Patent Description:
In <CIT> a concept is described, as, despite the intrinsically limited to <NUM>% quantum efficiency of direct light emission of a fluorescent blue emitter, the overall efficiency of a white-light OLED can be made to <NUM>%, by using a fluorescent blue emitter with a triplet energy, which is higher than the triplet energy of at least one phosphorescent emitter used. By diffusion of the non-radiative triplet excitons through the blue emitting layer to a further emission layer containing the phosphorescent emitter, and subsequent exothermic energy transfer the triplet excitons of the blue emitter may be used for light emission. In conclusion in this case, a transfer from the fluorescent to the phosphoreszent compuont is described.

<CIT> relates to organic light emitting devices (OLED) comprising a heterostructure for producing luminescence, comprising an emissive layer,.

wherein the emissive layer is a combination of a conductive host material and a fluorescent emissive molecule, such as, for example, DCM2, present as a dopant in said host material: wherein the emissive molecule is adapted to luminesce when a voltage is applied across the heterostructure ; and.

wherein the heterostructure comprises an intersystem crossing molecule, such as, for example, Ir(ppy)<NUM>, which is an efficient phosphor whose emission spectrum substantially overlaps with the absorption spectrum of the emissive molecule.

In <FIG> an OLED is shown with alternating thin layers (5x) of CBP (<NUM>%) and Ir(ppy)<NUM> (<NUM> %) and CBP (<NUM> %) and DCM2 (<NUM> %), respectively.

<CIT> discloses organic light emitting devices, wherein the emission layer comprises at least one mainly emitting in the blue or blue-green spectrum light, fluorescent emitter and at least one predominantly in the non-blue spectral light emitting phosphorescent emitter. The observed small decrease in the quantum efficiency is explained as follows: The problem, that a large accumulation of triplet excitons is produced at the necessary high current densities in the fluorescent emission layer, resulting in the efficiency of the so-called "roll-off " effect, is solved by the direct blending of one or more phosphorescent emitter, since thus the triplet formed on one or all fluorescent emitters are transferred directly to the phosphorescent emitter and the triplet-triplet accumulation cannot arise.

<CIT> (<CIT>) proposes a so-called "singlet harvesting" process. The T<NUM> state is occupied by the already known effects of triplet harvesting, and the usual T<NUM>->S<NUM> phosphorescence results, but with the unfavourably long emission lifetime. The complex compounds proposed for use in accordance with <CIT> have a very small energetic separation ΔE between the singlet S<NUM> and the triplet T<NUM>. In this case, very efficient thermal re-occupation from the initially very efficiently occupied T<NUM> state into the S<NUM> state can occur at room temperature. The thermal re-occupation process described opens a fast emission channel from the short-lived S<NUM> state, and the overall lifetime is significantly reduced.

Baldo et al. , Nature <NUM> (<NUM>) <NUM> use a phosphorescent sensitizer to excite a fluorescent dye. The mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as <NUM>%. In <FIG> of <NPL>) 750an organic light emitting device having the following structure is shown: glass substrate / indium tin oxide (anode) / N,N' -diphenyl-N,N' -bis(<NUM>-methylphenyl)-[<NUM>,<NUM>' -biphenyl]-<NUM>,<NUM>' -diamine (TPD, hole transport layer) /<NUM> alternating layers of <NUM>% Ir(ppy)<NUM>/ CBP and <NUM>% DCM2/CBP / <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-diphenyl-<NUM>,<NUM>-phenanthroline (BCP, blocking layer) / tris-(<NUM>-hydroxyquinoline) aluminium (Alq3, electron transport layer) / Mg/Ag (cathode). The intermolecular energy transfer is dominated by the slow transfer rate out of the T<NUM>-state of the donor (<FIG>). Since intersystem crossing is very fast (~ fs) also the singlet states end up in the T<NUM>-state, which therefore limits the rate of the transfer due to its partly forbidden nature. The sensitized electroluminescence (EL) decay time is measured to be around <NUM> ns. Measurements of the EL decay time in devices is hindered by secondary processes such as charge transport (depending on charge mobility), trapping processes and capacitive processes, which leads to distortions of the radiative decay time of the excited states of emitter species, especially in the range equal, or smaller than <NUM> ns. Therefore a measurement of the EL decay kinetics is not instructive for determining emissive decay times in the present invention.

<NPL>) reports high-efficiency yellow organic light-emitting devices (OLEDs) employing [<NUM>-methyl-<NUM>-[<NUM>,<NUM>,<NUM>,<NUM>-tetrahydro-<NUM>,<NUM>-benzo[ij]quinolizin-<NUM>-yl]ethenyl]-<NUM>-pyran-<NUM>-ylidene] propane-dinitrile (DCM2) as a fluorescent lumophore, with a green electrophosphorescent sensitizer, fac-tris(<NUM>-phenylpyridine) iridium (Ir(ppy)<NUM>) co-doped into a <NUM>,<NUM>' -N,N' -dicarbazole-biphenyl host. The devices exhibit peak external fluorescent quantum and power efficiencies of <NUM>%±<NUM>% (<NUM> cd/A) and <NUM>±<NUM> Im/W at <NUM> mA/cm<NUM>, respectively. The exceptionally high performance for a fluorescent dye is due to the ~<NUM>% efficient transfer of both singlet and triplet excited states in the doubly doped host to the fluorescent material using Ir(ppy)<NUM> as a sensitizing agent.

<NPL> disclose PVK-based single-layer phosphorescent polymer OLEDs (organic light emitting diodes) with different rubrene concentrations. The structure of fabricated devices was: ITO / PEDOT:PSS / PVK + Flr-pic (bis[(<NUM>,<NUM>-difluorophenyl)-pyridinato-N,C<NUM>](picolinate) iridium(III)) + rubrene (<NUM>,<NUM>,<NUM>,<NUM>-tetraphenylnaphthacene) + OXD7/LiF/Al. PVK (poly(N-vinylcarbazole)) is used as a hole transporting host polymer and OXD7 (<NUM>-bis (<NUM>-tert-butylphenyl-<NUM>,<NUM>,<NUM>-oxadiazoyl)phenylene) is used as an electron transporting moiety. The weight ratio of PVK:OXD7 was <NUM>:<NUM> and the weight percent of Flrpic was10 wt% of total amount of organics. The amount of rubrene was varied from <NUM> to 10wt% of Flrpic. Below <NUM>% doping of rubrene the emission from rubrene was hardly detected. At <NUM>% doping of rubrene, however, significant energy transfer from Flrpic to rubrene occurred.

<NPL> report improved efficiency and colour purity of blue electrophosphorescent devices based on Flrpic by codoping a fluorescent emitter <NUM>,<NUM>,<NUM>,<NUM>-tetra-t-butyl-perylene (TBPe). The optimized device codoped with <NUM> wt% Flrpic and <NUM> wt% TBPe shows a maximum current efficiency and power efficiency of <NUM> cd A- <NUM> and <NUM> ImW- <NUM>, which were increased by <NUM>% and <NUM>%, respectively, compared with that of the reference device.

The devices have a structure of ITO/<NUM>-TNATA (<NUM>)/NPB (<NUM>)/mCP : Flrpic : TBPe (<NUM>)/Bphen (<NUM>)/Alq3 (<NUM>)/LiF (<NUM>)/Al (<NUM>). The doping concentration of Flrpic in the EML was fixed at <NUM> wt%, while the concentration of TBPe was varied from <NUM> to <NUM> wt%.

With a few exceptions, the electronic excited state, which can also be formed by energy transfer from a suitable precursor exciton, is either a singlet or triplet state, consisting of three sub-states. Since the two states are generally occupied in a ratio of <NUM>:<NUM> on the basis of spin statistics, the result is that the emission from the singlet state, which is referred to as fluorescence, leads to maximum emission of only <NUM>% of the excitons produced. In contrast, triplet emission, which is referred to as phosphorescence, exploits and converts all excitons and emits them as light (triplet harvesting) such that the internal quantum yield in this case can reach the value of <NUM>%, provided that the additionally excited singlet state, which is above the triplet state in terms of energy, relaxes fully to the triplet state (intersystem crossing, ISC), and radiationless competing processes remain insignificant.

The triplet emitters suitable for triplet harvesting used are generally transition metal complexes in which the metal is selected from the third period of the transition metals and which show emission lifetimes in the µs range. The long decay times of the triplet emitters give rise to interaction of triplet excitons (triplet-triplet annihilation), or interaction of triplet-polaron interaction (triplet-polaron quenching). This leads to a distinct decline in efficiency of the OLED device with rising current density (called "roll-off" behavior). For instance, disadvantages are found particularly in the case of use of emitters with long emission lifetimes for OLED illuminations where a high luminance, for example of more than <NUM> cd/m<NUM>, is required (cf. Furthermore, molecules in electronically excited states are frequently more chemically reactive than in ground states so that the likelihood of unwanted chemical reactions increases with the length of the emission lifetime. The occurrence of such unwanted chemical reactions has a negative effect on the lifetime of the device.

