Organic emitter layer, organic light-emitting diode and use of heavy atoms in an organic emitter layer of an organic light-emitting diode

Abstract

Organic emitter layer (100), comprising - organic emitter molecules (1), each having at least one excited triplet state (TE1) and at least one excited singlet state (SE1), wherein the proportion of emitter molecules (1) in the emitter layer (100) is between 1 vol% and 40 vol% inclusive - an organic matrix material (10) comprising organic first matrix molecules (2), wherein the first matrix molecules (2) each have at least one excited triplet state (TA1) and at least one excited singlet state (SA1) and are selected from fluorene derivatives, wherein - the emitter molecules (1) are embedded in the matrix material (10), - during operation of the emitter layer (100), the triplet states (TA1) and the singlet states (SA1) of the first matrix molecules (2) are excited, - during operation, the excitation energy of these states is at least partially is transferred to the emitter molecules (1),such that the singlet states (SE1) in the emitter molecules (1) are excited, - during operation, a transition from the singlet states (SE1) of the emitter molecules (1) to the ground state (SE0]) of the emitter molecules (1) occurs with at least partial emission of electromagnetic radiation, - in the first matrix molecules (2), the magnitude of the energy level difference |ΔE(SA1-TA1)| between the triplet state (TA1) and the singlet state (SA1) is at most 2500 cm-1, - a time constant τA for the transition from the triplet state (TA1) to the singlet state (SA1) in the first matrix molecules (2) is at most 1 10-6 s, - heavy atoms (3) with an atomic number of at least 16 are intentionally introduced into the matrix material (10),wherein the heavy atoms (3) are free or quasi-free atoms in the matrix material (10) or wherein the heavy atoms (3) are present in heavy atom-containing compounds and are coordinatively or covalently bound to organic or inorganic ligands, wherein the proportion of heavy atoms (3) and / or heavy atom-containing compounds in the emitter layer (100) is at least 3 vol%.

Description

[0001] An organic emitter layer is specified. Furthermore, an organic light-emitting diode is specified. Furthermore, the use of heavy atoms in an emitter layer of an organic light-emitting diode is specified.

[0002] A salt of an organometallic complex cation and an organometallic complex anion is known from US 2011 / 0 177 630 A1. US 2005 / 0 194 586 A1 describes a light-emitting element and a method for its production. The publication Furukawa T. et al., Scientific Reports, Vol. 5, 2015, 8429, 1-8, describes a dual increase in electroluminescent efficiency and operational stability through rapid upconversion of triple excitons in OLEDs.

[0003] One problem to be solved is to specify an organic emitter layer that exhibits a particularly high luminous efficacy or quantum efficiency. Further problems to be solved include specifying an organic light-emitting diode (OLED) with such an emitter layer and the use of heavy atoms in an OLED emitter layer.

[0004] These objects are solved by the subject matter of the independent patent claims. Advantageous embodiments and further developments are the subject matter of the dependent patent claims.

[0005] The invention relates to an organic emitter layer according to claim 1. Furthermore, the invention relates to the use of heavy atoms having an atomic number of at least 16 in an organic emitter layer of an organic light-emitting diode according to claim 13.

[0006] According to at least one embodiment, the organic emitter layer comprises organic emitter molecules, each having at least one excited triplet state and at least one excited singlet state. An excited state is a state that is energetically higher than the ground state of the molecule. During operation of the emitter layer, the triplet and singlet states of the emitter molecules can be excited. The triplet state is a spin S = 1 state, the singlet state a spin S = 0 state. Each triplet state can exist in three configurations, m S = -1, 0, 1, the singlet state in only one configuration, m S = 0, be occupied.

[0007] According to at least one embodiment, the emitter layer comprises an organic matrix material comprising organic first matrix molecules. The matrix material can thus be a mixture of various organic and inorganic molecules, wherein some or all of the organic molecules are first organic matrix molecules. The first matrix molecules each have at least one excited triplet state and at least one excited singlet state. The triplet states and singlet states of the first matrix molecules can also be excited during operation of the emitter layer.

[0008] In general, the triplet state in both the emitter molecules and the first matrix molecules is energetically lower than the corresponding singlet state.

[0009] According to at least one embodiment, the emitter molecules are embedded in the matrix material. This means, in particular, that the emitter molecules are partially or completely surrounded by the matrix material and the first matrix molecules. The emitter layer is therefore preferably a homogeneous mixture of emitter molecules and the matrix material.

[0010] According to at least one embodiment, the triplet states and the singlet states of the first matrix molecules are excited or populated during operation of the emitter layer. The excitation can be achieved, for example, by either electrical or optical excitation.

[0011] For example, the emitter layer is arranged between two electrodes, an anode and a cathode. Electrons can then enter the emitter layer from the cathode, and holes from the anode. An electron and a hole can then, if they come close enough, form an exciton. For example, a hole is first trapped within a first matrix molecule, which then forms an exciton with an approaching electron. The exciton can be formed either in the spin singlet state, S = 0, or in the spin triplet state, S = 1. If the electron of the exciton is then close enough to the first matrix molecule with the corresponding hole, the electron can quickly jump into the first matrix molecule and thus occupy an excited state in the first matrix molecule. Depending on whether the previously formed exciton was an S = 0 or an S = 1 exciton, the singlet or triplet states can be occupied in this way.

