4.020 −25 6.150 +9 +34 E4 Sm 2 3.806 −29 5.600 0 +29 E4 Yb 2 3.844 −28 5.390 −4 +24 E5 Mg 5 3.29 −29 5.45 −3 +26 E6 Mg 5 3.53 −34 7.73 +38 +72 E6 Ca 2 3.350 −37 5.650 +0 +37 E6 Ba 2 3.710 −31 6.320 +12 +43 E6 Sm 2 3.429 −36 6.040 +7 +43 E6 Yb 2 3.427 −36 5.965 +6 +42 E7 Mg 5 5.2 −3 6.48 +15 +18 E8 Mg 5 3.36 −37 5.6 0 +37 E8 Ca 2 3.26 −39 5.24 −7 +32 E8 Ba 2 3.329 −38 5.990 +6 +44 E9 Mg 5 4.51 −16 7.5 +33 +49 E10 Mg 5 3.81 −29 4.7 −17 +12 E11 Mg 5 3.88 −28 4.53 −20 +8 E11 Sr 1 3.642 −32 5.500 −2 +30 E11 Sr 3 3.653 −32 5.075 −10 +22 E11 Sm 2 4.113 −23 5.365 −5 +18 E11 Sm 5 4.067 −24 4.435 −21 +3 E11 Yb 2 3.693 −31 5.485 −3 +28 E11 Yb 5 3.796 −29 5.105 −9 +20 B6 Mg 5 3.44 −36 4.00 −29 +7 B2 Mg 5 5.67 +5 0.66 −89 −94 B4 Ca 2 7.549 +40 0.49 −92 −132 B4 Ba 2 9.784 +82 2.260 −60 −142 B4 Sm 2 7.993 +48 1.400 −75 −123 B4 Yb 2 8.689 +65 1.960 −65 −130 C1 Mg 5 4.2 −22 2.6 −54 −32 C2 Mg 5 5.4 0 5.6 0 0 C3 Mg 5 7.11 +32 0.85 −85 −117 C4 Mg 5 8.3 +54 2.32 −59 −114 C5 Mg 5 6.8 +26 2.9 −49 −75 C6 Mg 5 8.78 +63 3.78 −33 −96 C6 Ca 2 5.500 +2 4.045 −28 −30 C6 Ba 2 7.101 +32 3.865 −31 −63 C6 Sm 2 8.167 +52 2.355 −58 −110 C6 Yb 2 8.130 +51 3.075 −46 −97 C7 Mg 5 4.17 −22 0.9 −84 −62 C7 Sm 2 5.362 0 1.680 −70 −70 C7 Yb 2 5.866 +9 1.890 −67 −76 C8 Mg 5 4.17 −22 1.04 −82 −60 C9 Mg 5 4.2 −22 1 −83 −61 D1 Ca 2 6.731 +25 2.230 −61 −86 D1 Ba 2 8.515 +58 2.295 −60 −118 D1 Sm 2 7.972 +48 2.250 −60 −108 D1 Yb 2 8.006 +49 2.765 −51 −100
(73) In the second phase of the research, various metals were tested in device 2 in matrices E1, E2 and C1, with two different ETL thicknesses 40 nm (U.sub.1 and U.sub.3) and 80 nm (U.sub.2 and U.sub.4) and with two different doping concentrations 5 wt % (U.sub.1 and U.sub.2) and 25 wt %/o (U.sub.3 and U.sub.4), all for current density 10 mA/cm.sup.2.
(74) The results summarized in Table 2 led to a preliminary conclusion that metals that are able to form stable compounds in oxidation state II are especially appropriate for n-doping in phosphine oxide matrices despite their significantly lower reactivity and higher air stability in comparison with the least reactive alkali metal (Li). From the divalent metals tested, only zinc having extremely high sum of the first and second ionization potential failed as n-dopant, whereas aluminium with typical oxidation state III gave reasonably low operational voltages only if present in the doped ETL in the high 25 wt % concentration that afforded ETLs with impractically high light absorption. Transmittance assigned as “OD” that stands for “optical density” is reported in Table 2 only for 25 wt % doping concentration (OD.sub.3 for layer thickness 40 nm and OD.sub.4 for layer thickness 80 nm), as the measurements for lower doping concentrations suffered from bad reproducibility.
(75) The typically trivalent bismuth failed as n-dopant completely, despite its ionization potential does not differ much, e.g. from manganese that showed, quite surprisingly, good doping action at least in E1.
(76) Low values of differences U.sub.1−U.sub.2 and U.sub.3−U.sub.4 can be assigned to doped materials having high conductivity (voltage of the device depends only weakly on the thickness of the doped layer).