Thus, it is the object of the present invention to provide an emitting system which makes use of <NUM>% of the triplet excitons and enables decay times below <NUM> ns, which result in an increased stability of the emitting system.

It was surprisingly found that doping, for example, an emitting layer containing a luminescent organometallic complex having a small S<NUM>-T<NUM> splitting, with a fluorescent emitter can significantly shorten the emission decay time well below <NUM> ns without sacrificing external quantum efficiency (EQE) because of very efficient energy transfer (<FIG>). Here the transfer originates mainly from the singlet state of the donor molecule in contrast to the scenario shown in <FIG>. Additional positive effects can be an improved OLED stability and a lower roll-off at high luminance.

Accordingly, the present invention relates to organic electronic devices, especially organic light-emitting devices comprising.

To determine the S<NUM>-T<NUM>-splitting a combined approach involving temperature dependent determination of excited state lifetimes and quantum chemical calculations are used.

A <NUM> thin film of the luminescent organometallic complex X in PMMA (<NUM>%) is prepared by doctor blading from dichloromethane onto a quartz substrate. A cryostat (Optistat CF, Oxford Instruments) is used for cooling the sample with liquid helium. The photoluminescence (PL) spectra and the PL decay time at the maximum of the emission are measured with a spectrometer (Edinburgh Instruments FLS 920P) at the following temperatures: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

The temperature dependence of the averaged PL decay time provides information about the energy levels and decay rates of different states that are populated according to the Boltzmann distribution (<NPL>; <NPL>). For a system with two populated excited states the following expression can be fitted to the measured data kav vs T: <MAT>.

For a system with three populated excited states equation <NUM> is used. <MAT> where kav is the decay rate determined from the measurement, kI, kII, kIII are the decay rates of the respective excited states, EI,II and EI,III are the energy differences of the excited states I and II compared to the lowest excited state, kB is the Boltzmann constant and T is the temperature.

A high value of k (><NUM>*<NUM><NUM> s-<NUM>) is an indication that the respective excited state could be a singlet. However, since the spin multiplicity of the excited states cannot be proven by PL measurements, additional quantum chemical calculations were carried out and compared to the excited-state levels found from the fitting of the measurement.

First the triplet geometries of the potential donor molecules were optimized at the unrestricted BP86 [<NPL>) and <NPL>)]/SV(P) [<NPL>)]-level of theory including effective core potentials in case of iridium transition metal complexes [<NPL>)]. Based on these triplet geometries relativistic all electron calculations were performed to determine the S<NUM>-T<NUM>-splitting. Specifically we used the B3LYP-functional [<NPL>)] in combination with an all-electron basis set of double zeta quality [<NPL>)]. Scalar relativistic effects were included at the SCF level via the ZORA approach [<NPL>)]. Based on that wavefunction time dependent density functional calculations were performed including spin orbit coupling via perturbation theory [<NPL>)]. The S<NUM>-T<NUM>-splitting is then finally determined as the energy difference of the lowest T<NUM>-sublevel to the first spin-orbit corrected S<NUM>-state. Relativistic calculations were carried out using the ADF program package [<NUM>. <NUM>, SCM, Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands, http://www. com] whereas for the geometry optimisations the TURBOMOLE program package [<NPL>)] was used. According to the present invention the difference of the singlet energy (ES1(X)) and the triplet energy (ET1(X)) is the experimentally determined value.

The present invention is also directed to the use of a fluorescent emitter Y for doping an emitting layer comprising a luminescent organometallic complex X having a difference of the singlet energy (ES1(X)) and the triplet energy (ET1(X)) of smaller than <NUM> eV [Δ (ES1(X)) - (ET1(X)) < <NUM> eV] and having a singlet energy (ES1(X)) which is greater than the singlet energy of the fluorescent emitter Y (ES1(Y)) [(ES1(X)) > ES1(Y)] and a host compound(s) wherein the emissive lifetime τ<NUM> is in the range of <NUM> to <NUM>.

In accordance with the present invention the decay time of the emission is the emissive lifetime τ<NUM>, which is calculated by τ<NUM>=τv/QY, of thin films consisting of the luminescent organometallic complex X (<NUM> to <NUM> % by weight), fluorescent emitter Y (<NUM> to <NUM> % by weight) and host compound(s) (<NUM> to <NUM> % by weight). The quantum-yields (QY) of the prepared thin films are measured with the integrating-sphere method using the Absolute PL Quantum Yield Measurement System (Hamamatsu, Model C9920-<NUM>) (excitation wavelength: <NUM>).

The excited-state lifetime (τv) of the prepared thin films is measured by exciting the thin films with a pulsed diode laser with an excitation wavelength of <NUM> operated at <NUM> and detecting the emission with time correlated single photon counting (TCSPC).

The emissive lifetime τ<NUM> is in the range of <NUM> to <NUM> ns, more preferably <NUM> to <NUM> ns, most preferred <NUM> to <NUM> ns.

The difference of the singlet energy and the triplet energy of the luminescent organometallic complex X is preferably smaller than <NUM> eV, more preferably smaller than <NUM> eV.

Preferably, the emitting layer comprises <NUM> to <NUM> % by weight of the luminescent organometallic complex X, <NUM> to <NUM> % by weight of the fluorescent emitter Y and <NUM> to <NUM> % by weight of a host compound(s), wherein the amount of the organometallic complex X, the fluorescent emitter Y and the host compound(s) adds up to a total of <NUM>% by weight. More preferably, the emitting layer comprises <NUM> to <NUM> % by weight of the luminescent organometallic complex X, <NUM> to <NUM> % by weight of the fluorescent emitter Y and <NUM> to <NUM> % by weight of a host compound(s), wherein the amount of the organometallic complex X, the fluorescent emitter Y and the host compound(s) adds up to a total of <NUM>% by weight. Most preferred, the emitting layer comprises <NUM> to <NUM> % by weight of the luminescent organometallic complex X, <NUM> to <NUM> % by weight of the fluorescent emitter Y and <NUM> to <NUM> % by weight of a host compound(s), wherein the amount of the organometallic complex X, the fluorescent emitter Y and the host compound(s) adds up to a total of <NUM>% by weight.

Suitable structures of organic light emitting devices are known to those skilled in the art and are specified below.

Substrate may be any suitable substrate that provides desired structural properties.

Substrate may be flexible or rigid. Substrate may be transparent, translucent or opaque. Plastic and glass are examples of preferred rigid substrate materials. Plastic and metal foils are examples of preferred flexible substrate materials. Substrate may be a semiconductor material in order to facilitate the fabrication of circuitry. For example, substrate may be a silicon wafer upon which circuits are fabricated, capable of controlling organic light emitting devices (OLEDs) subsequently deposited on the substrate. Other substrates may be used. The material and thickness of substrate may be chosen to obtain desired structural and optical properties.

In a preferred embodiment the organic light-emitting device according to the present invention comprises in this order:.

In a particularly preferred embodiment the organic light-emitting device according to the present invention comprises in this order:.

The properties and functions of these various layers, as well as example materials are known from the prior art and are described in more detail below on basis of preferred embodiments.

The anode is an electrode which provides positive charge carriers. It may be composed, for example, of materials which comprise a metal, a mixture of different metals, a metal alloy, a metal oxide or a mixture of different metal oxides. Alternatively, the anode may be a conductive polymer. Suitable metals comprise the metals of groups <NUM>, <NUM>, <NUM> and <NUM> of the Periodic Table of the Elements, and also the transition metals of groups <NUM> to <NUM>. When the anode is to be transparent, mixed metal oxides of groups <NUM>, <NUM> and <NUM> of the Periodic Table of the Elements are generally used, for example indium tin oxide (ITO). It is likewise possible that the anode (a) comprises an organic material, for example polyaniline, as described, for example, in <NPL>). Preferred anode materials include conductive metal oxides, such as indium tin oxide (ITO) and indium zinc oxide (IZO), aluminum zinc oxide (AlZnO), and metals. Anode (and substrate) may be sufficiently transparent to create a bottom-emitting device. A preferred transparent substrate and anode combination is commercially available ITO (anode) deposited on glass or plastic (substrate). A reflective anode may be preferred for some top-emitting devices, to increase the amount of light emitted from the top of the device. At least either the anode or the cathode should be at least partly transparent in order to be able to emit the light formed. Other anode materials and structures may be used.