[0012] The functioning of organic emitter layers, in particular the excitation of molecules via excitons, is described, for example, in the publication DE 10 2011 089 687 A1 or in the paper "The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs" by Hartmut Yersin et al., Coordination Chemistry Reviews, Volume 255, Issues 21-22, November 2011, Pages 2622-2652.

[0013] Alternatively, it is also possible to populate the singlet and triplet states of the first matrix molecules by optical excitation, so-called photoexcitation, for example by irradiation with electromagnetic radiation.

[0014] According to at least one embodiment, during operation of the emitter layer, the excitation energy of the triplet states and the singlet states of the first matrix molecules is at least partially transferred to the emitter molecules, so that the singlet states of the emitter molecules are excited or populated. During operation, the first matrix molecules are preferably excited first, and in some or all cases, at least part of the corresponding excitation energy is then transferred to the emitter molecules, so that the emitter molecules are excited.

[0015] According to at least one embodiment, transitions from the singlet states of the emitter molecules to the ground state occur with at least partial emission of electromagnetic radiation. The emitter molecules are thus configured to emit electromagnetic radiation during normal operation of the emitter layer. In addition to the radiative transition from an excited state to the ground state, a non-radiative transition is also conceivable.

[0016] According to at least one embodiment, the magnitude of the energy level difference |ΔE(S A1 -T A1 )| between the triplet state T A1 and the singlet state S A1 of the first matrix molecules at most 2500 cm -1 or a maximum of 1000 cm -1 or a maximum of 500 cm -1 . In this case, the energy is expressed by the wavenumber k, where the wavenumber k corresponds to the inverse of the wavelength λ emitted by a photon with energy |ΔE(SA1 -T A1 )|. The conversion between energy and wavenumber is done using the following formula: E=h⋅cλ=h⋅c⋅k

[0017] The wavenumber of k = 2500 cm -1 corresponds to approximately 0.30996 eV. The splitting between the triplet state and the singlet state of the first matrix molecules is therefore small, so that according to Boltzmann statistics even at room temperature (k B T = 8.617·10 -5 eV / K · 298 K = 0.026 eV), a thermal transition between the triplet and singlet states of the first matrix molecules is possible. In particular, the organic emitter layer can also be operated at room temperature or temperatures between -40°C and +100°C.

[0018] According to at least one embodiment, the time constant τ in the first matrix molecules is A for the transition from the triplet state to the singlet state at most 1·10 -6 s or at most 1·10-7 s or at most 1·10 -8 s or at most 1·10 -9 s or at most 1·10 -10 This triplet-singlet transition is also called inter-system crossing, or ISC for short. Such processes are also known, for example, from the publication DE 10 2011 089 687 A1. The transition probability between the triplet state and the singlet state (ISC process) and thus the time constant τ A depends, among other things, on the strength of the spin-orbit coupling.

[0019] According to at least one embodiment, heavy atoms are intentionally introduced into the matrix material, in particular heavy atoms with an atomic number of at least 16. The atomic number 16 corresponds to the element sulfur.

[0020] In at least one embodiment, the organic emitter layer comprises organic emitter molecules, each having at least one excited triplet state and at least one excited singlet state. Furthermore, the emitter layer comprises an organic matrix material comprising organic first matrix molecules, wherein the first matrix molecules have at least one excited triplet state and at least one excited singlet state. The emitter molecules are embedded in the matrix material. During operation of the emitter layer, the triplet and singlet states of the first matrix molecules are excited, and the excitation energy is subsequently transferred to the emitter molecules, so that the singlet states are excited there. From the singlet states of the emitter molecules, a transition to the ground state takes place during operation, with at least partial emission of electromagnetic radiation. The magnitude of the energy level difference |ΔE(SA1 -T A1 )| between the triplet state and the singlet state of the first matrix molecules is at most 2500 cm -1 . In the first matrix molecules, the time constant τ is A for the transition from the triplet state to the singlet state at most 1·10 -6 s. Furthermore, heavy atoms with an atomic number of at least 16 are intentionally introduced into the matrix material.

[0021] Organic light-emitting diodes use light-emitting organic molecules that are excited during operation. Electromagnetic radiation is emitted upon transition to the ground state. Typically, the transition to the ground state occurs either from a triplet or a singlet state. Due to spin statistics, 75% of excitations lead to the triplet state and only 25% to the singlet state. Since the ground state is also predominantly a singlet state, the radiative transition from the excited singlet state to the ground state is strongly allowed, with typical lifetimes of 1 ns to 100 ns. This rapid radiation-emitting transition is called fluorescence.

[0022] The transition from the triplet state to the ground state, however, is generally strongly suppressed due to the often weak spin-orbit coupling in purely organic molecules, resulting in a large time constant for the transition, for example, ≥ 100 µs or ≥ 1 ms. The radiative transition from the triplet state to the ground state, also called phosphorescence, then competes strongly with non-radiative transitions. Non-radiative transitions often even predominate. In the worst case, 75% of the excitations in the LED—namely, all triplet state excitations—are lost, i.e., recombine without emitting radiation.

[0023] This consideration explains why the internal quantum efficiency, i.e. the number of photons generated per excitation, in such fluorescent emitter materials or light-emitting diodes is only a maximum of 25%.

[0024] The invention described here utilizes, among other things, the idea of not directly exciting the emitter molecules, but rather first exciting the first matrix molecules and causing an increased population of the singlet states within the first matrix molecules. The excitation energy is then transferred to the emitter molecules. In this process, the excited singlet states of the first matrix molecules result in excited singlet states in the emitter molecules.

