Surface plasmon pumped light-emitting device

Abstract

This application relates to surface plasmon pumped light emitting devices. Apparatus and techniques are provided for implementing an OLED device including one or more plasmonic materials exhibiting surface plasmon resonance and one or more outcoupling layers.

Description

[0001] Cross - Reference to Related Applications

[0002] This application is a non - provisional application of U.S. Provisional Patent Application No. 62 / 773,299, filed on Nov. 30, 2018, and U.S. Provisional Patent No. 62 / 817,334, filed on Mar. 12, 2019, the entire contents of each of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to light - emitting devices including a plasma - acting layer and an out - coupling layer, related structures for organic light - emitting diodes, and devices including such structures. Background Art

[0004] For a variety of reasons, optoelectronic devices using organic materials have become increasingly popular. Many of the materials used to fabricate such devices are relatively inexpensive, so organic optoelectronic devices have the potential for a cost advantage over inorganic devices. Additionally, the inherent properties of organic materials, such as their flexibility, can make them more suitable for certain applications, such as fabrication on flexible substrates. Examples of organic optoelectronic devices include organic light - emitting diodes / devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, organic materials can have performance advantages over conventional materials. For example, the wavelength of light emitted by an organic emissive layer can generally be easily adjusted with appropriate dopants.

[0005] OLEDs utilize organic thin films that emit light when a voltage is applied across the device. OLEDs are becoming an increasingly attractive technology for applications such as flat panel displays, lighting, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entireties.

[0006] One application of phosphorescent emissive molecules is full - color displays. Industry standards for such displays require pixels that are suitable for emitting specific colors (referred to as “saturated” colors). Specifically, these standards require saturated red, green, and blue pixels. Alternatively, an OLED can be designed to emit white light. In a conventional liquid crystal display, absorption filters are used to filter the emission from a white backlight to produce red, green, and blue emissions. The same technique can be used for OLEDs. White OLEDs can be single - EML devices or stacked structures. Color can be measured using CIE coordinates well - known in the art.

[0007] As used herein, the term "organic" includes polymeric materials and small molecule organic materials that can be used to fabricate organic optoelectronic devices. "Small molecule" refers to any organic material that is not a polymer, and a "small molecule" can actually be quite large. In some cases, a small molecule can include repeating units. For example, the use of a long-chain alkyl group as a substituent does not remove a molecule from the "small molecule" category. Small molecules can also be incorporated into polymers, such as as pendant groups on a polymer backbone or as part of the backbone. Small molecules can also serve as the core portion of a dendrimer, which consists of a series of chemical shells built on the core portion. The core portion of a dendrimer can be a fluorescent or phosphorescent small molecule emitter. Dendrimers can be "small molecules", and all dendrimers currently used in the OLED field are considered to be small molecules.

[0008] As used herein, "top" means furthest from the substrate, and "bottom" means closest to the substrate. Where a first layer is described as being "disposed over" a second layer, the first layer is disposed further from the substrate. There can be other layers between the first and second layers unless it is specified that the first layer "contacts" the second layer. For example, even though there are various organic layers between the cathode and the anode, the cathode can still be described as being "disposed over" the anode.

[0009] As used herein, "solution processable" means capable of being dissolved, dispersed, and / or transported in a liquid medium in the form of a solution or suspension and / or deposited from a liquid medium.

[0010] When a ligand is considered to directly contribute to the photosensitive properties of an emissive material, the ligand can be referred to as "photosensitive". When a ligand is not considered to contribute to the photosensitive properties of an emissive material, the ligand can be referred to as "auxiliary", but an auxiliary ligand can modify the properties of a photosensitive ligand.

[0011] As used herein, and as would be generally understood by one of ordinary skill in the art, if the first energy level is closer to the vacuum energy level, then the first "highest occupied molecular orbital" (HOMO) or "lowest unoccupied molecular orbital" (LUMO) energy level is "greater than" or "higher than" the second HOMO or LUMO energy level. Since the ionization potential (IP) is measured as a negative energy relative to the vacuum energy level, a higher HOMO energy level corresponds to an IP with a smaller absolute value (a less negative IP). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) with a smaller absolute value (a less negative EA). On a conventional energy level diagram with the vacuum energy level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A "higher" HOMO or LUMO energy level appears closer to the top of this diagram than a "lower" HOMO or LUMO energy level.

[0012] As used herein, and as would be generally understood by one of ordinary skill in the art, if the first work function has a higher absolute value, then the first work function is "greater than" or "higher than" the second work function. Since the work function is typically measured as a negative number relative to the vacuum energy level, this means that a "higher" work function is more negative. On a conventional energy level diagram with the vacuum energy level at the top, a "higher" work function is illustrated as being farther from the vacuum energy level in the downward direction. Thus, the definitions of the HOMO and LUMO energy levels follow different rules than the work function.

[0013] More details regarding OLEDs and the definitions described above can be found in U.S. Patent No. 7,279,704, which is incorporated herein by reference in its entirety. SUMMARY OF THE INVENTION

[0014] According to one embodiment, an organic light emitting diode / device (OLED) is also provided. The OLED may include an anode, a cathode, and an organic layer disposed between the anode and the cathode. According to one embodiment, the organic light emitting device is incorporated into one or more of the following devices: a consumer product, an electronic component module, and / or a lighting panel.

[0015] According to one embodiment, there is provided an organic emitting device, comprising: a substrate; a first electrode disposed on the substrate; an emission stack disposed on the first electrode, the emission stack comprising a first organic emitting material; a second electrode disposed on the emission stack; a first enhancement layer comprising a plasmonic material, the plasmonic material exhibiting surface plasmon resonance of a non-radiative mode that non-radiatively couples to the organic emitting material in the organic emitting layer and transfers excited state energy from the organic emitting material to surface plasmon polaritons of the enhancement layer; and an emitting outcoupling layer, which is disposed on the substrate and comprises a second emitting material; wherein the device is configured to transfer energy from the surface plasmon polaritons of the enhancement layer to the second emitting material.