(77) TABLE-US-00002 TABLE 2 ETL ETL U.sub.1 U.sub.2 U.sub.1 − U.sub.2 U.sub.3 U.sub.4 U.sub.3 − U.sub.4 matrix dopant (V) (V) (V) (V) (V) (V) OD.sub.3 OD.sub.4 E.sub.1 Li 9.042 >10 na 5.814 6.666 0.853 38 43 E.sub.1 Na 2.863 2.864 0.001 5.354 7.186 1.832 70 64 E.sub.1 Mg 2.954 2.970 0.016 2.965 2.960 0.005 62 33 E.sub.1 Ca 4.625 4.340 −0.286 5.590 9.081 3.491 63 52 E.sub.1 Sr 3.650 3.700 0.050 — — — — — E.sub.1 Ba 4.085 4.023 −0.062 4.360 4.567 0.207 67 73 E.sub.1 Sm 3.138 3.136 −0.002 7.889 — — 63 61 E.sub.1 Eu — — — 4.090 4.119 0.029 — — E.sub.1 Yb 3.022 3.032 0.009 5.578 6.932 1.354 66 68 E.sub.1 Mn 3.38 3.40 0.017 — — — — — E.sub.1 Zn 6.124 8.842 2.718 5.592 7.545 1.954 65 76 E.sub.1 Al 7.614 >10 na 3.321 3.301 −0.020 48 31 E.sub.1 Bi 6.129 8.768 2.640 5.430 7.275 1.845 56 54 E.sub.2 Li 6.333 8.362 2.029 3.307 3.324 0.017 51 32 E.sub.2 Na 3.735 4.533 0.798 >10 >10 na 65 38 E.sub.2 Mg 3.189 3.232 0.043 3.464 3.489 0.025 68 72 E.sub.2 Ca 4.426 4.503 0.078 3.911 4.501 0.590 64 50 E.sub.2 Sr 3.842 3.832 −0.010 — — — — — E.sub.2 Ba 2.929 2.935 0.006 3.397 3.397 0.000 74 71 E.sub.2 Sm 3.610 3.894 0.284 6.053 7.939 1.887 72 63 E.sub.2 Eu — — — 4.516 4.838 0.322 — — E.sub.2 Yb 2.932 2.933 0.001 5.442 6.625 1.183 73 65 E.sub.2 Mn 6.02 8.09 0.99 — — — — — E.sub.2 Zn 7.898 >10 na 7.000 >10 na 66 71 E.sub.2 Al 8.650 >10 na 3.203 3.196 −0.007 39 27 E.sub.1 Bi 7.814 >10 na 7.173 >10 na 64 61 C1 Li 6.997 >10 na 6.209 8.314 2.105 72 48 C1 Na — — — 4.417 4.455 0.037 56 31 C1 Mg 4.180 4.178 −0.002 4.174 4.167 −0.007 62 57 C1 Ca 4.031 4.104 0.074 3.619 3.616 −0.004 38 21 C1 Sr 4.033 4.071 0.0038 — — — — — C1 Ba 3.916 3.909 −0.006 3.969 4.605 0.636 63 39 C1 Sm 4.208 4.207 0.000 4.106 4.104 −0.002 63 48 C1 Eu 3.972 3.984 0.012 — — — — — C1 Yb 4.017 4.167 −0.003 4.148 4.173 0.025 33 29 C1 Mn 4.27 4.26 −0.01 — — — — — C1 Zn 5.084 7.758 2.674 4.699 6.402 1.703 57 50 C1 Al 4.152 4.949 0.797 3.135 3.123 −0.011 45 26 C1 Bi 4.842 6.355 1.513 4.306 4.603 0.297 59 68
(78) It has been observed that in matrices with deep LUMO, like C1, the operational voltage is often surprisingly higher than in devices comprising matrices with the LUMO levels in the range according to invention, despite good conductivity of many doped semiconducting materials based on C1. Apparently, the good conductivity of a semiconducting material is not a sufficient condition for low operational voltage of the device comprising it. Based on this finding, it is supposed that doped semiconducting materials according to this invention enable, besides the reasonable conductivity, also efficient charge injection from the doped layer in the adjacent layer.
(79) In the third research phase, the observed effects were confirmed in OLEDs of example 3 comprising alternative emitter systems and further embodiments of the invention described in examples 4-7 were implemented. The achieved results summarized in the Table 3 confirmed the surprising superiority of phosphine oxide ETL matrices having higher LUMO levels (closer to vacuum level), despite these matrices should be more difficult to dope with the relatively weakly reducing metals used in the present invention in comparison with the phosphine oxide matrices of the previous art (like C1) which were thought to be dopable with Mg owing to their deeper LUMO (further away from vacuum level) and specific structure comprising the metal complexing unit.
(80) This series of experiments confirmed that also with other emitters, the matrix compounds like E1 and E2 having rather high LUMO energy levels perform better than other phosphine oxide matrix compounds, and much better in comparison with matrices lacking the phosphine oxide group.