[0025] In the present invention, the energy splitting between the triplet state and the singlet state in the first matrix molecules is chosen to be so small that a transition from the triplet state—which is usually energetically lower than the corresponding singlet state—to the singlet state is already possible due to thermal excitations (ISC process). The above-mentioned value, according to which only 25% of excitations lead to an excited singlet state, can thus be increased to a larger percentage. When the excitation is transferred to the emitter molecules, a larger percentage of the singlet states in the emitter molecules are also occupied, which can increase the internal quantum efficiency to over 25%.

[0026] However, since for the thermal excitation in the first matrix molecules from the triplet state to the singlet state not only the energy level separation |ΔE(S A1 -T A1)| of the two states is crucial, but also the spin-orbit coupling, heavy atoms are intentionally introduced into the matrix material in the present invention. The additional heavy atoms cause an additional, preferably greatly increased spin-orbit coupling in the first matrix molecules. This then further increases the transition probability from the triplet state to the singlet state in the first matrix molecules. Together with the small energy level separation |ΔE(S A1 -T A1)|, a particularly efficient population of the singlet states from the triplet states is achieved in the first matrix molecules, so that a large portion of the excitations generated in the emitter layer leads to excitations of the singlet states in the emitter molecules, which then decay to the ground state with fluorescence. Compared to conventional organic emitter layers, the emitter layer described here thus exhibits a particularly high quantum efficiency.

[0027] The energy splitting |ΔE(S A1 -T A1) | between the triplet state and the singlet state can be determined in various ways. One possibility is to determine the energy splitting through quantum mechanical calculations using well-known computer programs. For example, TDDFT calculations using commercially available Gaussian 09 or ADF Amsterdam Density Functional Software programs are suitable (see also publication DE 10 2011 089 687 A1).

[0028] In addition, it is also possible to determine the energy splitting between the triplet and singlet states experimentally. The intensity ratio of fluorescence and phosphorescence, i.e., the ratio of the intensity of the transition from the singlet state to the ground state (Int(S1 → S0)) to the intensity of the transition from the triplet state to the ground state (Int(T1 → S0)), is as follows (see publication DE 10 2011 089 687 A1): Int(S1→S0)Int(S1→S0)=k(S1)k(T1)⋅exp(−ΔEkBT)

[0029] Where k B is the Boltzmann constant and T is the absolute temperature in Kelvin. k(S1) / k(T1) is the transition moment ratio of the transition processes from the singlet state S1 and from the triplet state T1 to the electronic ground state S0. For organic molecules without additional spin-orbit coupling by heavy atoms, this transition moment ratio is usually around 10 4 . An additional spin-orbit coupling can in particular increase the transition moment k(T1).

[0030] The above equation (2) can be transformed to: ln(Int(S1→S0)Int(T1→S0))=ln(k(S1)k(T1))−ΔEkBT

[0031] The measurement of the intensities Int(S1 → S0) and Int(T1 → S0) of fluorescence and phosphorescence can be performed using commercially available spectrophotometers. If this intensity measurement is performed at different temperatures and the ratio is plotted graphically as a function of 1 / T, the energy splitting ΔE can be determined from the slope of the resulting straight line.

[0032] Also the transition probability from a triplet to a singlet state (ISC process) and thus the time constant τ A can be determined experimentally. One way to perform such a measurement is shown, for example, in the paper "Direct Observation of the Intersystem Crossing in Poly(3-Octylthiophene)" by B. Kraabel et al., J. Chem. Phys., Volume 103, No. 12, 1995.

[0033] According to at least one embodiment, the intended heavy atoms in the matrix material cause an increased spin-orbit coupling in the first matrix molecules, so that the time constant τ A sets.

[0034] According to at least one embodiment, the emitter molecules are selected from the group of the following molecules or classes of molecules: DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethylamino-styryl)4H-pyran), DCM2 (4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran), rubrene (5,6,11,12-tetraphenyl-naphthacene), coumarin (C545T), TBSA (9,10-bis[(2'',7''''-di-t-butyl)-9',9''-spirobifluorenyl]anthracene), Zn complexes, Cu complexes, aluminum tris(8-hydroxyquinoline).

[0035] According to at least one embodiment, the first matrix molecules are selected from the group of the following molecules or classes of molecules: (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), TCTA (4,4',4''-tris(n--(naphth-2-yl)-N-phenyl-amino)triphenylamine), mCP, TCP (1,3,5-tris-carcazol-9-yl-benzene), CDBP (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), DPVBi (4,4-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), Spiro-PVBi (spiro-4,4'-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), ADN (9,10-di(2-naphthyl)anthracene), perylene, carbazole derivatives, Fluorene derivatives, CZ-PS,2CzPN, m-ATP-ACR, ACRFLCN,PTZ-TRZ, CC2BP, BDPCC-TPTA, DPAA-AF, AcPmBPX. PIC-TRZ2, ACRSA, 4CzIPN, PxPmBPX, DHPT-2Bi, m-ATP-PXZ, 2PXZ-OXD, 4CzTPN, 4CzPN, 3DPA3CN, 4CzTPN-Me, Spiro-CN, 4CzTPN-Ph, DDCzIPN, PPZ-DPO, PPZ-3TPT, PPZ-4TPT, PPZ-DPS, PXZ-DPS, PXZ-TRZ, DMAC-DPS, PXZ-DPS, MAD-DPS, 2,4-bis{3-(9H-carbazol-9-yl)-9H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA), 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-90-phenyl-3,30-bicarbazole (CzT).