[0016] The first enhancement layer may include the first electrode or the second electrode, and / or an adhesion layer. The device may include a second enhancement layer, which may also include one of an adhesion layer and / or an electrode. More generally, any of the enhancement layers may include any of the electrodes. The device may include a separation layer such as a dielectric material, which may be disposed between the first electrode and the out-coupling layer or between the second electrode and the out-coupling layer. The out-coupling layer may be disposed at a distance of at least 1 nm from the first electrode, not more than 100 nm from the first electrode, at least 1 nm from the second electrode, and / or not more than 100 nm from the second electrode. Any one or all of the first electrode, the second electrode, the first enhancement layer, and the second enhancement layer may include Au, Ag, Mg, Al, Ir, Pt, Ni, Cu, W, Ta, Fe, Cr, Ga, Rh, Ti, Cr, Ru, Pd, In, Bi, small organic molecules, polymers, SiO2, TiO2, Al2O3, insulating nitrides, Si, Ge, and stacks or alloys of these materials. The second emissive material may include quantum dots, perovskite nanocrystals, metal-organic frameworks, covalent organic frameworks, thermally activated delayed fluorescence (TADF) emitters, fluorescent emitters, and / or phosphorescent organic emitters. The second emissive material comprises a material having a Stokes shift of not more than 20 nm, not more than 10 nm, or not more than 5 nm. The second emissive material may include a down-conversion material that converts a high-energy excited state into an emission of a lower energy wavelength. The second emissive material may include a molecule that changes the orientation of one or more transition dipole moments (TDMs) upon excitation. The second emissive material may include an emissive triplet-emitting material having non-parallel transition dipole moments (TDMs) for the absorbing singlet state and the emitting triplet state. The angle between the TDMs of the absorbing singlet state and the emitting triplet state may be 30 - 63°. The second emissive material may be arranged such that the singlet TDM is not parallel to the second electrode. The angle between the singlet TDM and the second electrode may be 30 - 63°. The second emissive material may be arranged such that the triplet TDM is not perpendicular to the second electrode. The angle between the triplet TDM and the second electrode may be 37 - 60°. The second emissive material may include a fluorophore having a lowest-energy singlet TDM that is not parallel to one or more higher-energy singlet TDMs within the same fluorophore. The angle between the lowest-energy singlet TDM and at least one higher-energy singlet TDM may be 30 - 63°. The second emissive material may be arranged such that one or more higher-energy singlet TDMs are not perpendicular to the second electrode. The angle between at least one higher-energy singlet TDM and the second electrode may be 37 - 60°. The second emissive material may include a multi-emitter cascade. The concentration of the second emissive material within the out-coupling layer may vary.For example, the concentration can vary gradually in proportion to the distance from the interface of the emitting outcoupling layer. The device can include a second emitting outcoupling layer adjacent to the first emitting outcoupling layer, which includes a third emitting material. The first emitting outcoupling layer can be disposed between the first electrode and the substrate. Additionally, the device can include a second emitting outcoupling layer disposed on the second electrode, which includes a third emitting material. The third emitting material includes a material selected from the group consisting of: quantum dots, perovskite nanocrystals, metal-organic frameworks, covalent organic frameworks, thermally activated delayed fluorescence (TADF) emitters, fluorescent emitters, or phosphorescent organic emitters. The third emitting material can be a material having a Stokes shift of no more than 20 nm, no more than 10 nm, or no more than 5 nm. The third emitting material can include a down-conversion material that converts a high-energy excited state into an emission of a lower energy wavelength.

[0017] According to one embodiment, an OLED display is provided, in which a plurality of independently addressable OLED pixels are disposed on a substrate. Each of the pixels can include: a first electrode disposed on the substrate; an emission stack disposed on the first electrode, the emission stack including a first organic emitting material; and a second electrode disposed on the emission stack; wherein each OLED pixel includes the same first organic emitting material, and each OLED pixel further includes a first emitting outcoupling layer disposed on the second electrode or between the first electrode and the substrate, the first emitting outcoupling layer including a second emitting material that is different between at least two of the plurality of pixels; and wherein within each OLED pixel, the first electrode or the second electrode is disposed between the emission stack and the emitting outcoupling layer and non-radiatively transfers energy from the first organic emitting material to the emitting outcoupling layer. Each OLED pixel can emit a color determined by the second emitting material. Within each OLED pixel, the emission stack can include a single emission layer. Brief Description of the Drawings

[0018] Figure 1 An organic light-emitting device is shown.

[0019] Figure 2 An inverted organic light-emitting device without an independent electron transport layer is shown.

[0020] Figures 3A - 3C An example device structure according to the embodiments disclosed herein is shown. Each device includes an emitting OLED stack, top and bottom electrode contacts, and at least one emitting outcoupling layer; Figure 3A including a bottom emitting outcoupling layer that contains an emitting material; Figure 3B including a top emitting outcoupling layer that contains an emitting material; and Figure 3C including top and bottom emitting outcoupling layers, each containing an emitting material.

[0021] Figure 4 Exemplary variants are shown that emit out-couple adjacent top electrode contacts, including in each layer a multilayer stack of combined molecules with different transition dipole moment orientations (configuration (a)), or a spacer layer that separates the emitters in the emit out-couple layer by a certain distance from the contacts (configuration (b)). The corresponding structures can be applied to the emit out-couple layer adjacent to the bottom contact. Detailed Description

[0022] Generally, an OLED includes at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer. The injected holes and electrons each migrate towards the electrode of opposite charge. When an electron and a hole are located on the same molecule, an "exciton" is formed, which is a localized electron-hole pair with an excited energy state. When the exciton relaxes through a light emission mechanism, light is emitted. In some cases, the exciton can be localized on an excimer or an exciplex. Non-radiative mechanisms such as thermal relaxation can also occur, but are generally considered undesirable.

[0023] Initial OLEDs used emissive molecules that emit light from singlet states ("fluorescence"), as disclosed, for example, in U.S. Patent No. 4,769,292, which is incorporated herein by reference in its entirety. Fluorescent emission typically occurs within a time frame of less than 10 nanoseconds.

[0024] Recently, OLEDs with emissive materials that emit light from triplet states ("phosphorescence") have been demonstrated. Baldo et al., "Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices", Nature, Vol. 395, 151-154, 1998 ("Baldo-I"); and Baldo et al., "Very high-efficiency green organic light-emitting devices based on electrophosphorescence", Appl. Phys. Lett., Vol. 75, No. 3, 4-6 (1999) ("Baldo-II"), which are incorporated herein by reference in their entirety. Phosphorescence is described in more detail in columns 5-6 of U.S. Patent No. 7,279,704, which is incorporated by reference.