Generally, injection layers are comprised of a material that may improve the injection of charge carriers from one layer, such as an electrode or a charge generating layer, into an adjacent organic layer. Injection layers may also perform a charge transport function. The hole injection layer may be any layer that improves the injection of holes from anode into an adjacent organic layer. A hole injection layer may comprise a solution deposited material, such as a spin-coated polymer, or it may be a vapor deposited small molecule material, such as, for example, CuPc or MTDATA. Polymeric hole-injection materials can be used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, self-doping polymers, such as, for example, sulfonated poly(thiophene-<NUM>-[<NUM>[(<NUM>-methoxyethoxy)ethoxy]-<NUM>,<NUM>-diyl) (Plexcore® OC Conducting Inks commercially available from Plextronics), and copolymers such as poly(<NUM>,<NUM>-ethylenedioxythiophene)/poly(<NUM>-styrenesulfonate) also called PEDOT/PSS.

Either hole-transporting molecules or polymers may be used as the hole transport material. Suitable hole transport materials for layer (c) of the inventive OLED are disclosed, for example, in <NPL>, <CIT>, <CIT>, <CIT> (triarylamines with (di)benzothiophen/(di)benzofuran; <NPL> (indolocarbazoles), <CIT> (substituted phenylamine compounds) and <CIT> (in particular the hole transport materials mentioned on pages <NUM> and <NUM> of <CIT>). Combination of different hole transport material may be used. Reference is made, for example, to <CIT>, wherein
<CHM>
and
<CHM>
constitute the hole transport layer.

Customarily used hole-transporting molecules are selected from the group consisting of
<CHM>
<CHM>
(<NUM>-phenyl-N-(<NUM>-phenylphenyl)-N-[<NUM>-[<NUM>-(N-[<NUM>-(<NUM>-phenyl-phenyl)phenyl]anilino)phenyl]phenyl]aniline),
<CHM>
(<NUM>-phenyl-N-(<NUM>-phenylphenyl)-N-[<NUM>-[<NUM>-(<NUM>-phenyl-N-(<NUM>-phenylphenyl)anilino)phenyl]phenyl]a niline),
<CHM>
(<NUM>-phenyl-N-[<NUM>-(<NUM>-phenylcarbazol-<NUM>-yl)phenyl]-N-(<NUM>-phenylphenyl)aniline),
<CHM>
(<NUM>,<NUM>',<NUM>,<NUM>'-tetraphenylspiro[<NUM>,<NUM>,<NUM>-benzodiazasilole-<NUM>,<NUM>'-3a,7a-dihydro-<NUM>,<NUM>,<NUM>-b enzodiazasilole]),
<CHM>
(N2,N2,N2',N2',N7,N7,N7',N7'-octa-kis(p-tolyl)-<NUM>,<NUM>'-spirobi[fluorene]-<NUM>,<NUM>',<NUM>,<NUM>'-tetramine), <NUM>,<NUM>'-bis[N-(<NUM>-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), N,N'-diphenyl-N,N'-bis(<NUM>-methylphenyl)-[<NUM>,<NUM>'-biphenyl]-<NUM>,<NUM>'-diamine (TPD), <NUM>,<NUM>-bis[(di-<NUM>-tolylamino)phenyl]cyclohexane (TAPC), N,N'-bis(<NUM>-methylphenyl)-N,N'-bis(<NUM>-ethylphenyl)-[<NUM>,<NUM>'-(<NUM>,<NUM>'-dimethyl)-biphenyl]-<NUM>,<NUM>'-diamine (ETPD), tetrakis(<NUM>-methylphenyl)-N,N,N',N'-<NUM>,<NUM>-phenylenediamine (PDA), α-phenyl-<NUM>-N,N-diphenylaminostyrene (TPS), p-(diethylamino)benzaldehyde diphenylhydrazone (DEH), triphenylamine (TPA), bis[<NUM>-(N,N-diethylamino)-<NUM>-methylphenyl](<NUM>-methylphenyl)methane (MPMP), <NUM>-phenyl-<NUM>-[p-(diethylamino)styryl]-<NUM>-[p-(diethylamino)phenyl]pyrazoline (PPR or DEASP), <NUM>,<NUM>-trans-bis(<NUM>-carbazol-<NUM>-yl)-cyclobutane (DCZB), N,N,N',N'-tetrakis(<NUM>-methylphenyl)-(<NUM>,<NUM>'-biphenyl)-<NUM>,<NUM>'-diamine (TTB), fluorine compounds such as <NUM>,<NUM>',<NUM>,<NUM>'-tetra(N,N-di-tolyl)amino-<NUM>,<NUM>-spirobifluorene (spiro-TTB), N,N'-bis(naphthalen-<NUM>-yl)-N,N'-bis(phenyl)-<NUM>,<NUM>-spirobifluorene (spiro-NPB) and <NUM>,<NUM>-bis(<NUM>-(N,N-bis-biphenyl-<NUM>-yl-amino)phenyl-<NUM>-fluorene, benzidine compounds such as N,N'-bis(naphthalen-<NUM>-yl)-N,N'-bis(phenyl)-benzidine and porphyrin compounds such as copper phthalocyanines. In addition, polymeric hole-injection materials can be used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, self-doping polymers, such as, for example, sulfonated poly(thiophene-<NUM>-[<NUM>[(<NUM>-methoxyethoxy)ethoxy]-<NUM>,<NUM>-diyl) (Plexcore® OC Conducting Inks commercially available from Plextronics), and copolymers such as poly(<NUM>,<NUM>-ethylenedioxythiophene)/poly(<NUM>-styrenesulfonate) also called PEDOT/PSS.

In a preferred embodiment it is possible to use metal carbene complexes as hole transport materials. Suitable carbene complexes are, for example, carbene complexes as described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. One example of a suitable carbene complex is Ir(DPBIC)<NUM> with the formula:
<CHM>
Another example of a suitable carbene complex is Ir(ABIC)<NUM> with the formula:
<CHM>.

The hole-transporting layer may also be electronically doped in order to improve the transport properties of the materials used, in order firstly to make the layer thicknesses more generous (avoidance of pinholes/short circuits) and in order secondly to minimize the operating voltage of the device. Electronic doping is known to those skilled in the art and is disclosed, for example, in <NPL> (p-doped organic layers); <NPL> and <NPL> and <NPL>. For example it is possible to use mixtures in the hole-transporting layer, in particular mixtures which lead to electrical p-doping of the hole-transporting layer. p-Doping is achieved by the addition of oxidizing materials. These mixtures may, for example, be the following mixtures: mixtures of the abovementioned hole transport materials with at least one metal oxide, for example MoO<NUM>, MoO<NUM>, WOx, ReO<NUM> and/or V<NUM>O<NUM>, preferably MoO<NUM> and/or ReO<NUM>, more preferably MoO<NUM>, or mixtures comprising the aforementioned hole transport materials and one or more compounds selected from <NUM>,<NUM>,<NUM>,<NUM>-tetracyanoquinodimethane (TCNQ), <NUM>,<NUM>,<NUM>,<NUM>-tetrafluoro-<NUM>,<NUM>,<NUM>,<NUM>-tetracyanoquinodimethane (F<NUM>-TCNQ), <NUM>,<NUM>-bis(<NUM>-hydroxyethoxy)-<NUM>,<NUM>,<NUM>,<NUM>-tetracyanoquinodimethane, bis(tetra-n-butylammonium)tetracyanodiphenoquinodimethane, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>,<NUM>,<NUM>-tetracyanoquinodimethane, tetracyanoethylene, <NUM>,<NUM>,<NUM>,<NUM>-tetracyanonaphtho-<NUM>,<NUM>-quinodimethane, <NUM>-fluoro-<NUM>,<NUM>,<NUM>,<NUM>-tetracyanoquino-dimethane, <NUM>,<NUM>-difluoro-<NUM>,<NUM>,<NUM>,<NUM>-etracyanoquinodimethane, dicyanomethylene-<NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-hexafluoro-<NUM>-naphthalen-<NUM>-ylidene)malononitrile (F<NUM>-TNAP), Mo(tfd)<NUM> (from <NPL>), compounds as described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and quinone compounds as mentioned in <CIT>. Preferred mixtures comprise the aforementioned carbene complexes, such as, for example, the carbene complexes HTM-<NUM> and HTM-<NUM>, and MoO<NUM> and/or ReO<NUM>, especially MoO<NUM>. In a particularly preferred embodiment the holetransport layer comprises from <NUM> to <NUM> wt % of MoO<NUM> and <NUM> to <NUM> wt % carbene complex, especially of a carbene complex HTM-<NUM> and HTM-<NUM>, wherein the total amount of the MoO<NUM> and the carbene complex is <NUM> wt %.

Blocking layers may be used to reduce the number of charge carriers (electrons or holes) and/or excitons that leave the emissive layer. An electron/exciton blocking layer (d) may be disposed between the emitting layer (e) and the hole transport layer (c), to block electrons from emitting layer (e) in the direction of hole transport layer (c). Blocking layers may also be used to block excitons from diffusing out of the emissive layer. Suitable metal complexes for use as electron/exciton blocker material are, for example, carbene complexes as described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. One example of a suitable carbene complex is compound HTM-<NUM>. Another example of a suitable carbene complex is compound HTM-<NUM>.