[0036] According to at least one embodiment, the matrix material comprises the following molecules or molecule classes: CBP (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), TCTA (4,4',4''-tris(n-(naphth-2-yl)-N-phenyl-amino)triphenylamine), mCP, TCP (1,3,5-tris-carcazol-9-yl-benzene), CDBP (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), DPVBi (4,4-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), Spiro-PVBi (spiro-4,4'-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), ADN (9,10-di(2-naphthyl)anthracene), perylene, carbazole derivatives, fluorene derivatives, CZ-PS,2CzPN, m-ATP-ACR, ACRFLCN,PTZ-TRZ, CC2BP, BDPCC-TPTA, DPAA-AF, AcPmBPX. PIC-TRZ2, ACRSA, 4CzIPN, PxPmBPX, DHPT-2Bi, m-ATP-PXZ, 2PXZ-OXD, 4CzTPN, 4CzPN, 3DPA3CN, 4CzTPN-Me, Spiro-CN, 4CzTPN-Ph, DDCzIPN, PPZ-DPO, PPZ-3TPT, PPZ-4TPT, PPZ-DPS, PXZ-DPS, PXZ-TRZ, DMAC-DPS, PXZ-DPS, MAD-DPS, 2,4-bis{3-(9H-carbazol-9-yl)-9H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA), 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-90-phenyl-3,30-bicarbazole (CzT).

[0037] According to at least one embodiment, the heavy atoms are selected from the group of the following elements: S, Br, I, Kr, Xe, metals and semimetals of the third, fourth and fifth main group periods, metals of the first, second and third transition group periods, elements of the lanthanides and actinides.

[0038] The heavy atoms are particularly preferably selected from the following group: metals and semimetals of the fourth and fifth main group periods, metals of the second and third transition group periods, elements of the lanthanides and actinides.

[0039] By using heavy atoms, which cause a high spin-orbit coupling within the first matrix molecules, the ISC rate can be increased or the time constant τ A which further increases the quantum efficiency of the emitter layer.

[0040] According to at least one embodiment, during operation of the emitter layer, at least 80%, 90%, 95%, or 99% of the primary excitations occurring in the emitter layer are excitations of the singlet states of the first matrix molecules. This means, for example, that at least 80% of the electrons and holes fed into the emitter layer through electrodes combine to form excitons, which first, i.e., primarily, excite the first matrix molecules and thereby occupy the singlet state and / or initially occupy the triplet state in the first matrix molecules and subsequently transition from the triplet state to the singlet state. Alternatively, however, at least 80%, 90%, 95%, or 99% of radiation absorbed by the emitter layer can first, i.e., primarily, lead to excitations of the singlet states in the first matrix molecules.

[0041] According to at least one embodiment, the first matrix molecules are not intended or configured to emit electromagnetic radiation during operation. For example, in at most 10%, at most 5%, or at most 1% of cases, the excited first matrix molecules decay into the ground state of the first matrix molecules. For example, at least 90%, at least 95%, or at least 99% of the excitations of the first matrix molecules are then transferred to the emitter molecules during operation.

[0042] According to at least one embodiment, the amount of the energy level difference |ΔE(S E1 -T E1 )| between the triplet state and the singlet state at least 2500 cm -1 or at least 5000 cm -1 or at least 7500 cm -1Within the emitter molecules, a small energy split between the triplet and singlet states is unnecessary, since the ISC process in the present invention is intended to occur in the first matrix molecules and not in the emitter molecules. A large energy split between the triplet and singlet states of the emitter molecules reduces the probability of the ISC process occurring within the emitter molecules.

[0043] According to at least one embodiment, the triplet state and the singlet state in the first matrix molecules are each the first excited triplet and singlet states above the respective ground state of the first matrix molecules. In particular, during operation of the emitter layer, higher-lying triplet and singlet states of the first matrix molecules can also be populated, which then preferably decay to the lowest triplet and singlet states of the first matrix molecules in very fast, non-radiative processes, so-called internal conversion processes (IC processes for short). IC processes typically run with time constants in the order of 10 -12 s off.

[0044] According to at least one embodiment, the triplet state and the singlet state of the emitter molecules are each the first excited triplet and singlet state above the respective ground state of the emitter molecules.

[0045] According to at least one embodiment, during operation of the emitter layer, at least 90%, 95%, or 99% of the transitions in the emitter molecules are transitions from the singlet state to the respective ground state. This means, in particular, that the emitter layer is a singlet emitter or fluorescence emitter. The transition from the triplet state to the ground state within the emitter molecules is generally strongly suppressed, as already explained above.

[0046] The radiation emitted by the emitter molecules is preferably light in the visible spectral range, for example blue light in the spectral range from 420 nm to 510 nm inclusive and / or green light in the spectral range from 510 nm to 570 nm inclusive and / or yellow light in the spectral range from 570 nm to 590 nm inclusive and / or orange light in the spectral range from 590 nm to 610 nm inclusive and / or red light in the spectral range from 610 nm to 790 nm inclusive.

[0047] According to at least one embodiment, the heavy atoms are free or quasi-free atoms in the matrix material.

[0048] In particular, the heavy atoms are not bound to organic molecules of the matrix material via coordinate or covalent bonds. Rather, the heavy atoms are then purely dopant atoms within the matrix material.

[0049] According to at least one embodiment, the heavy atoms are at least partially bonded via coordinate or covalent bonds in organic or inorganic molecules of the matrix material. In other words, the matrix material comprises heavy-atom-containing compounds in which heavy atoms are coordinately or covalently bonded to organic or inorganic ligands. The heavy-atom-containing compounds are preferably not the first matrix molecules.