[0025] Figure 1An organic light emitting device 100 is shown. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emission layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a blocking layer 170. Cathode 160 is a composite cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers in sequence. The properties and functions of these various layers and exemplary materials are described in more detail in columns 6-10 of US 7,279,704, which is incorporated by reference.

[0026] More examples of each of these layers may be obtained. For example, a flexible and transparent substrate-anode combination is disclosed in US Patent No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F-TCNQ at a molar ratio of 50:1, as disclosed in US Patent Application Publication No. 2003 / 0230980, which is incorporated by reference in its entirety. Examples of light emitting and host materials are disclosed in US Patent No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in US Patent Application Publication No. 2003 / 0230980, which is incorporated by reference in its entirety. US Patents Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entirety, disclose examples of cathodes including a composite cathode having a thin layer of metal (such as Mg:Ag) with an overlying transparent, conductive, sputter-deposited ITO layer. The theory and use of the blocking layer are described in more detail in US Patent No. 6,097,147 and US Patent Application Publication No. 2003 / 0230980, which are incorporated by reference in their entirety. Examples of the injection layer are provided in US Patent Application Publication No. 2004 / 0174116, which is incorporated by reference in its entirety. A description of the protective layer can be found in US Patent Application Publication No. 2004 / 0174116, which is incorporated by reference in its entirety. 4 Examples of the layers are provided in US Patent Application Publication No. 2004 / 0174116, which is incorporated by reference in its entirety. A description of the protective layer can be found in US Patent Application Publication No. 2004 / 0174116, which is incorporated by reference in its entirety.

[0027] Figure 2Disclosed is an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. The device 200 can be fabricated by depositing the layers in sequence. Since the most common OLED configuration has the cathode disposed above the anode, and the device 200 has the cathode 215 disposed under the anode 230, the device 200 can be referred to as an "inverted" OLED. Materials similar to those described with respect to the device 100 can be used in the corresponding layers of the device 200. Figure 2 Provided is an example of how some layers can be omitted from the structure of the device 100.

[0028] Figure 1 and 2 The simple layered structure illustrated in and is provided by way of non-limiting example, and it should be understood that embodiments of the present invention can be used in combination with a variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures can be used. Functional OLEDs can be obtained by combining the various layers in different ways, or certain layers can be omitted entirely based on design, performance, and cost factors. Other layers not specifically described can also be included. Materials other than those specifically described can be used. Although many of the examples provided herein describe the various layers as including a single material, it should be understood that combinations of materials can be used, such as mixtures of host and dopant, or more generally, mixtures. In addition, the layers can have various sub-layers. The names given to the various layers herein are not intended to be strictly limiting. For example, in the device 200, the hole transport layer 225 transports holes and injects the holes into the emissive layer 220, and can be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED can be described as having an "organic layer" disposed between the cathode and the anode. This organic layer can comprise a single layer, or can further comprise multiple layers of different organic materials such as, for example, with respect to Figure 1 and 2 described.

[0029] Structures and materials not specifically described can also be used, such as OLEDs (PLEDs) comprising polymeric materials, as disclosed, for example, in U.S. Patent No. 5,247,190 to Friend et al., which is incorporated herein by reference in its entirety. By way of another example, an OLED having a single organic layer can be used. OLEDs can be stacked, for example, as described in U.S. Patent No. 5,707,745 to Forrest et al., which is incorporated herein by reference in its entirety. The OLED structure can deviate from Figure 1 and 2The simple layered structure described in, for example, the substrate may include angled reflective surfaces to improve out-coupling, such as the mesa structure described in U.S. Patent No. 6,091,195 to Forrest et al., and / or the dimpled structure described in U.S. Patent No. 5,834,893 to Bulovic et al., which patents are incorporated herein by reference in their entirety.

[0030] In some embodiments disclosed herein, the emissive layer or material, such as Figures 1 - 2 the emissive layer 135 and the emissive layer 220 shown respectively in, may include quantum dots. Unless explicitly indicated to the contrary or indicated otherwise as would be understood by a person skilled in the art in the circumstances, an "emissive layer" or "emissive material" as disclosed herein may include an organic emissive material and / or an emissive material containing quantum dots or equivalent structures. Such an emissive layer may include only quantum dot material that converts light emitted by a separate emissive material or other emitter, or it may also include the separate emissive material or other emitter, or it may itself emit light directly upon application of an electric current. Similarly, a color-changing layer, a color filter, an up-conversion or down-conversion layer or structure may include a material containing quantum dots, but such a layer may not be considered an "emissive layer" as disclosed herein. Generally, an "emissive layer" or material is an "emissive layer" or material that emits initial light that can be altered by another layer (such as a color filter or other color-changing layer) that does not itself emit initial light within the device, and that can also re-emit altered light having a different spectral content based on the initial light emitted by the emissive layer.

[0031] Unless otherwise specified, any one of the layers of the various embodiments can be deposited by any suitable method. For organic layers, preferred methods include thermal evaporation, inkjet (as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated herein by reference in their entirety), organic vapor phase deposition (OVPD) (as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated herein by reference in its entirety), and deposition by organic vapor jet printing (OVJP) (as described in U.S. Pat. No. 7,431,968, which is incorporated herein by reference in its entirety). Other suitable deposition methods include spin coating and other solution-based processes. Solution-based processes are preferably carried out in nitrogen or an inert atmosphere. For other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding (as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated herein by reference in their entirety), and patterning in combination with some of the deposition methods such as inkjet and OVJP. Other methods can also be used. The materials to be deposited can be modified to be suitable for a specific deposition method. For example, substituents such as alkyl and aryl groups, which can be branched or unbranched and preferably contain at least 3 carbons, can be used in small molecules to enhance their ability to withstand solution processing. Substituents having 20 or more carbons can be used, and a range of 3 to 20 carbons is preferred. Materials having an asymmetric structure can have better solution processability than materials having a symmetric structure because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents can be used to enhance the ability of small molecules to withstand solution processing.