(81) These results showed that if combined with phosphine oxide matrices having sufficiently high LUMO levels, even substantially air stable metals, possessing moreover further technically advantageous features like good evaporability, can afford electrically doped semiconductive materials and devices that perform equally well or even better than devices available in the art.
(82) TABLE-US-00003 TABLE 3 ETL ETL wt % U (U − U.sub.ref)/U.sub.ref EQE (EQE − EQE.sub.ref)/EQE.sub.ref LEL matrix dopant dopant (V) (%) (%) (%) score ABH- E1 Mg 5 3.498 −35 6.640 +18 +53 112/ E2 Mg 5 3.751 −30 5.975 +6 +36 NUBD- C1 Mg 5 4.545 −15 3.905 −30 −15 369 C10 Mg 5 — — 0 no light — Two- E1 Mg 5 3.480 −35 7.660 +36 +71 colour E2 Mg 5 3.83 −29 6.67 +19 +48 fluoresc. C1 Mg 5 4.970 −8 4.470 −20 −12 white* C10 Mg 5 6.950 +28 0.820 −85 −113 Spiro- E1 Mg 5 3.331 −38 6.19 +10 +48 Pye/ E1 Ca 5 3.311 −38 4.46 −20 +18 BCzVB E1 Ba 12 3.087 −42 3.44 −39 +3 E1 Sm 5 3.318 −38 4.53 −19 +19 E2 Mg 5 3.480 −35 6.08 +8 +43 E2 Ca 5 3.497 −35 3.56 −37 +1 E2 Ba 5 3.090 −42 3.59 −36 +6 C7 Mg 5 3.679 −31 0.32 −94 −63 C7 Ca 5 3.647 −33 0.52 −90 −57 *ABH-112/NUBD-369 + ABH-036/NRD129 (Sun Fine Chemicals)
(83) Finally, the focus returned to the starting point. The remaining goal was to make the redox potential of the comparative compound C2 significantly more negative, and test whether the corresponding LUMO level approaching closer to the zero in absolute energy scale has in phosphine oxide compounds comprising a small conjugated system of less than 10 delocalized electrons similarly positive effects as in the matrix compounds described above. This task was accomplished relatively easily with commercially available compounds A1-A4. All these compounds have redox potentials that are difficult to measure by the standard procedure using THF as a solvent, because their values are more negative than for compound B7.
(84) ##STR00023##
(85) Based on mostly discouraging results of previous experiments with C2 analogs and salt additives, rather negative results were expected from metal doping in matrices which are free of a conjugated system of delocalized electrons or comprising less than 10 delocalized electrons in a conjugated system. Contrary to these expectations, it was surprisingly found that sufficiently strong dopants can provide semiconducting materials of good quality even with compounds having conjugated systems of delocalized electrons that are as small as mere six-electron Hückel systems in isolated aromatic or heteroaromatic rings, provided that the compound still comprises polar groups selected from phosphine oxide and diazole. Subsequently, it was confirmed that such simple two-component semiconducting materials consisting of metal and the first compound having only six delocalized electrons in a conjugated system can be advantageously mixed with a second compound comprising larger conjugated systems of delocalized electrons without loss of performance, even though the second compound does not comprise any polar group at all. It was further surprisingly found that, contrary to previous experience with electron transport compounds comprising both polar group and the conjugated system of at least ten delocalized electrons, in matrices comprising polar group and a conjugated system of less than 10 delocalized electrons or free of the conjugated system of delocalized electrons, there is no significant difference anymore between the doping performance of divalent electropositive metals on one hand and other electropositive metals like alkali metals and typically trivalent rare earth metals like Sc, Y, La or Lu on the other hand. In this sense, it seems unnecessary to make any speculations about the extent of charge transfer between the doping electropositive element and the matrix and try to divide the electropositive elements used as n-dopants in semiconducting materials according to invention in groups of “strong” and “weak” dopants. It is, therefore, supposed that the electropositive element is still at least partially present in its substantially elemental form in the inventive semiconducting materials, and that the favourable results observed in matrices comprising polar phosphine oxide or diazole groups are to be linked to specific interactions of these polar groups with atoms or atom clusters of the electropositive element.
(86) Finally, subsequent experiments with matrix compounds comprising larger systems of delocalized electrons confirmed that with matrices having more negative reduction potentials than 4,7-diphenyl-1,10-phenanthroline and with electropositive elements selected from Li, Na, K, Be, Sc, Y, La, Lu, Ti and V, excellent OLED performance can be achieved basically irrespective of the presence and/or extent of the conjugated system of delocalized electrons in the substantially organic electron transport compound comprising the polar group as defined in the present invention.
(87) In the very final stage, it was additionally recognized that various combinations of polar matrices and doping metals can be advantageously used in combination with silver cathodes, particularly in case that the cathode is adjacent to the substantially organic layer comprising the polar matrix and the electropositive metal.