[0050] According to at least one embodiment, the proportion of heavy atoms and / or heavy atom-containing compounds in the emitter layer is at least 3 vol% or at least 5 vol% or at least 15 vol% or at least 20 vol%.

[0051] According to at least one embodiment, the proportion of the first matrix molecules in the emitter layer is at least 10 vol%, or at least 30 vol%, or at least 60 vol%. Alternatively or additionally, the proportion of the first matrix molecules is at most 96 vol%, or at most 80 vol%, or at most 70 vol%.

[0052] According to at least one embodiment, the proportion of emitter molecules in the emitter layer is at most 40 vol%, or at most 20 vol%, or at most 5 vol%. Alternatively or additionally, the proportion of emitter molecules in the emitter layer is at least 1 vol%, or at least 3 vol%, or at least 4 vol%.

[0053] Furthermore, an organic light-emitting diode is specified. The organic light-emitting diode comprises, for example, an organic emitter layer as described here. This means that all features disclosed in connection with the organic emitter layer are also disclosed for the organic light-emitting diode, and vice versa.

[0054] According to at least one embodiment, the organic light-emitting diode comprises an emitter layer as described above. Furthermore, the light-emitting diode preferably comprises an anode and a cathode, between which the emitter layer is arranged. The emitter layer is electrically contacted via the anode and the cathode, and electrons or holes are introduced into the emitter layer. The electrons and holes from the cathode and the anode can then form excitons, which excite the triplet and singlet states in the first matrix molecules.

[0055] According to at least one embodiment, the anode and / or the cathode are transparent to the radiation emitted by the emitter layer. In particular, the anode and / or the cathode are clear, non-absorbent, or milky-opaque to the radiation emitted by the emitter layer. The radiation from the emitter layer can then pass out of the organic light-emitting diode via the transparent anode and / or cathode. The anode and / or cathode can, for example, comprise or consist of a transparent conductive oxide, TCO for short, such as indium tin oxide, ITO for short. One of the two cathodes can further comprise or consist of a reflective, in particular specular, material, for example a metal, such as silver or gold, aluminum or titanium.

[0056] According to at least one embodiment, an electron injection layer and / or a hole blocking layer are arranged between the cathode and the emitter layer.

[0057] According to at least one embodiment, a hole injection layer and / or an electron blocking layer are arranged between the anode and the emitter layer.

[0058] Such injection and blocking layers are known, for example, from document EP 2422381 A1.

[0059] The injection layers are specifically designed to efficiently transport electrons or holes to the emitter layer. The blocking layers are designed to prevent the transport of holes to the cathode or electrons to the anode. Such injection and blocking layers further increase the efficiency of the LED.

[0060] Furthermore, the use of heavy atoms in an organic emitter layer of an organic light-emitting diode is specified. The organic light-emitting diode is, for example, an organic light-emitting diode described here with an organic emitter layer described here. This means that all features disclosed in connection with the use of heavy atoms in an organic light-emitting diode are also disclosed for the organic light-emitting diode or the organic emitter layer, and vice versa.

[0061] According to at least one embodiment, heavy atoms with an atomic number of at least 16 are used in an organic emitter layer of an organic light-emitting diode. The organic light-emitting diode comprises the organic emitter layer, which generates electromagnetic radiation during normal operation. The organic emitter layer has an organic matrix material with first organic matrix molecules. Organic emitter molecules are embedded in the matrix material. The heavy atoms are introduced into the organic matrix material as free or quasi-free atoms and / or in the form of heavy-atom-containing compounds. The proportion of heavy atoms and / or heavy-atom-containing compounds in the emitter layer is at least 3 vol%.

[0062] The first matrix molecules are selected from at least one of the following material classes: (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl),TCTA(4,4',4''-tris(n-(naphth-2-yl)-N-phenyl-amino)triphenylamine), mCP, TCP (1,3,5-tris-carcazol-9-yl-benzene), CDBP (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), DPVBi (4,4-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), Spiro-PVBi (spiro-4,4'-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), ADN (9,10-di(2-naphthyl)anthracene), perylene, carbazole derivatives, fluorene derivatives, CZ-PS,2CzPN, m-ATP-ACR, ACRFLCN,PTZ-TRZ, CC2BP, BDPCC-TPTA, DPAA-AF, AcPmBPX. PIC-TRZ2, ACRSA, 4CzIPN, PxPmBPX, DHPT-2Bi, m-ATP-PXZ, 2PXZ-OXD, 4CzTPN, 4CzPN, 3DPA3CN, 4CzTPN-Me, Spiro-CN, 4CzTPN-Ph, DDCzIPN, PPZ-DPO, PPZ-3TPT, PPZ-4TPT, PPZ-DPS, PXZ-DPS, PXZ-TRZ, DMAC-DPS, PXZ-DPS, MAD-DPS, 2,4-bis{3-(9H-carbazol-9-yl)-9H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA), 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-90-phenyl-3,30-bicarbazole (CzT).

[0063] The heavy atoms are selected from the following group: metals and semimetals of the third, fourth and fifth main group periods, metals of the first, second and third transition group periods, elements of the lanthanides and actinides.

[0064] In addition, in the first matrix molecules the amount of energy level difference |ΔE(S A1 -T A1 )| between a first excited triplet state T A1 and a first excited singlet state S A1 maximum 2500 cm -1 .