[0032] Devices fabricated according to embodiments of the present invention may further optionally include a barrier layer. One use of the barrier layer is to protect the electrodes and organic layers from damage by harmful substances in an environment that includes moisture, vapor, and / or gases. The barrier layer may be deposited on the substrate, on the electrodes, under the substrate, under the electrodes, beside the substrate, beside the electrodes, or on any other part of the device, including the edges. The barrier layer may include a single layer or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase and compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may include inorganic compounds, organic compounds, or both. A preferred barrier layer includes a mixture of a polymeric material and a non-polymeric material, as described in U.S. Patent No. 7,968,146, PCT Patent Application Nos. PCT / US2007 / 023098, and PCT / US2009 / 042829, which are hereby incorporated by reference in their entirety. For the purposes of being considered a "mixture," the foregoing polymeric material and non-polymeric material that make up the barrier layer should be deposited under the same reaction conditions and / or simultaneously. The weight ratio of the polymeric material to the non-polymeric material may range from 95:5 to 5:95. The polymeric material and the non-polymeric material may be produced from the same precursor material. In one example, the mixture of the polymeric material and the non-polymeric material consists essentially of polymeric silicon and inorganic silicon.

[0033] Devices fabricated in accordance with embodiments of the present invention can be incorporated into a wide variety of electronic component modules (or units), which can in turn be incorporated into a variety of electronic products or intermediate components. Examples of such electronic products or intermediate components include display screens, lighting devices (such as discrete light source devices or lighting panels) that can be utilized by end-user product manufacturers, and the like. The electronic component module can optionally include driving electronics and / or a power source. Devices fabricated in accordance with embodiments of the present invention can be incorporated into a wide variety of consumer products having one or more electronic component modules (or units) incorporated therein. Disclosed is a consumer product that includes an OLED which includes a compound of the present disclosure in an organic layer of the OLED. The consumer product should include any type of product that includes one or more of one or more light sources and / or certain types of visual displays. Some examples of the consumer product include flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and / or signaling, head-up displays, fully or partially transparent displays, flexible displays, laser printers, telephones, cellular phones, tablet computers, phablets, personal digital assistants (PDAs), wearable devices, laptop computers, digital cameras, video cameras, viewfinders, microdisplays (displays having a diagonal less than 2 inches), 3-D displays, virtual reality or augmented reality displays, vehicles, video walls comprising multiple tiled together displays, theater or stadium screens, and signage. A variety of control mechanisms can be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended to be used in a temperature range that is comfortable for humans, such as from 18 degrees Celsius to 30 degrees Celsius, and more preferably at room temperature (20 - 25 degrees Celsius), but can be used outside of this temperature range (e.g., from -40 degrees Celsius to 80 degrees Celsius).

[0034] The materials and structures described herein can be applied to devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors can employ the materials and structures. More generally, organic devices such as organic transistors can employ the materials and structures.

[0035] It has been found that, compared to conventional teachings that attempt to prevent or suppress non-radiative modes of exciton energy transfer to surface plasmon polaritons (SPPs) in a metal electrode, it can be beneficial to transfer as much energy as possible to these non-radiative modes and then extract the energy in the form of emitted light into free space using an outcoupling layer. This is contrary to the conventional understanding in the art because such energy is typically lost in conventional device structures. Specifically, in an organic light-emitting diode (OLED) device, positioning an emissive layer (EML) within a threshold distance of a metal electrode couples the excited-state energy of electro-excited excitons to the surface plasmon resonance (SPR) mode of an enhancement layer, which can be or include the metal electrode. Conventionally, such an arrangement has been regarded as an energy loss pathway and is thus undesirable. However, the embodiments disclosed herein utilize this energy pathway to extend the device lifetime by shortening the time that excitons reside on the emitter molecules.

[0036] It has been found that methods and arrangements for coupling energy out of the SPR mode in the form of light can be beneficial for obtaining OLEDs with longer lifetimes at display brightness levels.

[0037] U.S. Patent No. 9,960,386 provides examples of devices, outcoupling layers, enhancement layers, and device structures that utilize this effect, the disclosure of which is incorporated herein by reference in its entirety.

[0038] It has been found that further benefits can be obtained by incorporating the emissive layer into the electrode, which can also be an enhancement layer as disclosed herein, pumped by surface plasmon energy generated by quenching of excitons from the emitter in the OLED stack to the metal contact electrode / enhancement layer.

[0039] Figures 3A - 3C Shows an example device configuration in accordance with embodiments disclosed herein. In each instance, the emission stack 310 can include previously described with respect to Figures 1 - 2Any one or all of the various layers and structures disclosed, including hole and electron injection layers (HIL / EIL), hole and electron transport layers (HTL / ETL), emission layers (EML), and top and bottom electrodes (also referred to as "contacts"). The electrodes can be or include an enhancement layer as disclosed herein, or an enhancement layer as disclosed herein can include the electrodes. As used herein, an "enhancement layer" refers to a layer comprising a plasmonic material that exhibits a non-radiative mode of surface plasmon resonance of surface plasmon polaritons (SPP) that are non-radiatively coupled to an organic emissive material and transfer excited state energy from the organic emissive material to the enhancement layer. Unless otherwise specified, a metal contact, anode, cathode, or electrode as disclosed herein can act as, provide, or be included in an enhancement layer. The enhancement layer can include multiple electrode layers that can be the same or different materials. It can also include other layers, such as adhesion layers.

[0040] Each device also includes one or more out-coupling layers 310, 320, which can be disposed between the substrate and the lower electrode ( Figure 3A ), on the upper electrode ( Figure 3B ), or both ( Figure 3C ). Generally, an enhancement layer as disclosed herein can be relatively closely proximate to the out-coupling layer. For example, in Figure 3A , the bottom electrode of the emission stack 310 can be relatively closely proximate to the out-coupling layer 320, for example, in direct contact or separated by a single layer such as a spacer layer. In this arrangement, the bottom electrode can act as an enhancement layer as disclosed herein because it is expected to exhibit surface plasmon resonance that non-radiatively couples to the emissive material in the EML of the emission stack and transfers excited state energy from the emissive material to the SPP of the bottom electrode. The top electrode of the emission stack 310 can be a conventional electrode, or it can also be an enhancement layer. Similarly, Figure 3B , the top electrode of the emission stack 310 can be an enhancement layer as disclosed herein, while the bottom electrode can be a conventional electrode or an enhancement layer. In Figure 3C , each of the top and bottom electrodes can be an enhancement layer as disclosed herein.