VI. EXAMPLES
(88) Auxiliary Materials
(89) ##STR00024## ##STR00025##
(90) Auxiliary Procedures
(91) Cyclic Voltammetry
(92) The redox potentials given at particular compounds were measured in an argon deaerated, dry 0.1 M THF solution of the tested substance, under argon atmosphere, with 0.1M tetrabutylammonium hexafluorophosphate supporting electrolyte, between platinum working electrodes and with an Ag/AgCl pseudo-standard electrode, consisting of a silver wire covered by silver chloride and immersed directly in the measured solution, with the scan rate 100 mV/s. The first run was done in the broadest range of the potential set on the working electrodes, and the range was then adjusted within subsequent runs appropriately. The final three runs were done with the addition of ferrocene (in 0.1M concentration) as the standard. The average of potentials corresponding to cathodic and anodic peak of the studied compound, after subtraction of the average of cathodic and anodic potentials observed for the standard Fc.sup.+/Fc redox couple, afforded finally the values reported above. All studied phosphine oxide compounds as well as the reported comparative compounds showed well-defined reversible electrochemical behaviour.
SYNTHESIS EXAMPLES
(93) The synthesis of phosphine oxide ETL matrix compounds is well described in many publications, besides the literature cited at particular compounds listed above and describing typical multistep procedures used for these compounds, the compound E6 was prepared, according to Bull. Chem. Soc. Jpn., 76, 1233-1244 (2003), quite specifically by an anionic rearrangement of the compound E2.
(94) For yet unpublished compounds, the typical procedures were used, as exemplified below specifically for the compounds E5 and E8. All synthesis steps were carried out under argon atmosphere. Commercial materials were used without additional purification. Solvents were dried by appropriate means and deaerated by saturation with argon.
Synthesis Example 1
[1,1′:4′,1″-terphenyl]-3,5-diylbis-diphenylphosphine oxide (E5)
Step 1: 3,5-dibromo-1,1′:4′,1″-terphenyl
(95) ##STR00026##
(96) All components (10.00 g (1.0 eq, 50.50 mmol) [1,1′-biphenyl]-4-yl-boronic acid, 23.85 g (1.5 eq, 75.75 mmol) 1,3,5-tribromobenzene, 1.17 g (2.0 mol %, 1.01 mmol) tetrakis(triphenyl phosphine)palladium(0), 10.70 g (2 eq, 101 mmol) sodium carbonate in 50 mL water, 100 mL ethanol and 310 mL toluene) were mixed together and stirred at reflux for 21 hours. The reaction mixture was cooled to room temperature and diluted with 200 mL toluene (three layers appear). The aqueous layer was extracted with 100 mL toluene, the combined organic layers were washed with 200 mL water, dried and evaporated to dryness. The crude material was purified via column chromatography (SiO.sub.2, hexane/DCM 4:1 v/v) The combined fractions were evaporated, suspended in hexane and filtered off to give 9.4 g of a white glittering solid (yield 48%, HPLC purity 99.79%).
Step 2: [1,1′:4′,1″-terphenyl]-3,5-diylbis-diphenylphosphine oxide
(97) ##STR00027##
(98) All components (5.00 g (1.0 eq, 12.9 mmol) 3,5-dibromo-1,1′:4′,1″-terphenyl from the previous step, 12.0 g (5.0 eq, 64.4 mmol) diphenyl phosphine, 114 mg (5 mol %, 6.44×10.sup.−4 mol) palladium(II) chloride, 3.79 g (3.0 eq, 38.6 mmol) potassium acetate and 100 mL N,N-dimethylformamide) were mixed together and stirred at reflux for 21 hours. Then the reaction mixture was cooled to room temperature; water was added (100 mL) and the mixture was stirred for 30 min, then filtered off. The solid was re-dissolved in DCM (100 mL), H.sub.2O.sub.2 (30 wt % aqueous solution) was added dropwise, and the solution was stirred overnight at room temperature. Then the organic layer was decanted, washed with water (100 mL) twice, dried over MgSO.sub.4, and evaporated to dryness. The resulting oil was triturated in hot MeOH (100 mL) which induced the formation of a solid. After filtration hot, the resulting solid was rinsed with MeOH and dried, yielding 9.7 g of crude product. The crude material was re-dissolved in DCM and chromatographed on a short silica column, elution with ethyl acetate. After evaporation of the eluate to dryness, the resulting solid was triturated in hot MeOH (100 mL), followed by trituration in hot ethyl acetate (50 mL). After drying, the desired compound was obtained in 70% yield (5.71 g). Finally, the product was purified using vacuum sublimation. The pure sublimed compound was amorphous, with no detectable melting peak on the DSC curve, glass transition onset at 86° C., and started to decompose at 490° C.