The device comprises a light-emitting layer (e).

The luminescent organometallic complex X has a difference of the singlet excited state and the triplet excited state of smaller than <NUM> eV [Δ(ES1(X)) - (ET1(X)) < <NUM> eV], especially of smaller than <NUM> eV, very especially of smaller than <NUM> eV. Therefore all organometallic complexes fulfilling this criteria are, in principle, suitable as luminescent organometallic complex X. Criteria, which help to identify most adequate structures fulfilling the requirements stated above, are described below:.

In an embodiment of the present invention the luminescent organometallic complex X is a luminescent iridium complex. Suitable luminescent iridium complexes are specified in the following publications: <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

Preferably, the luminescent organometallic iridium complex X is a luminescent homoleptic meridional iridium carbene complex, or a luminescent heteroleptic iridium carbene complex.

The luminescent iridium complex is preferably a compound of formula
<CHM>
<CHM>
<CHM>
which are, for example, described in <CIT>, <CIT>, <CIT> and <CIT>, wherein the ligand(s) are each bidentate ligands;.

The homoleptic metal-carbene complexes may be present in the form of facial or meridional isomers, wherein the meridional isomers are preferred.

A particularly preferred embodiment of the present invention therefore relates to an OLED comprising at least one homoleptic metal-carbene complex of the general formula (IXa),(IXb), or (IXc) as luminescent organometallic complex X, the homoleptic metal-carbene complex of the formula (IXa),(IXb), or (IXc) preferably being used in the form of the meridional isomer thereof.

In the case of the heteroleptic metal-carbene complexes, four different isomers may be present.

Examples of particularly preferred luminescent iridium complexes are compounds (BE-35a), (BE-<NUM>) to (BE-<NUM>) shown in claim <NUM>. In addition, luminescent iridium complexes described in <CIT> are preferred. Among the luminescent iridium complexes described in <CIT> iridium complexes of formula
<CHM>
are more preferred, wherein X and Y are independently of each other CH, or N, with the proviso that at least one of X and Y is N;.

Examples of iridium complexes described in <CIT>, which can advantageously be used as luminescent metal complex, are shown below. <CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
and
<CHM>.

Luminescent homoleptic meridional iridium carbene complexes are preferred.

Among the luminescent iridium complexes (BE-<NUM>) to (BE-<NUM>) the luminescent iridium complexes (BE-<NUM>), (BE-<NUM>), (BE-<NUM>) and (BE-<NUM>) to (BE-<NUM>) are more preferred.

The homoleptic metal-carbene complexes may be present in the form of facial or meridional isomers, preference being given to the meridional isomers.

In another preferred embodiment of the present invention the luminescent organometallic complex X is a luminescent copper complex having a difference of the singlet energy (ES1(X)) and the triplet energy (ET1(X)) of smaller than <NUM> eV, especially <NUM> eV, very especially <NUM> eV. Such luminescent copper complexes are, for example, described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

<CIT> and <CIT> discloses organic emitter molecules, this molecules having a ΔE(S<NUM>-T<NUM>) value between the lowermost excited singlet state (S<NUM>) and the triplet state beneath it (T<NUM>) of less than <NUM>-<NUM>.

<CIT> discloses neutral mononuclear copper(I) complexes for the emission of light with a structure according to formula
<CHM>
with:.

<CIT> discloses dimeric copper
<CHM>
complexes, wherein: Cu: Cu(I), X: Cl, Br, I, SCN, CN, and/or alkinyl, and NnP: a phosphane ligand substituted with an N-heterocycle.

<CIT> describes copper (I) complexes of the formula
<CHM>.

<CIT> describes copper(I) complexes of formula
<CHM>
wherein.

<CIT> relates to a copper(I) complex of the formula
<CHM>
wherein X* = Cl, Br, I, CN, SCN, alkinyl, and/or N<NUM> (independently of one another); N*nE = a bidentate ligand in which E = phosphanyl/arsenyl group of the form R<NUM>E (in which R = alkyl, aryl, alkoxyl, phenoxyl, or amide); N* = imine function, which is a component of an N-heteroaromatic <NUM>-ring that is selected from the group consisting of pyrazole, isoxazole, isothiazole, triazole, oxadiazole, thiadiazole, tetrazole, oxatriazole, and thiatriazole; and "n" = at least one carbon atom which is likewise a component of the aromatic group, said carbon atom being located directly adjacent both to the imine nitrogen atom as well as to the phosphor or arsenic atom.

Examples of luminescent copper complexes, which can advantageously be used according to the present invention are compounds (Cu-<NUM>) to (Cu-<NUM>) shown in claim <NUM>.

Additional luminescent copper complexes are described, for example, in <NPL>, <NPL>, <NPL> and <NPL>.

The copper complexes (Cu-<NUM>) to (Cu-<NUM>) can advantageously be used in combination with fluorescent emitters (FE-<NUM>), (FE-<NUM>), (FE-<NUM>), (FE-<NUM>), (FE-<NUM>) and (FE-<NUM>).

In addition, the Pd and Pt complexes with small S<NUM>-T<NUM> splitting described in <CIT> may be used as luminescent metal complex.

For efficient light emission the triplet energy of the host material should be larger than the triplet energy of the luminescent organometallic complex X used. Therefore all host materials fulfilling this requirement with respect to luminescent organometallic complex X used are, in principle, suitable as host.

Suitable as host compounds are carbazole derivatives, for example <NUM>,<NUM>'-bis(carbazol-<NUM>-yl)-<NUM>,<NUM>'-dimethylbiphenyl (CDBP), <NUM>,<NUM>'-bis(carbazol-<NUM>-yl)biphenyl (CBP), <NUM>,<NUM>-bis(N-carbazolyl)benzene (mCP), and the host materials specified in the following applications: <CIT>, <CIT>.

Further suitable host materials, which may be small molecules or (co)polymers of the small molecules mentioned, are specified in the following publications: <CIT> (H-<NUM> to H-<NUM>), preferably H-<NUM> to H-<NUM> and H-<NUM> to H-<NUM>, most preferably H-<NUM>, H-<NUM>, H-<NUM>, H-<NUM>, <CIT> (Host <NUM> to Host <NUM>), <CIT> (compounds <NUM> to <NUM> and Host-<NUM> to Host-<NUM> and Host-<NUM>), <CIT> compounds No.<NUM> to No.<NUM>, preferably No.<NUM>, No.<NUM>, No.<NUM> to No. <NUM>, No.<NUM>, No.<NUM>, No. <NUM> to No.<NUM>, more preferably No. <NUM>, No. <NUM> to No. <NUM>, No. <NUM>, No. <NUM>, No.<NUM>, No.<NUM>, and No. <NUM>, <CIT> compounds No. <NUM> to No. <NUM>, <CIT> compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> compounds OC-<NUM> to OC-<NUM> and the polymers of Mo-<NUM> to Mo-<NUM>, <CIT> H-<NUM> to H-<NUM>, <CIT> compounds <NUM> to <NUM>, preferably <NUM>, <NUM>, <NUM>-<NUM>, <NUM>, <NUM>-<NUM>, <NUM>, <NUM>-<NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <CIT> the polymers of monomers <NUM>-<NUM> to <NUM>-<NUM>, preferably of <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, <CIT> the (polymers of) compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> HS-<NUM> to HS-<NUM> and BH-<NUM> to BH-<NUM>, preferably BH-<NUM> to BH-<NUM>, <CIT> the (co)polymers based on the monomers <NUM> to <NUM>, <CIT>, <CIT> the (co)polymers based on the monomers <NUM>-<NUM>, <CIT> preferably the (co)polymers based on the monomers <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds a-<NUM> to a-<NUM> and <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the (co)polymers based on the monomers <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the (co)polymers based on the monomers <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the (co)polymers based on the monomers <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the (co)polymers based on the monomers <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds HA-<NUM> to HA-<NUM>, HB-<NUM> to HB-<NUM>, HC-<NUM> to HC-<NUM> and the (co)polymers based on the monomers HD-<NUM> to HD-<NUM>, <CIT>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds H1 to H42, <CIT>, <CIT> the compounds HS-<NUM> to HS-<NUM> and Poly-<NUM> to Poly-<NUM>, <CIT> the compounds PH-<NUM> to PH-<NUM>, <CIT> the compounds <NUM> to <NUM> and H1 to H71, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds H-<NUM> to H-<NUM>, preferably H-<NUM>, <CIT> the compounds H-<NUM> to H-<NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT>, <CIT>, <CIT>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM>-<NUM> to <NUM>-<NUM>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds <NUM> to <NUM>, <CIT> the compounds H-<NUM> to H-<NUM>, <CIT> the compounds HOST-<NUM> to HOST-<NUM>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>,.

<CIT>, <CIT> and European patent applications <CIT> and <CIT>. and <CIT> (in particular page <NUM> to <NUM> of <CIT>).