[0041] The out-coupling layer as disclosed herein differs from a conventional out-coupling layer such as a microlens, out-coupling grating, diffraction grating, etc. in that the out-coupling layer not only out-couples light from, for example, a substrate mode to an air mode. The out-coupling layer as disclosed herein also includes one or more emissive materials that can be excited by energy transferred to the out-coupling layer and then emit light. In fact, the devices and structures disclosed herein can use an out-coupling layer as disclosed herein as well as one or more conventional out-coupling structures, features, or layers.

[0042] For example, as disclosed in further detail herein, the emissive material can be excited by energy transferred from surface plasmon polaritons in the adjacent electrode, and then the energy can be emitted in the form of light. Thus, the emissive outcoupling layer as disclosed herein can be understood as a plasmon-pumped emissive layer. The proximity of this layer to the electrode means that the energy from the excited molecules can be back-coupled into the metal contact of the electrode and thus represents a significant loss pathway. If the emissive outcoupling layer is farther from the metal contact, then it will be less effectively coupled to the surface plasmon mode for exciting the emissive outcoupling layer and the efficiency will be reduced. Thus, preferably, the emissive outcoupling layer is close to the metal contact to increase the near-field coupling to the surface plasmon mode of the metal, but includes additional features or arrangements to reduce the back-coupling energy loss pathway. The present disclosure provides such techniques to achieve strong coupling to the plasmon mode to pump the emissive outcoupling layer while reducing the back-coupling loss pathway.

[0043] To enhance the stability of the emitter in the OLED stack, the exciton energy can be rapidly quenched into, for example, the metal contact of the electrode or an enhancement layer containing the electrode or other metal contacts. Such techniques are disclosed in further detail in U.S. Patent No. 9,960,386, the disclosure of which is incorporated herein by reference in its entirety. This quenching generates surface plasmon modes that can be coupled to the opposite side of the metal contact and near-field coupled to the emissive outcoupling layer as disclosed herein. As previously disclosed, the emissive outcoupling layer contains one or more emissive materials that can be excited by the energy of surface plasmon polaritons in the adjacent contact. Examples of emissive materials suitable for the emissive outcoupling layer as disclosed herein include quantum dots, fluorescent emitters, phosphorescent organic emitters, perovskite nanocrystals, metal-organic frameworks, covalent organic frameworks, and thermally activated delayed fluorescence (TADF) emitters. In embodiments using multiple emissive outcoupling layers, the emissive material in each layer can be the same as or different from the emissive material in other layers, and each material can include any property or combination of the materials as disclosed herein.

[0044] In one embodiment, the concentration of the emissive material within the emissive outcoupling layer may not be uniform throughout the emissive outcoupling layer. For example, the concentration of the emissive material within the emissive outcoupling layer can vary gradually in proportion to the distance from the interface of the emissive outcoupling layer with the adjacent layer, i.e., the concentration is higher or lower as the distance from the boundary of the emissive outcoupling layer increases.

[0045] In one embodiment, preferably, the emissive layer and one or more enhancement layers are within a "threshold distance" of each other, which corresponds to the distance at which the total non-radiative decay rate constant equals the total radiative decay rate constant. In some embodiments disclosed herein, preferably, the emissive layer is disposed within the threshold distance of one or two enhancement layers in the device. For example, the emissive layer may be disposed within the threshold distance of each of the anode and the cathode, where the two electrodes are configured as enhancement layers as disclosed herein. The threshold distance can be understood and defined for a given pair of luminescent material and enhancement layer. For any such pair, there are a total non-radiative decay rate constant and a total radiative decay rate constant. As the luminescent material layer approaches the enhancement layer, the non-radiative decay rate constant increases in a manner different from the radiative decay rate constant. At a certain distance, the total non-radiative decay rate constant of the luminescent material in the presence of the enhancement layer first equals the total radiative decay rate constant of the luminescent material in the presence of the enhancement layer. This distance can be defined as the threshold distance. For distances closer to the enhancement layer than this distance, the total non-radiative decay rate is greater than the radiative decay rate, and the quantum yield is less than 0.5% or 50%. When the distance is greater than the threshold distance, the total radiative decay rate constant is greater than the total non-radiative decay rate constant; however, the quantum yield of the luminescent material decreases compared to the case when the enhancement layer is absent. The emission is still quenched; however, when an outcoupling layer is introduced, this quenching is still beneficial to the device because it is recycled in the form of light. Additionally, the emission acceleration caused by the increase in the rate constant can enhance the operational stability of the device.

[0046] The physical value of the threshold distance disclosed herein depends on various factors, including the frequency of surface plasmon polaritons, the oscillator strength of the luminescent material, the orientation of the transition dipole moment of the luminescent material, and the dielectric constant of the luminescent material layer. Thus, the threshold distance can be adjusted by selecting a suitable set of materials for the organic luminescent material and the plasmonic material of the enhancement layer.

[0047] The threshold distance and related calculations when the total non-radiative decay rate constant of the luminescent material in the presence of the enhancement layer equals the total radiative decay rate constant of the luminescent material in the presence of the enhancement layer are further discussed in detail in U.S. Patent No. 9,960,386, the disclosure of which is incorporated herein by reference in its entirety.

[0048] In one embodiment, the emissive material in the outcoupling layer as disclosed herein preferably has absorption and emission spectra that exhibit a small Stokes shift such that there is only a small red shift between the OLED exciton energy quenched into the enhancement layer and the light emitted from the outcoupling layer. This can maintain the emission color of the device. As a specific example, the emissive material in the outcoupling layer as disclosed herein can have a Stokes shift of no more than 20 nm, no more than 10 nm, no more than 5 nm, or any intermediate value. Generally, a smaller Stokes shift is more preferred. However, in some arrangements, an especially small Stokes shift may have an adverse effect on other characteristics of the outcoupling layer or the device, and little additional benefit is achieved relative to a slightly larger Stokes shift. In such cases, a slightly larger Stokes shift within the scope disclosed herein may be required.

