Organic light-emitting diodes with thermally activated delayed fluorescence under strong light-matter coupling

Abstract

The invention relates to a layer structure for an OLED having organic and inorganic material layers, comprising: a. a first metal electrode (AN), b. a second metal electrode (KAT), the first and / or the second metal electrode (AN, KAT) being designed to be semi-transparent, c. one or more hole transport layers (LTS) consisting of exactly one organic material, d. one or more electron transport layers (ETS) consisting of exactly one organic material, e. an emission layer (EMS) provided between the hole transport layer (LTS) and the electron transport layer (ETS), the emission layer (EMS) comprising an emitter molecule which is designed for thermally activated delayed fluorescence, and f. a strong coupling layer (SKS) provided between the hole transport layer (LTS) and one of the two metal electrodes (AN, KAT), the strong coupling layer (SKS) comprising a hole transport layer (dLTS), which is doped with an electrical doping molecule or atom, and a strong coupling material (SKM). The invention further relates to an OLED comprising the aforementioned layer stack.

Description

[0001] Organic light-emitting diodes with thermally activated delayed fluorescence under strong light-matter coupling

[0002] The invention relates to a layered structure for an OLED with organic and inorganic material layers.

[0003] Furthermore, the invention relates to an OLED comprising the above layer structure.

[0004] OLEDs (Organic Light Emitting Diodes) are thin-film devices made of organic semiconductor materials. These materials are arranged in thin amorphous layers between two electrodes and deposited on a transparent substrate, usually glass. To ensure that the emitted light can escape unimpeded, the electrode on the substrate must also be transparent. This is typically the anode, for which indium tin oxide (ITO) is often used.

[0005] The fundamental operating principle of OLEDs is based on the injection of charge carriers into the layered structure. Electrons are injected from the cathode and holes from the anode into the organic layers. These charge carriers migrate through the layered structure and preferentially recombine in the emitter layer, thereby forming excitons. The layered structure of the OLED is designed such that the recombination of charge carriers occurs selectively in the emitter layer, where the excitons are generated. These excitons can be divided into singlet and triplet excitons, which are formed in a 1:3 ratio due to spin statistics.

[0006] During recombination, excitons release energy corresponding to the energy level of the excited state minus the exciton binding energy. Singlet excitons typically emit this energy in the form of photons, while triplet excitons usually decay non-radiatively and generate heat. One of the central challenges in OLED design is therefore the development and synthesis of emitters that allow triplet excitons to contribute to light emission. One way to utilize the generated triplet excitons for light emission is to exploit TADF (thermally activated delayed fluorescence) in special emitter molecules. Triplet excitons generally decay non-radiatively and generate heat because the transition from the first triplet state (T1) to the ground state (SO) is spin-forbidden.However, TADF emitters utilize the thermally activated transition between the triplet state and the excited singlet state (S1) to increase the efficiency of light emission.

[0007] Organic light-emitting diodes (OLEDs) have revolutionized the display industry over the past 25 years. Today, OLED displays are found in most high-end smartphones, as well as in televisions, smartwatches, and many other consumer devices. While OLEDs offer high efficiency, simple manufacturing, and chemical diversity, they often exhibit a wide emission linewidth and thus low color brilliance, which is determined by the inherent disorder in organic layers. This is particularly true for OLEDs that use highly efficient emitters utilizing thermally activated delayed fluorescence (TADF). To meet the color brilliance demands of modern display applications, an emission spectrum linewidth of less than 30 nm is necessary at optimized wavelengths and across the entire emission cone.Current research often focuses on the development of materials that exhibit such narrow linewidths, including multiresonant TADF molecules, collided quantum dots, or inorganic quantum well structures.

[0008] Besides improving the light-emitting material, color purity can also be enhanced by using a resonant microcavity, in which the OLED structure is sandwiched between highly reflective mirror layers. These mirror layers, such as metal layers, can simultaneously act as electrodes, forming a microcavity that encloses the other OLED layers and has an optical thickness approximately an integer multiple of half the resonant wavelength X. The resulting constructive and destructive interference within this microcavity can significantly narrow the OLED's emission spectrum by this resonant wavelength. This approach is particularly desirable for integrating top-emitting OLEDs onto a CMOS (complementary metal-oxide semiconductor) control electronics board.

[0009] However, the use of microcavities has a major drawback: the resonance condition depends on the viewing angle of the device, leading to a significant blueshift (shift to shorter wavelengths) at increasing angles. In the publication Nat. Photon. 17, 393-400 (2023), it was shown that this blueshift can be substantially reduced by exploiting the strong light-matter interaction. This interaction between photons and the material resonances of the OLED layers (excitons) results in an energetic Rabi split into upper and lower exciton-polariton (or simply polariton) branches. If the coupling parameters are correctly set, the resulting polariton dispersion can be close to the angle-independent exciton dispersion.

[0010] Based on this, the object of the invention is to increase the efficiency of OLEDs and in particular of OLEDs with a low angular dependence.

[0011] This problem is solved by a layered structure for an OLED with organic and inorganic material layers, comprising: a. a first metal electrode, b. a second metal electrode, wherein the first and / or the second metal electrode is semi-transparent, c. one or more components consisting of exactly one organic material

[0012] Hole transport layers, i.e., one or more consisting of exactly one organic material

[0013] Electron transport layers, e. an emission layer arranged between the hole transport layer and the electron transport layer, wherein the emission layer comprises an emitter molecule configured for thermally activated delayed fluorescence (TADF), and f. a strong coupling layer arranged between the hole transport layer and one of the two metal electrodes, wherein the strong coupling layer comprises a hole transport layer doped with an electrical doping molecule or atom, and a strong coupling material.