Synthesis Example 2
(9,9-dihexyl-9H-fluorene-2,7-diyl)bis-diphenylphosphine oxide E8
(99) ##STR00028##
(100) 2,7-Dibromo-9,9-dihexylfluorene (5.00 g, 1.0 eq, 10.2 mmol) was placed in a flask and deaerated with argon. Then anhydrous THF (70 mL) was added, and the mixture was cooled to −78° C. 9.7 mL (2.5M solution in hexanes, 2.4 eq, 24.4 mmol) n-butyllithium were then added dropwise; the resulting solution was stirred for 1 h at −78° C., and then progressively warmed to −50° C. After slow addition of pure chlorodiphenylphosphine (4.0 mL, 2.2 eq, 22.4 mmol), the mixture was left to stir overnight till room temperature. MeOH (20 mL) was added to quench the reaction, and the solution was evaporated to dryness. The solid was re-dissolved in DCM (50 mL), H.sub.2O.sub.2(30 wt % aqueous solution, 15 mL) was added dropwise, and the mixture left under stirring. After 24 h, the organic phase was separated, washed subsequently with water and brine, dried over MgSO.sub.4, and evaporated to dryness. Purification by chromatography (silica, gradient elution from hexane/EtOAc 1:1 v/v to neat EtOAc) provided the desired compound in 34% yield (2.51 g). The material was then further purified by vacuum sublimation.
(101) The pure sublimed compound was amorphous, with no detectable melting peak on the DSC curve, and decomposed at 485° C.
Synthesis Example 3
Diphenyl-(3-(spiro[fluorene-9,9′-xanthen]-2-yl)phenyl)phosphine oxide (E14)
Step 1
Synthesis of 2-bromospiro[fluorene-9,9′-xanthene]
(102) ##STR00029##
(103) 2-Bromo-9-fluorenone (10.00 g, 1.0 eq, 38.6 mmol) and phenol (34.9 g, 9.6 eq., 0.37 mol) were placed in a two-necked flask and degassed with argon. Methanesulfonic acid (10.0 mL, 4.0 eq, 0.15 mol) was added, and the resulting mixture was refluxed for 4 days at 135° C. After cooling to room temperature, DCM (80 mL) and water (130 mL) were added. Upon stirring, the material precipitates. After filtration and abundant washing with MeOH, it was finally triturated in hot EtOH (60 mL) for 1 h, which after filtration afforded the desired compound (11.0 g, 69%), >99% purity according to GCMS.
Step 2
Synthesis of diphenyl(3-(spiro[fluorene-9,9′-xanthen]-2-yl)phenyl)phosphine oxide
(104) ##STR00030##
(105) 2-Bromospiro[fluorene-9,9′-xanthene] (10.0 g, 1.2 eq, 24.3 mmol) was charged in a two-necked flask, degassed with argon, and dissolved in anhydrous THF (240 mL). To this solution were added Mg.sup.0 (827 mg, 1.4 eq, 34.0 mmol), followed by iodomethane (414 mg, 0.12 eq., 2.92 mmol), and the resulting mixture was refluxed for 2 hours. Then, this Grignard solution was cannulated to an anhydrous solution of (3-bromophenyl)diphenylphosphine oxide (7.23 g, 1.0 eq., 203 mmol) and [1,3-bis(diphenylphosphino)propene]nickel(II) chloride (263 mg, 2.0 mol %, 0.49 mmol) in THF (200 mL). The resulting mixture was refluxed overnight after which it was quenched by addition of water (5 mL). The organic solvent was removed under reduced pressure, and the compound extracted with CHCl.sub.3 (200 mL) and water (100 mL); the organic phase was decanted, further washed with water (2×200 mL), dried over MgSO.sub.4 and evaporated to dryness. The crude product was filtered over silica; upon elution with n-hexane/DCM 2:1, apolar impurities was removed, while the desired was isolated using pure DCM. After removal of the DCM, the product was triturated in ethylacetate (100 mL), filtered off, and dried under vacuum yielding the title compound (7.5 g, 61%). Finally, the product was purified by sublimation (78% yield).