The above-mentioned small molecules are more preferred than the above-mentioned (co)polymers of the small molecules.

Further suitable host materials, are described in <CIT> (for example,
<CHM>
best results are achieved if said compounds are combined with
<CHM>
); <CIT> (for example,
<CHM>
and
<CHM>
); <CIT> (for example,
<CHM>
and
<CHM>
); and <CIT> (for example,
<CHM>
).

In a particularly preferred embodiment, one or more compounds of the general formula (X) specified hereinafter are used as host material. <CHM>
wherein.

Additional host materials on basis of dibenzofurane are, for example, described in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. Examples of particularly preferred host materials are shown below:
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

In the above-mentioned compounds T is O, or S, preferably O. If T occurs more than one time in a molecule, all groups T have the same meaning. Compounds SH-<NUM> to SH-<NUM> shown in claim <NUM> are most preferred.

The fluorescent emitter is preferably selected from the following: styrylamine derivatives, indenofluorene derivatives, polyaromatic compounds, anthracene derivatives, tetracene derivatives, xanthene derivatives, perylene derivatives, phenylene derivatives, fluorene derivatives, arylpyrene derivatives, arylenevinylene derivatives, rubrene derivatives, coumarine derivatives, rhodamine derivatives, quinacridone derivatives, dicyanomethylenepyran derivatives, thiopyran, polymethine derivatives, pyrylium and thiapyrylium salts, periflanthene derivatives, indenoperylene derivatives, bis(azinyl)imineboron compounds, bis(azinyl)methine compounds, carbostyryl compounds, monostyrylamines, distyrylamines, tristyrylamines, tetrastyrylamines, styrylphosphines, styryl ethers, arylamines, indenofluorenamines and indenofluorenediamines, benzoindenofluorenamines, benzoindenofluorenediamines, dibenzoindenofluorenamines, dibenzoindenofluorenediamines, substituted or unsubstituted tristilbenamines, distyrylbenzene and distyrylbiphenyl derivatives, triarylamines, triazolo derivatves, naphthalene derivatives, anthracene derivatives, tetracene derivatives, fluorene derivatives, periflanthene derivatives, indenoperylene derivatives, phenanthrene derivatives, perylene derivatives, pyrene derivatives, triazine derivatives, chrysene derivatives, decacyclene derivatives, coronene derivatives, tetraphenylcyclopentadiene derivatives, pentaphenylcyclopentadiene derivatives, fluorene derivatives, spirofluorene derivatives, pyran derivatives, oxazone derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, pyrazine derivatives, cinnamic acid esters, diketopyrrolopyrrole derivatives, and acridone derivatives.

Fluorescent emitter compounds can preferably be polyaromatic compounds, such as, for example, <NUM>,<NUM>-di(<NUM>-naphthylanthracene) and other anthracene derivatives, derivatives of tetracene, xanthene, perylene, such as, for example, <NUM>,<NUM>,<NUM>,<NUM>-tetra-t-butylperylene, phenylene, for example <NUM>,<NUM>'-(bis(<NUM>-ethyl-<NUM>-carbazovinylene)-<NUM>,<NUM>'-biphenyl, fluorene, arylpyrenes (<CIT>), arylenevinylenes (<CIT>, <CIT>), derivatives of rubrene, coumarine, rhodamine, quinacridone, such as, for example, N,N'-dimethylquinacridone (DMQA), dicyanomethylenepyrane, such as, for example, <NUM> (dicyanoethylene)-<NUM>-(<NUM>-dimethylaminostyryl-<NUM>-methyl)-<NUM>-pyrane (DCM), thiopyrans, polymethine, pyrylium and thiapyrylium salts, periflanthene, indenoperylene, bis(azinyl)imineboron compounds (<CIT>), bis(azinyl)methene compounds and carbostyryl compounds.

Furthermore preferred fluorescent emitter compounds can be emitters which are described in <NPL> and "<NPL>.

A monostyrylamine here is a compound which contains one substituted or unsubstituted styryl group and at least one, preferably aromatic, amine. A distyrylamine is preferably a compound which contains two substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. A tristyrylamine is preferably a compound which contains three substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. A tetrastyrylamine is preferably a compound which contains four substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. The styryl group is particularly preferably a stilbene, which may be further substituted. The corresponding phosphines and ethers which can be employed in accordance with the invention are defined analogously to the amines. For the purposes of this invention, arylamine or aromatic amine denotes a compound which contains three substituted or unsubstituted aromatic or heteroaromatic ring systems bonded directly to a nitrogen atom. At least one of these aromatic or heteroaromatic ring systems can be a condensed ring. Preferred examples thereof are aromatic anthracenamines, aromatic anthracenediamines, aromatic pyrenamines, aromatic pyrenediamines, aromatic chrysenamines and aromatic chrysenediamines. An aromatic anthracenamine can be a compound in which one diarylamine group is bonded directly to an anthracene group, preferably in position <NUM>. An aromatic anthracenediamine can be a compound in which two diarylamine groups are bonded directly to an anthracene group, preferably in positions <NUM> and <NUM>. Aromatic pyrenamines, pyrenediamines, chrysenamines and chrysenediamines are defined analogously thereto, in which the diarylamine groups on the pyrene are preferably bonded in position <NUM> or in positions <NUM> and <NUM>.

Furthermore preferred fluorescent emitter compounds are indenofluorenamines and indenofluorenediamines, for example in accordance with <CIT>, benzoindenofluorenamines and benzoindenofluorenediamines, for example in accordance with <CIT>, and dibenzoindenofluorenamines and dibenzoindenofluorenediamines, for example in accordance with <CIT>.

Examples of further fluorescent emitter compounds from the class of the styrylamines which can be employed in accordance with the invention are substituted or unsubstituted tristilbenamines or those described in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. Distyrylbenzene and distyrylbiphenyl derivatives are described in <CIT>. Further styrylamines can be found in <CIT>. Particularly preferred styrylamines and triarylamines are the compounds of the formulae (<NUM>) to (<NUM>) and those which are disclosed in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

Furthermore preferred fluorescent emitter compounds can be taken from the group of the triarylamines as disclosed in <CIT> and <CIT>.

Furthermore preferred fluorescent emitter compounds can be selected from the derivatives of naphthalene, anthracene, tetracene, fluorene, periflanthene, indenoperylene, phenanthrene, perylene (<CIT>), pyrene, chrysene, decacyclene, coronene, tetraphenylcyclopentadiene, pentaphenylcyclopentadiene, fluorene, spirofluorene, rubrene, coumarine (<CIT>, <CIT>, <CIT>), pyran, oxazone, benzoxazole, benzothiazole, benzimidazole, pyrazine, cinnamic acid esters, diketopyrrolopyrrole, acridone and quinacridone (<CIT>).

Of the anthracene compounds, the <NUM>,<NUM>-substituted anthracenes, such as, for example, <NUM>,<NUM>-diphenylanthracene and <NUM>,<NUM>-bis(phenylethynyl) anthracene, are preferred. <NUM>,<NUM>-Bis(<NUM>'-ethynylanthracenyl)benzene may also be preferred as fluorescent emitter compound.

Suitable fluorescent emitter units are furthermore the structures depicted in the following table, and the structures disclosed in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>; <CIT>; <CIT>, <CIT>, <CIT>; <CIT>; <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

<NUM>-<NUM>% emission intensity, relative to the <NUM>% emission maximum, is used to determine the emission onset. For efficient energy transfer the emission onset of the fluorescent emitter (acceptor) should be red-shifted with respect to the emission onset of the luminescent organometallic complex (donor) by <NUM> to <NUM>. Therefore all fluorescent emitters fulfilling this requirement with respect to luminescent organometallic complex X are suitable as fluorescent emitter in this invention.

An important loss channel regarding quantum efficiency can be due to direct transfer of T<NUM>-excitons from the donor molecule to the fluorescent acceptor. Although a significant singlet population in the donor systems described above is expected, still some triplet population will be present. Triplet-transfer according to the Dexter-mechanism (<NPL>)) is a short range process based on electron exchange mechanism between donor and acceptor. For an exchange interaction to be large a good overlap between the HOMOs of the donor and acceptor and simultaneously the overlap of the LUMOs of the donor and acceptor is required. To make this unwanted process as unlikely as possible, spatial separation of HOMO and LUMO on the acceptor should be achieved. Standard quantum chemical calculations (DFT) can give a clear guidance here. For example, the orbital structure of FE-<NUM> is spatially separated and the orbital structure of FE-<NUM> is delocalized according to BP86/SV(P)-level of theory.

Another option is the sterical shielding of the acceptor chromophor to avoid any good overlap between donor and acceptor. FE-<NUM> uses this concept to partly compensate for the lack of spatially separated HOMO/LUMO.

Examples of the fluorescent emitter, which can be advatageously be used according to the present invention are shown below:
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
or
<CHM>.