[0014] One aspect of the invention is therefore that in a layer stack for an OLED, whose emitter molecule is a TADF emitter, in addition to the hole transport layer consisting of exactly one organic material and the electron transport layer consisting of exactly one organic material, i.e. in addition to the undoped hole transport layer and the undoped electron transport layer, the strong coupling layer is present, which in turn comprises the doped hole transport layer and the strong coupling material.

[0015] By incorporating this strong coupling layer, the layer structure can be brought into the strong coupling regime, resulting in a reduction of the emission linewidth with low angular dependence of the emitted wavelength. This makes it possible to drastically increase the color brilliance of the layer structure for OLEDs while maintaining high efficiency.

[0016] According to a preferred embodiment of the invention, the strong coupling material in the layer structure exhibits exciton resonance-based absorption, and the spectral maximum of the absorption is shifted towards shorter wavelengths by 5 nm to 100 nm relative to the emission maximum of the emitter molecule. Tuning the absorption maximum of the exciton resonance-based absorption of the strong coupling material in the strong coupling layer to the emission maximum of the emitter molecule in the emission layer results in high light-matter interaction, which contributes to increased efficiency.

[0017] According to a further preferred embodiment of the invention, the strong coupling material in the layer structure has an extinction coefficient of at least 0.1 at the absorption maximum. In this context, the extinction coefficient refers to the imaginary part of the complex refractive index of the layer structure containing the strong coupling material. The extinction coefficient is dimensionless and describes the attenuation capacity of the layer structure: the larger the coefficient, the more strongly the incident electromagnetic wave is absorbed by the material of the layer structure, and in particular by the strong coupling material.

[0018] According to a preferred embodiment of the invention, the strong coupling material is a coumarin dye and is particularly preferably 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,51-1,11H-(1jbenzopyro-pyrano(6,7-8-l,j)quinolizin-11-one (C545T). This material allows for the fabrication of particularly efficient layer structures for OLEDs.

[0019] In this context, according to a further preferred embodiment of the invention, the hole transport layer doped with the electrical doping molecule or atom comprises 2,2',7,7'-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB). In other words, Spiro-TTB is preferably used as the support for the doping molecule or atom of the doped hole transport layer.

[0020] According to a further preferred embodiment of the invention, the hole transport layer doped with the electrical doping molecule or atom comprises as electrical doping molecule or atom 1 , 3, 4, 5,7,8- hexafluorotetracyanonaphthoquinodimethane (F6TCNQ).

[0021] In this context, it is further preferred that the doping level of the hole transport layer doped with the electrical doping molecule or atom is between 2% and 6%, and preferably 4%. It has been shown that doping levels in this range lead to particularly efficient OLEDs.

[0022] According to a further preferred embodiment of the invention, the layer structure forms a second-order microcavity in which both the emission layer and the strong coupling layer are arranged at a maximum of the cavity's electric field. By arranging the emission layer and the strong coupling layer at the respective maximums of the cavity's electric field, particularly efficient layer structures for OLEDs can be provided. To ensure that the layer structure forms the second-order cavity without negatively affecting the charge carrier balance, the layer structure includes the doped hole transport layer. With regard to the strong coupling layer, according to a further preferred embodiment of the invention, the strong coupling layer has a thickness of 30 nm to 500 nm, and preferably 50 nm to 500 nm.The high conductivity of the doped hole transport layer compared to undoped layers allows a high layer thickness >100 nm of the strong coupling layer to be used without compromising the hole conductivity up to the emission layer.

[0023] The strong coupling layer can be configured as a homogeneous layer or as multiple layers. In this context, according to a further preferred embodiment of the invention, the strong coupling layer has the following layer structure: a doped hole transport layer, preferably with a layer thickness of 10 nm to 200 nm; a layer comprising or consisting of the strong coupling material, preferably with a layer thickness of 10 nm to 50 nm; and a doped hole transport layer, preferably with a layer thickness of 10 nm to 200 nm. Alternatively, a layer consisting of or comprising the strong coupling material is arranged between two layers of the doped hole transport layer.

[0024] In this context, according to a further preferred embodiment of the invention, the strong coupling layer comprises or is configured as a mixed layer, wherein the mixed layer consists of the hole transport layer doped with the electrical dopant molecule or atom and the strong coupling material. In this context, a mixed layer is understood to be a homogeneous layer comprising several materials.

[0025] For example, it is possible that the mixing layer is arranged between the two doped hole transport layers. Alternatively, it is possible that the strong coupling layer consists exclusively of the mixing layer. Furthermore, it is possible that a layer consisting of the strong coupling material is arranged between the two doped hole transport layers. With regard to the mixing layer, it is further preferred that the mixing layer be configured with the following mixing ratios: hole transport layer: 49 wt%–80 wt%, electrical dopant molecule or atom: 1 wt%–10 wt%, strong coupling material: 10 wt%–50 wt%.

[0026] As already mentioned, the emitter molecule is a TADF emitter. In this regard, according to a further preferred embodiment of the invention, the emitter molecule is 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA).

[0027] In a first embodiment of the invention, the light emitted by the layer structure is emitted via the first metal electrode, preferably the anode. Preferably, the first metal electrode is applied to a transparent substrate, for example, made of glass.