(106) Material Properties:
(107) DSC: Melting point: 264° C. (peak), sublimed material
(108) CV: LUMO vs. Fc (THF): −2.71 V (reversible)
Synthesis Example 4
Diphenyl-(4-(spiro[fluorene-9,9′-xanthen]-2-yl)phenyl)phosphine oxide (E15)
(109) ##STR00031##
(110) 2-Bromospiro[fluorene-9,9′-xanthene] (10.0 g, 1.2 eq, 243 mmol) was charged in a two-necked flask, degassed with argon, and dissolved in anhydrous THF (240 mL). To this solution were added Mg.sup.0 (827 mg, 1.4 eq, 34.0 mmol), followed by iodomethane (414 mg, 0.12 eq., 2.92 mmol), and the resulting mixture was refluxed for 2 hours. Then, this Grignard solution was cannulated to an anhydrous solution of (4-bromophenyl)diphenylpbosphine oxide (7.23 g, 1.0 eq., 20.3 mmol) and [1,3-bis(diphenylphosphino)propene]nickel(II) chloride (263 mg, 2.0 mol %, 0.49 mmol) in THF (200 mL). The resulting mixture was refluxed overnight after which it was quenched by addition of water (5 mL). The organic solvent was removed under reduced pressure, and the compound extracted with DCM (2 L) and water (500 mL); the organic phase was decanted, dried over MgSO.sub.4 and evaporated to dryness. The crude product was purified by chromatography over silica, elution with DCM/MeOH 99:1. The fractions containing the product were merged and evaporated to dryness. The resulting solid was then triturated in ethylacetate (50 mL), filter off, and dried under vacuum yielding the title compound (4.0 g, 32%). Finally, the product was purified by sublimation (77% yield).
(111) Material Properties:
(112) DSC: Melting point: 255° C. (peak), sublimed material
(113) CV: LUMO vs. Fe (THF): −2.65 V (reversible)
Device Examples
Comparative Example 1 (Blue OLED)
(114) A first blue emitting device was made by depositing a 40 nm layer of HTM2 doped with PD2 (matrix to dopant weight ratio of 97:3 wt %) onto an ITO-glass substrate, followed by a 90 nm undoped layer of HTM1. Subsequently, a blue fluorescent emitting layer of ABH113 (Sun Fine Chemicals) doped with NUBD370 (Sun Fine Chemicals) (97:3 wt %) was deposited with a thickness of 20 nm. A 36 nm layer of the tested compound was deposited on the emitting layer together with the desired amount of the metallic element (usually, with 5 wt % Mg) as ETL. Subsequently, an aluminium layer with a thickness of 100 nm was deposited as a cathode.
(115) The observed voltages and quantum efficiencies at a current density 10 mA/cm.sup.2 are reported in the Table 1.
Comparative Example 2 (Organic Diode)
(116) A similar device was produced as in Example 1, with the difference that the emitter was omitted, and each combination matrix-dopant was tested in two different thicknesses of the ETL (40 and 80 nm) and with two different dopant concentrations (5 and 25 wt %). The observed voltages at the current density 10 mA/cm.sup.2 and, wherever measured, optical absorbances of the device, are reported in the Table 2.
Comparative Example 3 (Blue or White OLED)
(117) A similar device was produced as in Example 1, with the difference that there were combined various compositions of semiconducting materials in the ETL with various emitter systems. The results were evaluated similarly as in Example 1 and are summarized in Table 3
Comparative Example 4 (Blue OLED)
(118) In device of Example 1, Al cathode was replaced with the sputtered indium tin oxide (ITO) cathode in combination with the Mg or Ba doped ETL. The results showed that ETLs based on divalent metal doped phosphine oxide matrices having redox potentials vs Fc+/Fc in the range from −2.24 V to −2.81 V are applicable also in top emitting OLEDs with cathode made of transparent semiconductive oxide.
Comparative Example 5 (Transparent OLED)
(119) In transparent devices having p-side (substrate with ITO anode, HTL, EBL) as in Example 1, and sputtered 100 nm thick ITO cathode as in Example 4, polymeric emitting layer comprising blue emitting polymer (supplied by Cambridge Display Technology) was successfully tested. The results reported in Table 4 (together with the n-side composition of the device, which in all cases comprised a 20 nm thick HBL consisting of F2 and ETL1 consisting of E2 and D3 in weight ratio 7:3 and having a thickness given in the table) show that ETLs based on phosphine oxide compounds doped with divalent metals are applicable even with polymeric LELs having very high LUMO levels about −2.8 V (in terms of their redox potential vs. Fc+/Fc reference). Without metal doped ETL, the devices had (at current density 10 mA/cm.sup.2) very high voltages, even when EILs made of pure metal were deposited under the ITO electrode.
(120) TABLE-US-00004 TABLE 4 ETL1 ETL2 (nm) (30 nm) EIL U (V) EQE (%) CIE1931x CIE1931y 20 E2/Mg 8:2 5 nm Mg—Ag (9:1) 4.2 1.6 0.16 0.11 10 E2/Mg 9:1 5 nm Ba 4.5 1.3 0.16 0.13 20 E2/Mg 8:2 5 nm Al 5.4 1.1 0.16 0.14 5 E2/Ba 8:2 — 4.6 1.3 0.16 0.18 20 — 5 nm Mg—Ag (9:1) 7.5 1.8 0.17 0.22 10 — 5 nm Ba 6.4 2.2 0.10 0.13
Comparative Example 6 (Metal Deposition Using Linear Vaporization Source)
(121) Evaporation behaviour of Mg in a linear evaporation source was tested. It was demonstrated that Mg can be deposited from linear sources with the rate as high as 1 nm/s without spitting, whereas point evaporation sources spit Mg particles at the same deposition rate significantly.