[0065] An organic emitter layer described herein and an organic light-emitting diode described herein are explained in more detail below with reference to drawings using exemplary embodiments. Like reference numerals indicate like elements in the individual figures. However, they are not drawn to scale; rather, individual elements may be exaggerated for clarity.

[0066] They show: Fig. 1 an embodiment of an emitter layer in cross-sectional view, Fig. 2 Energy level schemes of various first matrix molecules and emitter molecules, Fig. 3 an embodiment of an organic light-emitting diode in cross-sectional view.

[0067] Fig. Figure 1 shows a cross-sectional view of an organic emitter layer 100 described here. The emitter layer 100 comprises an organic matrix material 10 in which emitter molecules 1 are embedded. The emitter molecules 1 are preferably distributed randomly and / or homogeneously in the matrix material 10. Furthermore, the matrix material 10 comprises organic first matrix molecules 2.

[0068] During operation of the emitter layer 100, the emitter molecules 1 are designed to emit electromagnetic radiation, in particular visible light, by a transition from a singlet state S E1into the ground state S E0 The singlet state S E1 in the emitter molecules 1 preferably around the first excited singlet state above the ground state S E0 . In addition, the emitter molecules 1 exhibit a triplet state T E1 which also prefers the first excited triplet state above the ground state S E0 is.

[0069] The occupation of the singlet states S E1 within the emitter molecules 1 preferably occurs predominantly, for example at least 90%, by the transfer of excitation energy from the first matrix molecules 2 to the emitter molecules 1. During operation of the emitter layer 100, the first matrix molecules 2 are excited, for example, electronically. In this case, both triplet states T A1 as well as singlet states S A1 of the first matrix molecules 2 are excited or occupied. The triplet states T A1and singlet states S A1 of the first matrix molecules 2 are, for example, the first excited triplet and singlet states above the ground state S A0 of the first matrix molecules 2. The excitation energy of the first matrix molecules 2 can then be transferred at least partially, for example in at least 90% of cases, to the emitter molecules 1, which leads to the excitation or occupation of the singlet states S E1 in the emitter molecules 1. During the transition to the ground state S E0 electromagnetic radiation is then emitted. For example, at least 90% of the visible radiation emitted by the emitter layer 100 results from a fluorescence transition from singlet states S E1 into the ground state S E0 the emitter molecules 1.

[0070] Furthermore, Fig. 1 Heavy atoms 3, which are either embedded as free or quasi-free atoms within the matrix material 10 or which are present in the form of heavy atom-containing compounds.

[0071] The first matrix molecules are selected from at least one of the following material classes: (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), TCTA (4,4,4-tris(n-(naphth-2-yl)-N-phenyl-amino)triphenylamine), mCP, TCP (1,3,5-tris-carcazol-9-yl-benzene), CDBP (4,4'-bis(carbazol-9-yl)-2,2'-dimethyl-biphenyl), DPVBi (4,4-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), Spiro-PVBi (spiro-4,4'-bis(2,2-diphenyl-ethen-1-yl)-diphenyl), ADN (9,10-di(2-naphthyl)anthracene), perylene, carbazole derivatives, fluorene derivatives, CZ-PS,2CzPN, m-ATP-ACR, ACRFLCN,PTZ-TRZ, CC2BP, BDPCC-TPTA, DPAA-AF, AcPmBPX. PIC-TRZ2, ACRSA, 4CzIPN, PxPmBPX, DHPT-2Bi, m-ATP-PXZ, 2PXZ-OXD, 4CzTPN, 4CzPN, 3DPA3CN, 4CzTPN-Me, Spiro-CN, 4CzTPN-Ph, DDCzIPN, PPZ-DPO, PPZ-3TPT, PPZ-4TPT, PPZ-DPS, PXZ-DPS, PXZ-TRZ, DMAC-DPS, PXZ-DPS, MAD-DPS, 2,4-bis{3-(9H-carbazol-9-yl)-9H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA), 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-90-phenyl-3,30-bicarbazole (CzT).

[0072] The heavy atoms are selected from the following group: metals and semimetals of the fourth and fifth main group periods, metals of the second and third transition group periods, elements of the lanthanides and actinides.

[0073] Fig. 2 shows energy level schemes of different emitter molecules 1 and first matrix molecules 2. In Fig. Figure 2A shows the energy level diagram of a first matrix molecule 2 and an emitter molecule 1 from the prior art. In operation, the excitation ratio between the singlet state S A1 and the triplet state T A1 In the first matrix molecule 2, for example, the ratio is 25:75, which results from the spin statistics of the triplet and singlet states. The excitation energy of the singlet state S A1 of the first matrix molecule 2 is then transferred to the emitter molecule 1, causing an excitation of the singlet state S E1of the emitter molecule 1. Analogously, the transfer of the excitation energy from the triplet state T A1 of the first matrix molecule 2 to excite the triplet state T E1 of the emitter molecule 1.

[0074] In the emitter molecule 1, for example, a transition to the ground state S E0 The transition from the singlet state S E1 into the ground state S E0 within the emitter molecule 1, for example, radiatively and very quickly, for example with a lifetime of less than 100 ns. The transition from the triplet state T E1 of the emitter molecule 1 into the ground state S E0 is strongly suppressed due to the necessary spin flip and can be radiative or non-radiative. The lifetime of the triplet state T E1 in emitter molecule 1 can be, for example, 1 ms or more.