[0028] In this context, a further preferred embodiment provides that the first metal electrode has a layer thickness between 10 nm and 50 nm, and preferably a layer thickness between 10 nm and 15 nm. Thus, the first metal electrode allows the emission of light. Preferably, the first metal electrode is designed as a semi-transparent metal electrode and / or consists of silver.

[0029] With regard to the second metal electrode, preferably the cathode, a further preferred embodiment of the invention provides that the second metal electrode has a layer thickness between 50 nm and 500 nm. Since the first metal electrode is semi-transparent, the second metal electrode can have a considerable layer thickness. Preferably, the second metal electrode is designed as an opaque metal electrode and / or is made of aluminum.

[0030] In a second embodiment of the invention, the light emitted by the layer structure is emitted via the second metal electrode, preferably the cathode. This configuration is also referred to as top emission. Preferably, the second metal electrode has a layer thickness between 10 nm and 50 nm, and more preferably a layer thickness between 10 nm and 15 nm. Thus, the second metal electrode allows the emission of light. Preferably, the second metal electrode is designed as a semi-transparent metal electrode and / or is made of silver.

[0031] For the top emitter, it is preferably further provided that the first metal electrode has a layer thickness between 50 nm and 500 nm. Since the second metal electrode is semi-transparent, the first metal electrode can have a greater layer thickness. Preferably, the first metal electrode is designed as an opaque metal electrode and / or consists of aluminum or silver.

[0032] In a further preferred embodiment of the invention, the hole transport layer has a thickness between 5 nm and 100 nm, in relation to the undoped hole transport layer. Preferably, the hole transport layer (LTS) consists of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB).

[0033] In a further preferred embodiment of the invention, the undoped electron transport layer has a thickness between 5 nm and 100 nm. Preferably, the electron transport layer consists of 1,3,5-tris(3-pyridyl-3-phenyl)benzene (TmPyPB).

[0034] Furthermore, the layer structure can comprise additional layers. According to a further preferred embodiment, the layer structure includes an electron injection layer and / or a hole injection layer and / or an electron blocking layer.

[0035] In other words, it is preferably provided that the layer structure is composed of organic and inorganic materials designed for operation as an organic light-emitting diode and preferably includes the following: a. A semi-transparent metal electrode, for example silver, with a layer thickness between 10 nm and 50 nm, and more preferably a layer thickness between 10 nm and 25 nm; b. Another opaque metal electrode, for example aluminum, with a layer thickness of 50 nm to 500 nm; c. One or more hole transport layers, for example NPB, TCTA, consisting of a single material ("undoped") with layer thicknesses between 5 nm and 100 nm; d. One or more electron transport layers, for example TmPyPB, consisting of a single material ("undoped") with layer thicknesses between 5 nm and 100 nm; e. An emission layer between the hole transport layer and

[0036] An electron transport layer containing an emitter molecule (doped or undoped) exhibiting thermally activated delayed fluorescence (TADF). A strong coupling layer between a hole transport layer and a metal electrode, consisting of a hole transport layer, such as SpiroTTB, an electrical dopant molecule or atom, such as F6TCNNQ, and a strong coupling material. This strong coupling material exhibits strong absorption through exciton resonance, with the spectral maximum of absorption preferably shifted towards shorter wavelengths (blue-shifted) by 5 nm to 100 nm relative to the emission maximum of the TADF material, and preferably having an extinction coefficient of at least 0.1 at the absorption maximum. The entire structure of the strong coupling layer can be divided into substructures and preferably has a total layer thickness of 50 nm to 500 nm.

[0037] The document Nat. Photon. 17, 393-400 (2023) describes how OLEDs can be driven into the strong-coupling regime by the insertion of an assisting strong-coupling layer, resulting in a reduction of the emission linewidth with low angular dependence of the emitted wavelength. The OLED structure described in the document is based on the use of phosphorescent emitters based on iridium complexes and thus achieves maximum quantum efficiencies of approximately 10%. The layer structure of the phosphorescent OLEDs inherently includes thick doped transport layers, which facilitates the integration of the assisting strong-coupling layer into the reference structure.

[0038] In contrast, instead of phosphorescent emitters, emitters with TADF character are used here, which are described in the literature exclusively in connection with undoped transport layers.

[0039] The present OLED structure therefore features, among other things, a combination of undoped transport layers (hole transport layer and electron transport layer), which ensure the high efficiency of the TADF-OLED, and a doped strong coupling layer, which provides the necessary high light-matter interaction. By combining and optimizing these strategies, the efficiency of polariton-based OLEDs can be increased to, for example, over 27%.

[0040] In particular, the use of a triple mixed layer consisting of hole transport material, electrical doping molecule or atom and strong coupling material has not yet been described in this form in the specialist literature.

[0041] Preferably, the strong coupling layer has the following substructure: doped hole transport layer with a layer thickness of 10 nm to 200 nm | strong coupling material with a layer thickness of 10 nm to 50 nm | doped hole transport layer with a layer thickness of 10 nm to 200 nm.

[0042] More preferably, the strong coupling layer comprises and consists of a mixed layer of hole transport layer, electrical dopant molecule or atom, and strong coupling material. The mixing ratios are approximately as follows in weight percent: hole transport layer: 49%–80%, electrical dopant molecule or atom: 1%–10%, strong coupling material: 10%–50%.

[0043] The layered structure demonstrated that, by utilizing an assistant layer—specifically, the strong coupling layer—the strong coupling regime can also be achieved in efficient OLED structures based on phosphorescent emitters. This results in a very high external quantum efficiency of 10% for polariton-based OLEDs. While OLEDs utilizing emitter molecules with TADF character can currently achieve efficiencies well over 20%, their design, low absorption, and consequently low light-matter interaction, as well as their use at low concentrations, make them unsuitable for polariton OLEDs. Furthermore, due to their donor-acceptor nature, TADF molecules often exhibit high linewidths (>40 nm) and therefore low color brilliance.