Comparative Example 7 (Metal+Metal Salt Electrical Doping in the Same ETL)
(122) Mixed ETL comprising a matrix combined with LiQ+either Mg or W.sub.2(hpp).sub.4 a combined two-component doping system showed the superiority of the salt+metal combination.
Comparative Example 8 (Tandem White OLED)
(123) On an ITO substrate, following layers were deposited by vacuum thermal evaporation:
(124) 10 nm thick HTL consisting of 92 wt % auxiliary material F4 doped with 8 wt % PD2, 135 nm thick layer of neat F4, 25 nm thick blue emitting layer ABH113 (Sun Fine Chemicals) doped with NUBD370 (Sun Fine Chemicals) (97:3 wt %), 20 nm thick layer ABH036 (Sun Fine Chemicals), 10 nm thick COL consisting of 95 wt % inventive compound E12 doped with 5 wt % Mg, 10 nm thick HTL consisting of 90 wt % auxiliary material F4 doped with 10 wt % PD2, 30 nm thick layer of neat F4, 15 nm thick layer of neat F3, 30 nm thick proprietary phosphorescent yellow emitting layer, 35 nm thick ETL of auxiliary material F5, 1 nm thick LiF layer and aluminium cathode. The diode operated at 6.81 V had EQE 24.4%.
Comparative Example 9 (Tandem White OLED)
(125) The example 8 was repeated with Yb in the CGL instead of Mg. The diode operated at 6.80 V had EQE 23.9%.
Comparative Example 10 (Tandem White OLED)
(126) The example 9 was repeated with compound E6 instead of E12 in the CGL. The diode operated at 6.71 V had EQE 23.7%.
Comparative Example 11 (Charge Injection into Adjacent or Admixed High-LUMO ETM in a Blue OLED)
(127) Example 1 was repeated with following modifications:
(128) On the ITO substrate, 10 nm thick HTL consisting of 92 wt % auxiliary material F4 doped with 8 wt % PD2 followed by 130 nm thick layer of neat F4 were deposited by VTE. On top of the same emitting layer as in example 1, a 31 nm thick HBL of F6 and on top of it the doped ETL according to Table 5 were deposited subsequently, followed with the aluminium cathode. All deposition steps were done by VTE under pressure below 10.sup.−2 Pa.
(129) TABLE-US-00005 TABLE 5 Mg Yb Ba Li 36 nm 36 nm 36 nm 36 nm E.sub.0 ETM:Mg(95:5) ETM:Yb(95:5) ETM:Ba(95:5) ETM:Li(99.5:0.5) ETM V V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 E5 −2.58 4.2 3.7 E6 −2.62 6.1 3.5 E7 −2.81 >5.2 3.7 E13 −2.78 3.9 3.2 3.2 3.4 E14 −2.71 3.3 A2 <−3.10 3.9 3.9 3.3 A4 <−3.10 4.1 3.2 A2:F6 <−3.10:−2.63 3.3 3.3 A2:B10 <−3.10:−2.91 3.9 3.7 C11 −2.45 >10.0 5.9 5.3
(130) The experiments convincingly showed that compounds E5, E6, E7, E13 and E14 as well as A2 and A4 and their mixtures with ETMs which are free of a polar group provided very good electron injection into adjacent F6 layer, despite its highly negative reduction potential. Due to highly negative reduction potential and low polarity of the F6 layer, the model device mimicks also the properties of devices comprising emitting layers made of light emitting polymers.
Comparative Example 12 (Charge Injection into Adjacent or Admixed High-LUMO ETM in a Blue OLED)
(131) Example 11 was repeated under replacement F6 in HBL with B10. Composition of ETLs and results are shown in Table 6.
(132) TABLE-US-00006 TABLE 6 Ba Yb Yb (EIL) Ba (EIL) 36 nm 36 nm 2-5 nm 2 nm E.sub.0 ETM:Ba(95:5) ETM:Yb(95:5) ETM:Yb(95:5) ETM:Ba(95:5) ETM V V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 E5 −2.58 E6 −2.62 8.1 E7 −2.81 E13 −2.78 5.4 A2 <−3.10 5.6 6.8 5.9 A4 <−3.10 A2:F6 <−3.10:−2.63 7.1 7 A2:B10 <−3.10:−2.91 6.9 7.1
(133) The results showed that semiconducting materials based on phosphine oxide matrices doped with divalent metals allow an efficient electron injection also into a CBP layer having even more negative redox potential than the HBL matrix of the previous example.
Comparative Example 13 (Applicability of Semiconducting Materials Based on Phosphine Oxide Matrices Doped with Divalent Metals in Very Thick ETLs)
(134) Example 11 was repeated with ETLs having thickness 150 nm. The results are shown in Table 7.