[0049] In one embodiment, the emissive material can be selected to down-convert higher energy excitations into lower energy wavelengths (e.g., convert blue emission to green or red). This enables a single OLED structure to be used in each pixel of a display, where the color is selected by the outcoupling layer. For example, this can be achieved by depositing quantum dots of different sizes in the outcoupling layers of different pixels to tune the emission wavelength.

[0050] In one embodiment, molecular engineering can be used to minimize the energy loss caused by the back-coupling of the energy of the plasma-pumped molecule into the surface plasmon mode of the adjacent contact (back-coupling). For emissive materials that emit triplets, the molecule can be designed to have orthogonal transition dipole moments (TDMs) for the absorption singlet and emission triplet. Preferably, the singlet TDM is perpendicular to the contact to maximize the coupling of this TDM to the plasmon mode, and the triplet TDM is parallel to the contact to minimize the back-coupling of the emitter energy into the surface plasmon mode of the contact. As another example, for fluorophore (non-emitting triplet) emissive materials, the molecule can be designed to have orthogonal TDMs for the lowest energy (S1) and higher energy (S2, S3, etc.) singlets. Preferably, the higher energy (e.g., S2) singlet TDM is perpendicular to the contact to maximize the coupling of this TDM to the plasmon mode, and the lowest energy (S1) singlet TDM is parallel to the contact to minimize the back-coupling of the emitter energy into the surface plasmon mode of the contact.

[0051] In one embodiment, the molecule can be designed such that it changes its orientation or the orientation of its TDM when excited. For example, for an organometallic complex, the complex can be designed to have two ligands with slightly dissimilar energies. Wherein the chemical composition of the molecule forces the TDM of the higher energy ligand to be perpendicularly aligned with the plasma surface, and the TDM of the lower energy ligand to be parallel to the surface. The plasma will preferentially excite the higher energy ligand, but the energy will be transferred to the lower energy ligand, which will limit back coupling.

[0052] Figure 4 Exhibit various schematic arrangements of the out-coupling layer as disclosed herein. Generally, as previously disclosed, the out-coupling layer 310 can be disposed above or adjacent to the enhancement layer, which can include an electrode contact. Although Figure 4 the examples shown are with respect to a top electrode contact provided, corresponding arrangements including the same out-coupling layer structure can be used for any out-coupling layer as disclosed herein.

[0053] In structure (a), the device structure can also be used to reduce back-coupling. In one embodiment, the emissive material in one or more out-coupling layers 410, 420 can include one or more emissive materials having non-parallel transition dipole moments (TDMs) for singlet absorption and triplet emission. The angle between the TDMs of the absorption state and the emission state can be 30 - 63°. For example, two or more emitter molecules can be incorporated into two or more out-coupling layers 410, 420 such that the molecules closest to the electrode in layer 420 have a TDM perpendicularly aligned with the electrode and one or more additional layers 410 (farther from the electrode) contain molecules having a TDM parallelly aligned with the contact. More generally, based on the limit that the emissive TDM becomes horizontally aligned more than vertically aligned, the angle between the singlet TDM and the electrode can be 30 - 63° and / or the angle between the triplet TDM and the electrode can be 37 - 60°, where the absorption TDM is completely vertical. Such an arrangement can maximize the out-coupling efficiency of the emissive TDM. Additionally, the molecules can be designed to efficiently and rapidly transfer energy from an emitter with a perpendicular TDM to an emitter with a parallel TDM, i.e., before quenching to the surface plasmon mode occurs. Such a configuration can move the energy further away from the electrode contact, thereby reducing the probability of back-coupling to the surface plasmon mode. The final emission from the parallel TDM molecules can also reduce waveguide losses in the out-coupling layers. In a variation of this structure, two emitter molecules with perpendicular TDMs can be mixed into the same layer, for example, by co-evaporation. In another variation, the out-coupling layer emitter molecules can be doped into a host matrix, where for the layer farther from the contact, the host molecules have a (relatively) high refractive index to cause a redshift in the absorption and emission spectra, and for the layer closer to the contact, a host with a lower refractive index is utilized. In another variation, the out-coupling layer emitter molecules can be doped into a host matrix, where the host molecules can couple to the surface plasmon mode and transfer energy to the out-coupling layer emitter molecules. Preferably, the absorption TDM of the host is perpendicular to the contact to maximize the coupling of this TDM to the plasmon mode, and the absorption TDM of the out-coupling layer emitter molecules is parallel to the contact to minimize the back-coupling of the emitter energy to the surface plasmon mode of the contact. A variety of materials can be used for one or both of the emissive materials in these out-coupling layers. For example, one or two can include fluorophores having a lowest energy singlet TDM that is not parallel to one or more higher energy singlet TDMs within the same fluorophore. Alternatively or additionally, a structure providing a multi-emitter cascade can be used as the emissive material. Such a configuration uses a series of layers with different emitters or a single layer with a graded concentration of different emitters. The multi-emitter can include at least one emitter having an excited state with an energy similar to the plasmon energy placed close to the enhancement layer, and / or at least one emitter having a lower energy excited state placed farther from the enhancement layer.This cascaded "pulling" emits the excited state within the outcoupling layer away from the plasma enhancement layer in order to reduce or prevent back-transfer of energy to the enhancement layer, which would reduce the efficiency and effectiveness of the device. Such a structure facilitates energy transfer from a first higher-energy emitter to a second lower-energy emitter, thereby attracting excitons away from the enhancement layer.

[0054] More generally, the embodiments disclosed herein are designed such that the absorbing excited state is at a higher energy level than the emitting excited state. The absorbing excited state receives plasma energy transfer, while the emitting excited state is used to effectively outcouple light. As previously disclosed, one way to achieve this is to use the S1 state to absorb energy and the T1 state to emit. However, other arrangements can be used to achieve the same effect. As another example, emitters with orthogonal singlets can be used. In this case, the emitter can have an S2 or other singlet Sn for absorption and an S1 state for emission. Then the energy is internally converted from the S2 / Sn state to the S1 state, thereby achieving an equivalent energy transfer.