[0044] The invention underlying this patent application originated in a project funded by the ERC Advanced Grants under the registration number 101097878 and the project name “HYANGLE”.

[0045] The invention is explained below by way of example with reference to the accompanying drawings and preferred embodiments, wherein the features shown below can represent an aspect of the invention, either individually or in combination. The drawings show:

[0046] Fig. 1 shows a schematic diagram of a layered structure from the prior art,

[0047] Fig. 2 shows a schematic representation of a layer structure according to a first embodiment of the invention,

[0048] Fig. 3 shows two schematic representations of a layer structure according to two further embodiments of the invention,

[0049] Fig. 4 shows a simulation calculation of the electric field for the layer structure from Figure 2.

[0050] Fig. 5 shows a simulation calculation of the angle-resolved reflection for the layer structure from Figure 2, Fig. 6 shows a spectrum of the layer structure from Figure 1, i.e., the layer structure from the prior art.

[0051] Fig. 7 in a) to c) each shows a spectrum of the layer structures from Figures 2 and 3,

[0052] Fig. 8 shows the external quantum efficiency of the layer structures from Figures 2 and 3.

[0053] Fig. 9 shows a schematic representation of a layer structure according to a further embodiment of the invention,

[0054] Fig. 10 shows an angle-resolved electroluminescence of the layer structure from Figure 9, and

[0055] Fig. 11 in a) the current density - luminescence - voltage characteristic and in b) the external quantum efficiency of the layer structure from Figure 9.

[0056] Figure 1 schematically shows a multi-layered TADF-OLED known in the prior art as described in Nature Photon 12, 235, 240 (2018). The TADF-OLED consists of a stack of organic materials sandwiched between electrodes, typically metals or conductive metal oxides, and typically has the following structure: anode (e.g., indium tin oxide, ITO); hole transport layer (LTS) (e.g., N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine, NPB); electron blocking layer (EBS) (e.g., tris(4-carbazoyl-9-ylphenyl)amine, TCTA); emission layer (EMS); Electron transport and hole blocking layer (ETS) (e.g., 1,3,5-tris(3-pyridyl-3-phenyl)benzene, TmPyPB); electron injection layer (EIS) (e.g., lithium fluoride, LiF); and cathode (e.g., aluminum). The emission layer (EMS) typically includes a matrix or host material (e.g., 4,4'-bis(N-carbazolyl)-1,T-biphenyl, CBP) into which the TADF emitter (e.g.,5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene, CzDBA) is diluted in a lower concentration, approximately between 1 and 20%. The structure of such a TADF-OLED according to the state of the art typically exhibits the following characteristics: The transport and blocking layers are usually undoped, meaning they typically consist of a single layer of a molecule, with layer thicknesses between 10 and 100 nm. The emission layer consists of a matrix molecule in which the emitter molecule is embedded in a lower concentration and which typically has a layer thickness between 10 and 50 nm. For optimal efficiency, the individual layer thicknesses must be precisely matched to maintain the balance of charge carriers, i.e., electrons and holes, in the emission layer and thus the device efficiency; they cannot be chosen arbitrarily.

[0057] Integrating a TADF-OLED into a structure with strong light-matter coupling proves very difficult due to the structure's lack of flexibility.

[0058] Starting from the prior art TADF-OLED, two steps were carried out to achieve the strong coupling regime in TADF-OLEDs: (1) the transparent conductive metal oxide contact was replaced by a semi-transparent and semi-reflective metal contact; (2) due to the low light-matter interaction of the TADF emitter, another layer with high interaction (high absorption) was introduced into the OLED structure, which is referred to below as the strong coupling layer (SCC).

[0059] For step (1) the ITO contact is preferably replaced by a high-quality thin metal layer (ideally silver, Ag) in combination with a hole injection layer (e.g. molybdenum oxide, MoO3).

[0060] Step (2) is not readily possible because additional layers can lead to additional energy barriers and increased resistance in the transport layers, negatively impacting the charge carrier balance. Furthermore, the SKS must be positioned at a maximum of the electric field. However, conventional TADF OLEDs are designed as first-order cavities, with the emission layer located at the single maximum of the electric field. To enable step (2), the OLED structure was extended to a second-order cavity, with the SKS positioned at the second maximum of the electric field. In order to increase the layer thickness of the OLED to the second order without disturbing the charge carrier balance, an electrically doped hole transport layer (e.g. 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9- spirobifluorene, Spiro-TTB, doped with 1 , 3, 4, 5,7,8- hexafluorotetracyanonaphthoquinodimethane,F6TCNNQ) is preferably used.Such a doped transport layer is not typically used in TADF-OLEDs because it can reduce the external quantum efficiency. The high conductivity of the doped transport layer compared to undoped layers allows for a large layer thickness (>100 nm) without compromising hole conductivity up to the emission layer. Finally, the doped hole transport layer can be combined with the SKS to achieve the strong light-matter interaction regime.