(135) TABLE-US-00007 TABLE 7 Mg Yb Li 150 nm 150 nm Ba 150 nm E.sub.0 ETM:Mg(95:5) ETM:Yb(95:5) 150 nm ETM:Li(99.5:0.5) ETM V V at 10 mA/cm.sup.2 V at 10 mA/cm.sup.2 ETM:Ba(95:5) V at 10 mA/cm.sup.2 E5 −2.58 E6 −2.62 7.50 3.6 E7 −2.81 E13 −2.78 3.3 3.2 3.4 E14 −2.71 3.3 A2 <−3.10 3.8 A4 <−3.10 3.5 A2:F6 <−3.10:−2.63 3.3 A2:B10 <−3.10:−2.91 4.8 C11 −2.45 5.2
(136) Comparison with Table 5 demonstrates that devices utilizing in ETLs the inventive devices comprising compounds with highly negative reduction potentials E5, E6, E7, E13, E14, A2 and A4 show practically the same operational voltages as devices of Example 11, despite the thickness of the ETL increased more than four times. The experiment shows that the OLED design according to present invention enables easily tuning the size of optical cavity in electronic devices comprising emitting layers with very negative redox potentials, like light emitting polymers.
Inventive Example 14 (Bottom Emitting OLED with Reflecting Silver Cathode)
(137) The device of Example 11 was reproduced with replacement of aluminium in the cathode with silver, compound C1 as the electron transport matrix and Mg as the electropositive element. With Ag and A1 cathode, the device operated at comparable voltages 4.0 and 3.9 V, but the quantum efficiency with Ag was 5.3%, whereas with Al 4.9%. The comparative device comprising as ETL compound C1 doped with D1 operated with A1 cathode at the voltage 4.7 V with quantum efficiency 3.3%, and with Ag cathode at 5.7 V and quantum efficiency 2.5%.
(138) The features disclosed in the foregoing description, in the claims and in the accompanying drawings may both separately and in any combination be material for realizing the invention in diverse forms thereof. Reference values of physico-chemical properties relevant for the present invention (first and second ionization potential, normal boiling point, standard redox potential) are summarized in Table 8.
(139) TABLE-US-00008 TABLE 8 I.sub.p.sup.I I.sub.p.sup.II Σ I.sub.p.sup.I-II b.p..sup.1 E.sup.0 Element eV .sup.2 eV .sup.2 eV .sup.2 ° C. V Li 5.391 75.640 81.031 1330 −3.04 Na 5.139 47.286 52.425 890 −2.713 Mg 7.646 15.035 22.681 1110 −2.372 Al 5.986 18.829 24.815 2470 −1.676 Ca 6.113 11.872 17.985 1487 −2.84 Mn 7.434 15.640 23.074 2100 −1.18 Zn 9.394 17.964 27.358 907 −0.793 Sr 5.695 11.030 16.725 1380 −2.89 Ba 5.212 10.004 15.216 1637 −2.92 Sm 5.644 11.07 16.714 1900 ** Eu 5.670 11.241 16.911 1440 −1.99 Yb 6.254 12.176 18.430 1430 −2.22 Bi 7.286 16.69 23.976 1560 0.317 .sup.1Yiming Zhang, Julian R. G. Evans, Shoufeng Yang: Corrected Values for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. From: Journal of Chemical & Engineering Data. 56, 2011, p. 328-337; the values fit with values given in articles for individual elements in current German version of Wikipedia. .sup.2 http://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_%28data_page%29
USED ABBREVIATIONS
(140) CGL charge generating layer
(141) CV cyclic voltammetry
(142) DCM dichloromethane
(143) DSC differential scanning calorimetry
(144) EIL electron injecting layer
(145) EQE external quantum efficiency of electroluminescence
(146) ETL electron transporting layer
(147) ETM electron transport matrix
(148) EtOAc ethyl acetate
(149) Fc.sup.+/Fc ferrocenium/ferrocene reference system
(150) h hour
(151) HBL hole blocking layer
(152) HIL hole injecting layer
(153) HOMO highest occupied molecular orbital
(154) HTL hole transporting layer
(155) HTM hole transport matrix
(156) ITO indium tin oxide
(157) LUMO lowest unoccupied molecular orbital
(158) LEL light emitting layer
(159) LiQ lithium 8-hydroxyquinolinolate
(160) MeOH methanol
(161) mol % molar percent
(162) mp melting point
(163) OLED organic light emitting diode
(164) QA quality assurance
(165) RT room temperature
(166) THF tetrahydrofuran
(167) UV ultraviolet (light)
(168) vol % volume percent
(169) v/v volume/volume (ratio)
(170) VTE vacuum thermal evaporation
(171) wt % weight (mass) percent