The fluorescent emitters are commercially available at Luminescence Technology Corp. The fluorescent emitters (FE-<NUM>) and (FE-<NUM>) can advantageously be used with iridium complexes of formula (XIa) and (XIb) as well as iridium complex (BE-<NUM>). The fluorescent emitter (FE-<NUM>) can advantageously be used with iridium complex (BE-<NUM>). The fluorescent emitters (FE-<NUM>), (FE-<NUM>), (FE-<NUM>), (FE-<NUM>), (FE-<NUM>) and (FE-<NUM>) can advantageously be used with iridium complexes of formula (Xlc).

The fluorescent emitters (FE-<NUM>) and (FE-<NUM>) are preferred, the fluorescent emitter (FE-<NUM>) is most preferred.

In a particularly preferred embodiment the emitting layer comprises.

The host compound can be one compound or it can be a mixture of two or more compounds. Advantageously compounds HTM-<NUM> and HTM-<NUM> may be added as co-host.

The preferred combinations of host compound(s), luminescent organometallic complex X and fluorescent emitter Y used in the emitting layer are shown in the tables below:
<CHM>.

Blocking layers may be used to reduce the number of charge carriers (electrons or holes) and/or excitons that leave the emissive layer. The hole blocking layer may be disposed between the emitting layer (e) and electron transport layer (g), to block holes from leaving layer (e) in the direction of electron transport layer (g). Blocking layers may also be used to block excitons from diffusing out of the emissive layer. Suitable hole/exciton material are, in principle, the host compounds mentioned above. The same preferences apply as for the host material.

The at present most preferred hole/exciton blocking materials are compounds SH-<NUM> to SH-<NUM>.

Electron transport layer may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Suitable electron-transporting materials for layer (g) of the inventive OLEDs comprise metals chelated with oxinoid compounds, such as tris(<NUM>-hydroxyquinolato)aluminum (Alq<NUM>), compounds based on phenanthroline such as <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-diphenyl-<NUM>,10phenanthroline (DDPA = BCP), <NUM>,<NUM>-diphenyl-<NUM>,<NUM>-phenanthroline (Bphen), <NUM>,<NUM>,<NUM>,<NUM>-tetraphenyl-<NUM>,<NUM>-phenanthroline, <NUM>,<NUM>-diphenyl-<NUM>,<NUM>-phenanthroline (DPA) or phenanthroline derivatives disclosed in <CIT>, in <CIT>, or in <CIT>, and azole compounds such as <NUM>-(<NUM>-biphenylyl)-<NUM>-(<NUM>-t-butylphenyl)-<NUM>,<NUM>,<NUM>-oxadiazole (PBD) and <NUM>-(<NUM>-biphenylyl)-<NUM>-phenyl-<NUM>-(<NUM>-t-butylphenyl)-<NUM>,<NUM>,<NUM>-triazole (TAZ).

It is likewise possible to use mixtures of at least two materials in the electron-transporting layer, in which case at least one material is electron-conducting. Preferably, in such mixed electron-transporting layers, at least one phenanthroline compound is used, preferably BCP, or at least one pyridine compound according to the formula (VIII) below. More preferably, in mixed electron-transporting layers, in addition to at least one phenanthroline compound, alkaline earth metal or alkali metal hydroxyquinolate complexes, for example Liq, are used. Suitable alkaline earth metal or alkali metal hydroxyquinolate complexes are specified below (formula VII). Reference is made to <CIT>.

The electron-transporting layer may also be electronically doped in order to improve the transport properties of the materials used, in order firstly to make the layer thicknesses more generous (avoidance of pinholes/short circuits) and in order secondly to minimize the operating voltage of the device. Electronic doping is known to those skilled in the art and is disclosed, for example, in <NPL> (p-doped organic layers); <NPL> and <NPL> and <NPL>. For example, it is possible to use mixtures which lead to electrical n-doping of the electron-transporting layer. n-Doping is achieved by the addition of reducing materials. These mixtures may, for example, be mixtures of the abovementioned electron transport materials with alkali/alkaline earth metals or alkali/alkaline earth metal salts, for example Li, Cs, Ca, Sr, Cs<NUM>CO<NUM>, with alkali metal complexes, for example <NUM>-hydroxyquinolatolithium (Liq), and with Y, Ce, Sm, Gd, Tb, Er, Tm, Yb, Li<NUM>N, Rb<NUM>CO<NUM>, dipotassium phthalate, W(hpp)<NUM> from <CIT>, or with compounds described in <CIT>, <CIT>, <CIT> and <CIT>.

In a preferred embodiment, the electron-transporting layer comprises at least one compound of the general formula (VII)
<CHM>
in which.

A very particularly preferred compound of the formula (VII) is
<CHM>
(Liq), which may be present as a single species, or in other forms such as LigQg in which g is an integer, for example Li<NUM>Q<NUM>. Q is an <NUM>-hydroxyquinolate ligand or an <NUM>-hydroxyquinolate derivative.

In a further preferred embodiment, the electron-transporting layer comprises at least one compound of the formula (VIII),
<CHM>
in which.

Preferred compounds of the formula (VIII) are compounds of the formula (VIIIa) in which Q is:
<CHM>
<CHM>.

Particular preference is given to a compound of the formula
<CHM>.

In a further, very particularly preferred embodiment, the electron-transporting layer comprises a compound Liq and a compound ETM-<NUM>.

In a preferred embodiment, the electron-transporting layer comprises the compound of the formula (VII) in an amount of <NUM> to <NUM>% by weight, preferably <NUM> to <NUM>% by weight, more preferably about <NUM>% by weight, where the amount of the compounds of the formulae (VII) and the amount of the compounds of the formulae (VIII) adds up to a total of <NUM>% by weight.

The preparation of the compounds of the formula (VIII) is described in <NPL>, <NPL> and <CIT>, or the compounds can be prepared analogously to the processes disclosed in the aforementioned documents.

It is likewise possible to use mixtures of alkali metal hydroxyquinolate complexes, preferably Liq, and dibenzofuran compounds in the electron-transporting layer. Reference is made to <CIT>. Dibenzofuran compounds A-<NUM> to A-<NUM> and B-<NUM> to B-<NUM> described in <CIT> are preferred, wherein dibenzofuran compound
<CHM>
is most preferred.

In a preferred embodiment, the electron-transporting layer comprises Liq in an amount of <NUM> to <NUM>% by weight, preferably <NUM> to <NUM>% by weight, more preferably about <NUM>% by weight, where the amount of Liq and the amount of the dibenzofuran compound(s), especially ETM-<NUM>, adds up to a total of <NUM>% by weight.

In a preferred embodiment, the electron-transporting layer comprises at least one phenanthroline derivative and/or pyridine derivative.

In a further preferred embodiment, the electron-transporting layer comprises at least one phenanthroline derivative and/or pyridine derivative and at least one alkali metal hydroxyquinolate complex.

In a further preferred embodiment, the electron-transporting layer comprises at least one of the dibenzofuran compounds A-<NUM> to A-<NUM> and B-<NUM> to B-<NUM> described in <CIT>, especially ETM-<NUM>.

In a further preferred embodiment, the electron-transporting layer comprises a compound described in <CIT>, <CIT>, <CIT>, such as, for example, a compound of formula
<CHM><CIT>
, such as, for example, a compound of formula
<CHM>
and <CIT>, such as for example, such as, for example, a compound of formula
<CHM>.

The electron injection layer may be any layer that improves the injection of electrons into an adjacent organic layer. Lithium-comprising organometallic compounds such as <NUM>-hydroxyquinolatolithium (Liq), CsF, NaF, KF, Cs<NUM>CO<NUM> or LiF may be applied between the electron transport layer (g) and the cathode (i) as an electron injection layer (h) in order to reduce the operating voltage.

The cathode (i) is an electrode which serves to introduce electrons or negative charge carriers. The cathode may be any metal or nonmetal which has a lower work function than the anode. Suitable materials for the cathode are selected from the group consisting of alkali metals of group <NUM>, for example Li, Cs, alkaline earth metals of group <NUM>, metals of group <NUM> of the Periodic Table of the Elements, comprising the rare earth metals and the lanthanides and actinides. In addition, metals such as aluminum, indium, calcium, barium, samarium and magnesium, and combinations thereof, may be used.

In general, the different layers, if present, have the following thicknesses:.

The inventive OLED can be produced by methods known to those skilled in the art. In general, the inventive OLED is produced by successive vapor deposition of the individual layers onto a suitable substrate. Suitable substrates are, for example, glass, inorganic semiconductors or polymer films. For vapor deposition, it is possible to use customary techniques, such as thermal evaporation, chemical vapor deposition (CVD), physical vapor deposition (PVD) and others. In an alternative process, the organic layers of the OLED can be applied from solutions or dispersions in suitable solvents, employing coating techniques known to those skilled in the art.