[0061] Using the reference TADF-OLED shown in Figure 1 as an example, various implementations are presented for extending it to a Polariton TADF-OLED. The reference TADF-OLED known from the prior art has the following structure:

[0062] - first metal electrode AN (anode) made of indium tin oxide (ITO),

[0063] - Hole transport layer LTS with a layer thickness of 40 nm made of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,T-biphenyl)-4,4'-diamine (NPB),

[0064] - Electron blocking layer, EBS with a layer thickness of 10 nm made of tris(4-carbazoyl-9-ylphenyl)amine (TCTA),

[0065] - an emission layer EMS, with a layer thickness of 30 nm, consisting of the matrix molecule 4,4'-Bis(N-carbazolyl)-1,T-biphenyl (CBP) in which the emitter molecule 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA) is embedded for 10 wt%,

[0066] - Electron transport layer ETS with a thickness of 60 nm made of 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB),

[0067] - Electron injection layer (EIS) with a layer thickness of 1 nm made of lithium fluoride (LiF),

[0068] - Second metal electrode KAT (cathode) made of aluminum with a layer thickness of 100 nm.

[0069] The aforementioned layers are applied to a substrate SUB. Figure 2 shows a first variant A of the layer stack according to a preferred embodiment of the invention. The layer stack has the following structure:

[0070] - first metal electrode AN (anode) made of silver (Ag) with a layer thickness of 20 nm to 35 nm,

[0071] - a HIL hole injection layer with a thickness of 1 nm made of molybdenum oxide (MoO3),

[0072] - Doped hole transport layer dLTS with a thickness of 70 nm made of 2, 2', 7,7'- Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ),

[0073] - a layer of strong coupling material SKM with a layer thickness of 40 nm or 20 nm of 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1 ,1 ,7,7-tetramethyl-1 H,5H, 11 H-(1 )benzopyropyrano(6,7-8-l,j)quinolizin-11 -one (C545T),

[0074] - doped hole transport layer dLTS with a layer thickness of 20 nm or 40 nm

[0075] Layer thickness of 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ),

[0076] - Hole transport layer LTS with a layer thickness of 50 nm made of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,T-biphenyl)-4,4'-diamine (NPB),

[0077] - Electron blocking layer EBS with a layer thickness of 10 nm made of tris(4-carbazoyl-9-ylphenyl)amine (TCTA),

[0078] - an emission layer EMS with a layer thickness of 30 nm made of the matrix molecule 4,4'-Bis(N-carbazolyl)-1,T-biphenyl (CBP) in which the emitter molecule 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA) is embedded for 10 wt%,

[0079] - Electron transport layer ETS with a thickness of 40 nm made of 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB),

[0080] - Electron injection layer (EIS) with a layer thickness of 1 nm made of lithium fluoride (LiF),

[0081] - Second metal electrode KAT (cathode) made of aluminum with a layer thickness of 100 nm.

[0082] The layer stack is deposited on a substrate SUB. The doped hole transport layer dLTS, the layer of strong coupling material SKM, and the further doped hole transport layer dLTS together form the strong coupling layer SKS. Figure 2 shows two embodiments of variant A based on the possible layer thicknesses: in the first variant A1, the layer of strong coupling material SKM is 40 nm thick and the doped hole transport layer dLTS is 20 nm thick; and in the second variant A2, the layer of strong coupling material SKM is 20 nm thick and the doped hole transport layer dLTS is 40 nm thick.

[0083] In other words, variant A shown in Figure 2 extends the reference OLED by adding an Ag anode (20-35 nm), a hole injection layer (HIL, MoO3), and a doped hole transport layer (Spiro-TTB: 4% F6TCNQ) with an inserted SKS (here 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1 , 1 ,7,7-tetramethyl-1 H,5H, 11 H- (1 )benzopyropyrano(6,7-8-l,j)quinolizin-11 -one, C545T) in the following structure: Ag | MoO3 | Spiro-TTB: F6TCNQ | C545T | Spiro-TTB: F6TCNQ | Reference OLED.

[0084] Figure 3 shows two further variants, variant B and C, of ​​the layer structure according to two further preferred embodiments of the invention.

[0085] The layer stack of variant B has the following structure:

[0086] - first metal electrode AN (anode) made of silver (Ag) with a layer thickness of 20 nm to 35 nm,

[0087] - a HIL hole injection layer with a thickness of 1 nm made of molybdenum oxide (MoO3),

[0088] - Doped hole transport layer dLTS with a thickness of 70 nm made of 2, 2', 7,7'- Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ),

[0089] - a mixed MS layer with a layer thickness of 40 nm made from the doped

[0090] Hole transport layer and the strong coupling material SKM. The mixing ratios are as follows: 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ) and 50% 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)benzo-pyropyrano(6,7-8-l,j)quinolizin-11-one (C545T), - doped hole transport layer dLTS with a layer thickness of 20 nm or 40 nm

[0091] Layer thickness of 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ),

[0092] - Hole transport layer LTS with a layer thickness of 50 nm made of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB),

[0093] - Electron blocking layer EBS with a layer thickness of 10 nm made of tris(4-carbazoyl-9-ylphenyl)amine (TCTA),

[0094] - an emission layer EMS with a layer thickness of 30 nm made of the matrix molecule 4,4'-Bis(N-carbazolyl)-1,1'-biphenyl (CBP) in which the emitter molecule 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA) is embedded for 10 wt%,

[0095] - Electron transport layer ETS with a thickness of 40 nm made of 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB),

[0096] - Electron injection layer (EIS) with a layer thickness of 1 nm made of lithium fluoride (LiF),

[0097] - Second metal electrode KAT (cathode) made of aluminum with a layer thickness of 100 nm.

[0098] The layer stack is applied to a substrate SUB. The doped hole transport layer dLTS, the mixed layer MS, and the further doped hole transport layer dLTS together form the strong coupling layer SKS.