[0055] As another example, device structure (b) shows an arrangement where the outcoupling layer is spaced apart from the plasma active enhancement layer, which can be used, for example, to position the outcoupling layer at an optimal location for optimizing the trade-off between plasma pumping intensity and back-coupling losses. A spacer layer 430 can be disposed between the enhancement layer and the outcoupling layer to achieve the desired spacing. The spacer layer can be formed of any suitable material, such as a dielectric, and is selected such that it has little optical effect on the overall operation of the emission stack or device. The spacer layer can be disposed anywhere in the device where an additional distance is needed between otherwise adjacent layers, including between the bottom electrode or enhancement layer and the outcoupling layer in a device as shown in Figure 3A the device shown; between the top electrode or enhancement layer and the outcoupling layer in a device as shown in Figure 3B the device shown; or for both cases of the device shown in Figure 3C Similarly, one or more spacer layers can be used throughout the device to achieve the desired spacing of multiple layers as disclosed herein, thereby achieving the desired "threshold distance" between the emission layer and one or more enhancement layers.

[0056] In a particular exemplary arrangement, the outcoupling layer can be at least 1 nm, about 10 - 20 nm, 1 - 20 nm, within 1 - 10 nm, not more than 50 nm, not more than 100 nm, or any intermediate distance from the closest enhancement layer or electrode.

[0057] In one embodiment, the out-coupling layer or the entire device stack may be corrugated to enable out-coupling of waveguide modes in the out-coupling layer and direct scattering of surface plasmon mode energy in the contacts. Examples of corrugated structures are described in further detail in U.S. Application No. 16 / 685,161, filed November 15, 2019 (Attorney Docket No. UDC-1378US), the disclosure of which is incorporated herein by reference in its entirety.

[0058] In addition to using emitters in the out-coupling layer as a way to convert the energy stored in the plasmon mode into light, it can also be used to down-convert the energy out-coupled from the plasmon mode. For example, a display can be made of blue plasmonic OLED devices, where the red and green sub-pixels are presented by down-converting the blue light out-coupled from the plasmon mode into red and green light, respectively. These methods are independent of each other, such that the blue emitter in the out-coupling layer can be used to out-couple light from the plasmon mode, and then additional emitters are added in the out-coupling layer to down-convert the emitted blue light into lower energy photons. Alternatively or additionally, out-coupling of light can occur via corrugations or scattering from a set of periodic, quasi-periodic, or random structures equivalent to the wavelength of light. Additionally, the device may have color filters to further change the emitted color. The device may also include layers that change the radiation pattern, such as diffusers, etc.

[0059] A variety of materials can be used to fabricate the layers and devices disclosed herein. For example, the enhancement layer and electrodes may include one or more of the following: Au, Ag, Mg, Al, Ir, Pt, Ni, Cu, W, Ta, Fe, Cr, Ga, Rh, Ti, Cr, Ru, Pd, In, Bi, small organic molecules, polymers, SiO2, TiO2, Al2O3, insulating nitrides, Si, Ge, and stacks or alloys of these materials.

[0060] The embodiments disclosed herein can be used in a variety of electronic devices, such as OLED displays and similar devices. In one embodiment, an OLED display can include a plurality of independently addressable OLED pixels, each of which has a structure as previously disclosed with respect to FIGS. 3-4. For example, each pixel can include an emission stack disposed between two electrodes and an outcoupling layer arranged in any of the previously disclosed configurations. In some cases, the emission stack in each pixel can include the same emission material in one or more emission layers. The outcoupling layer in each pixel can include the same emission material or different emission materials. As a specific example, the blue pixels in a display can have the same emission material in the emission stack as the green and / or red pixels in the display, but different emission materials in the outcoupling layer. In some embodiments, the color emitted by each pixel may be determined by the emission material in the outcoupling layer of each pixel. Continuing the previous example, the blue and green / red pixels can include an emission stack that initially generates energy from the same emission material in the stack. This energy can be coupled to one or more enhancement layers and / or electrodes and then coupled to different outcoupling layers as previously disclosed, where light is emitted with a color determined by the specific emission material in each pixel. Each emission stack can include one or more emission layers, and each outcoupling layer can include one or more emission materials.

[0061] In some embodiments, the OLED has one or more characteristics selected from the group consisting of flexible, rollable, foldable, stretchable, and bendable. In some embodiments, the OLED is transparent or translucent. In some embodiments, the OLED further includes a layer comprising carbon nanotubes.

[0062] In some embodiments, the OLED further includes a layer comprising a delayed fluorescence emitter. In some embodiments, the OLED includes an RGB pixel arrangement or a white plus color filter pixel arrangement. In some embodiments, the OLED is a mobile device, a handheld device, or a wearable device. In some embodiments, the OLED is a display panel with a diagonal less than 10 inches or an area less than 50 square inches. In some embodiments, the OLED is a display panel with a diagonal of at least 10 inches or an area of at least 50 square inches. In some embodiments, the OLED is a lighting panel.

[0063] In some embodiments of the emission region, the emission region further includes a host.

[0064] In some embodiments, the compound can be an emission dopant. In some embodiments, the compound can generate emission via phosphorescence, fluorescence, thermally activated delayed fluorescence (i.e., TADF, also known as E-type delayed fluorescence), triplet-triplet annihilation, or a combination of these processes.

[0065] The OLEDs disclosed herein can be incorporated into one or more of consumer products, electronic component modules, and lighting panels. The organic layer can be an emissive layer, and the compound can be an emissive dopant in some embodiments, while the compound can be a non-emissive dopant in other embodiments.

[0066] The organic layer can also include a host. In some embodiments, two or more hosts are preferred. In some embodiments, the host used can be a) bipolar, b) electron transporting, c) hole transporting, or d) wide bandgap material that plays a minimal role in charge transport. In some embodiments, the host can include a metal complex. The host can be an inorganic compound.

[0067] Combinations with other materials

[0068] The materials described herein as suitable for specific layers in an organic light-emitting device can be used in combination with a wide variety of other materials present in the device. For example, the emissive dopants disclosed herein can be combined with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes, and other layers that may be present. The materials described or mentioned below are non-limiting examples of materials that can be used in combination with the compounds disclosed herein, and those skilled in the art can readily consult the literature to identify other materials that can be used in combination.