[0075] Overall, the Fig. 2A, only an internal quantum efficiency of the emitter layer 100 of approximately 25% is achieved, since only the singlet states contribute significantly to radiation generation during decay. Within the first matrix molecule 2, a (thermal) transition between the triplet state T A1 and the singlet state S A1 (so-called Inter-System Crossing, ISC for short) is possible, but due to the low transition moment and the large energy level splitting between the triplet state T A1 and the singlet state S A1 of, for example, more than 5000 cm -1 strongly suppressed. Overall, therefore, only a small or negligible fraction of the triplet states T A1 to singlet states S A1 , which then subsequently decay radiatively in the emitter molecules 1.

[0076] The example of Fig. 2B shows, in contrast to, for example, the Fig. 2A a first matrix molecule 2, in which the splitting between the triplet state T A1 and the singlet state S A1 is chosen smaller, for example the energy level difference |ΔE(S A1 -T A1 )| here a maximum of 2500 cm -1 . Due to this smaller energy level splitting, the thermal transition from the triplet state T A1 into the singlet state S A1 within the first matrix molecule 2 stronger than in Fig. 2A. This can increase the internal quantum efficiency of the emitter layer 100.

[0077] However, the transition probability depends on the triplet state T A1 into the singlet state S A1 not only depends on a small energy level splitting between the two states, but also on the transition moment.

[0078] In Fig. Figure 2C shows an embodiment according to the invention described here. Within the first matrix molecule 2, the transition from the triplet state T A1 into the singlet state S A1 This is enhanced by the fact that heavy atoms 3 are embedded in the matrix material 10. The heavy atoms 3 cause an increased spin-orbit coupling within the first matrix molecule 2, which increases the transition moment between the two states.

[0079] For example, in the first matrix molecule 2 the time constant τ A for the transition from the triplet state T A1 into the singlet state S A1 then at most 1·10 -6 s. In this way, a particularly large number, and not only 25%, of the excitations within the first matrix molecule 2 can reach the singlet state S A1 and from there to the singlet state S E1of the emitter molecule 1. This allows the internal quantum efficiency of the entire emitter layer 100 to be increased to up to 100%, preferably to at least 90%.

[0080] Fig. 3 shows an embodiment of an organic light-emitting diode 1000 in which a described emitter layer 100 is arranged between an anode 101 and a cathode 102.

[0081] The emitter layer 100 can be electrically contacted via the anode 101 and the cathode 102, and then emit electromagnetic radiation. The anode 101 and / or the cathode 102 are formed, for example, from a transparent conductive material such as indium tin oxide, or ITO for short. The anode and / or the cathode can also be formed from a metallic material such as silver, gold, aluminum, or titanium.

[0082] In Fig. 3, an electron injection layer 112 and a hole blocking layer 122 are also arranged between the cathode 102 and the emitter layer 100. The electron injection layer 112 is arranged between the cathode 102 and the hole blocking layer 122.

[0083] Between the anode 101 and the emitter layer 100, Fig. 3, a hole injection layer 111 and an electron blocking layer 121 are arranged. The electron blocking layer 121 is arranged between the emitter layer 100 and the hole injection layer 111.

[0084] Furthermore, Fig. 3 the organic layer sequence is applied to a substrate 200. In the present case, the cathode 102 faces away from the substrate 200, the anode 101 faces the substrate 200. Alternatively, this can also be the other way around. The substrate 200 is, for example, a glass substrate that is transparent, for example, clear, to the radiation emitted by the emitter layer 100. In this case, the anode 101 is preferably also clear or transparent. The light-emitting diode 1000 then emits radiation beyond the substrate 200 from the light-emitting diode 1000 and is a so-called bottom emitter. If the anode 101 is reflective for the radiation emitted by the emitter layer 100 and the cathode 102 is transparent or clear for the radiation emitted by the emitter layer 100, the light-emitting diode 1000 is the Fig. 3 is a top emitter. List of reference symbols 1 organic emitter molecule 2 organic first matrix molecule 3 Heavy atom or compound containing heavy atoms 10 organic matrix material 100 organic emitter layer 101 Anode 102 Cathode 111 Hole injection layer 112 Electron injection layer 121 Electron blocking layer 122 hole blocking layer 1000 organic light-emitting diodes S E1 Singlet state of emitter molecule 1 T E1 Triplet state of emitter molecule 1 S A1 Singlet state of the first matrix molecule 2 T A1 Triplet state of the first matrix molecule 2 S E0 Ground state of the emitter molecule 1 S A0 Ground state of the first matrix molecule 2 τ A Time constant