[0099] The layer stack of variant C has the following structure:

[0100] - first metal electrode AN (anode) made of silver (Ag) with a layer thickness of 20 nm to 35 nm,

[0101] - a HIL hole injection layer with a thickness of 1 nm made of molybdenum oxide (MoO3),

[0102] - a mixed MS layer with a layer thickness of 136 nm made from the doped

[0103] Hole transport layer and the strong coupling material SKM. The mixing ratios are as follows: 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ) and 20% 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,51-1,11H-(1)benzo-pyropyrano(6,7-8-1,j)quinolizin-11-one (C545T), - Hole transport layer LTS with a thickness of 50 nm made of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1 '-biphenyl)-4,4'-diamine (NPB),

[0104] - Electron blocking layer EBS with a layer thickness of 10 nm made of tris(4-carbazoyl-9-ylphenyl)amine (TCTA),

[0105] - an emission layer EMS with a layer thickness of 30 nm made of the matrix molecule 4,4'-Bis(N-carbazolyl)-1,1'-biphenyl (CBP) in which the emitter molecule 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA) is embedded for 10 wt%,

[0106] - Electron transport layer ETS with a thickness of 40 nm made of 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB),

[0107] - Electron injection layer (EIS) with a layer thickness of 1 nm made of lithium fluoride (LiF),

[0108] - Second metal electrode KAT (cathode) made of aluminum with a layer thickness of 100 nm.

[0109] The layer stack is applied to a substrate SUB. In variant C, the strong coupling layer SKM is designed as a mixed layer, consisting of the hole transport layer dLTS doped with the electrical dopant molecule or atom and the strong coupling material.

[0110] In other words, in variant B shown in Figure 3, the strong coupling layer SKS comprises a triple mixed layer, while in variant C, the strong coupling layer SKS is designed as a triple mixed layer. The triple mixed layer consists of the hole transport layer (dLTS) doped with the electrical dopant molecule or atom and the strong coupling material: Variant B: Ag | MoO3 | Spiro-TTB: F6TCNQ | 46% Spiro-TTB: 4% F6TCNQ: 50% C545T | Spiro-TTB: F6TCNQ | Reference OLED. Variant C: Ag | MoO3 | 76% Spiro-TTB: 4% F6TCNQ: 20% C545T | Reference OLED.

[0111] In all variants shown in Figures 2 and 3, the second-order cavity allows both the strong coupling layer SKS and the TADF emitter layer EMS to be positioned at a maximum of the electric field.

[0112] Figure 4 shows a simulation of the electric field using variant A1 as an example. The structure has a second-order cavity and thus exhibits two field maxima at layer thicknesses of approximately 150 nm and approximately 310 nm. The TADF emitter layer EMS is located at the first maximum, and the strong coupling layer SKS at the second maximum.

[0113] Figure 5 shows, in false color, a simulation of the angle-resolved reflection of the Polariton-TADF OLED variant A1. The crosses in Figure 5 represent the experimentally measured positions of the upper and lower polariton branches (OPA / UPA). The lines in Figure 5 are model calculations of the polariton branches using the coupled Hamiltonian oscillator. The Polariton-TADF OLED exhibits excellent agreement with the theory of strong coupling. Furthermore, Figure 5 illustrates the splitting of the cavity resonance into the upper and lower polariton branches for variant A, thus confirming the attainment of the strong-coupling regime.

[0114] By combining a highly conductive doped hole transport layer dLTS and a strongly absorbing coupling layer SKS, all three variants can achieve the regime of strong light-matter interaction.

[0115] By achieving the strong coupling regime, the linewidth of the emission spectrum can be greatly reduced, thus greatly improving the brilliance of the reproduced color.

[0116] Figure 7 shows the angle-resolved emission spectra of the Polariton TADF OLED variants AC, and Figure 6 shows the spectrum of a reference OLED for comparison. Figure 7a) shows the emission spectrum of variant A1, Figure 7b) shows the emission spectrum of variant B, and Figure 7c) shows the emission spectrum of variant C. The Polariton variants in Figure 7 exhibit a linewidth reduced by at least half compared to the reference structure in Figure 6, making them suitable for use in ultra-high-definition (UHD) displays.

[0117] Figure 8 shows the external quantum efficiency of the Polariton TADF OLED variants A1, A2, B, and C. The efficiency of the Polariton TADF OLEDs has been significantly increased compared to previous Polariton-based OLEDs, which achieved a maximum external quantum efficiency (EQE) of 10%. Variant A exhibits a maximum EQE of over 27%, as shown in Figure 8. This high efficiency results from the unique combination of an optimized reference OLED with the electrically doped hole transport layers (dLTS) and the strong coupling layer (SKS). This ensures the charge carrier balance and performance of the TADF OLED while simultaneously allowing the entire cavity structure to operate in the strong coupling region. With this exceptionally high EQE, the efficiency of the new Polariton TADF OLEDs is comparable to that of the best conventional (i.e., non-polariton-based) OLEDs available worldwide.This makes the new Polariton OLEDs of particular interest for industrial applications.

[0118] Figure 9 shows a layer structure according to a further preferred embodiment, wherein the layer structure in this embodiment is designed for TOP emission with light emission through the cathode CAT.