The OLEDs can be used in all apparatus in which electroluminescence is useful. Suitable devices are preferably selected from stationary and mobile visual display units and illumination units. Stationary visual display units are, for example, visual display units of computers, televisions, visual display units in printers, kitchen appliances and advertising panels, illuminations and information panels. Mobile visual display units are, for example, visual display units in cellphones, tablet PCs, laptops, digital cameras, MP3 players, vehicles and destination displays on buses and trains. Further apparatus in which the inventive OLEDs can be used are, for example, keyboards; items of clothing; furniture; wallpaper.

Accordingly, the present invention relates to an apparatus selected from the group consisting of stationary visual display units such as visual display units of computers, televisions, visual display units in printers, kitchen appliances and advertising panels, illuminations, information panels, and mobile visual display units such as visual display units in cellphones, tablet PCs, laptops, digital cameras, MP3 players, vehicles and destination displays on buses and trains; illumination units; keyboards; items of clothing; furniture; wallpaper, comprising at least one inventive organic light-emitting device, or emitting layer.

Another aspect of the invention is an emitting layer, comprising.

Another subject of the present invention is the use of a fluorescent emitter Y for doping an emitting layer comprising a luminescent organometallic complex X having a difference of the singlet energy (ES1(X)) and the triplet energy (ET1(X)) of smaller than <NUM> eV and having a singlet energy (ES1(X)) which is greater than the singlet energy of the fluorescent emitter Y (ES1(Y)) and a host compound(s) to decrease the emissive lifetime τ<NUM> below <NUM> ns, which is calculated by τ<NUM>=τv/QY, of thin films consisting of the luminescent organometallic complex X, fluorescent emitter Y and host compound(s). The decrease of the emissive lifetime τ<NUM> below <NUM> ns take place without sacrificing QY. i.e. the EQE remains fundamentally the same, or is improved.

The emitting layer can be used in light-emitting electrochemical cells (LEECs), OLEDs, OLED sensors, especially in a gas and vapor sensor not hermetically sealed from the outside, optical temperature sensors, organic solar cells (OSCs; organic photovoltaics, OPVs), organic field-effect transistors, organic diodes and organic photodiodes.

The following examples are included for illustrative purposes only and do not limit the scope of the claims. Unless otherwise stated, all parts and percentages are by weight.

The examples which follow, more particularly the methods, materials, conditions, process parameters, apparatus and the like detailed in the examples, are intended to support the present invention, but not to restrict the scope of the present invention. All experiments are carried out in protective gas atmosphere. The percentages and ratios mentioned in the examples below - unless stated otherwise - are % by weight and weight ratios. The meridionale isomers of BE-<NUM>, BE-<NUM>, BE-<NUM>, BE-<NUM>, BE-<NUM>, BE-<NUM>, BE-<NUM> and BE-<NUM> are used in the Examples.

The photoluminescence (PL) spectra of the emissive donor and/or emissive acceptor molecule are measured on thin polymer films doped with the respective molecules. The thin films are prepared by the following procedure: a <NUM>%-w/w polymer solution is made by dissolving <NUM> of the polymer " Plexiglas 6N" (Evonik) in <NUM> of dichloromethane, followed by stirring for one hour. The respective molecules are added to the PMMA solution according to the desired doping concentrations, and stirring is continued for one minute. The solutions are cast by doctor-blading with a film applicator (Model <NUM><NUM>, Erichsen) with a <NUM> gap onto quartz substrates providing thin doped polymer films (thickness ca.

The same procedure described above for the PMMA matrix is used, except that instead of the PMMA polymer <NUM> of the host molecule (SH-<NUM>) are dissolved in <NUM>µl dichloromethane, followed by stirring for one hour.

The PL spectra and quantum yields (QY) of these films are measured with the integrating-sphere method using the absolute PL Quantum Yield Measurement System (Hamamatsu, Model C9920-<NUM>) (excitation wavelength: <NUM> for table <NUM>, <NUM> for tables <NUM> - <NUM>).

The excited-state lifetime (τv) of the prepared films is measured by the following procedure: For excitation a pulsed diode laser with excitation wavelength <NUM> operated at <NUM> is used. Detection is carried out with time correlated single photon counting (TCSPC). The emissive lifetime τ<NUM> is calculated by τ<NUM>=τv/QY.

The luminescent organometallic complex BE-<NUM> is used as donor. The fluorescent emitters FE-<NUM> and FE-<NUM> are used as acceptor.

The first part of the table shows samples with <NUM> % of the donor BE-<NUM> and varying concentrations of the acceptor FE-<NUM> in the host PMMA. The first line shows that the pure donor (<NUM> % doping concentration) has an excited-state lifetime (τv) of <NUM> ns in combination with a quantum yield of <NUM> % and an emission maximum at <NUM>. The pure acceptor (doping concentration of <NUM> %) has an excited-state lifetime of <NUM> ns at ~ <NUM> % quantum efficiency. The emission maximum is at <NUM>. Using now the donor as well as the acceptor as dopands it is shown that a very efficient energy transfer from the donor to the acceptor occurs (<NUM> % quantum efficiency with <NUM> % acceptor doping compared to <NUM> % without acceptor doping). The shift in the emission maximum from <NUM> (donor) to <NUM>-<NUM> (acceptor) supports this interpretation (see <FIG> and <FIG>). It is shown in the table that the excited-state lifetime is reduced to as little as <NUM> ns without substantially sacrificing quantum efficiency.

In the second part of the table the donor concentration is increased to <NUM> %. An overall similar behavior is observed as described for the <NUM> % doping concentration, however with smaller quantum efficiencies.

The third part of table <NUM> describes a system, where PMMA is replaced by the host material SH-<NUM>. FE-<NUM> is significantly blue shifted by ~ <NUM> relative to PMMA. Again the same basic trends are shown including a reduction of the excited-state lifetime below <NUM> ns for <NUM> % of the fluorescent acceptor, FE-<NUM>. Even with the very small difference in emission wavelength between donor and acceptor an efficient transfer occurs.

In the fourth part another fluorescent acceptor molecule is introduced (FE-<NUM>). Here significantly higher concentrations of the acceptor molecule are necessary. With <NUM> % concentration of FE-<NUM> high quantum efficiencies of <NUM> % are achieved in combination with <NUM> ns excited-state lifetime.

Quantum Yield (QY) (%), CIEx,y, and emissive lifetime τ<NUM> (ns) measured for different samples are shown in the Tables <NUM> to <NUM> below. Excitation for determining the QY is carried out at <NUM>, here the absorption is almost exclusively from the donor.

As evident from tables <NUM> to <NUM> the emissive lifetime τ<NUM> can be reduced by the inventive concept to values well below <NUM> ns while maintaining or even increasing the QY. The CIEy coordinate shows that efficient transfer takes place already at low concentrations, as the emission comes from the acceptor.

To determine the S<NUM>-T<NUM>-splitting we use a combined approach involving temperature dependent determination of excited-state lifetimes and quantum chemical calculations.

A <NUM> thin film of the Iridium complex in PMMA (<NUM>%) is prepared by doctor blading from dichloromethane onto a quartz substrate. A cryostat (Optistat CF, Oxford Instruments) is used for cooling the sample with liquid helium. The PL spectra and the PL decay time at the maximum of the emission are measured with a spectrometer (Edinburgh Instruments FLS 920P) at the following temperatures: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

For a system with three populated excited states equation <NUM> is used. <MAT> where kav is the decay rate determined from the measurement, kI, kII, kIII are the decay rates of the respective excited states, EI,III and EI,III are the energy differences of the excited states I and II compared to the lowest excited state, kB is the Boltzmann constant and T is the temperature.

A high value of k (><NUM>*<NUM><NUM> s-<NUM>) is an indication that the respective excited state is a singlet. However, since the spin multiplicity of the excited states cannot be proven by PL measurements, additional quantum chemical calculations have to be carried out and compared to the excited-state levels we find from the fitting of the measurement.

First the triplet geometries of the potential donor molecules were optimized at the unrestricted BP86 [<NPL>) and <NPL>)]/SV(P) [<NPL>)]-level of theory including effective core potentials in case of iridium transition metal complexes [<NPL>)]. Based on these triplet geometries relativistic all electron calculations were performed to determine the S<NUM>-T<NUM>-splitting. Specifically we used the B3LYP-functional [<NPL>)] in combination with an all-electron basis set of double zeta quality [<NPL>)]. Scalar relativistic effects were included at the SCF level via the ZORA approach [<NPL>)]. Based on that wavefunction time dependent density functional calculations were performed including spin orbit coupling via perturbation theory [<NPL>)]. The S<NUM>-T<NUM>-splitting is then finally determined as the energy difference of the lowest T<NUM>-sublevel to the first spin-orbit corrected S<NUM>-state. Relativistic calculations were carried out using the ADF program package [<NUM>. <NPL>] whereas for the geometry optimisations the TURBOMOLE program package [<NPL>)] was used.