Claims

[1] Organic emitter layer (100), comprising - organic emitter molecules (1), each having at least one excited triplet state (T E1 ) and at least one excited singlet state (S E1 ), wherein the proportion of emitter molecules (1) in the emitter layer (100) is between 1 vol% and 40 vol% inclusive - an organic matrix material (10) comprising organic first matrix molecules (2), wherein the first matrix molecules (2) each have at least one excited triplet state (T A1 ) and at least one excited singlet state (S A1 ) and are selected from fluorene derivatives, wherein - the emitter molecules (1) are embedded in the matrix material (10), - during operation of the emitter layer (100) the triplet states (T A1 ) and the singlet states (S A1 ) of the first matrix molecules (2) are excited, - during operation, the excitation energy from these states is at least partially transferred to the emitter molecules (1), so that in the emitter molecules (1) the singlet states (S E1 ) are encouraged, - in operation from the singlet states (S E1 ) of the emitter molecules (1) a transition to the ground state (S E0] ) of the emitter molecules (1) with at least partial emission of electromagnetic radiation, - in the first matrix molecules (2) the amount of the energy level difference |ΔE(S A1 -T A1 )| between the triplet state (T A1 ) and the singlet state (S A1 ) maximum 2500 cm -1 amounts, - a time constant τ A for the transition from the triplet state (T A1 ) into the singlet state (S A1 ) in the first matrix molecules (2) at most 1·10 -6 s is, - heavy atoms (3) having an atomic number of at least 16 are intentionally introduced into the matrix material (10), wherein the heavy atoms (3) are free or quasi-free atoms in the matrix material (10) or wherein the heavy atoms (3) are present in heavy atom-containing compounds and are coordinatively or covalently bound to organic or inorganic ligands, wherein the proportion of heavy atoms (3) and / or heavy atom-containing compounds in the emitter layer (100) is at least 3 vol%. [2] Organic emitter layer (100) according to claim 1, wherein the heavy atoms (3) cause an increased spin-orbit coupling in the first matrix molecules (2), so that the time constant τ A sets. [3] Organic emitter layer (100) according to claim 1 or 2, wherein - the emitter molecules (1) are selected from the group of the following molecules: DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethylamino-styryl)4H-pyran), DCM2 (4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran), rubrene (5,6,11,12-tetraphenyl-naphthacene), coumarin (C545T), TBSA (9,10-bis[(2'',7''''-di-t-butyl)-9',9''-spirobifluorenyl]anthracene), Zn complexes, Cu complexes, aluminum tris(8-hydroxyquinoline), - the heavy atoms (3) are selected from the group of the following elements: S, Br, I, Kr, Xe, metals and semimetals of the third, fourth and fifth main group periods, metals of the first, second and third subgroup periods, elements of the lanthanides and actinides. [4] Organic emitter layer (100) according to claim 3, wherein the heavy atoms are selected from the following group: metals and semimetals of the fourth and fifth main group period, metals of the second and third subgroup period, elements of the lanthanides and actinides. [5] Organic emitter layer (100) according to one of the preceding claims, wherein the time constant τ A for the transition from the triplet state (T A1 ) into the singlet state (S A1 ) in the first matrix molecules (2) at most 1·10 -8 s is. [6] Organic emitter layer (100) according to one of the preceding claims, wherein during operation at least 80% of the primary excitations occurring in the emitter layer (100) are excitations of the singlet states (S A1 ) of the first matrix molecules (2). [7] Organic emitter layer (100) according to one of the preceding claims, wherein the first matrix molecules (2) are not configured to emit electromagnetic radiation during operation. [8] Organic emitter layer (100) according to the preceding claim, wherein in the emitter molecules (1) the amount of the energy level difference |ΔE(S E1 -T E1 )| between the triplet state (T E1) and the singlet state (S E1 ) at least 2500 cm -1 amounts. [9] Organic emitter layer (100) according to one of the preceding claims, wherein - the triplet state (T A1 ) and the singlet state (S A1 ) in the first matrix molecules (2) by the first excited triplet and singlet state above the ground state (S A0 ) of the first matrix molecule (2), - the triplet state (T E1 ) and the singlet state (S E1 ) in the emitter molecules (1) by the first excited triplet and singlet state above the ground state (S E0 ) of the emitter molecule (1), - during operation of the emitter layer (100) at least 90% of the transitions in the emitter molecules (1) are transitions from the singlet state (S A1 ) to the ground state (S E0 ) are. [10] Organic light-emitting diode (1000) with - at least one emitter layer (100) according to one of the preceding claims, - an anode (101) and a cathode (102), between which the emitter layer (100) is arranged. [11] Organic light-emitting diode (1000) according to the preceding claim, wherein the anode (101) and / or the cathode (102) are transparent to the radiation emitted by the emitter layer (100). [12] Organic light-emitting diode (1000) according to one of the preceding claims 10 and 11, - wherein an electron injection layer (112) and / or a hole blocking layer (122) is arranged between the cathode (102) and the emitter layer (100), and / or - wherein a hole injection layer (111) and / or an electron blocking layer (121) is arranged between the anode (101) and the emitter layer (100). [13] Use of heavy atoms (3) having an atomic number of at least 16 in an organic emitter layer (100) of an organic light-emitting diode (1000), wherein - the organic light-emitting diode (1000) comprises the organic emitter layer (100) and the emitter layer (100) generates electromagnetic radiation during normal operation, - the organic emitter layer (100) comprises an organic matrix material (10) with organic first matrix molecules (2), - organic emitter molecules (1) are embedded in the matrix material (10), the proportion of emitter molecules (1) in the emitter layer (100) being between 1 vol% and 40 vol%, - the heavy atoms (3) are introduced into the organic matrix material (10) as free or quasi-free atoms or in the form of heavy atom-containing compounds, - the proportion of heavy atoms (3) and / or the proportion of heavy atom-containing compounds in the emitter layer (100) is at least 3 vol%, - the first matrix molecules (2) are selected from fluorene derivatives, - the heavy atoms (3) are selected from the following group: metals and semimetals of the third, fourth and fifth main group periods, metals of the first, second and third subgroup periods, elements of the lanthanides and actinides, - the magnitude of the energy level difference |ΔE(S A1 -T A1 ) | between a first excited triplet state (T A1 ) and a first excited singlet state (S A1 ) of the first matrix molecules (2) at most 2500 cm -1 amounts.

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