[0069] A variety of emissive and non-emissive layers and arrangements disclosed herein can use a variety of materials. Examples of suitable materials are disclosed in U.S. Patent Application Publication No. 2017 / 0229663, which is incorporated herein by reference in its entirety.

[0070] Conductive dopants:

[0071] The charge transport layer can be doped with a conductive dopant to generally change its charge carrier density, which in turn will change its conductivity. Conductivity is increased by generating charge carriers in the matrix material, and depending on the type of dopant, a change in the Fermi level of the semiconductor can also be achieved. The hole transport layer can be doped with a p-type conductive dopant, and an n-type conductive dopant is used in the electron transport layer.

[0072] HIL / HTL:

[0073] The hole injection / transport materials used in the present invention are not particularly limited, and any compound can be used as long as the compound is generally used as a hole injection / transport material.

[0074] EBL:

[0075] An electron blocking layer (EBL) can be used to reduce the number of electrons and / or excitons leaving the emissive layer. The presence of such a blocking layer in a device can result in generally higher efficiency and / or longer lifetime compared to a similar device lacking a blocking layer. Additionally, a blocking layer can be used to confine emission to a desired region of the OLED. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and / or a higher triplet energy compared to the emitter closest to the EBL interface. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and / or a higher triplet energy compared to one or more of the hosts closest to the EBL interface. In one aspect, the compounds used in the EBL contain the same molecule or the same functional group as used in one of the hosts described below.

[0076] Host:

[0077] The light-emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as a light-emitting material, and may contain a host material using a metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complex or organic compound can be used as long as the triplet energy of the host is greater than the triplet energy of the dopant. Any host material can be used with any dopant as long as the triplet criterion is satisfied.

[0078] HBL:

[0079] A hole blocking layer (HBL) can be used to reduce the number of holes and / or excitons leaving the emissive layer. The presence of such a blocking layer in a device can result in generally higher efficiency and / or longer lifetime compared to a similar device lacking a blocking layer. Additionally, a blocking layer can be used to confine emission to a desired region of the OLED. In some embodiments, the HBL material has a lower HOMO (farther from the vacuum level) and / or a higher triplet energy compared to the emitter closest to the HBL interface. In some embodiments, the HBL material has a lower HOMO (farther from the vacuum level) and / or a higher triplet energy compared to one or more of the hosts closest to the HBL interface.

[0080] ETL:

[0081] The electron transport layer (ETL) can include materials capable of transporting electrons. The electron transport layer can be intrinsic (undoped) or doped. Doping can be used to enhance conductivity. Examples of ETL materials are not particularly limited, and any metal complex or organic compound can be used as long as it is commonly used to transport electrons.

[0082] Charge generation layer (CGL)

[0083] In tandem or stacked OLEDs, the CGL plays a fundamental role in performance and consists of an n-doped layer and a p-doped layer for electron and hole injection, respectively. Electrons and holes are supplied by the CGL and the electrodes. The electrons and holes consumed in the CGL are refilled by electrons and holes injected from the cathode and anode, respectively; subsequently, the bipolar current gradually reaches a steady state. Typical CGL materials include n- and p-conductive dopants used in the transport layer.

[0084] It should be understood that the various embodiments described herein are by way of example only and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be replaced with other materials and structures without departing from the spirit of the invention. The invention as claimed may thus include variations of the specific examples and preferred embodiments described herein, as will be apparent to those skilled in the art. It should be understood that the various theories as to why the invention works are not intended to be limiting.

Claims

1. An organic emission device, comprising: A substrate; A first electrode disposed on the substrate; An emission stack disposed on the first electrode, the emission stack comprising a first organic emission material; A second electrode disposed on the emission stack; A first enhancement layer comprising a plasmonic material that exhibits surface plasmon resonance of a non-radiative mode of surface plasmon polaritons that are non-radiatively coupled to the organic emission material in the organic emission layer and transfer excited state energy from the organic emission material to the surface of the enhancement layer; And A first outcoupling layer disposed on the substrate and comprising a second emission material; Wherein the device is configured to transfer energy from the non-radiative mode of surface plasmon polaritons of the enhancement layer to the second emission material.

2. The device according to claim 1, wherein the first enhancement layer comprises the first electrode or the second electrode.

3. The device according to claim 2, wherein the first enhancement layer comprises an adhesion layer.

4. The device according to claim 1, further comprising a second enhancement layer.

5. The device according to claim 1, wherein each of the first electrode and the second electrode, or each of the first electrode and the second electrode, comprises a material independently selected from the group consisting of: Au, Ag, Mg, Al, Ir, Pt, Ni, Cu, W, Ta, Fe, Cr, Ga, Rh, Ti, Cr, Ru, Pd, In, Bi, small organic molecules, polymers, SiO 2 , TiO 2 , Al 2 O 3 , insulating nitrides, Si, Ge, and stacks or alloys of these materials.

6. The device according to claim 1, wherein the second emission material comprises a material selected from the group consisting of: quantum dots, perovskite nanocrystals, metal-organic frameworks, covalent organic frameworks, thermally activated delayed fluorescence (TADF) emitters, fluorescent emitters, and phosphorescent organic emitters.

7. The device according to claim 1, wherein the second emission material comprises a material having a Stokes shift of no more than 20 nm.

8. The device according to claim 1, wherein the second emission material comprises a down-conversion material that converts a high-energy excited state into a lower-energy wavelength emission.

9. The device according to claim 1, wherein the second emission material comprises a molecule that changes the orientation of one or more transition dipole moments (TDMs) when the molecule is excited.

10. The device according to claim 9, wherein the concentration of the second emission material varies within the first outcoupling layer.

11. The device according to claim 10, wherein the concentration varies gradually in proportion to the distance from the interface of the first outcoupling layer.

12. The device according to claim 1, further comprising a second outcoupling layer adjacent to the first outcoupling layer.

13. The device according to claim 1, wherein the second emission material comprises an emissive triplet emission material having non-parallel transition dipole moments (TDMs) for singlet absorption and triplet emission.

14. The device according to claim 13, wherein the second emission material is arranged such that the singlet TDM is not parallel to the second electrode.

15. The device according to claim 1, wherein the second emission material comprises a fluorophore having a lowest-energy singlet TDM that is not parallel to one or more higher-energy singlet TDMs within the same fluorophore.

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