To illustrate the validity of the approach a comparison between experimentally fitted and calculated S<NUM>-T<NUM>-levels is given in the Table <NUM> below:.

A very good agreement between calculated and fitted data was obtained. The exceptionally small S<NUM>-T<NUM>-splitting of BE-<NUM> was clearly shown. Ir(ppy)<NUM> and Flrpic are included for extended comparison. S<NUM>-T<NUM>-splittings for Ir(ppy)<NUM> and Flrpic were taken from <NPL>) and literature cited therein. Please note, the S<NUM>-T<NUM>-splittings for Ir(ppy)<NUM> and Flrpic are very approximative in nature due to their determination from peak wavelengths/absorption onsets. Both theory and measurements also agree for these molecules in giving S<NUM>-T<NUM>-splittings significantly larger than <NUM> eV.

Quantum chemical calculations as well as low temperature photoluminescence measurements are performed in order to determine the S<NUM>-T<NUM>-splitting of compound (BE-<NUM>). By employing the following set of equations (<NUM>)-(<NUM>) <MAT> <MAT> <MAT> <MAT> and identifying the rate at <NUM> with the T<NUM>-rate one can fit the S<NUM> emissive rate and the S<NUM>-T<NUM>-splitting simultaneously. We obtain an emissive lifetime of <NUM> ns for the S<NUM>-state, <NUM> for the T<NUM>-state and <NUM> eV for the S<NUM>-T<NUM>-splitting. This exceptionally small value leads to an Boltzmann-population of the S<NUM>-state of - <NUM> %, thus also explaining the very efficient energy transfer described in the preceding section. Since the spin multiplicity of the states cannot be directly proven by the PL measurements we carried out additional relativistic quantum chemical calculations. Here we find in agreement with the above interpretation a very small S<NUM>-T<NUM>-splitting of <NUM> eV.

The ITO substrate used as the anode is cleaned first with commercial detergents for LCD production (Deconex® 20NS, and 250RGAN-ACID® neutralizing agent) and then in an acetone/isopropanol mixture in an ultrasound bath. To eliminate possible organic residues, the substrate is exposed to a continuous ozone flow in an ozone oven for a further <NUM> minutes. This treatment also improves the hole injection properties of the ITO. Thereafter, the organic materials specified below are applied by vapor deposition to the cleaned substrate at about <NUM>-<NUM>-<NUM>-<NUM> mbar at a rate of approx. <NUM>-<NUM>/min.

The hole injection, conductor and exciton blocker applied to the substrate is
<CHM>
with a thickness between <NUM> and <NUM>, of which the <NUM> to <NUM> are doped with MoO<NUM>. The remaining <NUM> of Ir(DPBIC)<NUM> serve as an exciton blocker. Subsequently, the emission layer (EML) is deposited as a mixture of luminescent organometallic complex BE-X (<NUM> to <NUM>% by wt. ), fluorescent emitter FE-X (<NUM> to <NUM>% by wt. ) and host compound
<CHM>
or
<CHM>
(SH-<NUM>) (<NUM> to <NUM>% by wt. ) by vapor deposition with a thickness of <NUM>. Subsequently, SH-<NUM> or SH-<NUM> is applied by vapor deposition with a thickness of <NUM> as a hole blocker.

Next, as an electron transporting layer, a mixture of
<CHM>
and
<CHM>
(Lia) (<NUM>:<NUM>) is applied bv vapor deposition (<NUM> to <NUM>). Then, following <NUM> of KF deposition by vapor deposition, a <NUM>-thick Al electrode is finally deposited by thermal evaporation. All components are adhesive-bonded to a glass lid in an inert nitrogen atmosphere.

Comparative Device <NUM> has the following architecture:
ITO - <NUM> Ir(DPBIC)<NUM>:MoO<NUM> (<NUM>:<NUM>) - <NUM> Ir(DPBIC)<NUM> - <NUM> BE-<NUM>/FE-<NUM>/SH-<NUM> (<NUM>:<NUM>:<NUM>) - <NUM> SH-<NUM> - <NUM> ETM-<NUM>:Liq (<NUM>:<NUM>) - <NUM> KF - <NUM> Al
Devices <NUM> is obtained in analogy to Comparative Device <NUM>. The device architecture of Device <NUM> is shown below:
ITO - <NUM> Ir(DPBIC)<NUM>:MoO<NUM> (<NUM>:<NUM>) - <NUM> Ir(DPBIC)<NUM> - <NUM> BE-<NUM>/FE-<NUM>/SH-<NUM> (<NUM>:<NUM>:<NUM>) - <NUM> SH-<NUM> - <NUM> ETM-<NUM>:Liq (<NUM>:<NUM>) - <NUM> KF - <NUM> Al.

To characterize the OLED, electroluminescence spectra are recorded at various currents and voltages. In addition, the current-voltage characteristic is measured in combination with the luminance to determine luminous efficiency and external quantum efficiency (EQE). Driving voltage U and EQE are given at luminance (L) = <NUM> cd/m<NUM> and Commission Internationale de l'Eclairage (CIE) coordinate are given at 5mA/cm<NUM> except otherwise stated. Furthermore, <NUM>% lifetime (LT50) is measured at constant current density J=25mA/cm<NUM>, the time spent until the initial luminance is reduced to <NUM>%. EQE and LT50 of the Comparative Application Examples are set to <NUM> and EQE and LT50 of the Application Examples are specified in relation to those of the Comparative Application Examples.

Device <NUM> and Devices <NUM> and <NUM> are obtained in analogy to Comp. Application Example <NUM>. The device architectures of Comp. Device <NUM> and Devices <NUM> and <NUM> are shown below:.

ITO - <NUM> Ir(DPBIC)<NUM>:MoO<NUM> (<NUM>:<NUM>) - <NUM> Ir(DPBIC)<NUM> - <NUM> BE-<NUM>/FE-<NUM>/SH-<NUM> (<NUM>:<NUM>:<NUM>) - <NUM> SH-<NUM> - <NUM> ETM-<NUM>:Liq (<NUM>:<NUM>) - <NUM> KF - <NUM> Al.

Device <NUM> and Devices <NUM> to <NUM> are obtained in analogy to Comp. Application Example <NUM>. The device architectures of Comp. Device <NUM> and Devices <NUM> to <NUM> are shown below:.

Device <NUM> and Device <NUM> are obtained in analogy to Comp. Application Example <NUM>. The device architectures of Comp. Device <NUM> and Device <NUM> are shown below:.

Device <NUM> and Devices <NUM> to <NUM> are obtained in analogy to Comp. Application Example <NUM>. The device architectures of Comp. Device <NUM> and Device <NUM> and <NUM> are shown below:.

Device <NUM> and Devices <NUM> to <NUM> are obtained in analogy to Comp. Application Example <NUM>. The device architectures of Comp. Device <NUM> and Device <NUM> to <NUM> are shown below:.

Device <NUM> and Devices <NUM> and <NUM> are obtained in analogy to Comp. Application Example <NUM>. The device architectures of Comp. Device <NUM> and Device <NUM> and <NUM> are shown below:.

As evident from Tables <NUM> to <NUM> the EQE and/or lifetime of devices of the present invention, comprising organometallic complex X, fluorescent emitter Y and host compound(s), is increased in comparison to devices, comprising only organometallic complex X and host compound(s).

Claim 1:
An organic light-emitting device comprising
(a) an anode,
(i) a cathode, and
(e) an emitting layer between the anode and cathode, comprising
<NUM> to <NUM> % by weight of a luminescent organometallic complex X having a difference of the singlet energy (Es1(X)) and the triplet energy (ET1(X)) of no more than <NUM> eV, wherein experimental measurements involving temperature dependent determination of excited state lifetimes and quantum chemical calculations are useable to calculate the singlet energy and triplet energy difference, and wherein the difference of the singlet energy (Es1(X)) and the triplet energy (ET1(X)) is determined as the energy difference of the lowest T<NUM>-sublevel to the first spin-orbit corrected S<NUM>-state,
<NUM> to <NUM> % by weight of a fluorescent emitter Y and
<NUM> to <NUM> % by weight of a host compound(s), wherein the amount of the organometallic complex X, the fluorescent emitter Y and the host compound(s) adds up to a total of <NUM>% by weight and the singlet energy of the luminescent organometallic complex X (Es1(X)) is greater than the singlet energy of the fluorescent emitter Y (Es1(Y));
wherein the emissive lifetime τo, which is calculated by τo=τv/QY, of thin films consisting of the luminescent organometallic complex X (<NUM> to <NUM> % by weight), fluorescent emitter Y (<NUM> to <NUM> % by weight) and host compound(s) (<NUM> to <NUM> % by weight) is in the range <NUM> to <NUM> ns, wherein the decay time of the emission is the emissive lifetime τo, the excited state lifetime of the emitting layer is τv, and QY is the quantum yield of the emitting layer.