[0119] The stack of layers in Figure 9 has the following structure:

[0120] - first metal electrode AN (anode) made of silver (Ag) with a layer thickness of 100 nm,

[0121] - a HIL hole injection layer with a thickness of 1 nm made of molybdenum oxide (MoO3),

[0122] - Doped hole transport layer dLTS with a thickness of 70 nm made of 2, 2', 7,7'- Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ),

[0123] - a layer of strong coupling material SKM with a layer thickness of 40 nm consisting of 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1 , 1 ,7,7-tetramethyl-1 H,5H, 11 H-

[0124] (1 )benzopyropyrano(6,7-8-l,j)quinolizin-11-one (C545T),

[0125] - doped hole transport layer dLTS with a layer thickness of 20 nm or 40 nm

[0126] Layer thickness of 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB) doped with 4% 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNQ),

[0127] - Hole transport layer LTS with a layer thickness of 50 nm made of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,T-biphenyl)-4,4'-diamine (NPB),

[0128] - Electron blocking layer EBS with a layer thickness of 10 nm made of tris(4-carbazoyl-9-ylphenyl)amine (TCTA),

[0129] - an emission layer EMS with a layer thickness of 30 nm made of the matrix molecule 4,4'-Bis(N-carbazolyl)-1,T-biphenyl (CBP) in which the emitter molecule 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA) is embedded for 10 wt%,

[0130] - Electron transport layer ETS with a thickness of 40 nm made of 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB),

[0131] - Electron injection layer (EIS) with a layer thickness of 1 nm made of lithium fluoride (LiF),

[0132] - Second metal electrode KAT (cathode) consisting of a 1 nm aluminum layer and a 20 nm silver layer,

[0133] - Cover layer CL with a layer thickness of 60 nm made of N,N'-Di(1 -naphthyl)-N,N'-diphenyl- (1 ,T-biphenyl)-4,4'-diamine (NPB).

[0134] The layer stack in Figure 9 is deposited on a substrate SUB. The doped hole transport layer dLTS, the layer of strong coupling material SKM, and the further doped hole transport layer dLTS together form the strong coupling layer SKS. The capping layer CL improves the extraction of light at the cathode-air interface.

[0135] Figure 10 shows the angle-resolved emission spectra of the polariton TADF OLED from Figure 9. Figure 11 shows in a) the current density-luminescence-voltage characteristic and in b) the external quantum efficiency of the polariton TADF OLED from Figure 9. All layer thicknesses are optimized for efficient top emission and flat dispersion along the lower polariton branch (solid line LPB in Figure 9).

[0136] The Polariton TADF OLEDs were fabricated using physical vapor deposition (PVD). This method enabled the precise deposition of the various organic and metallic layers of an OLED.

[0137] The evaporator used for the process has 13 vapor sources, 4 of which are designed for the evaporation of metals and salts, and 9 for the evaporation of organic semiconductor materials. The evaporation process took place in a vacuum chamber to ensure the vaporizability of the materials and the purity of the layers. Several sensors are installed in the chamber to monitor and measure the thickness of the evaporated layers during the process.

[0138] One process run involved the fabrication of 16 OLEDs on a glass substrate. These 16 OLEDs were vapor-deposited onto the square substrate in a 4x4 array. The specific layer structures were applied using interchangeable vapor masks.

[0139] In the fabrication of Polariton-TADF-OLEDs, a silver layer with an anode mask was first deposited onto a pure glass substrate. Subsequently, the organic layer structure was deposited onto the substrate using an organic mask, and the aluminum cathode was deposited onto the substrate using a cathode mask.

[0140] To allow for variations within the 16 OLEDs, shutters were used. These shutters could be moved both horizontally and vertically in front of one of the four substrate rows, enabling the creation of 16 different OLED variations within a single process run.

[0141] To fabricate polariton-TADF OLEDs, a layer of a strongly absorbing material, SKM, was integrated into the organic layer structure as a strong coupling layer, SKS. The requirements for this material included absorption compatible with the emission of the emitter used, as well as strong interaction with light. This creates a second-order microcavity, with the emission layer, EMS, positioned at the first maximum of the electromagnetic field and the strong coupling layer, SKM, comprising the strong coupling material SKM, at the second maximum to maximize the interaction of photons resonant within the microcavity with the material. In variant A, the layer containing the strong coupling material SKM was positioned between the doped hole-guide layers, dLTS.In variant B, the layer with the strong coupling material SKM was also positioned between the doped hole transport layers dLTS; however, the layer with the strong coupling material itself also encompasses the doped hole transport layer dLTS. In variant C, the strong coupling layer SKS is designed as a hybrid layer consisting of the doped hole transport layer dLTS and the strong coupling material SKM. The coumarin dye C545T was selected as the material for the strong coupling layer SKS, i.e., as the strong coupling material SKM.

[0142] Reference symbol list

[0143] AN Anode

[0144] CAT cathode

[0145] LTS hole transport layer dLTS doped hole transport layer

[0146] EBS electron blocking layer

[0147] EMS emission layer

[0148] ETS electron transport layer

[0149] EIS electron injection layer

[0150] HIL (Hyper-Injection Layer)

[0151] SKS strong coupling layer

[0152] SKM strong coupling material

[0153] SUB Substrat

[0154] MS mixed layer

[0155] CL topcoat

Claims

Patent claims 1. Layered structure for an OLED with organic and inorganic material layers, comprising: a. a first metal electrode (AN), b. a second metal electrode (KAT), wherein the first and / or the second metal electrode (AN, KAT) is semi-transparent, c. one or more hole transport layers (LTS) consisting of exactly one organic material, d. one or more electron transport layers (ETS) consisting of exactly one organic material, e. an emission layer (EMS) arranged between the hole transport layer (LTS) and the electron transport layer (ETS), wherein the emission layer (EMS) comprises an emitter molecule configured for thermally activated delayed fluorescence, and f.a strong coupling layer (SCM) arranged between the hole transport layer (LTS) and one of the two metal electrodes (AN, KAT), wherein the strong coupling layer (SCM) comprises a hole transport layer (dLTS) doped with an electrical doping molecule or atom, and a strong coupling material (SCM).

2. Layer structure according to claim 1, wherein the strong coupling material (SCM) in the layer structure exhibits an exciton resonance-based absorption, and wherein a spectral maximum of the absorption is shifted towards shorter wavelengths by 5 nm to 100 nm relative to an emission maximum of the emitter molecule.

3. Layer structure according to claim 1 or 2, wherein the strong coupling material (SKM) in the layer structure has at least an extinction coefficient of 0.1 at the absorption maximum.

4. Layer structure according to one of the preceding claims, wherein the strong coupling material (SKM) is a coumarin dye and is particularly preferably 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1 , 1 ,7,7-tetramethyl-1 H,5H, 11 H- (1 )benzopyropyrano(6,7-8-l,j)quinolizin-11 -one (C545T).

5. Layer structure according to one of the preceding claims, wherein the hole transport layer (dLTS) doped with the electrical doping molecule or atom comprises 2,2',7,7'-Tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene (Spiro-TTB).

6. Layer structure according to one of the preceding claims, wherein the hole transport layer (dLTS) doped with the electrical doping molecule or atom comprises as electrical doping molecule or atom 1 , 3, 4, 5,7,8- hexafluorotetracyanonaphthoquinodimethane (F6TCNQ).

7. Layer structure according to one of the preceding claims, wherein the degree of doping of the hole transport layer (dLTS) doped with the electrical doping molecule or atom is between 2% and 6% and preferably 4%.

8. Layer structure according to one of the preceding claims, wherein the layer structure forms a second-order microcavity in which both the emission layer (EMS) and the strong coupling layer (SKS) are each arranged in a maximum of the electric field of the cavity.

9. Layer structure according to one of the preceding claims, wherein the strong coupling layer (SKS) has a layer thickness of 30 nm to 500 nm and preferably of 50 nm to 500 nm.

10. Layer structure according to one of the preceding claims, wherein the strong The coupling layer (SCL) has the following layer structure: doped Hole transport layer (dLTS) preferably with a layer thickness of 10 nm to 200 nm, layer comprising or consisting of the strong coupling material (SKM) preferably with a layer thickness of 10 nm to 50 nm; doped hole transport layer (dLTS) preferably with a layer thickness of 10 nm to 200 nm.

11. Layer structure according to one of the preceding claims, wherein the strong coupling layer (SKS) comprises a mixed layer (MS) or is configured as a mixed layer (MS), wherein the mixed layer (MS) consists of the hole transport layer (dLTS) doped with the electrical doping molecule or atom and the strong coupling material (SKM).

12. Layer structure according to the preceding claim, wherein the mixed layer (MS) is configured with the following mixing ratios: hole transport layer: 49 wt%-80 wt%, electrical doping molecule or atom: 1 wt%-10 wt%, strong coupling material: 10 wt%-50 wt%.

13. Layer structure according to one of the preceding claims, wherein the emitter molecule is 5,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-5,10-dihydroboranthrene (CzDBA).

14. Layer structure according to one of the preceding claims, wherein the first metal electrode (AN) has a layer thickness between 10 nm and 50 nm, preferably a layer thickness between 10 nm and 25 nm and more preferably between 10 nm and 15 nm.

15. Layer structure according to one of the preceding claims, wherein the first metal electrode (AN) is designed as a semi-transparent metal electrode and / or consists of silver.

16. Layer structure according to one of the preceding claims, wherein the second metal electrode (CAT) has a layer thickness between 50 nm and 500 nm.

17. Layer structure according to one of the preceding claims, wherein the second metal electrode (CAT) is designed as an opaque metal electrode and / or is made of aluminum.

18. Layer structure according to one of claims 1 to 13, wherein the second metal electrode (CAT) has a layer thickness between 10 nm and 50 nm, preferably a layer thickness between 10 nm and 25 nm and more preferably between 10 nm and 15 nm.

19. Layer structure according to one of claims 1 to 13 or 18, wherein the second metal electrode (CAT) is designed as a semi-transparent metal electrode and / or consists of silver.

20. Layer structure according to one of claims 1 to 13 or 18 or 19, wherein the first metal electrode (AN) has a layer thickness between 50 nm and 500 nm.

21. Layer structure according to one of claims 1 to 13 or 18 to 20, wherein the first metal electrode (AN) is designed as an opaque metal electrode and / or is made of aluminium or silver.

22. Layer structure according to one of the preceding claims, wherein the hole transport layer (LTS) has a layer thickness between 5 nm and 100 nm.

23. Layer structure according to one of the preceding claims, wherein the hole transport layer (LTS) consists of N,N'-Di(1 -naphthyl)-N,N'-diphenyl-(1 ,1 '- biphenyl)-4,4'-diamine (NPB).

24. Layer structure according to one of the preceding claims, wherein the electron transport layer (ETS) has a layer thickness between 5 nm and 100 nm.

25. Layer structure according to one of the preceding claims, wherein the electron transport layer (ETS) consists of 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB).

26. Layer structure according to one of the preceding claims, wherein the layer structure comprises an electron injection layer (EIS) and / or a hole injection layer (HIL) and / or an electron blocking layer (EBS).

27. OLED comprising a layer structure according to any of the preceding claims.

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